ORCID Profile
0000-0002-1113-5205
Current Organisations
University College Dublin
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Monash University
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Publisher: Wiley
Date: 26-05-2017
Publisher: American Chemical Society (ACS)
Date: 05-1993
DOI: 10.1021/IC00063A035
Publisher: Elsevier BV
Date: 06-1974
DOI: 10.1016/0039-9140(74)80189-X
Abstract: The performance of short drop-time a.c. polarography has been examined in detail, and found to be better than that for natural drop-times in almost every respect. Uncompensated resistance terms are smaller and potentiostat stability is improved. In addition, faster potential scanrates and more rapid data acquisition are possible. A variation of the drop-time over at least three orders of magnitude is possible and this, coupled with excellent instrumental performance, should offer considerable scope in studies of electrode kinetics.
Publisher: Elsevier BV
Date: 10-1994
Publisher: American Chemical Society (ACS)
Date: 04-04-2018
Publisher: American Chemical Society (ACS)
Date: 03-1988
DOI: 10.1021/IC00279A008
Publisher: American Chemical Society (ACS)
Date: 04-06-2014
DOI: 10.1021/JP501220V
Abstract: Detailed electrochemical studies have been undertaken on molecular aggregation of the organic semiconductor 7,14-bis((triisopropylsilyl)-ethynyl)dibenzo[b,def]chrysene (TIPS-DBC), which is used as an electron donor material in organic solar cells. Intermolecular association of neutral TIPS-DBC molecules was established by using (1)H NMR spectroscopy as well as by the pronounced dependence of the color of TIPS-DBC solutions on concentration. Diffusion limited current data provided by near steady-state voltammetry also reveal aggregation. Furthermore, variation of concentration produces large changes in shapes of transient DC and Fourier transformed AC (FTAC) voltammograms for oxidation of TIPS-DBC in dichloromethane. Subtle effects of molecular aggregation on the reduction of TIPS-DBC are also revealed by the highly sensitive FTAC voltammetric method. Simulations of FTAC voltammetric data provide estimates of the kinetic and thermodynamic parameters associated with oxidation and reduction of TIPS-DBC. Significantly, aggregation of TIPS-DBC facilitates both one-electron oxidation and reduction by shifting the reversible potentials to less and more positive values, respectively. EPR spectroscopy is used to establish the identity of one-electron oxidized and reduced forms of TIPS-DBC. Implications of molecular aggregation on the HOMO energy level in solution are considered with respect to efficiency of organic photovoltaic devices utilizing TIPS-DBC as an electron donor material.
Publisher: Health Affairs (Project Hope)
Date: 02-2014
DOI: 10.1377/HLTHAFF.2013.0747
Abstract: Private insurers pay widely varying prices for inpatient care across hospitals. Previous research indicates that certain hospitals use market clout to obtain higher payment rates, but there have been few in-depth examinations of the relationship between hospital characteristics and pricing power. This study used private insurance claims data to identify hospitals receiving inpatient prices significantly higher or lower than the median in their market. High-price hospitals, compared to other hospitals, tend to be larger be major teaching hospitals belong to systems with large market shares and provide specialized services, such as heart transplants and Level I trauma care. High-price hospitals also receive significant revenues from nonpatient sources, such as state Medicaid disproportionate-share hospital funds, and they enjoy healthy total financial margins. Quality indicators for high-price hospitals were mixed: High-price hospitals fared much better than low-price hospitals did in U.S. News & World Report rankings, which are largely based on reputation, while generally scoring worse on objective measures of quality, such as postsurgical mortality rates. Thus, insurers may face resistance if they attempt to steer patients away from high-price hospitals because these facilities have good reputations and offer specialized services that may be unique in their markets.
Publisher: American Chemical Society (ACS)
Date: 15-11-2012
DOI: 10.1021/JO301403V
Abstract: Careful control of the reaction stoichiometry and conditions enables the synthesis of both LiTCNQF(4) and Li(2)TCNQF(4) to be achieved. Reaction of LiI with TCNQF(4), in a 4:1 molar ratio, in boiling acetonitrile yields Li(2)TCNQF(4). However, deviation from this ratio or the reaction temperature gives either LiTCNQF(4) or a mixture of Li(2)TCNQF(4) and LiTCNQF(4). This is the first report of the large-scale chemical synthesis of Li(2)TCNQF(4). Attempts to prepare a single crystal of Li(2)TCNQF(4) have been unsuccessful, although air-stable (Pr(4)N)(2)TCNQF(4) was obtained by mixing Pr(4)NBr with Li(2)TCNQF(4) in aqueous solution. Pr(4)NTCNQF(4) was also obtained by reaction of LiTCNQF(4) with Pr(4)NBr in water. Li(2)TCNQF(4), (Pr(4)N)(2)TCNQF(4), and Pr(4)NTCNQF(4) have been characterized by UV-vis, FT-IR, Raman, and NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and electrochemistry. The structures of single crystals of (Pr(4)N)(2)TCNQF(4) and Pr(4)NTCNQF(4) have been determined by X-ray crystallography. These TCNQF(4)(2-) salts will provide useful precursors for the synthesis of derivatives of the dianions.
Publisher: American Chemical Society (ACS)
Date: 03-1971
DOI: 10.1021/AC60298A017
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 10-1985
Publisher: American Chemical Society (ACS)
Date: 03-1988
DOI: 10.1021/OM00093A007
Publisher: Wiley
Date: 13-10-2009
Abstract: The new ligand, [Fc(cyclen)(2)] (5) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane), and corresponding Zn(II) complex receptor, [Fc{Zn(cyclen)(CH(3)OH)}(2)](ClO(4))(4) (1), consisting of a ferrocene moiety bearing one Zn(II)-cyclen complex on each cyclopentadienyl ring, have been designed and prepared through a multi-step synthesis. Significant shifts in the (1)H NMR signals of the ferrocenyl group, cf. ferrocene and a previously reported [Fc{Zn(cyclen)}](2+) derivative, indicated that the two Zn(II)-cyclen units in 1 significantly affect the electronic properties of the cyclopentadienyl rings. The X-ray crystal structure shows that the two positively charged Zn(II)-cyclen complexes are arranged in a trans like configuration, with respect to the ferrocene bridging unit, presumably to minimise electrostatic repulsion. Both 5 and 1 can be oxidized in 1:4 CH(2)Cl(2)/CH(3)CN and Tris-HCl aqueous buffer solution under conditions of cyclic voltammetry to give a well defined ferrocene-centred (Fc(0/+)) process. Importantly, 1 is a highly selective electrochemical sensor of thymidilyl(3'-5')thymidine (TpT) relative to other nucleobases and nucleotides in Tris-HCl buffer solution (pH 7.4). The electrochemical selectivity, detected as a shift in reversible potential of the Fc(0/+) component, is postulated to result from a change in the configuration of bis(Zn(II)-cyclen) units from a trans to a cis state. This is caused by the strong 1:1 binding of the two deprotonated thymine groups in TpT to different Zn(II) centres of receptor 1. UV-visible spectrophotometric titrations confirmed the 1:1 stoichiometry for the 1:TpT adduct and allowed the determination of the apparent formation constant of 0.89+/-0.10x10(6) M(-1) at pH 7.4.
Publisher: Elsevier BV
Date: 02-1991
Publisher: American Chemical Society (ACS)
Date: 05-1986
DOI: 10.1021/AC00297A018
Publisher: American Chemical Society (ACS)
Date: 1974
DOI: 10.1021/IC50131A016
Publisher: Springer Science and Business Media LLC
Date: 02-2003
DOI: 10.1007/S00775-002-0416-5
Abstract: The reversible formal potentials of auracyanin A and auracyanin B, two closely related "blue" copper proteins from the photosynthetic bacterium Chloroflexus aurantiacus, have been determined by protein film voltammetry in the range 4<or=pH<or=9. At pH 7 in 0.1 M NaCl, the values of for auracyanin A and auracyanin B are 205+/-7 mV and 215+/-7 mV, respectively, versus the standard hydrogen electrode. In both cases there is a smooth but non-sigmoidal change in from approximately 190 mV at pH 9 to approximately 240 mV at pH 4. The small changes in as a function of pH indicate that auracyanin A and auracyanin B differ from those "blue" copper proteins in which the Cu site in the reduced (Cu(I)) state switches to a redox-inhibited form at low pH. For auracyanin A, the results obtained by protein film voltammetry are closely similar to those obtained by the conventional spectroelectrochemical method. The findings are discussed in relation to the putative role of auracyanin in biological electron transfer.
Publisher: Wiley
Date: 26-06-2014
Publisher: American Chemical Society (ACS)
Date: 08-1978
DOI: 10.1021/IC50186A024
Publisher: Royal Society of Chemistry (RSC)
Date: 15-05-2002
DOI: 10.1039/B108474G
Publisher: No publisher found
Date: 2008
DOI: 10.5517/CCQ5N1K
Publisher: Elsevier BV
Date: 03-1992
Publisher: No publisher found
Date: 2008
DOI: 10.5517/CCQHDJ3
Publisher: Proceedings of the National Academy of Sciences
Date: 03-1933
Publisher: American Chemical Society (ACS)
Date: 05-05-2011
DOI: 10.1021/JP111977Q
Abstract: Electrochemical studies in room temperature ionic liquids are often h ered by their relatively high viscosity. However, in some circumstances, fast exchange between participating electroactive species has provided beneficial enhancement of charge transport. The iodide (I¯)/iodine (I(2))/triiodide (I(3)¯) redox system that introduces exchange via the I¯ + I(2) ⇌ I(3)¯ process is a well documented ex le because it is used as a redox mediator in dye-sensitized solar cells. To provide enhanced understanding of ion movement in RTIL media, a combined electrochemical and NMR study of diffusion in the {SeCN¯-(SeCN)(2)-(SeCN)(3)¯} system has been undertaken in a selection of commonly used RTILs. In this system, each of the Se, C and N nuclei is NMR active. The electrochemical behavior of the pure ionic liquid, [C(4)mim][SeCN], which is synthesized and characterized here for the first time, also has been investigated. Voltammetric studies, which yield readily interpreted diffusion-limited responses under steady-state conditions by means of a Random Assembly of Microdisks (RAM) microelectrode array, have been used to measure electrochemically based diffusion coefficients, while self-diffusion coefficients were measured by pulsed field gradient NMR methods. The diffusivity data, derived from concentration and field gradients respectively, are in good agreement. The NMR data reveal that exchange processes occur between selenocyanate species, but the voltammetric data show the rates of exchange are too slow to enhance charge transfer. Thus, a comparison of the iodide and selenocyanate systems is somewhat paradoxical in that while the latter give RTILs of low viscosity, sluggish exchange kinetics prevent any significant enhancement of charge transfer through direct electron exchange. In contrast, faster exchange between iodide and its oxidation products leads to substantial electron exchange but this effect does not compensate sufficiently for mass transport limitations imposed by the higher viscosity of iodide RTILs.
Publisher: Elsevier BV
Date: 11-2010
Publisher: Wiley
Date: 05-1998
DOI: 10.1002/(SICI)1521-4109(199805)10:6<387::AID-ELAN387>3.0.CO;2-W
Publisher: American Chemical Society (ACS)
Date: 23-06-2020
Publisher: Wiley
Date: 04-1994
Publisher: Royal Society of Chemistry (RSC)
Date: 1991
DOI: 10.1039/DT9910000411
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B401761G
Abstract: The reactions of bidentate diimine ligands (L2) with cationic bis(diimine)[Ru(L)(L1)(CO)Cl]+ complexes (L, L1, L2 are dissimilar diimine ligands), in the presence of trimethylamine-N-oxide (Me3NO) as a decarbonylation reagent, lead to the formation of heteroleptic tris(diimine) ruthenium(II) complexes, [Ru(L)(L1)(L2)]2+. Typically isolated as hexafluorophosphate or perchlorate salts, these complexes were characterised by UV-visible, infrared and mass spectroscopy, cyclic voltammetry, microanalyses and NMR spectroscopy. Single crystal X-ray studies have elucidated the structures of K[Ru(bpy)(phen)(4,4'-Me(2)bpy)](PF(6))(3).1/2H(2)O, [Ru(bpy)(5,6-Me(2)phen)(Hdpa)](ClO(4))(2), [Ru(bpy)(phen)(5,6-Me(2)phen)](ClO(4))(2), [Ru(bpy)(5,6'-Me(2)phen)(4,4'-Me(2)bpy)](PF(6))(2).EtOH, [Ru(4,4'-Me(2)bpy)(phen)(Hdpa)](PF(6))(2).MeOH and [Ru(bpy)(4,4'-Me(2)bpy)(Hdpa)](ClO(4))(2).1/2Hdpa (where Hdpa is di(2-pyridyl)amine). A novel feature of the first complex is the presence of a dinuclear anionic adduct, [K(2)(PF(6))(6)](4-), in which the two potassium centres are bridged by two fluorides from different hexafluorophosphate ions forming a K(2)F(2) bridging unit and by two KFPFK bridging moieties.
Publisher: Proceedings of the National Academy of Sciences
Date: 02-07-2012
Abstract: Photoreduction of [P 2 W 18 O 62 ] 6- , [S 2 Mo 18 O 62 ] 4- , and [S 2 W 18 O 62 ] 4- polyoxometalate anions (POMs) and oxidation of water occurs when water–ionic liquid and water–diethylether interfaces are irradiated with white light (275–750 nm) or sunlight. The ionic liquids (ILs) employed were aprotic ([Bmim]X Bmim = (1-butyl-3-methylimidazolium,X = BF 4 ,PF 6 ) and protic (DEAS = diethanolamine hydrogen sulphate DEAP = diethanolamine hydrogen phosphate). Photochemical formation of reduced POMs at both thermodynamically stable and unstable water–IL interfaces led to their initial diffusion into the aqueous phase and subsequent extraction into the IL phase. The mass transport was monitored visually by color change and by steady-state voltammetry at microelectrodes placed near the interface and in the bulk solution phases. However, no diffusion into the organic phase was observed when [P 2 W 18 O 62 ] 6- was photo-reduced at the water–diethylether interface. In all cases, water acted as the electron donor to give the overall process: 4POM + 2H 2 O + h ν → 4POM - + 4H + + O 2 . However, more highly reduced POM species are likely to be generated as intermediates. The rate of diffusion of photo-generated POM - was dependent on the initial concentration of oxidized POM and the viscosity of the IL (or mixed phase system produced in cases in which the interface is thermodynamically unstable). In the water-DEAS system, the evolution of dioxygen was monitored in situ in the aqueous phase by using a Clark-type oxygen sensor. Differences in the structures of bulk and interfacial water are implicated in the activation of water. An analogous series of reactions occurred upon irradiation of solid POM salts in the presence of water vapor.
Publisher: American Chemical Society (ACS)
Date: 29-04-1998
DOI: 10.1021/IC971406O
Publisher: Wiley
Date: 28-08-1956
Publisher: American Chemical Society (ACS)
Date: 17-04-2007
DOI: 10.1021/IC061622+
Abstract: The reaction of Cu(NO3)2.3H2O with the ligand 1-(ferrocenemethyl)-1,4,7,10-tetraazacyclododecane (L) in acetonitrile leads to the formation of a blue complex, [Cu(L)(NO3)][NO3] (C1). The X-ray structure determination shows an unexpected binding of a nitrate anion in that the CuII center is surrounded by four N atoms of the 1,4,7,10-tetraazacyclododecane (cyclen) macrocycle and two O atoms from a chelating nitrate anion, both Cu-O distances being below the sums of the van de Waals radii. Hydrogen-bonding interactions in the crystal lattice and a weak interaction between a second nitrate O and the CuII center in C1 give rise to a highly distorted CuII geometry relative to that found in the known structure of [Cu(cyclen)(NO3)][NO3] (C5). Electrochemical studies in acetonitrile containing 0.1 M [Bu4N][NO3] as the supporting electrolyte showed that oxidation of C1 in this medium exhibits a single reversible one-electron step with a formal potential E degrees f of +85 mV vs Fc0/+ (Fc = ferrocene). This process is associated with oxidation of the ferrocenyl pendant group. Additionally, a reversible one-electron reduction reaction with an E degrees f value of -932 mV vs Fc0/+, attributed to the CuII/I redox couple, is detected. Gradual change of the supporting electrolyte from 0.1 M [Bu4N][NO3] to the poorly coordinating [Bu4N][PF6] electrolyte, at constant ionic strength, led to a positive potential shift in E degrees f values by +107 and +39 mV for the CuII/I(C1) and Fc0/+(C1) redox couples, respectively. Analysis of these electrochemical data and UV-vis spectra is consistent with the probable presence of the complexes C1, [Cu(L)(CH3CN)2]2+ (C2), [Cu(L)(CH3CN)(NO3)]+ (C3), and [Cu(L)(NO3)2] (C4) as the major species in nitrate-containing acetonitrile solutions. In weakly solvating nitromethane, the extent of nitrate complexation remains significant even at low nitrate concentrations, due to the lack of solvent competition.
Publisher: Springer Science and Business Media LLC
Date: 06-2012
Publisher: American Chemical Society (ACS)
Date: 1983
DOI: 10.1021/IC00144A010
Publisher: Elsevier BV
Date: 06-1996
Publisher: American Chemical Society (ACS)
Date: 13-03-2014
DOI: 10.1021/LA404872P
Abstract: New insights into electrochemical kinetics of the flavin adenine dinucleotide (FAD) redox center of glucose-oxidase (GlcOx) immobilized on reduced graphene oxide (rGO), single- and multiwalled carbon nanotubes (SW and MWCNT), and combinations of rGO and CNTs have been gained by application of Fourier transformed AC voltammetry (FTACV) and simulations based on a range of models. A satisfactory level of agreement between experiment and theory, and hence establishment of the best model to describe the redox chemistry of FAD, was achieved with the aid of automated e-science tools. Although still not perfect, use of Marcus theory with a very low reorganization energy (≤0.3 eV) best mimics the experimental FTACV data, which suggests that the process is gated as also deduced from analysis of FTACV data obtained at different frequencies. Failure of the simplest models to fully describe the electrode kinetics of the redox center of GlcOx, including those based on the widely employed Laviron theory is demonstrated, as is substantial kinetic heterogeneity of FAD species. Use of a SWCNT support lifies the kinetic heterogeneity, while a combination of rGO and MWCNT provides a more favorable environment for fast communication between FAD and the electrode.
Publisher: No publisher found
Date: 2008
DOI: 10.5517/CCQHDK4
Publisher: Elsevier BV
Date: 11-1999
Publisher: Wiley
Date: 26-01-2009
Abstract: Electrode-dependent potential windows (see picture, GC=glassy carbon) are determined for five dialkylammonium carbamate (dialcarb) room-temperature ionic liquids in a systematic study of their physical and electrochemical properties. The viscosity and conductivity of the dialcarb ionic liquids, which are "distillable" at low temperature, are comparable to those of some conventional room-temperature ionic liquids. The physical and electrochemical properties of five "distillable" room-temperature ionic liquids from the dialcarb family (dialkylammonium carbamates formed from CO(2) and dialkyl amines) are systematically investigated. In particular dimethyl (DIMCARB), diethyl (DIECARB), dipropyl (DIPCARB), methylethyl (MEETCARB), and methylpropyl (MEPRCARB) carbamate ionic liquids are studied. The temperature dependence of the viscosity and conductivity of MEETCARB exhibit an Arrhenius-type relationship. Except for DIPCARB, which has too high a resistance, a reference potential scale is available by using the IUPAC recommended redox system, that is the cobalticenium/cobaltocene (Cc(+)/Cc) process, which exhibits an ideal reversible voltammetric response. Oxidation of decamethylferrocene, but not ferrocene, also is ideal in DIMCARB, DIECARB, MEETCARB, and MEPRCARB. The magnitudes of the potential windows of the electrochemically viable dialcarbs are investigated and follow the order of glassy carbon>Au>Pt>Hg. Diffusion coefficients of Cc(+), DmFc, and double-layer capacitance values are compared in each dialcarb. Despite the considerable viscosity of the dialcarbs, steady-state voltammetric behavior is achieved at a rotating disk electrode for rotation rates of 1000 rpm or higher.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CC03870D
Abstract: A review of the insight into biological redox chemistry which has been enabled by the development of large litude Fourier transform ac voltammetry.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TA02429D
Abstract: Stannate derived bimetallic systems can achieve highly efficient electrocatalytic CO 2 reduction to formate.
Publisher: Elsevier BV
Date: 1986
Publisher: American Chemical Society (ACS)
Date: 06-1986
DOI: 10.1021/JA00272A032
Publisher: American Chemical Society (ACS)
Date: 08-1983
DOI: 10.1021/JA00354A067
Publisher: American Chemical Society (ACS)
Date: 04-02-2014
DOI: 10.1021/AC4036422
Abstract: The robustness of convolution voltammetry for determining accurate values of the diffusivity (D), bulk concentration (C(b)), and stoichiometric number of electrons (n) has been demonstrated by applying the technique to a series of electrode reactions in molecular solvents and room temperature ionic liquids (RTILs). In acetonitrile, the relatively minor contribution of nonfaradaic current facilitates analysis with macrodisk electrodes, thus moderate scan rates can be used without the need to perform background subtraction to quantify the diffusivity of iodide [D = 1.75 (±0.02) × 10(-5) cm(2) s(-1)] in this solvent. In the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, background subtraction is necessary at a macrodisk electrode but can be avoided at a microdisk electrode, thereby simplifying the analytical procedure and allowing the diffusivity of iodide [D = 2.70 (±0.03) × 10(-7) cm(2) s(-1)] to be quantified. Use of a convolutive procedure which simultaneously allows D and nC(b) values to be determined is also demonstrated. Three conditions under which a technique of this kind may be applied are explored and are related to electroactive species which display slow dissolution kinetics, undergo a single multielectron transfer step, or contain multiple noninteracting redox centers using ferrocene in an RTIL, 1,4-dinitro-2,3,5,6-tetramethylbenzene, and an alkynylruthenium trimer, respectively, as ex les. The results highlight the advantages of convolution voltammetry over steady-state techniques such as rotating disk electrode voltammetry and microdisk electrode voltammetry, as it is not restricted by the mode of diffusion (planar or radial), hence removing limitations on solvent viscosity, electrode geometry, and voltammetric scan rate.
Publisher: CSIRO Publishing
Date: 1986
DOI: 10.1071/CH9861167
Abstract: The generation of methylmercury species by reactions between inorganic mercury and methylated forms of lead and tin in seawater and other matrices is described. The reactions were investigated by 119Sn, 199Hg and 207Pb multinuclear Fourier transform magnetic resonance spectroscopy and by differential pulse polarography and anodic stripping voltammetry. Methylmercury chloride is shown to be produced from mixtures of inorganic mercury with methyltin or methyllead species over the 10-2-10-8 M concentration range at ambient temperatures in seawater and artificial seawater.
Publisher: American Chemical Society (ACS)
Date: 04-09-2012
DOI: 10.1021/LA300886S
Abstract: Thin films of the adduct formed from the electrostatic association of the metallopolymer, [Ru(bpy)(2)(PVP)(10)](2+), and the Dawson polyoxomolybdate α-[Mo(18)O(54)(SO(4))(2)](4-), POMo, have been formed on ITO electrodes using an alternate immersion approach. The Ru/POMo ratio is 4.5:1, which exceeds the 2:1 ratio expected on the basis of the charges of the Ru(2+) and POMo(4-) building blocks. This behavior arises because of the polymeric character of the cation. In the presence of a substrate that has an abstractable proton such as benzyl alcohol, these ruthenium-sensitized polyoxomolybdate films generate significant photocurrents under visible irradiation. Significantly, increasing the surface coverage of the adduct from 1.4 × 10(-10) to 8.1 × 10(-10) mol cm(-2) does not measurably increase the photocurrent observed. Scan-rate-dependent cyclic voltammetry reveals that the rate of homogeneous charge transport through the film is slow, which most likely results in only a fraction of the film thickness being active for photoelectrocatalysis. The photocurrent increases markedly when the driving force for the oxidation of POMo(5-), created by the photoelectrocatalytic oxidation of benzyl alcohol, is increased. This result is consistent with the dynamics of heterogeneous electron transfer being centrally important to the regeneration of the photoelectrocatalyst. A system in which the surface coverage and applied overpotential are optimized produces a photocurrent density of 190 ± 18 nA cm(-2) under 480 ± 5 nm irradiation.
Publisher: Elsevier BV
Date: 02-1992
Publisher: American Chemical Society (ACS)
Date: 1978
DOI: 10.1021/IC50179A023
Publisher: American Chemical Society (ACS)
Date: 14-04-2005
DOI: 10.1021/JP044614S
Abstract: Fourier transform analysis of r ed square-wave voltammograms indicates the availability of a novel form of kinetic selectivity for surface-confined electron-transfer processes. Thus, for all the even harmonic components, quasi-reversible processes are sensitive to the surface coverage, the reversible potential, the electron-transfer rate constant (k(0')), and the electron-transfer coefficient (alpha), as well as to the litude (DeltaE) and frequency (f) of the square wave and dc scan rate. Additionally, it is insensitive to background capacitance current. In contrast, reversible processes and background currents are predicted to be absent from the even harmonics and only detectable in the odd harmonic components. The square-wave voltammetry of the surface-confined quasi-reversible azurin process azurin[Cu(II)] + e(-) right arrow over left arrow azurin[Cu(I)] at a paraffin-impregnated graphite electrode has been employed as a model system to test theoretical predictions. Most voltammetric characteristics of the even harmonic components obtained from the Fourier analysis are consistent with electrode kinetic values of k(0') = 90 s(-1) and alpha = 0.48, although some nonideality possibly due to kinetic dispersion also is apparent. Conditions also have been determined under which a readily generated waveform constructed from the Fourier series of sine waves produces voltammograms that are essentially indistinguishable from those predicted when an ideal square wave is employed.
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTTZYJ
Publisher: American Chemical Society (ACS)
Date: 29-08-2006
DOI: 10.1021/JO060868T
Abstract: A new ferrocenyl uracil peptide nucleic acid (PNA) monomer, tert-butyl-2-(N-(2-(((9H-floren-9-yl)methoxy)carbonylamino)ethyl)-2-(5-(N-ferrocenylmethylbenzamido)-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)acetamido)acetate (1), has been successfully prepared in good yield by a procedure involving the one-pot reaction of the key synthon, 5-(ferrocenylmethylamino)pyrimidine-2,4(1H,3H)-dione (4), itself prepared from the reaction of (ferrocenylmethyl)trimethylammonium iodide and 5-aminouracil, with benzoyl chloride followed by ethyl bromoacetate. After hydrolysis of the ester, the acid was coupled with a protected PNA backbone to generate 1. NMR spectroscopy showed that 1 hydrogen bonds 9-ethyladenine (EA) in a 1:1 mixture of CD3CN:CDCl3 with an association constant Ka of 70 M(-1) at 30 degrees C. This value is comparable with those observed for model receptors and shows that the ferrocenyl moiety of 1 does not hinder the hydrogen bonding of our new PNA monomer to the complementary DNA base or if it does, not significantly. 1 is oxidized to 1+ with a reversible potential of +538 mV vs the DMFc(0/+) (decamethylferrocene) couple under voltammetric conditions in a 1:1 mixture of CH3CN:CHCl3 (0.1 M Bu4NPF6). For this reversible process, a slightly larger diffusion coefficient of 4.2 x 10(-6) cm(2).s(-1) than usually found for these compounds was determined from these electrochemical studies, which should be analytically useful as it will readily afford submicromolar voltammetric detection limits.
Publisher: American Chemical Society (ACS)
Date: 08-02-2002
DOI: 10.1021/IC010780S
Abstract: Reaction of excess Fe(cp)(2) (cp = eta(5)-C(5)Me(5)) dissolved in Et(2)O with [NHex(4)](4)[S(2)Mo(18)O(62)] in acetonitrile, followed by recrystallization of the precipitated solid from N,N'-dimethylformamide (DMF), leads to isolation of the complex [Fe(cp)(2)](5)[HS(2)Mo(18)O(62)].3DMF.2Et(2)O. The solid has been characterized by microanalysis, by voltammetric analysis, by (1)H NMR, diffuse reflectance infrared, EPR, and Mössbauer spectroscopies, and by temperature-dependent magnetic susceptibility measurements. The data are consistent with the presence of a paramagnetic [Fe(cp)(2)](+) cation and a diamagnetic two-electron-reduced [HS(2)Mo(18)O(62)](5-) anion. The related salt [NBu(4)](5)[HS(2)Mo(18)O(62)].2H(2)O crystallizes in space group C2/c with a = 25.1255(3) A, b = 15.4110(2) A, c = 35.8646(4) A, beta = 105.9381(4), V = 13353.3(3) A(3), and Z = 4. The (2 e(-), 1 H(+))-reduced anion exists as the alpha-Dawson isomer, and its structure may be compared with those of the oxidized and (4 e(-), 3 H(+))-reduced anions as they exist in [NEt(4)](4)[S(2)Mo(18)O(62)].MeCN and [NBu(4)](5)[H(3)S(2)Mo(18)O(62)].4MeCN, respectively. Overall, the anion expands significantly upon the addition of two and then four electrons. However, the Mo...Mo distances along the bonds which connect the two equatorial belts decrease in the order 3.801, 3.780, and 3.736 A, making these distances the shortest for the three inequivalent sets of corner-sharing octahedra in each anion. This is consistent with the two or four added electrons localizing essentially in molecular orbitals which are bondiing with respect to interactions between the belts.
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CCPMC5T
Publisher: American Chemical Society (ACS)
Date: 04-2006
DOI: 10.1021/IC0519943
Abstract: Voltammetric studies on the reduction of alpha and beta isomers of the Keggin polyoxometalate anion [SiW12O40]4- reveal a series of electrochemically reversible processes in acidic aqueous media. In the presence of NO2-, catalytic current is detected in the potential region of the [SiW12O40]4-/5- process. Electronic spectroscopy and simulation of voltammetric data undertaken at variable [NO2-] and [H+] allow the following mechanism to be postulated, [SiW12O40]4- + e- [SiW12O40]5-, H+ + HNO2 NO+ + H2O, NO+ + [SiW12O40]5- --> NO + [SiW12O40]4-. The second-order rate constant for the rate-determining step is faster for the alpha isomer than for the beta one. This may be attributed to the different reversible potentials of -0.144 V (alpha isomer) and -0.036 V vs Ag/AgCl (beta isomer) and, hence, smaller driving force for an assumed outer sphere electron-transfer reaction in the case of beta isomer. A stable, water-insoluble, thin-film [Ru(bipy)3]2[alpha-SiW12O40] chemically modified electrode was generated electrochemically via ion-exchange of [Ru(bipy)3]2+ with Bu4N+ in the [Bu4N]4[alpha-SiW12O40] solid. The first reduction process with this modified electrode gives rise to the reaction [Ru(bipy)3]2[alpha-SiW12O40](solid) + H+(soln) + e- H[Ru(bipy)3]2[alpha-SiW12O40](solid). The need to transfer a proton from the solution to the solid phase for charge neutralization purposes introduces a hydrogen-ion concentration dependence into this reaction, which is not found in the solution-phase study. Nevertheless, the voltammetric catalytic activity with respect to nitrite reduction is retained with the chemically modified electrode. However, nitrite catalysis with the [Ru(bipy)3]2[alpha-SiW12O40]-modified electrode is now independent of concentration of H+, rather than exhibiting a first-order dependence, and full mechanistic details for this process are unknown.
Publisher: Elsevier BV
Date: 11-1994
Publisher: American Chemical Society (ACS)
Date: 02-1986
DOI: 10.1021/JA00264A042
Publisher: American Chemical Society (ACS)
Date: 18-02-2000
DOI: 10.1021/JP9933370
Publisher: Elsevier BV
Date: 12-1995
Publisher: Wiley
Date: 08-2018
Publisher: American Chemical Society (ACS)
Date: 06-1997
DOI: 10.1021/OM960749B
Publisher: Elsevier BV
Date: 05-2015
Publisher: Elsevier BV
Date: 02-2013
Publisher: Elsevier BV
Date: 1972
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CCPMC4S
Publisher: CSIRO Publishing
Date: 1986
DOI: 10.1071/CH9861385
Abstract: A series of Co(RR′dsc)3 and [Co2(RR′dsc)5]+ complexes (R, R′ = two alkyl groups or one heterocyclic group dsc = NCSe2) have been synthesized and their redox behaviour, chemical reactivity and spectroscopic properties compared with the corresponding dithiocarbamate (RR′dtc) complexes. Electrochemical oxidation of Co(RR′dsc)3 in dichloromethane at platinum electrodes occurs at potentials about 0.34 V less positive than for Co(RR′dsc)3. The formally cobalt(IV) complexes [Co(RR′dsc)3]+ can be identified as a product which is then converted into [Co2(RR′dsc)5]+ via dimerization and an internal redox reaction. Despite the enhanced thermodynamic stability implied by the redox potentials, [Co(RR′dsc)3]+ has similar kinetic stability to the analogous dithiocarbamate complexes. Co(RR′dsc)3 is reduced at fairly negative potentials on both platinum and mercury electrodes with extremely rapid loss of [RR′dsc]-. [Co(RR′dsc)3]- is therefore thermodynamically and kinetically more unstable than [Co(RR′dtc)3]- . The [Co2(RR′dsc)5]+ complexes are also more readily oxidized and harder to reduce than the sulfur analogues. Oxidation of [Co2(RR′dsc)5]+ produces [Co2(RR′dsc)5]2+ at low temperatures and fast scan rates, but no stable reduced form of the dimer is accessible on the voltammetric time scale examined. The reduction process for the dimer is consistent with the reaction [Co2(RR′dsc)5]+ +e- → Co(RR′dsc)3+ Co(RR dsc)2. Electrochemical oxidation data obtained at mercury electrodes for the diselenocarbamate complexes are complicated by adsorption but are similar to that found at platinum electrodes. This contrasts with the dithiocarbamates where a mercury electrode specific pathway is observed. Cobalt-59 n.m.r. spectroscopy in dichloromethane shows the non- equivalence of the two cobalt atoms in [Co2(RR′dsc)5]+. The chemical shifts for Co(RR′dsc)3 complexes exhibit similar substituent effects to the dithiocarbamates in cobalt-59 n.m.r. measurements as was the case in oxidative electrochemistry. Cobalt-59 n.m.r. spectroscopy and mass spectrometry demonstrate that exchange, substitution and redox reactions can lead to the formation of mixed ligand diselenocarbamate complexes and mixed dithiocarbamate/diselenocarbamate complexes for both the cobalt(III) monomers and dimers.
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CCPJ5BP
Publisher: Elsevier BV
Date: 10-1995
Publisher: American Chemical Society (ACS)
Date: 10-1989
DOI: 10.1021/OM00112A019
Publisher: American Chemical Society (ACS)
Date: 1970
DOI: 10.1021/J100697A018
Publisher: Elsevier BV
Date: 1986
Publisher: Springer Science and Business Media LLC
Date: 29-08-2016
Publisher: Elsevier BV
Date: 02-1987
Publisher: American Chemical Society (ACS)
Date: 18-05-2020
Publisher: Elsevier BV
Date: 12-1972
Publisher: Royal Society of Chemistry (RSC)
Date: 1994
DOI: 10.1039/AN994190001R
Publisher: Elsevier BV
Date: 10-1989
Publisher: Elsevier
Date: 1994
Publisher: Elsevier BV
Date: 1984
Publisher: Elsevier BV
Date: 08-2018
Publisher: American Chemical Society (ACS)
Date: 08-02-2011
DOI: 10.1021/AC103149T
Abstract: Sinusoidal large litude ac voltammetric techniques gene-rate very large data sets. When analyzed in the frequency domain, using a Fourier transform (FT)-band filtering- inverse FT sequence, the data may be resolved into the aperiodic dc, fundamental, second, and higher order ac harmonics. Each of these components exhibit a different level of sensitivity to electrode kinetics, uncompensated resistance and capacitance. Detailed simulations illustrate how the heuristic approach for evaluation of each data subset may be implemented and exploited in the assessment of the electrode kinetics for the fast Fc [symbol:see text] Fc(+) + e (Fc = ferrocene) oxidation process at a glassy carbon macrodisk electrode. The simulations presented in this study are based on the Butler-Volmer model and incorporate consideration of the uncompensated resistance (R(u)), double-layer capacitance (C(dl)), rate constant (k(0)), and charge transfer coefficient (α). Error analysis of the heuristically evaluated simulation-experiment comparison is used to assist in establishing the best fit of data for each harmonic. The result of the heuristic pattern recognition type approach for analysis of the oxidation of ferrocene (0.499, 0.999, and 5.00 mM) at a glassy carbon macrodisk electrode in acetonitrile (0.1 M Bu(4)NPF(6)) implies that k(0) ≥ 0.25 cm s(-1) on the basis of analysis of the first 4 harmonics and plausibly lies in the range of 0.25-0.5 cm s(-1) with α = 0.25-0.75 when analysis of the next four harmonics is undertaken. The k(0) value is significantly faster then indicated in most literature reports based on use of dc cyclic voltammetry under transient conditions at glassy carbon macrodisk electrode. The data analysis with a sinusoidal litude of 80 mV is conducted at very low frequency experiments of 9 Hz to minimize contribution from electrode heterogeneity, frequency dispersion, and adsorption, all of which can complicate the response for the oxidation of Fc in acetonitrile at a glassy carbon electrode.
Publisher: American Chemical Society (ACS)
Date: 12-1994
DOI: 10.1021/OM00024A063
Publisher: Elsevier BV
Date: 10-1998
Publisher: American Chemical Society (ACS)
Date: 03-1981
DOI: 10.1021/AC00226A027
Publisher: American Chemical Society (ACS)
Date: 03-1973
DOI: 10.1021/J100626A013
Publisher: American Chemical Society (ACS)
Date: 04-1989
DOI: 10.1021/IC00307A018
Publisher: American Chemical Society (ACS)
Date: 21-08-2003
DOI: 10.1021/CM0341336
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3EE41892H
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CC7M0F8
Publisher: Elsevier BV
Date: 02-1981
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7TA04742H
Abstract: A simple one pot hydrothermal procedure for the synthesis of cobalt selenide (CoSe) decorated reduced graphene oxide (rGO) is reported along with the application of this hybrid material as a new electrocatalyst for glucose oxidation.
Publisher: Royal Society of Chemistry (RSC)
Date: 1979
DOI: 10.1039/C39790001022
Publisher: American Chemical Society (ACS)
Date: 19-06-1999
DOI: 10.1021/JP990926X
Publisher: Elsevier BV
Date: 10-1991
Publisher: Wiley
Date: 10-10-2020
Abstract: Two-dimensional (2D) materials are attractive catalysts for the electrochemical reduction of carbon dioxide reaction (eCO
Publisher: Elsevier BV
Date: 11-1991
Publisher: No publisher found
Date: 2001
DOI: 10.5517/CC5BKDF
Publisher: American Chemical Society (ACS)
Date: 1979
DOI: 10.1021/AC50037A037
Publisher: American Chemical Society (ACS)
Date: 11-1980
DOI: 10.1021/AC50063A050
Publisher: American Chemical Society (ACS)
Date: 04-04-2011
DOI: 10.1021/IC102588H
Abstract: The reaction of [Fe(II)(BF(4))(2)]·6H(2)O with the nitroxide radical, 4,4-dimethyl-2,2-di(2-pyridyl) oxazolidine-N-oxide (L(•)), produces the mononuclear transition metal complex [Fe(II)(L(•))(2)](BF(4))(2) (1) which has been investigated using temperature dependent susceptibility, Mössbauer spectroscopy, electrochemistry, density functional theory (DFT) calculations, and X-ray structure analysis. Single crystal X-ray diffraction analysis and Mössbauer measurements reveal an octahedral low spin Fe(2+) environment where the pyridyl donors from L(•) coordinate equatorially while the oxygen containing the radical from L(•) coordinates axially forming a linear O(•)··Fe(II)··O(•) arrangement. Magnetic susceptibility measurements show a strong radical-radical intramolecular antiferromagnetic interaction mediated by the diamagnetic Fe(2+) center. This is supported by DFT calculations which show a mutual spatial overlap of 0.24 and a spin density population analysis which highlights the antiparallel spin alignment between the two ligands. Similarly the monocationic complex [Fe(III)(L(-))(2)](BPh(4))·0.5H(2)O (2) has been fully characterized with Fe-ligand and N-O bond length changes in the X-ray structure analysis, magnetic measurements revealing a Curie-like S = 1/2 ground state, electron paramagnetic resonance (EPR) spectra, DFT calculations, and electrochemistry measurements all consistent with assignment of Fe in the (III) state and both ligands in the L(-) form. 2 is formed by a rare, reductively induced oxidation of the Fe center, and all physical data are self-consistent. The electrochemical studies were undertaken for both 1 and 2, thus allowing common Fe-ligand redox intermediates to be identified and the results interpreted in terms of square reaction schemes.
Publisher: American Chemical Society (ACS)
Date: 15-12-2000
DOI: 10.1021/AC000732+
Abstract: The reversible reduction of [S2Mo18O62]4- to [S2Mo18O62]5- and [S2Mo18O62]6- at a glassy carbon macrodisk electrode has been studied by cyclic voltammetry in acetonitrile as a function of the concentration of [(C6H13)4N]4[S2Mo18O62] in the absence and presence of [(C6H13)4N]ClO4 as the added supporting electrolyte. Consideration is given to the influence of scan rate, reference-working electrode distance, [(C6H13)4N]4[S2Mo18O62], and electrolyte concentrations. Experimental data confirm theoretical predictions that cyclic voltammetry at a macrodisk electrode is a viable technique for studies of multiply charged electroactive species without added electrolyte, provided the influence of enhanced complexities associated with effects of increased solution resistance, the mass transport contribution from migration, and convection arising from enhanced density gradients are considered. Enhanced density gradients present in the absence of added supporting electrolyte give rise to a more marked dependence of voltammograms on the angle of the electrode and hence lead to significant distortion of wave shapes at low scan rates. The summation of all these obstacles implies that quantitative evaluation of cyclic voltammograms of multiply charged species requires significantly greater care in the absence than in the presence of added supporting electrolyte.
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CC7M0G9
Publisher: American Chemical Society (ACS)
Date: 25-06-1999
DOI: 10.1021/AC9814290
Abstract: Quantitative analysis of the complex problem of coupled electron- and proton-transfer steps during reduction of the polyoxo anions α-[P(2)W(18)O(62)](6)(-) and α-[H(2)W(12)O(40)](6)(-) in aqueous NaCl (0.5 M) has been achieved by simulation of cyclic voltammograms (Rudolph, M. Reddy, D. P. Feldberg, S. W. Anal. Chem. 1994, 66, 589A) over wide ranges of anion concentration, pH, and scan rate. Since there are too many unknown parameters to attempt a one-step global form of simulation, a systematic, stepwise approach has been adopted by progressively accessing regimes of increasing voltammetric complexity. This protocol allows experimental behavior in each system over 5 orders of magnitude in proton concentration to be simulated by estimation of three protonation constants combined with experimentally determined reversible half-wave potentials for the two one-electron processes involved. Fast electron transfer and protonation kinetics are assumed. The importance of the values chosen for the diffusion coefficients of the proton and polyoxo anion species is considered. The simulations account for the fact that pairs of one-electron processes coalesce to give an apparent two-electron process in the pH range 1-6 for reduction of both anions.
Publisher: American Chemical Society (ACS)
Date: 10-1973
DOI: 10.1021/AC60334A018
Publisher: Elsevier BV
Date: 07-1991
Publisher: Elsevier BV
Date: 07-1994
Publisher: Elsevier BV
Date: 1998
Publisher: Elsevier BV
Date: 04-1996
Publisher: Elsevier BV
Date: 10-1988
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1AN15103G
Abstract: The ionic liquid (IL) 2-butylthiolonium bis(trifluoromethanesulfonyl)amide, [mimSBu][NTf(2)], facilitates the efficient extraction of silver(I) from aqueous media via interaction with both the cation and anion components of the IL. Studies with a conventional aqueous-IL two phase system as well as microextraction of silver(I) by a thick IL film adhered to an electrode monitored in situ by cyclic voltammetry, established that [mimSBu][NTf(2)] can extract electroactive silver(I) ions from an aqueous solution. The pH of the aqueous phase decreases upon addition of [mimSBu](+), which is attributed to partial release of the hydrogen attached to the N(3) nitrogen atom of the imidazolium ring. The presence of silver(I) further increase the acidity of the aqueous phase as a consequence of coordination with the IL cation component. Voltammetric and (1)H and (13)C NMR techniques have been used to establish the nature of the silver(I) complexes extracted, and show that the form of interaction with the IL differs from that outlined previously for the extraction of copper(II). Insights on the competition established when silver(I) is extracted in the presence of copper(II) are provided. Finally, it is noted that metallic silver can be directly electrodeposited at the electrode surface after extraction of silver(I) into [mimSBu][NTf(2)] and that back extraction of silver(I) into aqueous media is achieved by addition of an acidic aqueous solution.
Publisher: Elsevier BV
Date: 02-1988
Publisher: Annual Reviews
Date: 12-06-2018
DOI: 10.1146/ANNUREV-ANCHEM-061417-010022
Abstract: Nonhaloaluminate ionic liquids (ILs) have received considerable attention as alternatives to molecular solvents in erse applications spanning the fields of physical, chemical, and biological science. One important and often overlooked aspect of the implementation of these designer solvents is how the properties of the IL formulation affect (electro)chemical reactivity. This aspect is emphasized herein, where recent (voltammetric) studies on the energetics of proton (H + ) transfer and electrode reaction mechanisms of the H + /H 2 process in IL media are highlighted and discussed. The energetics of proton transfer, quantified using the p K a (minus logarithm of acidity equilibrium constant, K a ) formalism, is strongly governed by the constituent IL anion, and to a lesser extent, the IL cation. The H + /H 2 process, a model inner-sphere reaction, also displays electrochemical characteristics that are strongly IL-dependent. Overall, these studies highlight the need to carry out systematic investigations to resolve IL structure and function relationships in order to realize the potential of these erse and versatile solvents.
Publisher: American Chemical Society (ACS)
Date: 10-2019
DOI: 10.1021/ACS.INORGCHEM.9B01983
Abstract: The rational design of binuclear Au(I)-Au(I), Au(II)-Au(II), and Au(I)-Au(III) complexes requires an understanding of how the redox states interconvert. Herein, the electrochemical interconversion of the three oxidation states I, II, and III is reported on the voltammetric (cyclic and rotating disk electrode) time scales for binuclear gold complexes containing C
Publisher: No publisher found
Date: 2001
DOI: 10.5517/CC5BKCD
Publisher: Wiley
Date: 19-09-2017
Abstract: The electrocatalytic reduction of CO
Publisher: Royal Society of Chemistry (RSC)
Date: 1992
DOI: 10.1039/AN9921700857
Publisher: Wiley
Date: 10-05-2016
Abstract: The electroreduction of CO2 in the distillable ionic liquid dimethylammonium dimethylcarbamate (dimcarb) has been investigated with 17 metal electrodes. Analysis of the electrolysis products reveals that aluminum, bismuth, lead, copper, nickel, palladium, platinum, iron, molybdenum, titanium and zirconium electroreduce the available protons in dimcarb to hydrogen rather than reducing CO2 . Conversely, indium, tin, zinc, silver and gold are able to catalyze the reduction of CO2 to predominantly carbon monoxide (CO) and to a lesser extent, formate ([HCOO](-) ). In all cases, the applied potential was found to have a minimal influence on the distribution of the reduction products. Overall, indium was found to be the best electrocatalyst for CO2 reduction in dimcarb, with faradaic efficiencies of approximately 45 % and 40 % for the generation of CO and [HCOO](-) , respectively, at a potential of -1.34 V versus Cc(+/0) (Cc(+) =cobaltocenium) employing a dimethylamine to CO2 ratio of less than 1.8:1.
Publisher: American Chemical Society (ACS)
Date: 19-07-2006
DOI: 10.1021/LA060408V
Abstract: The electrochemical reduction of TCNQ to TCNQ*- in acetonitrile in the presence of [Cu(MeCN)4]+ has been undertaken at boron-doped diamond (BDD) and indium tin oxide (ITO) electrodes. The nucleation and growth process at BDD is similar to that reported previously at metal electrodes. At an ITO electrode, the electrocrystallization of more strongly adhered, larger, branched, needle-shaped phase I CuTCNQ crystals is detected under potential step conditions and also when the potential is cycled over the potential range of 0.7 to -0.1 V versus Ag/AgCl (3 M KCl). Video imaging can be used at optically transparent ITO electrodes to monitor the growth stage of the very large branched crystals formed during the course of electrochemical experiments. Both in situ video imaging and ex situ X-ray diffraction and scanning electron microscopy (SEM) data are consistent with the nucleation of CuTCNQ taking place at a discrete number of preferred sites on the ITO surface. At BDD electrodes, ex situ optical images show that the preferential growth of CuTCNQ occurs at the more highly conducting boron-rich areas of the electrode, within which there are preferred sites for CuTCNQ formation.
Publisher: American Chemical Society (ACS)
Date: 15-01-2016
DOI: 10.1021/ACS.ANALCHEM.5B04332
Abstract: The electrochemical behavior of iodine remains a contemporary research interest due to the integral role of the I(-)/I3(-) couple in dye-sensitized solar cell technology. The neutral (I2) and positive (I(+)) oxidation states of iodine are known to be strongly electrophilic, and thus the I(-)/I2/I(+) redox processes are sensitive to the presence of nucleophilic chloride or bromide, which are both commonly present as impurities in nonhaloaluminate room temperature ionic liquids (ILs). In this study, the electrochemistry of I(-), I2, and ICl has been investigated by cyclic voltammetry at a platinum macrodisk electrode in a binary IL mixture composed of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2mim][NTf2]). In the absence of chloride (e.g., in neat [C2mim][NTf2]), I(-) is oxidized in an overall one electron per iodide ion process to I2 via an I3(-) intermediate, giving rise to two resolved I(-)/I3(-) and I3(-)/I2 processes, as per previous reports. In the presence of low concentrations of chloride ([Cl(-)] and [I(-)] are both <30 mM), an additional oxidation process appears at potentials less positive than the I3(-)/I2 process, which corresponds to the oxidation of I3(-) to the interhalide complex anion [ICl2](-), in an overall two electron per iodide ion process. In the presence of a large excess of Cl(-) ([I(-)] ≈ 10 mM and [Cl(-)] ≈ 3.7 M), I(-) is oxidized in an overall two electron per iodide ion process to [ICl2](-) via an [I2Cl](-) intermediate (confirmed by investigating the voltammetric response of ICl and I2 under these conditions). In summary, the I(-)/I2/I(+) processes in nonhaloaluminate ILs involve a complicated interplay between multiple electron transfer pathways and homogeneous chemical reactions which may not be at equilibrium on the voltammetric time scale.
Publisher: Elsevier BV
Date: 2004
Publisher: American Chemical Society (ACS)
Date: 04-1973
DOI: 10.1021/IC50122A036
Publisher: American Chemical Society (ACS)
Date: 08-06-2000
DOI: 10.1021/LA991699T
Publisher: Elsevier BV
Date: 10-2001
Publisher: Springer Science and Business Media LLC
Date: 03-11-1999
Publisher: American Chemical Society (ACS)
Date: 21-04-2007
DOI: 10.1021/IC062470L
Abstract: The facile solid-solid phase transformation of TCNQ microcrystals into semiconducting and magnetic Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures is achieved by reduction of TCNQ-modified electrodes in the presence of Ni2+(aq)-containing electrolytes. Voltammetric probing revealed that the chemically reversible TCNQ/Ni[TCNQ]2(H2O)2 conversion process is essentially independent of electrode material and the identity of nickel counteranion but is significantly dependent on scan rate, Ni2+(aq) electrolyte concentration, and the method of solid TCNQ immobilization (drop casting or mechanical attachment). Data analyzed from cyclic voltammetric and double-potential step chrono erometric experiments are consistent with formation of the Ni[TCNQ]2(H2O)2 complex via a rate-determining nucleation/growth process that involves incorporation of Ni2+(aq) ions into the reduced TCNQ crystal lattice at the triple phase TCNQ|electrode|electrolyte interface. The reoxidation process, which includes the conversion of solid Ni[TCNQ]2(H2O)2 back to TCNQ0 crystals, is also controlled by nucleation/growth kinetics. The overall redox process associated with this chemically reversible solid-solid transformation, therefore, is described by the equation: TCNQ0(S) + 2e- + Ni2+(aq)+ 2 H2O {Ni[TCNQ]2(H2O)2}(S). SEM monitoring of the changes that accompany the TCNQ/Ni[TCNQ]2(H2O)2 transformation revealed that the morphology and crystal size of electrochemically generated Ni[TCNQ]2(H2O)2 are substantially different from those of parent TCNQ crystals. Importantly, the morphology of Ni[TCNQ]2(H2O)2 can be selectively manipulated to produce either 1-D/2-D nanowires or 3-D flowerlike architectures via careful control over the experimental parameters used to accomplish the solid-solid phase interconversion process.
Publisher: Elsevier BV
Date: 1967
Publisher: American Chemical Society (ACS)
Date: 1996
DOI: 10.1021/IC960642G
Publisher: American Chemical Society (ACS)
Date: 04-1996
DOI: 10.1021/AC9506701
Abstract: The synthetic pyrethroid insecticide tetramethrin may be reduced reversibly (E°' = -1.650 V vs Ag/Ag(+)) in acetonitrile at hanging mercury drop electrodes (HMDE) and glassy carbon electrodes. On the voltammetric time scale, the initial electron-transfer process involves the reversible formation of a radical anion. Data obtained from electron paramagnetic resonance spectroscopy indicate that the unpaired electron of the radical is located within the phthalimide system of the molecule. The radical anion may be further reduced at very negative applied potentials with the number of processes being dependent on the nature of the voltammetric technique. The detection limit (3σ) for the determination of tetramethrin in acetonitrile at a glassy carbon electrode, using differential pulse voltammetry, was found to be 2.1 × 10(-6) M. At a HMDE the detection limit is lower, having a value of 9.6 × 10(-7) M. The limit of determination (10σ) at a glassy carbon electrode is 3.5 × 10(-6) M and at a HMDE is 3.0 × 10(-6) M. Tetramethrin was selectively determined in an insecticide formulation, at a glassy carbon electrode using differential pulse voltammetry, at a concentration (w/v) of 0.34 ± 0.02%. The determined concentration is in good agreement with the stated value of 0.350 ± 0.018% (w/v).
Publisher: American Chemical Society (ACS)
Date: 1971
DOI: 10.1021/AC60296A014
Publisher: Elsevier BV
Date: 06-1981
Publisher: Springer Science and Business Media LLC
Date: 12-09-2007
Publisher: Wiley
Date: 1989
Publisher: Wiley
Date: 09-06-2012
DOI: 10.1002/DNEU.22022
Publisher: Wiley
Date: 1989
Publisher: Wiley
Date: 09-1990
Publisher: Elsevier BV
Date: 08-2001
Publisher: American Chemical Society (ACS)
Date: 18-03-2019
DOI: 10.1021/ACS.ANALCHEM.9B00129
Abstract: Estimation of parameters of interest in dynamic electrochemical (voltammetric) studies is usually undertaken via heuristic or data optimization comparison of the experimental results with theory based on a model chosen to mimic the experiment. Typically, only single point parameter values are obtained via either of these strategies without error estimates. In this article, Bayesian inference is introduced to Fourier-transformed alternating current voltammetry (FTACV) data analysis to distinguish electrode kinetic mechanisms (reversible or quasi-reversible, Butler-Volmer or Marcus-Hush models) and quantify the errors. Comparisons between experimental and simulated data were conducted across all harmonics using public domain freeware (MECSim).
Publisher: American Chemical Society (ACS)
Date: 16-03-2010
DOI: 10.1021/LA903387N
Abstract: A debate as to whether heme remains bound or is released in myoglobin molecules incorporated into a didodecyldimethylammonium bromide (DDAB) film adhered to a pyrolytic graphite electrode has prompted a comparison of their electrochemistry by the highly sensitive large- litude Fourier transformed ac voltammetric method. The accessibility of third, fourth, and higher harmonic components that are devoid of background current and the enhanced resolution relative to that available in dc voltammetry have allowed a detailed comparison of the Fe(III)/Fe(II) and Fe(II)/Fe(I) redox processes of myoglobin and heme molecules to be undertaken as a function of buffer composition and pH and in the presence and absence of NaBr in the buffer and/or film. Under most conditions examined, only very subtle differences, in the Fe(III)/Fe(II) process were found, implying this process cannot be used to indicate the intactness or otherwise of myoglobin in myoglobin-DDAB films. In contrast, higher order ac harmonics obtained from myoglobin-DDAB and heme-DDAB films reveal pH dependent differences with respect to the Fe(II)/Fe(I) couple. Analysis of the ac harmonics, and with the hypothesis that the Fe(II)/Fe(I) process reflects the myoglobin state, suggests that the majority of the iron heme is released from myoglobin-DDAB (pH 5.0, no NaBr) films in contact with pH 5.0 (0.1 M sodium acetate) buffer solution devoid of or containing NaBr. However, myoglobin films prepared with pH 5.0 buffer containing NaBr shows significant difference in the higher harmonic shapes and midpoint potentials in the Fe(II)/Fe(I) process relative to the case when heme molecules are used, although as noted in other studies, a significant fraction of the Mb is rendered electroinactive in the presence of NaBr. The voltammetric responses of myoglobin and heme-DDAB (pH 5.0) films in contact with pH 7.0 (0.1 M) phosphate buffer solution also exhibit significant differences in the Fe(II)/Fe(I) redox couple in the higher harmonics in contrast to a report [de Groot, M.T. Merkx, M. Koper, M. T. M. J. Am. Chem. Soc. 2005, 127, 16224] that claimed identical midpoint potentials apply to both films under conditions of dc cyclic voltammetry. The FT-ac voltammetric data therefore suggest that a substantial fraction of myoglobin in myoglobin-DDAB (pH 5.0) films in contact with pH 7.0 phosphate buffer solution remains intact. No evidence of a catalytic effect that enhanced the released of heme from myoglobin was found at the pyrolytic graphite electrode surface. In summary, higher harmonic ac voltammetric data indicate that the Fe(II)/Fe(I) process but not the Fe(III)/Fe(II) reflects the state of myoglobin in DDAB films. On this basis, films prepared at pH 5.0 should include NaBr, or else films should be prepared at neutral pH to achieve films with myoglobin remains in its intact near native state when a myoglobin-DDAB film is confined to a graphite electrode surface. Otherwise, the release of heme in myoglobin molecules incorporated into a DDAB film is likely to be a dominant reaction pathway.
Publisher: American Chemical Society (ACS)
Date: 02-1987
DOI: 10.1021/IC00250A015
Publisher: No publisher found
Date: 2003
DOI: 10.5517/CC6L3NJ
Publisher: Wiley
Date: 20-08-2022
Abstract: Fluorine substituent effects associated with the and (n=0, 2, 4, TCNQ=7,7,8,8‐tetracyanoquinodimethane) half‐cell reactions provide access to a wide driving force range (∼850 mV) which is available to tune redox reactions in this case the oxidation of to by or . The ‐ / redox chemistry was studied by steady‐state and transient cyclic voltammetry and UV‐visible spectrophotometry in acetonitrile containing 5 % water and as the supporting electrolyte. In this mixed solvent system, all the (n=0, 2, 4)‐ / reactions were thermodynamically favourable, as were those of (n=2, 4). However, does not oxidize . These findings lead to a prediction that the reversible potential for the / half‐cell reaction lies between −0.083 and −0.278 V vs SHE. Interestingly, in the investigation of the reaction of and in a 1 : 2 concentration ratio, a protonated intermediate was detected. In contrast, when the oxidant was (2,5‐difluoro‐7,7,8,8‐tetracyanoquinodimethane) or (2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquino‐dimethane), no evidence for an analogous protonated intermediate was found. However, if equimolar ratios of (n=0, 2, 4) and were used, the intermediate was again detected. The structure of the intermediate, described as for convenience, is unknown, but this derivative of the redox chemistry is kinetically very stable and only very slowly deprotonated to or reduced by excess to give oxidized and deprotonated . Mechanisms are provided to explain the formation of the protonated intermediate.
Publisher: Elsevier BV
Date: 02-2017
DOI: 10.1016/J.MCE.2016.09.034
Abstract: Within the superfamily of cytochrome P450 enzymes (P450s), there is a small class which is functionally employed for steroid biosynthesis. The enzymes in this class appear to have a small active site to accommodate the steroid substrates specifically and snuggly, prior to the redox transformation or hydroxylation to form a product. Cytochrome P450c17 is one of these and is also a multi-functional P450, with two activities, the first 17α-hydroxylation of pregnenolone is followed by a subsequent 17,20-lyase transformation to dehydroepiandrosterone (DHEA) as the dominant pathways to cortisol precursors or androgens in humans, respectively. How P450c17 regulates these two redox reactions is of special interest. There is a paucity of direct electrochemical studies on steroidogenic P450s, and in this mini-review we provide an overview of these studies with P450c17. Historical consideration as to the difficulties in obtaining reliable electrochemistry due to issues of handling proteins on an electrode, together with advances in the electrochemical techniques are addressed. Recent work using Fourier transformed alternating current voltammetry is highlighted as this technique can provide both catalytic information simultaneously with the underlying redox transfer with the P450 haem.
Publisher: Elsevier BV
Date: 10-1996
Publisher: American Chemical Society (ACS)
Date: 20-05-2008
DOI: 10.1021/JP711804J
Abstract: Eighteen protic ionic liquids containing different combinations of cations and anions, hydrophobicity, viscosity, and conductivity have been synthesized and their physicochemical properties determined. In one series, the diethanolammonium cations were combined with acetate, formate, hydrogen sulfate, chloride, sulfamate, and mesylate anions. In the second series, acetate and formate anions were combined with amine bases, triethylamine, diethylamine, triethanolamine, di-n-propylamine, and di-n-butylamine. The electrochemical characteristics of the eight protic ionic liquids that are liquid at room temperature (RTPILs) have been determined using cyclic, microelectrode, and rotating disk electrode voltammetries. Potential windows of the RTPILs have been compared at glassy carbon, platinum, gold, and boron-doped diamond electrodes and generally found to be the largest in the case of glassy carbon. The voltammetry of IUPAC recommended potential scale reference systems, ferrocene/ferrocenium and cobaltocenium/cobaltocene, have been evaluated and found to be ideal in the case of the less viscous RTPILs but involve adsorption in the highly viscous ones. Other properties such as diffusion coefficients, ionic conductivity, and double layer capacitance also have been measured. The influence of water on the potential windows, viscosity, and diffusion has been studied systematically by deliberate addition of water to the dried ionic liquids. The survey highlights the problems with voltammetric studies in highly viscous room temperature protic ionic liquids and also suggests the way forward with respect to their possible industrial use.
Publisher: Elsevier BV
Date: 04-1988
Publisher: Elsevier BV
Date: 08-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0DT01540G
Abstract: The spectroscopic and photophysical properties of [Ru(bpy)(3)](2)[[Mo(18)O(54)(SO(3))(2)], where bpy is 2,2'-bipyridyl and [Mo(18)O(54)(SO(3))(2)](4-) is either the α or β-sulfite containing polyoxomolybdate isomer, have been measured and compared with those for the well known but structurally distinct sulfate analogue, α-[Mo(18)O(54)(SO(4))(2)](4-). Electronic difference spectroscopy revealed the presence of new spectral features around 480 nm, although they are weak in comparison with the [Ru(bpy)(3)](2)[Mo(18)O(54)(SO(4))(2)] analogue. Surprisingly, Stern-Volmer plots of [Ru(bpy)(3)](2+) luminescence quenching by the polyoxometallate revealed the presence of both static and dynamic quenching for both α and β-[Mo(18)O(54)(SO(3))(2)](4-). The association constant inferred for the ion cluster [Ru(bpy)(3)](2)α-[Mo(18)O(54)(SO(4))(2)] is K = 5.9 ± 0.56 × 10(6) and that for [Ru(bpy)(3)](2)β-[Mo(18)O(54)(SO(4))(2)] is K = 1.0 ± 0.09 × 10(7). Unlike the sulfate polyoxometalates, both sulfite polyoxometalate-ruthenium adducts are non-luminescent. Despite the strong electrostatic association in the adducts resonance Raman and photoelectrochemical studies suggests that unlike the sulfato polyoxometalate analogue there is no sensitization of the polyoxometalate photochemistry by the ruthenium centre for the sulfite anions. In addition, the adducts exhibit photochemical lability in acetonitrile, attributable to decomposition of the ruthenium complex, which has not been observed for other [Ru(bpy)(3)](2+) -polyoxometalate adducts. These observations suggest that less electronic communication exists between the [Ru(bpy)(3)](2+) and the sulfite polyoxoanions relative to their sulfate polyoxoanion counterparts, despite their structural and electronic analogy. The main distinction between sulfate and sulfite polyoxometalates lies in their reversible reduction potentials, which are more positive by approximately 100 mV for the sulfite anions. This suggests that the capacity for [Ru(bpy)(3)](2+) or analogues to sensitize photoreduction in the adducts of polyoxometalates requires very sensitive redox tuning.
Publisher: American Chemical Society (ACS)
Date: 12-1995
DOI: 10.1021/IC00129A025
Publisher: Elsevier BV
Date: 10-2014
Publisher: American Chemical Society (ACS)
Date: 02-08-2007
DOI: 10.1021/AC070448J
Abstract: The analysis of dc cyclic voltammograms of surface-confined metalloproteins is complicated by large background currents, significant ohmic iRu drop, and frequency dispersion related to protein and electrode surface inhomogeneity. The use of large- litude Fourier transform ac voltammetry for the quantification of the electron-transfer properties of a thin film of redox-active protein azurin adsorbed onto edge-plane, basal-plane, and highly oriented pyrolytic graphite electrode surfaces has been evaluated and compared to results obtained by dc cyclic voltammetry. In principle, it has been established that fourth and higher harmonic sine-wave data are ideally suited for analysis of electron-transfer processes as they are almost completely devoid of background capacitance current contributions. However, uncompensated resistance has a higher impact on these components, as is the case with fast scan rate dc techniques, so strategies to include this term in the simulations have been investigated. Application of recommended strategies for the evaluation of the electron-transfer properties of azurin adsorbed onto three forms of graphite, each having different background or uncompensated resistance values, is described and compared to results obtained by traditionally used forms of cyclic voltammetry. The electron-transfer rate constant, k0', of azurin at a highly oriented pyrolytic graphite electrode surface was approximately 250 s(-1), compared with > or =1000 s(-1) at edge-plane and basal-plane graphite electrodes. The significantly lower k0' value found at the highly oriented pyrolytic graphite electrode was related to the relatively low level of edge-plane defect sites present at the surface of this electrode. However, analysis of high ac harmonics suggests that frequency dispersion is substantial at all electrode surfaces. Such effects in these diffusionless situations are significantly enhanced relative to solution-phase voltammetry, where overlay of diffusion layers minimizes the impact of heterogeneity.
Publisher: American Chemical Society (ACS)
Date: 23-10-2012
DOI: 10.1021/IC301370Y
Abstract: The electrochemistry of the water oxidation catalyst, Rb(8)K(2)[{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(γ-SiW(10)O(36))(2)] (Rb(8)K(2)-1(0)) has been studied in the presence and absence of potassium cations in both hydrochloric and sulfuric acid solutions by transient direct current (dc) cyclic voltammetry, a steady state dc method in the rotating disk configuration and the kinetically sensitive technique of Fourier transformed large- litude alternating current (ac) voltammetry. In acidic media, the presence of potassium ions affects the kinetics (apparent rate of electron transfer) and thermodynamics (reversible potentials) of the eight processes (A'/A to H/H') that are readily detected under dc voltammetric conditions. The six most positive processes (A'/A to F/F'), each involve a one electron ruthenium based charge transfer step (A'/A, B'/B are Ru(IV/V) oxidation and C/C' to F/F' are Ru(IV/III) reduction). The apparent rate of electron transfer of the ruthenium centers in sulfuric acid is higher than in hydrochloric acid. The addition of potassium cations increases the apparent rates and gives rise to a small shift of reversible potential. Simulations of the Fourier transformed ac voltammetry method show that the B'/B, E/E', and F/F' processes are quasi-reversible, while the others are close to reversible. A third Ru(IV/V) oxidation process is observed just prior to the positive potential limit via dc methods. Importantly, the ability of the higher harmonic components of the ac method to discriminate against the irreversible background solvent process allows this (process I) as well as an additional fourth reversible ruthenium based process (J) to be readily identified. The steady-state rotating disk electrode (RDE) method confirmed that all four Ru-centers in Rb(8)K(2)-1(0) are in oxidation state IV. The dc and ac data indicate that reversible potentials of the four ruthenium centers are evenly spaced, which may be relevant to understanding of the water oxidation electrocatalysis. A profound effect of the potassium cation is observed for the one-electron transfer process (G/G') assigned to Ru(III/II) reduction and the multiple electron transfer reduction process (H/H') that arise from the tungstate polyoxometalate framework. A significant shift of E°' to a more positive potential value for process H/H' was observed on removal of K(+) (~100 mV in H(2)SO(4) and ~50 mV in HCl).
Publisher: American Chemical Society (ACS)
Date: 02-1971
DOI: 10.1021/AC60297A028
Publisher: American Chemical Society (ACS)
Date: 25-09-2004
DOI: 10.1021/AC0495337
Abstract: Large- litude sinusoidal ac voltammetric techniques, when analyzed in the frequency domain using the Fourier transform-inverse Fourier transform sequence, produce the expected dc and fundamental harmonic ac responses in addition to very substantial second, third, and higher ac harmonics that arise from the presence of significant nonlinearity. A full numerical simulation of the process, Red right arrow over left arrow Ox + e(-), incorporates terms for the uncompensated resistance (R(u)), capacitance of the double layer (C(dl)), and slow electron transfer kinetics (in particular, the reversible potential (E degrees ), rate constant (k(0)), and charge transfer coefficient (alpha) from the Butler-Volmer model). Identification of intuitively obvious patterns of behavior (with characteristically different sensitivity regimes) in dc, fundamental, and higher harmonic terms enables simple protocols to be developed to estimate R(u), C(dl), E degrees , k(0), and alpha. Thus, if large- litude sinusoidal cyclic voltammograms are obtained for two concentrations of the reduced species, data obtained from analysis of the recovered signals provide initial estimates of parameters as follows: (a) the dc cyclic component provides an estimate of E degrees (because the R(u) and k(0) effects are minimized) (b) the fundamental harmonic provides an estimate of C(dl) (because it has a high capacitance-to-faradaic current ratio) and (c) the second harmonic provides an estimate of R(u), k(0), and alpha (because the C(dl) effect is minimized). Methods of refining the initial estimates are then implemented. As a check on the fidelity of the parameters (estimated on the basis of an essentially heuristic approach that solely utilizes the dc, fundamental, and second harmonic voltammograms), comparison of the predicted simulated and experimental third (or higher) harmonic voltammograms can be made to verify that agreement between theory and experiment has been achieved at a predetermined level. The use of the heuristic pattern recognition approach to evaluate the oxidation of ferrocene at a platinum electrode (a reversible process) in the very high resistance solvent dichloromethane (0.1 M Bu(4)NPF(6)) and the reduction of [Fe(CN(6))](3)(-) at a glassy carbon electrode (a quasi-reversible process) in much lower resistance but higher capacitance conditions found in aqueous (0.5 M KCl) media is described and verifies the inherent advantages of employing large- litude sinusoidal techniques in quantitative studies of electrode processes.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0DT00016G
Abstract: Four new complexes, [PdX(κ(2)-2-C(6)R(4)PPh(2))(PPh(2)Fc)] [X = Br, R = H (1), R = F (2) X = I, R = H (3), R = F (4)], containing ferrocenyldiphenylphosphine (PPh(2)Fc) have been prepared and fully characterised. The X-ray structures of complexes trans-1, cis-2 and cis-4, and that of a decomposition product of 4, [Pd(κ(2)-2-C(6)F(4)PPh(2))(μ-I)(μ-2-C(6)F(4)PPh(2))PdI(PPh(2)Fc)] (5), have been determined. These complexes show a distorted square planar geometry about the metal atom, the bite angles of the chelate ligands being about 69°, as expected. The cis/trans ratio of 1-4 in solution is strongly dependent on solvent. The new complexes and the uncoordinated PPh(2)Fc ligand were electrochemically characterised by cyclic and rotating disk voltammetry, UV-visible spectroelectrochemistry, and bulk electrolysis in dichloromethane and acetonitrile. In both cases, oxidation occurs at both the ferrocene and phosphine centres, but the complexes oxidise at more positive potentials than uncoordinated PPh(2)Fc subsequently, the metal-phosphorus bond is cleaved, leading to free PPh(2)Fc(+), which undergoes further chemical and electrochemical reactions.
Publisher: American Chemical Society (ACS)
Date: 05-1970
DOI: 10.1021/IC50087A004
Publisher: Elsevier BV
Date: 11-2010
Publisher: American Chemical Society (ACS)
Date: 10-1992
DOI: 10.1021/J100199A051
Publisher: Elsevier BV
Date: 02-1989
Publisher: Royal Society of Chemistry (RSC)
Date: 1999
DOI: 10.1039/A907542I
Publisher: Elsevier BV
Date: 1984
DOI: 10.1016/S0021-9673(01)90748-4
Abstract: Reversed-phase high-performance liquid chromatography with UV detection is studied for the determination of both progestogenic and oestrogenic components of oral contraceptive formulations. The applicability of the assay is demonstrated for a number of different progestogen-oestrogen combinations in both conventional tablet and novel "paper" formulations. The results show that the method developed is a versatile technique for the routine assay of these pharmaceutical formulations.
Publisher: Springer Science and Business Media LLC
Date: 03-2003
Publisher: Elsevier BV
Date: 02-1969
Publisher: American Chemical Society (ACS)
Date: 08-01-2021
Publisher: American Chemical Society (ACS)
Date: 05-2005
DOI: 10.1021/AC053370K
Publisher: Elsevier BV
Date: 10-2009
DOI: 10.1016/J.ACA.2009.05.015
Abstract: A systematic approach to quantifying the electrode kinetics of surface-confined proteins and identifying the impact of surface heterogeneity is presented. The evaluation approach is based on analysis of in idual harmonics derived from Fourier transformed large- litude ac voltammetry, and their peak current magnitude, I(p)(nomegat) versus frequency, f, relationships. Effectively, variability in the time-scale of each harmonic is expected, and advantage is taken of the fact that each in idual harmonic displays a different level of sensitivity with respect to the kinetic evaluation. The data strategy protocols have been examined for the azurin Cu(II)/Cu(I) process when this metalloprotein is immobilized on gold electrodes modified alkanethiols having different chain lengths, using both pure and mixed thiol systems. I(p)(nomegat) versusf relationships also offer the advantage of the ability to detect and allow for the ohmic IR(u) drop effect and allow analyses that are independent of protein surface coverage. Estimation of an electron transfer rate is achievable from this form of analysis. However, experimentally observed waveshapes for each in idual harmonic are consistently broader than that deduced theoretically on the basis of their rate constants because of kinetic and/or thermodynamic dispersion. In the mixed thiol systems, and with use of the ac method, kinetic discrimination is achieved for fast processes. This systematic study based on a model protein indicates that a more comprehensive level of evaluation of electrode kinetics can be derived from analysis of the ac harmonics available in large- litude ac voltammetry, by initially using I(p)(nomegat)-f data to evaluate the electrode kinetics followed by waveshape analysis to detect heterogeneity effects that give rise to kinetic or thermodynamic dispersion.
Publisher: American Chemical Society (ACS)
Date: 10-1978
DOI: 10.1021/IC50188A032
Publisher: Elsevier BV
Date: 06-1994
Publisher: American Chemical Society (ACS)
Date: 10-1978
DOI: 10.1021/IC50188A033
Publisher: CSIRO Publishing
Date: 2001
DOI: 10.1071/CH02030
Publisher: American Chemical Society (ACS)
Date: 08-1997
DOI: 10.1021/AC9700080
Publisher: American Chemical Society (ACS)
Date: 09-1993
DOI: 10.1021/IC00070A030
Publisher: American Chemical Society (ACS)
Date: 29-07-2005
DOI: 10.1021/AC050172K
Abstract: The two known phases of CuTCNQ and TCNQ (TCNQ = 7,7',8,8'-tetracyanoquinodimethane) have been probed by scanning electrochemical microscopy (SECM) in the feedback mode. The first use of this technique for distinguishing differences in the electronic properties of semiconductor phases exploits the large differences in conductivity that exist between CuTCNQ and the parent TCNQ material and also between the CuTCNQ phases I and II. However, the packing density of the in idual CuTCNQ crystals in a film structure also is shown to influence the SECM feedback response. Finally, it is shown that films of pure phase II material or mixtures of the phases can be mapped using feedback mode SECM. The SECM method provides valuable insights for elucidating properties of semiconducting solids that are mounted on insulating substrates.
Publisher: No publisher found
Date: 2003
DOI: 10.5517/CC6L3PK
Publisher: American Chemical Society (ACS)
Date: 10-1971
DOI: 10.1021/AC60306A034
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B901419E
Abstract: High valence states in manganese clusters are a key feature of the function of one of the most important catalysts found in nature, the water-oxidizing complex of photosystem II. We describe a detailed electrochemical investigation of two bio-inspired manganese-oxo complexes, [Mn(4)O(4)L(6)] (L = diphenylphosphinate (1) and bis(p-methoxyphenyl)phosphinate (2)), in solution, attached to an electrode surface and suspended within a Nafion film. These complexes contain a cubic [Mn(4)O(4)](6+) core stabilized by phosphinate ligands. They have previously been shown to be active and durable photocatalysts for the oxidation of water to dioxygen. A comparison of catalytic photocurrent generated by films deposited by two methods of electrode immobilization reveals that doping of the catalyst in Nafion results in higher photocurrent than was observed for a solid layer of cubane on an electrode surface. In dichloromethane solution, and under conditions of cyclic voltammetry, the one-electron oxidation processes 1/1(+) and 2/2(+) were found to be reversible and quasi-reversible, respectively. Some decomposition of 1(+) and 2(+) was detected on the longer timescale of bulk electrolysis. Both compounds also undergo a two-electron, chemically irreversible reduction in dichloromethane, with a mechanism that is dependent on scan rate and influenced by the presence of a proton donor. When immersed in aqueous electrolyte, the reduction process exhibits a limited level of chemical reversibility. These data provide insights into the catalytic operation of these molecules during photo-assisted electrolysis of water and highlight the importance of the strongly electron-donating ligand environment about the manganese ions in the ability of the cubanes to photocatalyze water oxidation at low overpotentials.
Publisher: Elsevier BV
Date: 06-2018
Publisher: American Chemical Society (ACS)
Date: 24-05-2003
DOI: 10.1021/JP027699A
Publisher: American Chemical Society (ACS)
Date: 10-1989
DOI: 10.1021/JA00203A034
Publisher: Wiley
Date: 19-10-2017
Publisher: Cold Spring Harbor Laboratory
Date: 26-03-2019
DOI: 10.1101/585232
Abstract: Wheat ( Triticum aestivum ) is one of the most important crops worldwide. Given a growing global population coupled with increasingly challenging climate and cultivation conditions, facilitating wheat breeding by fine-tuning important traits such as stress resistance, yield and plant architecture is of great importance. Since they are involved in virtually all aspects of plant development and stress responses, prime candidates for improving these traits are MIKC-type (type II) MADS-box genes. We present a detailed overview of number, phylogeny, and expression of 201 wheat MIKC-type MADS-box genes, which can be assigned to 15 subfamilies. Homoeolog retention is significantly above the average genome-wide retention rate for wheat genes, indicating that many MIKC-type homoeologs are functionally important and not redundant. Gene expression is generally in agreement with the expected subfamily-specific expression pattern, indicating broad conservation of function of MIKC-type genes during wheat evolution. We find the extensive expansion of some MIKC-type subfamilies to be correlated with their chromosomal location and propose a link between MADS-box gene duplications and the adaptability of wheat. A number of MIKC-type genes encode for truncated proteins that lack either the DNA-binding or protein-protein interaction domain and occasionally show novel expression patterns, possibly pointing towards neofunctionalization. Conserved and neofunctionalized MIKC-type genes may have played an important role in the adaptation of wheat to a ersity of conditions, hence contributing to its importance as a global staple food. Therefore, we propose that MIKC-type MADS-box genes are especially well suited for targeted breeding approaches and phenotypic fine tuning.
Publisher: American Chemical Society (ACS)
Date: 07-07-2000
DOI: 10.1021/AC991464M
Abstract: Voltammetric studies in the absence of added supporting electrolyte are presently dominated by the use of near-steady-state microelectrode techniques and millimolar or lower depolarizer concentrations. However, with this methodology, large departures from conventional migration-diffusion theory have been reported for the [Fe(CN)6](3-/4-) process at both carbon fiber and platinum microdisk electrodes. In contrast, data obtained in the present study reveal that use of the transient cyclic voltammetric technique at glassy carbon, gold, or platinum macrodisk electrodes and K4[Fe(CN)6] or K3[Fe(CN)6] concentrations of 50 mM or greater provides an approximately reversible response in the absence of added electrolyte. It is suggested that the use of very high [Fe(CN)6](3-) and [Fe(CN)6](4-) concentrations overcomes problems associated with a diffuse double layer and that large electrode surface areas and faster potential sweep rates minimize electrode blockage and passivating phenomena that can plague voltammetric studies at microelectrodes. The cyclic voltammetry of the [Fe(CN)6](3-/4-) couple at a range of concentrations at macroelectrodes in the absence of added inert electrolyte is compared with that obtained in the presence of 1 M KCl. The enhanced influences of uncompensated resistance, migration, and natural convection arising from density gradients under transient conditions at macrodisk electrodes also are considered.
Publisher: Elsevier BV
Date: 08-1995
Publisher: Springer Science and Business Media LLC
Date: 04-02-2014
Publisher: Elsevier BV
Date: 04-2000
Publisher: American Chemical Society (ACS)
Date: 10-05-2018
Publisher: Elsevier BV
Date: 10-1993
Publisher: Elsevier BV
Date: 03-1986
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CC9THQ9
Publisher: Elsevier BV
Date: 06-2000
Publisher: Elsevier BV
Date: 03-1990
Publisher: Elsevier BV
Date: 06-2006
Publisher: No publisher found
Date: 2008
DOI: 10.5517/CCP8W1V
Publisher: American Chemical Society (ACS)
Date: 30-01-2013
DOI: 10.1021/AC303042R
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CCPJ59N
Publisher: American Chemical Society (ACS)
Date: 07-1983
DOI: 10.1021/JA00352A022
Publisher: American Chemical Society (ACS)
Date: 1993
DOI: 10.1021/AC00049A012
Publisher: American Chemical Society (ACS)
Date: 1984
DOI: 10.1021/OM00079A002
Publisher: American Chemical Society (ACS)
Date: 09-1994
DOI: 10.1021/OM00021A018
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CC07549C
Abstract: Advanced data analysis tools such as mathematical optimisation, Bayesian inference and machine learning have the capability to revolutionise the field of quantitative voltammetry.
Publisher: Royal Society of Chemistry (RSC)
Date: 2003
DOI: 10.1039/B306521A
Publisher: American Chemical Society (ACS)
Date: 15-05-1988
DOI: 10.1021/AC00161A015
Abstract: Atherosclerotic lesions are asymmetric focal thickenings of the intima of arteries that consist of lipids, various cell types and extracellular matrix (ECM). These lesions lead to vascular occlusion representing the most common cause of death in the Western world. The main cause of vascular occlusion is rupture of atheromatous lesions followed by thrombus formation. Fibronectin (FN) is one of the earliest ECM proteins deposited at atherosclerosis-prone sites and was suggested to promote atherosclerotic lesion formation. Here, we report that atherosclerosis-prone apolipoprotein E-null mice lacking hepatocyte-derived plasma FN (pFN) fed with a pro-atherogenic diet display dramatically reduced FN depositions at atherosclerosis-prone areas, which results in significantly smaller and fewer atherosclerotic plaques. However, the atherosclerotic lesions from pFN-deficient mice lacked vascular smooth muscle cells and failed to develop a fibrous cap. Thus, our results demonstrate that while FN worsens the course of atherosclerosis by increasing the atherogenic plaque area, it promotes the formation of the protective fibrous cap, which in humans prevents plaques rupture and vascular occlusion.
Publisher: American Chemical Society (ACS)
Date: 06-1994
DOI: 10.1021/AC00083A024
Publisher: Elsevier BV
Date: 04-1998
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3TC32178A
Publisher: Elsevier BV
Date: 05-1984
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7CP07723H
Abstract: A Sn electrocatalyst for CO 2 reduction to formate with enhanced selectivity has been developed based on a new substrate effect.
Publisher: Elsevier BV
Date: 06-2017
Publisher: American Chemical Society (ACS)
Date: 10-1988
DOI: 10.1021/OM00100A022
Publisher: American Chemical Society (ACS)
Date: 02-02-2016
DOI: 10.1021/ACS.ANALCHEM.5B04354
Abstract: Alternating current (ac) voltammetry provides access to faster electrode kinetics than direct current (dc) methods. However, difficulties in ac and other methods arise when the heterogeneous electron-transfer rate constant (k(0)) approaches the reversible limit, because the voltammetric characteristics become insensitive to electrode kinetics. Thus, in this near-reversible regime, even small uncertainties associated with bulk concentration (C), diffusion coefficient (D), electrode area (A), and uncompensated resistance (Ru) can lead to significant systematic error in the determination of k(0). In this study, we have introduced a kinetically sensitive dual-frequency designer waveform into the Fourier-transformed large- litude alternating current (FTAC) voltammetric method that is made up of two sine waves having the same litude but with different frequencies (e.g., 37 and 615 Hz) superimposed onto a dc r to quantify the close-to-reversible Fc(0/+) process (Fc = ferrocene) in two nonhaloaluminate ionic liquids. The concept is that from a single experiment the lower-frequency data set, collected on a time scale where the target process is reversible, can be used as an internal reference to calibrate A, D, C, and Ru. These calibrated values are then used to calculate k(0) from analysis of the harmonics of the higher-frequency data set, where the target process is quasi-reversible. With this approach, k(0) values of 0.28 and 0.11 cm·s(-1) have been obtained at a 50 μm diameter platinum microdisk electrode for the close-to-diffusion-controlled Fc(0/+) process in two ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, respectively.
Publisher: Elsevier BV
Date: 04-2008
Publisher: American Chemical Society (ACS)
Date: 11-03-2004
DOI: 10.1021/AC035108M
Abstract: It has been found empirically that, for an E(rev)C(irrev) process, the forward/backward ratio of the peak height magnitudes in cyclic voltammetry equals 1 + ktau, where k is the rate constant of the chemical reaction and tau is the time required for the scan to travel between the half-wave and reversal potentials. The relationship is largely independent of the scan rate and the reversal potential, except insofar as these influence tau. Though not exact, the relationship is obeyed closely enough to provide accurate rate constants under favorable conditions. The utility of this simple formula in extracting homogeneous kinetic information is demonstrated using experimental data for the electron-transfer-induced isomerization of an octahedral manganese complex. An explanation of the relationship is presented, as is a more exact formula that reduces to 1 + ktau when k is small. A semiquantitative explanation of the relationship is provided.
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/P29950001327
Publisher: Wiley
Date: 12-2001
DOI: 10.1002/1521-4109(200112)13:18<1475::AID-ELAN1475>3.0.CO;2-F
Publisher: Elsevier BV
Date: 11-1997
Publisher: American Chemical Society (ACS)
Date: 06-2006
DOI: 10.1021/JP061896I
Abstract: Voltammetric techniques have been introduced to monitor the formation of gold nanoparticles produced via the reaction of the amino acid glycyl-L-tyrosine with Au(III) (bromoaurate) in 0.05 M KOH conditions. The alkaline conditions facilitate amino acid binding to Au(III), inhibit the rate of reduction to Au(0), and provide an excellent supporting electrolyte for voltammetric studies. Data obtained revealed that a range of time-dependent gold solution species are involved in gold nanoparticle formation and that the order in which reagents are mixed is critical to the outcome. Concomitantly with voltammetric measurements, the properties of gold nanoparticles formed are probed by examination of electronic spectra in order to understand how the solution environment present during nanoparticle growth affects the final distribution of the nanoparticles. Images obtained by the ex situ transmission electron microscopy (TEM) technique enable the physical properties of the nanoparticles isolated in the solid state to be assessed. Use of this combination of in situ and ex situ techniques provides a versatile framework for elucidating the details of nanoparticle formation.
Publisher: Elsevier BV
Date: 08-2015
Publisher: American Chemical Society (ACS)
Date: 31-03-2020
Publisher: American Chemical Society (ACS)
Date: 10-1983
DOI: 10.1021/AC00262A024
Publisher: Elsevier BV
Date: 04-1997
Publisher: American Chemical Society (ACS)
Date: 28-01-1998
DOI: 10.1021/JP972830D
Publisher: Elsevier BV
Date: 07-1978
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5DT01530H
Abstract: Voltammetric and spectroscopic data for the V V/IV couple in 1- and 4-[S 2 V V W 17 O 62 ] 5− are reported in acidified acetonitrile.
Publisher: Wiley
Date: 10-12-2020
Publisher: American Chemical Society (ACS)
Date: 12-01-2022
Abstract: A series of hybrid electrolytes composed of diglyme and ionic liquids (ILs) have been investigated for Na-O
Publisher: Elsevier BV
Date: 07-1971
Publisher: Elsevier BV
Date: 11-1983
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP00968B
Abstract: Complementary techniques reveal new insights on electron transfer rates at different electrode materials.
Publisher: American Chemical Society (ACS)
Date: 15-10-1993
DOI: 10.1021/AC00068A004
Publisher: Elsevier BV
Date: 05-1976
Publisher: American Chemical Society (ACS)
Date: 07-1974
DOI: 10.1021/AC60344A011
Publisher: Elsevier BV
Date: 1988
Publisher: American Chemical Society (ACS)
Date: 10-1983
DOI: 10.1021/IC00163A006
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD7CV
Publisher: Elsevier BV
Date: 03-1996
Publisher: Elsevier BV
Date: 1975
Publisher: Elsevier BV
Date: 1982
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCVZB48
Publisher: Elsevier BV
Date: 12-1989
Publisher: Elsevier BV
Date: 05-1987
Publisher: Elsevier BV
Date: 12-2010
Publisher: Wiley
Date: 09-10-2017
Abstract: Low-valent iron centers are critical intermediates in chemical and bio-chemical processes. Herein, we show the first ex le of a low-valent Fe
Publisher: Elsevier BV
Date: 03-1996
Publisher: Elsevier BV
Date: 1969
Publisher: Informa UK Limited
Date: 09-1983
Publisher: American Chemical Society (ACS)
Date: 03-1984
DOI: 10.1021/OM00081A015
Publisher: Elsevier BV
Date: 06-1987
Publisher: Wiley
Date: 10-2019
DOI: 10.1111/NPH.16122
Abstract: Wheat ( Triticum aestivum ) is one of the most important crops worldwide. Given a growing global population coupled with increasingly challenging cultivation conditions, facilitating wheat breeding by fine‐tuning important traits is of great importance. MADS ‐box genes are prime candidates for this, as they are involved in virtually all aspects of plant development. Here, we present a detailed overview of phylogeny and expression of 201 wheat MIKC ‐type MADS ‐box genes. Homoeolog retention is significantly above the average genome‐wide retention rate for wheat genes, indicating that many MIKC ‐type homoeologs are functionally important and not redundant. Gene expression is generally in agreement with the expected subfamily‐specific expression pattern, indicating broad conservation of function of MIKC ‐type genes during wheat evolution. We also found extensive expansion of some MIKC ‐type subfamilies, especially those potentially involved in adaptation to different environmental conditions like flowering time genes. Duplications are especially prominent in distal telomeric regions. A number of MIKC ‐type genes show novel expression patterns and respond, for ex le, to biotic stress, pointing towards neofunctionalization. We speculate that conserved, duplicated and neofunctionalized MIKC ‐type genes may have played an important role in the adaptation of wheat to a ersity of conditions, hence contributing to the importance of wheat as a global staple food.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3GC42404A
Abstract: High-yield electrocarboxylation of acetophenone can be achieved in dry [BMPyrd][TFSI].
Publisher: American Chemical Society (ACS)
Date: 23-09-2014
DOI: 10.1021/JP506990E
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD7DW
Publisher: American Chemical Society (ACS)
Date: 18-05-2017
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCVZB59
Publisher: Wiley
Date: 07-2004
Abstract: The influence of peptide‐protein interactions on the electrochemistry of copper‐containing pseudoazurin from Alcaligenes faecalis strain S‐6 has been investigated by covalently binding cysteine‐containing hexapeptides to a gold electrode surface. The hexapeptides contain three cysteines in the same positions with the remaining amino acids varied to give mixed charge (lysine, threonine, alanine), positive (lysine), overall neutral (alanine), and negative (glutamate) chemically modified electrode surfaces. These systematic variations in the amino acid sequence lead to large variations in voltammetric behavior for the Cu(II)→Cu(I) heterogeneous pseudoazurin redox process encompassing fully reversible and diffusional, transitionally adsorbed, or strongly adsorbed forms of voltammetry. The variations in voltammetric behavior may be related to electrostatic interactions between the charges from the hexapeptide electrode modifiers and surface charges of pseudoazurin. A possible description of the pseudoazurin‐electrode surface interaction is given.
Publisher: Springer Berlin Heidelberg
Date: 30-09-2010
Publisher: American Chemical Society (ACS)
Date: 04-1983
DOI: 10.1021/AC00255A031
Publisher: Elsevier BV
Date: 05-1998
Publisher: American Chemical Society (ACS)
Date: 08-1995
DOI: 10.1021/AC00111A015
Publisher: Springer Science and Business Media LLC
Date: 13-02-2017
DOI: 10.1038/S41598-017-00058-2
Abstract: Electro-scrubbing is being developed as a futuristic technology for the removal of air-pollutants. To date, only one homogeneous mediator for the removal of air pollutants has been generated in each experiment using a ided electrolytic flow cell in an acidic medium. This paper reports the concurrent generation of two homogenous mediators, one at the anodic half-cell containing an acidic solution and the other at the cathodic half-cell containing a basic solution. The concept was inspired by the change in pH that occurs during water electrolysis in a ided cell. A 10 M KOH electrolyte medium assisted in the electrochemical generation of low valent 14% Co 1+ ([Co I (CN) 5 ] 4− ) mediator formed from reduction of [Co II (CN) 5 ] 3− which was accompanied by a change in the solution 'oxidation reduction potential' (ORP) of −1.05 V Simultaneously, 41% of Co 3+ was generated from oxidation of Co II SO 4 in the anodic half-cell. No change in the solution ORP was observed at the cathodic half-cell when both half-cells contain 5 M H 2 SO 4 , and Co 3+ was formed in the anodic half-cell. An electro-scrubbing approach based on the above principles was developed and tested on gaseous-pollutants, CH 3 CHO and CCl 4 , by Co 3+ and Co 1+ , respectively, with 90 and 96% removal achieved, respectively.
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B618036A
Publisher: Elsevier BV
Date: 12-2023
Publisher: Wiley
Date: 10-08-2018
Publisher: Wiley
Date: 04-1990
Publisher: American Chemical Society (ACS)
Date: 16-03-2017
Abstract: A thin film of Nafion, of approximately 5 μm thickness, asymmetrically deposited onto a 6 μm thick film of poly(ethylene terephthalate) (PET) fabricated with a 5, 10, 20, or 40 μm microhole, is shown to exhibit prominent ionic diode behavior involving cation charge carrier ("cationic diode"). The phenomenon is characterized via voltammetric, chrono erometric, and impedance methods. Phenomenologically, current rectification effects are comparable to those observed in nanocone devices where space-charge layer effects dominate. However, for microhole diodes a resistive, a limiting, and an overlimiting potential domain can be identified and concentration polarization in solution is shown to dominate in the closed state.
Publisher: American Chemical Society (ACS)
Date: 07-1986
DOI: 10.1021/OM00138A023
Publisher: Wiley
Date: 11-1992
Publisher: The Electrochemical Society
Date: 02-1999
DOI: 10.1149/1.1391657
Publisher: Elsevier BV
Date: 02-2007
Publisher: Royal Society of Chemistry (RSC)
Date: 1998
DOI: 10.1039/A805860A
Publisher: American Chemical Society (ACS)
Date: 07-05-2004
DOI: 10.1021/JP049294R
Publisher: American Chemical Society (ACS)
Date: 22-11-2011
DOI: 10.1021/JO2018334
Abstract: The tetrabutylammonium complex with a 2:5 stoichiometry, (n-Bu(4)N)(2)(TCNQ)(5), has been prepared and structurally characterized by X-ray crystallography. Diagnostic bands in the Raman spectrum and signature features in the electrochemistry confirm that the TCNQ moieties are partially charged in the solid state. EPR, magnetic susceptibility, and electrical conductivity measurements are all consistent with (n-Bu(4)N)(2)(TCNQ)(5) behaving as a quasi-one-dimensional organic semiconductor.
Publisher: Elsevier BV
Date: 12-2000
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/P29950001365
Publisher: American Chemical Society (ACS)
Date: 06-1994
DOI: 10.1021/IC00090A013
Publisher: American Chemical Society (ACS)
Date: 02-1991
DOI: 10.1021/IC00003A023
Publisher: American Chemical Society (ACS)
Date: 03-1982
DOI: 10.1021/AC00240A053
Publisher: Wiley
Date: 08-1996
Abstract: Simultaneous voltammetric or double potential step and quartz crystal microbalance experiments combined with the results obtained from optical and surface analysis measurements have allowed new mechanistic aspects of the electrochemical oxidation of microcrystalline particles of tetrathiafulvalene (TTF) attached to a gold substrate, which is placed in aqueous electrolyte media, to be unravelled. The use of the microcrystalline form of the solid rather than thin films makes it possible to obtain short time domain data which enables features for the reduction and the oxidation process consistent with a nucleation process at the solid electrode‐aqueous electrolyte interface to be detected. Electrochemical quartz crystal microbalance (EQCM) and electron microprobe analysis experiments confirm that the overall process in the oxidation of microcrystals of TTF in aqueous KBr, KI, KClO 4 , NaBr and CsBr electrolyte media involves the uptake of the appropriate nonsolvated anion (X ‐ ) in order to maintain charge neutrality. Reduction of the oxidized TTF leads to the expulsion of the anion. The rates of uptake and expulsion are both very rapid for the bromide ion, but involve slower reaction steps for iodide and perchlorate anions. The oxidation of TTF particles attached to a gold electrode can be described by the equation The number of electrons transferred to the solid, n , may theoretically vary over a wide range, but in the case of X − =Br − is found to be fixed with only one product formed ( n =0.7). The peak potential and shape of voltammograms have been studied as a function of scan rate, electrolyte concentration and the nature of the anion and cation. A Nernstian change in peak potential is observed when the electrolyte anion concentration is varied. The wave shape, but not the charge, also varies with electrolyte anion and concentration. In contrast, no dependence on the electrolyte cation is found. All the data imply that incorporation of the anion into the solid provides the charge neutralization mechanism. This study confirms that use of microcrystalline forms of a solid enables a wide range of time domains (and techniques) to be applied to electrochemical studies of solids.
Publisher: American Chemical Society (ACS)
Date: 02-02-2010
DOI: 10.1021/AC902296R
Abstract: A general theory has been developed for voltammetric ion sensing of cations and anions based on the use of an electrode coated with a membrane containing an electroactive species, an ionophore, and a supporting electrolyte dissolved in a plasticizer. In experimental studies, a membrane coated electrode is fabricated by the drop coating method. In one configuration, a glassy carbon electrode is coated with a poly(vinyl chloride) based membrane, which contains the electroactive species, ionophore, plasticizer and supporting electrolyte. In the case of a cation sensor, ionophore facilitated transfer of the target cation from the aqueous solution to the membrane phase occurs during the course of the reduction of the electroactive species present in the membrane in order to maintain charge neutrality. The formal potential is calculated from the cyclic voltammogram as the average of the reduction and oxidation peak potentials and depends on the identity and concentration of the ion present in the aqueous solution phase. A plot of the formal potential versus the logarithm of the concentration exhibits a close to Nernstian slope of RT/F millivolts per decade change in concentration when the concentration of K(+) and Na(+) is varied over the concentration range of 0.1 mM to 1 M when K(+) or Na(+) ionophores are used in the membrane. The slope is close to RT/2F millivolts for a Ca(2+) voltammetric ion-selective electrode fabricated using a Ca(2+) ionophore. The sensor measurement time is only a few seconds. Voltammetric sensors for K(+), Na(+), and Ca(2+) constructed in this manner exhibit the sensitivity and selectivity required for determination of these ions in environmentally and biologically important matrixes. Analogous principles apply to the fabrication of anion voltammetric sensors.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CE05165B
Publisher: Wiley
Date: 2009
Publisher: American Chemical Society (ACS)
Date: 09-1997
DOI: 10.1021/IC970592V
Publisher: American Chemical Society (ACS)
Date: 11-09-2009
DOI: 10.1021/IC9011394
Abstract: Unlike the case with other alent transition metal M[TCNQ](2)(H(2)O)(2) (M = Fe, Co, Ni) analogues, the electrochemically induced solid-solid phase interconversion of TCNQ microcrystals (TCNQ = 7,7,8,8-tetracyanoquinodimethane) to Mn[TCNQ](2)(H(2)O)(2) occurs via two voltammetrically distinct, time dependent processes that generate the coordination polymer in nanofiber or rod-like morphologies. Careful manipulation of the voltammetric scan rate, electrolysis time, Mn(2+)((aq)) concentration, and the method of electrode modification with solid TCNQ allows selective generation of either morphology. Detailed ex situ spectroscopic (IR, Raman), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) characterization clearly establish that differences in the electrochemically synthesized Mn-TCNQ material are confined to morphology. Generation of the nanofiber form is proposed to take place rapidly via formation and reduction of a Mn-stabilized anionic dimer intermediate, [(Mn(2+))(TCNQ-TCNQ)(2)(*-)], formed as a result of radical-substrate coupling between TCNQ(*-) and neutral TCNQ, accompanied by ingress of Mn(2+) ions from the aqueous solution at the triple phase TCNQ/electrode/electrolyte boundary. In contrast, formation of the nanorod form is much slower and is postulated to arise from disproportionation of the [(Mn(2+))(TCNQ-TCNQ)(*-)(2)] intermediate. Thus, identification of the time dependent pathways via the solid-solid state electrochemical approach allows the crystal size of the Mn[TCNQ](2)(H(2)O)(2) material to be tuned and provides new mechanistic insights into the formation of different morphologies.
Publisher: Elsevier BV
Date: 02-1987
Publisher: American Chemical Society (ACS)
Date: 07-1987
DOI: 10.1021/IC00261A019
Publisher: Elsevier BV
Date: 12-1984
Publisher: American Chemical Society (ACS)
Date: 28-10-2004
DOI: 10.1021/IC0498790
Abstract: Reaction of 2-Li-4-MeC6H3AsPh2 with [PtCl2(SEt2)2] gives two isomeric dinuclear platinum(II) complexes, one containing a half-lantern structure with two chelating and two bridging C6H3-5-Me-2-AsPh2 ligands, [Pt2(kappa2As,C-C6H3-5-Me-2-AsPh2)2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)2], and the other, a full-lantern with four bridging C6H3-5-Me-2-AsPh2 ligands, [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4]. The lantern structure of the latter is retained in the dihalodiplatinum(III) complexes that are formed by oxidative addition of chlorine, bromine, or iodine to the isomeric mixture. The dichloro derivative undergoes metathesis reactions with silver or sodium salts, yielding the corresponding cyano, thiocyanato, cyanato, and fluoro species. The structures of all complexes have been determined by single-crystal X-ray analysis. The oxidative addition products have Pt-Pt distances in the range 2.65-2.79 A (cf. 2.89 A in the lantern diplatinum(II) structure), consistent with the presence of a Pt-Pt bond. Electrochemical data lead to the conclusion that an initial rapid one-electron process and subsequent chemical reactions produce the dihalodiplatinum(III) lantern structure when mixtures of the lantern and half-lantern complexes are oxidized by halogens. The electrochemical data also explain why chemical reduction of the dihalodiplatinum(III) complex produces only the lantern diplatinum(II) complex.
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD7BT
Publisher: The Royal Society
Date: 28-08-2011
Abstract: As in many scientific disciplines, modern chemistry involves a mix of experimentation and computer-supported theory. Historically, these skills have been provided by different groups, and range from traditional ‘wet’ laboratory science to advanced numerical simulation. Increasingly, progress is made by global collaborations, in which new theory may be developed in one part of the world and applied and tested in the laboratory elsewhere. e-Science, or cyber-infrastructure, underpins such collaborations by providing a unified platform for accessing scientific instruments, computers and data archives, and collaboration tools. In this paper we discuss the application of advanced e-Science software tools to electrochemistry research performed in three different laboratories – two at Monash University in Australia and one at the University of Oxford in the UK. We show that software tools that were originally developed for a range of application domains can be applied to electrochemical problems, in particular Fourier voltammetry. Moreover, we show that, by replacing ad-hoc manual processes with e-Science tools, we obtain more accurate solutions automatically.
Publisher: American Chemical Society (ACS)
Date: 02-1989
DOI: 10.1021/IC00302A034
Publisher: No publisher found
Date: 2002
DOI: 10.5517/CC5DNY4
Publisher: American Chemical Society (ACS)
Date: 22-10-2020
Publisher: Elsevier BV
Date: 07-1998
Publisher: American Chemical Society (ACS)
Date: 23-04-2014
DOI: 10.1021/JP501862N
Publisher: American Chemical Society (ACS)
Date: 1985
DOI: 10.1021/AC00279A043
Publisher: Elsevier BV
Date: 08-2003
Publisher: American Chemical Society (ACS)
Date: 06-1980
DOI: 10.1021/IC50208A067
Publisher: American Chemical Society (ACS)
Date: 06-10-2009
DOI: 10.1021/AC901318R
Abstract: Under most experimental conditions, a distinctly nonlinear background current is encountered in all forms of voltammetry which arises from the potential dependence of the capacitance. The nonlinear background current has been successfully modeled under large litude sinusoidal ac voltammetric conditions with a fourth order polynomial. The model was applied to a dummy cell containing a nonideal ceramic capacitor and commonly used electrodes. The nonlinearity in behavior of the background capacitance is particularly significant when considering the discrimination between the Faradaic and background contributions in the higher order harmonics resolved in ac voltammetry by Fourier transform-inverse Fourier transform approaches and in the simulation of the background current and hence double-layer capacitance as a function of potential. Typically, measurable background current under large litude conditions is detectable in the dc and fundamental to fourth harmonic components in large litude ac voltammetry. For analytical purposes, this background current can be corrected on a per harmonic basis without the need for any model. Background correction has been successfully applied to the first four harmonics for the oxidation of ferrocenemonocarboxylic acid over the concentration range of 5-500 microM in aqueous 0.5 M NaCl solution.
Publisher: Elsevier BV
Date: 03-1994
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CCN69NS
Publisher: American Chemical Society (ACS)
Date: 09-1972
DOI: 10.1021/AC60319A016
Publisher: American Chemical Society (ACS)
Date: 11-1983
DOI: 10.1021/AC00263A015
Publisher: American Chemical Society (ACS)
Date: 11-1983
DOI: 10.1021/AC00263A016
Abstract: The present study investigated the possibilities and feasibility of drug targeting for an arterial bifurcation lesion to influence the host healing response. A micrometer sized iron particle was used only to model the magnetic carrier in the experimental investigation (not intended for clinical use), to demonstrate the feasibility of the particle targeting at the lesion site and facilitate the new experimental investigations using coated superparamagnetic iron oxide nanoparticles. Magnetic fields were generated by a single permanent external magnet (ferrite magnet). Artery bifurcation exerts severe impacts on drug distribution, both in the main vessel and the branches, practically inducing an uneven drug concentration distribution in the bifurcation lesion area. There are permanently positioned magnets in the vicinity of the bifurcation near the diseased area. The generated magnetic field induced deviation of the injected ferromagnetic particles and were captured onto the vessel wall of the test section. To increase the particle accumulation in the targeted region and consequently avoid the polypharmacology (interaction of the injected drug particles with multiple target sites), it is critical to understand flow hemodynamics and the correlation between flow structure, magnetic field gradient, and spatial position.
Publisher: American Chemical Society (ACS)
Date: 12-1986
DOI: 10.1021/IC00245A012
Publisher: Springer Science and Business Media LLC
Date: 02-08-2014
Publisher: Elsevier BV
Date: 1991
DOI: 10.1016/0039-9140(91)80010-W
Abstract: The reverse-phase separation and electrochemical detection of alpha-, gg-, and delta-tocopherol at a potential of +0.90 V vs. a gold pseudo-reference electrode is possible down to 10(-7)M concentrations, with surface-modified platinum microdisc electrodes in a methanol/water (95:5) solvent mixture. The use of microclectrodes with radii of 10-70 mum, rather than electrodes of conventional size, minimizes problems associated with iR drop and obviates the need for deliberately added electrolyte. These features simplify the analytical procedure. The background response of an untreated platinum microelectrode in the methanol/water (95:5) system at positive potentials is characterized by processes arising from adsorption/oxidation of methanol and formation of surface oxides. Amperometric detection is of little use under these conditions. However, preoxidation of the electrode surface in 2M nitric acid inhibits the methanol adsorption/oxidation reaction but not the tocopherol response and therefore allows highly sensitive erometric detection.
Publisher: American Chemical Society (ACS)
Date: 23-04-2005
DOI: 10.1021/AC048151Y
Abstract: The underlying electron-transfer and coupled chemical processes associated with biologically important catalytic reactions can be resolved using a combination of Fourier transform ac voltammetry with an analysis of the separated dc and ac components. This outcome can be achieved because the response associated with generation of the catalytic current is essentially confined to the steady-state dc component, whereas the electron-transfer step is dominant in the fundamental and higher harmonics. For the mediated oxidation of glucose with glucose oxidase, it was found that the underlying reversible redox chemistry of the mediator, ferrocenemonocarboxylic acid, as detected in the third and higher harmonics, was totally unaffected by introduction of the catalytic process. In contrast, for the catalytic reduction of molecular oxygen by cytochrome P450, slight changes in the P450 redox process were detected when the catalytic reaction was present. Simulations of a simple catalytic reaction scheme support the fidelity of this novel FT ac voltammetric approach for examining mechanistic nuances of catalytic forms of electrochemical reaction schemes.
Publisher: American Chemical Society (ACS)
Date: 12-1987
DOI: 10.1021/OM00155A009
Publisher: American Chemical Society (ACS)
Date: 16-09-2015
Publisher: American Chemical Society (ACS)
Date: 16-09-2015
Publisher: The Electrochemical Society
Date: 1973
DOI: 10.1149/1.2403291
Publisher: American Chemical Society (ACS)
Date: 17-06-2000
DOI: 10.1021/JP994275G
Publisher: Elsevier BV
Date: 10-2013
Publisher: Elsevier BV
Date: 08-1988
Publisher: American Chemical Society (ACS)
Date: 27-01-2007
DOI: 10.1021/JA066874O
Abstract: A generic method for the synthesis of metal-7,7,8,8-tetracyanoquinodimethane (TCNQ) charge-transfer complexes on both conducting and nonconducting substrates is achieved by photoexcitation of TCNQ in acetonitrile in the presence of a sacrificial electron donor and the relevant metal cation. The photochemical reaction leads to reduction of TCNQ to the TCNQ(-) monoanion. In the presence of M(x+)(MeCN), reaction with TCNQ(-)(MeCN) leads to deposition of M(x+)[TCNQ]x crystals onto a solid substrate with morphologies that are dependent on the metal cation. Thus, CuTCNQ phase I photocrystallizes as uniform microrods, KTCNQ as microrods with a random size distribution, AgTCNQ as very long nanowires up to 30 mum in length and with diameters of less than 180 nm, and Co[TCNQ](2)(H(2)O)(2) as nanorods and wires. The described charge-transfer complexes have been characterized by optical and scanning electron microscopy and IR and Raman spectroscopy. The CuTCNQ and AgTCNQ complexes are of particular interest for use in memory storage and switching devices. In principle, this simple technique can be employed to generate all classes of metal-TCNQ complexes and opens up the possibility to pattern them in a controlled manner on any type of substrate.
Publisher: Elsevier BV
Date: 1980
Publisher: American Chemical Society (ACS)
Date: 11-01-2001
DOI: 10.1021/IC000793Q
Abstract: The synthesis and characterization of (Bu4N)4[S2W18O62].1.23MeCN.0.27H2O are reported. It crystallizes in the monoclinic space group C2/c with a = 22.389(6) A, b = 22.104(3) A, c = 25.505(5) A, beta = 95.690(15) degrees, V = 12560(5) A3, and Z = 4. The anion exists as the gamma* isomer, the second ex le of this isomer type to be characterized structurally. The equivalent molybdenum salt occurs as the alpha isomer. gamma*-[S2W18O62]4- in MeCN solution displayed four electrochemically reversible one-electron redox processes at E1/2 values of -0.24, -0.62, -1.18, and -1.57 V versus the Fc+/Fc couple. Upon addition of acid in MeCN/H2O (95/5 v/v), the two most cathodic processes converted to an overall two-electron process at -0.71 V. The total data suggested that this process actually comprises two one-electron transfer processes, occurring at different potentials, with associated proton-transfer reactions. The interpretation is supported by simulation of the effect of acid titration upon the cyclic voltammetry. While multiple pathways for correlated reduction and protonation are present in both the molybdenum and tungsten systems, only a single fast oxidation pathway is available. As the reduced forms of [S2W18O62]4- are much weaker bases than those of [S2Mo18O62]4-, the in idual oxidation pathways are not the same. However, their existence determines the highly reversible electrochemical behavior that is characteristic of these anions, and that of polyoxometalate systems in general.
Publisher: Elsevier BV
Date: 09-1991
Publisher: American Chemical Society (ACS)
Date: 27-07-2015
Abstract: A method has been developed for the efficient electrodeposition of cobalt and nickel nanostructures with the assistance of the Lindqvist ion [Nb6O19](8-). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry, and a range of electrochemical techniques have been used to characterize the morphology, composition, catalytic water oxidation activity and stability of the films in alkaline solution. SEM images show that films consisting of nanoparticles with diameters of ca. 30 to 40 nm are formed after 40-50 potential cycles of deposition. Nb and Co/Ni are detected in the films by EDX. ICP-MS results show an elemental ratio of 1:1 for Co:Nb and 1:3 for Ni:Nb, respectively. Raman spectra reveal the presence of both [Nb6O19](8-) and Co(OH)2/Ni(OH)2. The films exhibit excellent stability and efficiency for electrocatalytic water oxidation in alkaline solution. Turnover frequencies of 12.9 and 13.2 s(-1) were determined by rotating ring disk electrode voltammetry at an overpotential of 480 mV for Co and Ni films, respectively. Fourier transformed large litude alternating current (FTAC) voltammetry reveals an additional underlying oxidation process for Co under catalytic turnover conditions, which indicates that a Co(IV) species is involved in the efficient catalytic water oxidation reactions. FTAC voltammetric data also suggest that the Ni films undergoes a clear phase transformation upon aging in aqueous 1 M NaOH and the electrogenerated higher oxidation state Ni from β-NiOOH is the more active form of the catalyst.
Publisher: American Chemical Society (ACS)
Date: 11-1986
DOI: 10.1021/AC00126A060
Publisher: American Chemical Society (ACS)
Date: 05-1990
DOI: 10.1021/IC00335A043
Publisher: American Chemical Society (ACS)
Date: 04-1984
DOI: 10.1021/OM00082A005
Publisher: American Chemical Society (ACS)
Date: 07-1988
DOI: 10.1021/AC00164A024
Publisher: CSIRO Publishing
Date: 2011
DOI: 10.1071/CH11044
Abstract: Two methimazolium and two imidazolium-based salts derived from combination with the tetracyanoquinodimethane (TCNQ) radical anion have been synthesized (1–4). The 1:1 (cation:anion) stoichiometry of the chemically synthesized materials is fully supported by steady-state voltammetric measurements at a microdisc electrode in acetonitrile. The methimazolium TCNQ salts (1 and 2), which contain an acidic proton on the cation, exhibit a protonation step coupled to the TCNQ1–/2– charge-transfer process. Solid–solid transformations at a TCNQ-modified electrode also lead to electrochemical synthesis of 1–4, but also indicate that other cation:anion stoichiometries are accessible. Atomic force microscopy for electrochemically synthesized s les exhibit rod-like morphology. Conductivity measurements on chemically and electrochemically prepared salts are in the semiconducting range. Scanning electrochemical microscopy approach curve data support the substantial conductivity of these solids. Extensive physicochemical characterization of these materials is in complete accordance with the X-ray crystal structure of 1-acetonitrile-3-methylimidazolium tetracyanoquinodimethane, [AMim+][TCNQ1–], 4.
Publisher: American Chemical Society (ACS)
Date: 08-1988
DOI: 10.1021/OM00098A013
Publisher: American Chemical Society (ACS)
Date: 05-1986
DOI: 10.1021/IC00230A004
Publisher: Elsevier BV
Date: 05-2003
DOI: 10.1016/S0967-5868(02)00131-5
Abstract: The diagnosis of ulnar nerve entrapment at the elbow has relied primarily on clinical and electrodiagnostic findings. Magnetic resonance imaging (MRI) has been used in the evaluation of peripheral nerve entrapment disorders to document signal and configurational changes in nerves. In this case report we review the MRI and operative findings of a rare constriction band causing ulnar nerve compression at the elbow. We review the sensitivity and specificity in diagnosing ulnar nerve entrapment at the elbow as defined by MRI findings.
Publisher: Elsevier BV
Date: 1990
Publisher: Elsevier BV
Date: 1987
Publisher: American Chemical Society (ACS)
Date: 21-12-1999
DOI: 10.1021/JA992402G
Publisher: American Chemical Society (ACS)
Date: 07-1997
DOI: 10.1021/AC961255R
Publisher: Wiley
Date: 04-1991
Publisher: American Chemical Society (ACS)
Date: 05-1976
DOI: 10.1021/AC60370A032
Publisher: American Chemical Society (ACS)
Date: 29-01-1999
DOI: 10.1021/OM9807553
Publisher: Elsevier BV
Date: 02-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0JM03011B
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CCN69MR
Publisher: American Chemical Society (ACS)
Date: 06-1986
DOI: 10.1021/J100404A026
Publisher: American Chemical Society (ACS)
Date: 06-1995
DOI: 10.1021/IC00117A003
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCX4J6R
Publisher: Elsevier BV
Date: 03-1976
Publisher: The Electrochemical Society
Date: 05-1997
DOI: 10.1149/1.1837642
Publisher: American Chemical Society (ACS)
Date: 08-1988
DOI: 10.1021/OM00098A012
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C003248D
Abstract: The one electron electrochemical reduction of vanadium(V) substituted-Keggin type polyoxometalate anions [XV(V)M(11)O(40)](4-) (XV(V)M(11)) where X = P, As M = Mo or W has been investigated in CH(3)CN as a function of acid concentration. EPR studies confirm that the product is the highly basic and hence readily protonated V(IV), (XV(IV)M(11)), species. In the absence of acid or in the presence of a large concentration excess, the V(V/IV) redox couple gives one well defined chemically and electrochemically reversible process under conditions of cyclic voltammetry. In contrast, three well resolved V(V/IV) processes are observed in the presence of a moderate concentration of acid in the case of XV(V)Mo(11) but only two with XV(V)W(11). NMR and EPR spectra have been obtained as a function of acid concentration when the polyoxometalate anions are in the V(V) and V(IV) oxidation levels respectively. All voltammetric and spectroscopic data indicate that protonation reactions are coupled to the V(V) and V(IV) redox chemistry but that the reduced V(IV) state is much more basic than the V(V) one and that (XV(IV)Mo(11)) is more basic than (XV(IV)W(11)). Digital simulations of voltammograms for reduction of XV(V)Mo(11) and XV(V)W(11) have been undertaken in CH(3)CN as a function of acid concentration in order to define the thermodynamics and kinetics associated with the V(V/IV) process and the equilibrium constants that accompany the coupled acid-base chemistry. EPR spectra allow an estimation of the relative concentrations of protonated species present in frozen glasses derived from one-electron bulk electrolysis and also allow inferences to be drawn on their nature. This study provides a far more detailed analysis of the coupling of proton and electron transfer than previously available.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1DT10953G
Abstract: A potential model complex for the hydrogenase active site, [Fe(2){(μ-CH(2)S)(2)R}(CO)(6)] (1) (R = quinoxaline), was synthesized by condensation of [(μ-LiS)(2)Fe(2)(CO)(6)] with 2,3-bis(bromomethyl)quinoxaline. Reactions of 1 with bis(diphenylphosphino)methane (dppm) under a range of conditions yielded substituted complexes [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)(dppm)] (2), [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(k(2)-dppm)] (3) and [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(μ-dppm)] (4). X-ray crystallography confirms that in 2, the dppm is terminally bonded to an iron atom via one phosphorus atom, whereas in 3, it acts as a chelating ligand to coordinate to an iron center in a dibasal-substituted manner. In 4, the dppm bridges the two iron atoms in a cis basal/basal fashion with one phosphorus bonded to each iron atom. Treatment of 1 with various tertiary phosphines at room temperature in acetonitrile (MeCN) generates a range of mono-substituted products [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)L] (5, L = PEt(3) 6, PMe(3) 7, PPh(3) 8, Me(2)PPh). With Bu(t)NC, mono- and di-substituted [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)(Bu(t)NC)] (9) and [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(Bu(t)NC)(2)] (10) complexes are generated. All the complexes were characterized by elemental analysis, IR, MS and NMR spectroscopy. IR and NMR spectroscopic studies suggest that addition of excess HBF(4)·OEt(2) acid to 1-4 led to the protonation of quinoxaline nitrogen atoms. In contrast, 5-10 were not stable in acidic media. Electrochemistry of 1-4 was investigated in the acetonitrile medium (0.1 M Bu(4)NPF(6)). The electrochemical instability of the reduced ligand, quinoxaline, and the reduced forms of these complexes revealed from the electrochemical studies suggests that they do not provide ideal models of the hydrogenase active site.
Publisher: Elsevier BV
Date: 12-2002
Publisher: The Electrochemical Society
Date: 03-12-2015
DOI: 10.1149/2.0051604JES
Publisher: Elsevier BV
Date: 12-1977
Publisher: Elsevier BV
Date: 1985
Publisher: Elsevier BV
Date: 09-2017
Publisher: American Chemical Society (ACS)
Date: 10-1990
DOI: 10.1021/IC00347A038
Publisher: American Chemical Society (ACS)
Date: 13-10-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 22-08-2014
DOI: 10.1039/C4DT02074J
Abstract: Reactions of the expanded ring N-heterocyclic carbene, 6-Dip (:C{N(Dip)CH2}2CH2, Dip = 2,6-diisopropylphenyl), with group 15 element trichlorides have yielded the monomeric complexes, [(6-Dip)ECl3] (E = P, As or Sb), two ex les of which (E = P and Sb) have been crystallographically characterised. Reduction of [(6-Dip)PCl3] with KC8 yielded the unusual tetraphosphorus dicationic complex, [(6-Dip)2(μ-P4)]Cl2, the X-ray crystal structure of which shows it to be an ion-separate salt. The compound can also be prepared from the direct reaction of excess 6-Dip with PCl3. Treatment of the cyclic amidinium salt, [6-MesH]Br (6-MesH = [HC{N(Mes)CH2}2CH2](+), Mes = mesityl) with KC8, leads to reductive coupling of the heterocycle and formation of the hindered bis(hexahydropyrimidine), (6-MesH)2. An X-ray crystallographic analysis of (6-MesH)2 shows the compound to have a long central C-C bond, while an electrochemical analysis reveals it to undergo an irreversible two-electron oxidation in dichloromethane solutions.
Publisher: Wiley
Date: 17-03-2009
Abstract: Electrodeposition of aluminium is possible from solutions of AlCl(3) dissolved in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (C(4)mpyrNTf(2)) ionic liquid. However, electrodeposition is dependant on the AlCl(3) concentration as it only occurs at concentrations >1.6 mol L(-1). At these relatively high AlCl(3) concentrations the C(4)mpyrNTf(2)/AlCl(3) mixtures exhibit biphasic behaviour. Notably, at 1.6 mol L(-1) AlCl(3), aluminium can only be electrodeposited from the upper phase. Conversely, we found that at 3.3 mol L(-1) aluminium electrodeposition can only occur from the lower phase. The complex chemistry of the C(4)mpyrNTf(2)/AlCl(3) system is described and implications of aluminium speciation in several C(4)mpyrNTf(2)/AlCl(3) mixtures, as deduced from Raman and (27)Al NMR spectroscopic data, are discussed. The (27)Al NMR spectra of the C(4)mpyrNTf(2)/AlCl(3) mixtures revealed the presence of both tetrahedrally and octahedrally coordinated aluminium species. Raman spectroscopy revealed that the level of uncoordinated NTf(2)(-) anions decreased with increasing AlCl(3) concentration. Quantum chemical calculations using density functional and ab initio theory were employed to identify plausible aluminium-containing species and to calculate their vibrational frequencies, which in turn assisted the assignment of the observed Raman bands. The data indicate that the electroactive species involved are likely to be either [AlCl(3)(NTf(2))](-) or [AlCl(2)(NTf(2))(2)](-).
Publisher: American Chemical Society (ACS)
Date: 07-02-2003
DOI: 10.1021/JP027529Y
Publisher: American Chemical Society (ACS)
Date: 25-11-2003
DOI: 10.1021/AC034901C
Publisher: No publisher found
Date: 2009
DOI: 10.5517/CCSDXLN
Publisher: American Chemical Society (ACS)
Date: 08-1999
DOI: 10.1021/IC990344U
Publisher: Elsevier BV
Date: 07-1988
Publisher: American Chemical Society (ACS)
Date: 06-1985
DOI: 10.1021/OM00125A022
Publisher: Elsevier BV
Date: 04-1985
Publisher: CSIRO Publishing
Date: 2007
DOI: 10.1071/CH06269
Abstract: Prospects have been assessed for the application of the technique of scanning electrochemical microscopy (SECM) in viscous ionic liquids. Use of the Fc0/+ redox couple (Fc = ferrocene) to obtain microelectrode approach curves revealed that the required steady state behaviour needed for analysis of data relevant to conducting platinum and insulating glass substrates is moderately easy to achieve in a 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) ionic liquid. However, in the more highly viscous 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid, where significantly lower diffusion coefficients are encountered, approach-curve data that conform to steady state theory are only found with very small microelectrodes (e.g., ≤2 μm diameter), very slow electrode–substrate approach rates (e.g., ≤0.05 μm s–1), and long equilibration times (e.g., 50 s). A comparison is provided with SECM approach curves acquired in aqueous media. SECM images of an Ag substrate in contact with [BMIM][BF4] also are presented and are of only slightly inferior quality to images obtained in water.
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWG3L0
Publisher: American Chemical Society (ACS)
Date: 08-1998
DOI: 10.1021/OM980030Z
Publisher: American Chemical Society (ACS)
Date: 04-1981
DOI: 10.1021/JA00398A014
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CCPV8J9
Publisher: Wiley
Date: 13-03-2018
Abstract: Metal complexes of Cu
Publisher: American Chemical Society (ACS)
Date: 08-1971
DOI: 10.1021/J100686A019
Publisher: Elsevier BV
Date: 11-2001
Publisher: American Chemical Society (ACS)
Date: 24-03-2005
DOI: 10.1021/OM049117C
Publisher: American Chemical Society (ACS)
Date: 09-1991
DOI: 10.1021/J100172A063
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A701003F
Publisher: Elsevier BV
Date: 1988
Publisher: Elsevier BV
Date: 04-2014
Publisher: Wiley
Date: 10-1994
Publisher: American Chemical Society (ACS)
Date: 12-1985
DOI: 10.1021/IC00219A041
Publisher: Springer Science and Business Media LLC
Date: 19-03-2009
Publisher: American Chemical Society (ACS)
Date: 30-04-2014
DOI: 10.1021/IC402994Q
Abstract: Two vanadium(V)-substituted tungsto-polyoxometalate isomers, 1- and 4-[S2VW17O62](5-), were prepared as their tetra-alkyl ammonium salts from a W(VI)-H2SO4-V(V) reaction mixture in aqueous CH3CN solution. X-ray crystallographic structural analysis revealed that both isomers have a Wells-Dawson-type structure with a higher occupancy of vanadium at polar sites and belt sites for 1- and 4-[S2VW17O62](5-), respectively. The isomers were also characterized by elemental analysis, infrared, Raman, UV-vis, and (51)V NMR spectroscopies as well as voltammetry, and the data obtained were compared with that derived from [S2W18O62](4-). Significantly, the reversible potentials for the vanadium(V/IV) couple for both 1- and 4-[S2VW17O62](5-) in CH3CN (0.1 M n-Bu4NPF6) are considerably more positive than the tungstate reduction process exhibited by the [S2W18O62](4-) framework, implying that the presence of vanadium should be useful in catalytic reactions. The one-electron-reduced [S2V(IV)W17O62](6-) forms of both isomers were prepared in solution by controlled potential bulk electrolysis and characterized by voltammetry and EPR spectroscopy.
Publisher: American Chemical Society (ACS)
Date: 31-01-2007
DOI: 10.1021/JA067219J
Abstract: Electrocrystallization of single nanowires and/or crystalline thin films of the semiconducting and magnetic Co[TCNQ]2(H2O)2 (TCNQ=tetracyanoquinodimethane) charge-transfer complex onto glassy carbon, indium tin oxide, or metallic electrodes occurs when TCNQ is reduced in acetonitrile (0.1 M [NBu4][ClO4]) in the presence of hydrated cobalt(II) salts. The morphology of the deposited solid is potential dependent. Other factors influencing the electrocrystallization process include deposition time, concentration, and identity of the Co2+(MeCN) counteranion. Mechanistic details have been elucidated by use of cyclic voltammetry, chrono erometry, electrochemical quartz crystal microbalance, and galvanostatic methods together with spectroscopic and microscopic techniques. The results provide direct evidence that electrocrystallization takes place through two distinctly different, potential-dependent mechanisms, with progressive nucleation and 3-D growth being controlled by the generation of [TCNQ]*- at the electrode and the diffusion of Co2+(MeCN) from the bulk solution. Images obtained by scanning electron microscopy reveal that electrocrystallization of Co[TCNQ]2(H2O)2 at potentials in the range of 0.1-0 V vs Ag/AgCl, corresponding to the [TCNQ]0/*- diffusion-controlled regime, gives rise to arrays of well-separated, needle-shaped nanowires via the overall reaction 2[TCNQ]*-(MeCN)+Co2+(MeCN)+2H2O right harpoon over left harpoon {Co[TCNQ]2(H2O)2}(s). In this potential region, nucleation and growth occur at randomly separated defect sites on the electrode surface. In contrast, at more negative potentials, a compact film of densely packed, uniformly oriented, hexagonal-shaped nanorods is formed. This is achieved at a substantially increased number of nucleation sites created by direct reduction of a thin film of what is proposed to be cobalt-stabilized {(Co2+)([TCNQ2]*-)2} dimeric anion. Despite the potential-dependent morphology of the electrocrystallized Co[TCNQ]2(H2O)2 and the markedly different nucleation-growth mechanisms, IR, Raman, elemental, and thermogravimetric analyses, together with X-ray diffraction, all confirmed the formation of a highly pure and crystalline phase of Co[TCNQ]2(H2O)2 on the electrode surface. Thus, differences in the electrodeposited material are confined to morphology and not to phase or composition differences. This study highlights the importance of the electrocrystallization approach in constructing and precisely controlling the morphology and stoichiometry of Co[TCNQ]2-based materials.
Publisher: Elsevier BV
Date: 09-2003
Publisher: American Chemical Society (ACS)
Date: 02-07-2010
DOI: 10.1021/JA1021365
Abstract: A highly selective and sensitive electrochemical biosensor has been developed that detects DNA hybridization by employing the electrocatalytic activity of ferrocene (Fc) bearing cyclen complexes (cyclen = 1,4,7,10-tetraazacyclododecane, Fc[Zn(cyclen)H(2)O](2)(ClO(4))(4) (R1), Fc(cyclen)(2) (R2), Fc[Zn(cyclen)H(2)O](ClO(4))(2) (R3), and Fc(cyclen) (R4)). A sandwich-type approach, which involves hybridization of a target probe hybridized with the preimmobilized thiolated capture probe attached to a gold electrode, is employed to fabricate a DNA duplex layer. Electrochemical signals are generated by voltammetric interrogation of a Fc bearing Zn-cyclen complexes that selectively and quantitatively binds to the duplex layers through strong chelation between the cyclen complexes and particular nucleobases within the DNA sequence. Chelate formation between R1 or R3 and thymine bases leads to the perturbation of base-pair (A-T) stacking in the duplex structure, which greatly diminishes the yield of DNA-mediated charge transport and displays a marked selectivity to the presence of the target DNA sequence. Coupling the redox chemistry of the surface-bound Fc bearing Zn-cyclen complex and dimethylamine provides an electrocatalytic pathway that increases sensitivity of the assay and allows the 100 fM target DNA sequence to be detected. Excellent selectivity against even single-base sequence mismatches is achieved, and the DNA sensor is stable and reusable.
Publisher: American Chemical Society (ACS)
Date: 12-1978
DOI: 10.1021/IC50190A069
Publisher: American Chemical Society (ACS)
Date: 1991
DOI: 10.1021/IC00002A010
Publisher: Elsevier BV
Date: 02-1972
Publisher: No publisher found
Date: 2008
DOI: 10.5517/CCQGPLF
Publisher: American Chemical Society (ACS)
Date: 19-05-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2001
DOI: 10.1039/B101766G
Publisher: American Chemical Society (ACS)
Date: 07-1986
DOI: 10.1021/IC00234A020
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTZ946
Publisher: Elsevier BV
Date: 09-1983
Publisher: Elsevier BV
Date: 12-2007
Publisher: American Chemical Society (ACS)
Date: 15-12-1987
DOI: 10.1021/AC00151A007
Publisher: Elsevier BV
Date: 12-1980
Publisher: American Chemical Society (ACS)
Date: 02-1988
DOI: 10.1021/IC00277A027
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD79S
Publisher: Elsevier BV
Date: 10-1997
Publisher: American Chemical Society (ACS)
Date: 04-1986
DOI: 10.1021/AC00295A023
Publisher: No publisher found
Date: 2001
DOI: 10.5517/CC58VDN
Publisher: Elsevier BV
Date: 11-1997
Publisher: Elsevier BV
Date: 06-1997
Publisher: Elsevier BV
Date: 03-1976
Publisher: American Chemical Society (ACS)
Date: 12-1994
DOI: 10.1021/IC00103A025
Publisher: American Chemical Society (ACS)
Date: 12-1994
DOI: 10.1021/IC00103A024
Publisher: Elsevier BV
Date: 11-2001
Publisher: Springer Science and Business Media LLC
Date: 18-12-2009
Publisher: No publisher found
Date: 2008
DOI: 10.5517/CCQGPMG
Publisher: Elsevier BV
Date: 11-1978
Publisher: American Chemical Society (ACS)
Date: 03-1988
DOI: 10.1021/LA00080A016
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTZ935
Publisher: No publisher found
Date: 2002
DOI: 10.5517/CC642CR
Publisher: American Chemical Society (ACS)
Date: 04-1985
DOI: 10.1021/IC00203A008
Publisher: American Chemical Society (ACS)
Date: 28-01-2010
DOI: 10.1021/AC9020159
Abstract: Electrochemical studies on the Fc + e(-) Fc(+) (Fc = ferrocene) process have been undertaken via the oxidation of Fc and reduction of Fc(+) as the hexafluorophosphate (PF(6)(-)) or tetrafluoroborate (BF(4)(-)) salts and their mixtures in three ionic liquids (ILs) (1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium hexafluorophosphate). Data obtained at macro- and microdisk electrodes using conventional dc and Fourier-transformed large- litude ac (FT-ac) voltammetry reveal that diffusion coefficients for Fc and Fc(+) differ significantly and are a function of the Fc and Fc(+) concentration, in contrast to findings in molecular solvents with 0.1 M added supporting electrolyte media. Thus, the faradaic currents associated with the oxidation of Fc (Fc(0/+)) and reduction of FcPF(6) or FcBF(4) (Fc(+/0)) when both Fc and Fc(+) are simultaneously present in the ILs differ from values obtained when in idual Fc and Fc(+) solutions are used. The voltammetry for both the Fc(0/+) and Fc(+/0) processes exhibited near-Nernstian behavior at a glassy carbon macrodisk electrode and a platinum microdisk electrode, when each process was studied in idually in the ILs. As expected, the reversible formal potentials (E(o)') and diffusion coefficients (D) at 23 +/- 1 degrees C were independent of the electrode material and concentration. However, when Fc and FcPF(6) or FcBF(4) were both present, alterations to the mass transport process occurred and apparent D values calculated for Fc and Fc(+) were found to be about 25-39% and 32-42% larger, respectively, than those determined from in idual solutions. The apparent value of the double layer capacitance determined by FT-ac voltammetry from in idual and mixed Fc and Fc(+) conditions at the GC electrode was also a function of concentration. Double layer capacitance values increased significantly with the concentration of Fc and FcPF(6) or FcBF(4) when species were studied in idually or simultaneously, but had a larger magnitude under conditions where both species were present. Variation in the structure of the ILs and hence mobilities of the ionic species, when Fc and FcPF(6) or FcBF(4) are simultaneously present, is considered to be the origin of the nonadditivity of the faradaic currents and variation in capacitance.
Publisher: American Chemical Society (ACS)
Date: 30-08-2010
DOI: 10.1021/JP105626Z
Abstract: Large- litude ac voltammograms contain a wealth of kinetic information concerning electrode processes and can provide unique mechanistic insights compared to other techniques. This paper describes the effects homogeneous chemical processes have on ac voltammetry in general and provides experimental ex les using two well-known chemical systems: one simple and one complex. Oxidation of [Cp*Fe(CO)(2)](2) (Cp* = η(5)-pentamethylcyclopentadienyl) in noncoordinating media is a reversible one-electron process in the presence of nucleophiles, however, the resulting ligand-induced disproportionation changes the process to a multiple step regeneration. The chemical kinetic parameters of the regeneration mechanism were discerned via analysis of the third and higher harmonics of Fourier-transformed ac voltammetry data. Comparison of experimental data to digital simulations provides clear evidence that the reaction proceeds via a rapid pre-equilibrium between the electrogenerated monocation and the coordinating ligand simultaneous fitting of the first nine harmonics indicates that k(f) = 7500 M(-1) s(-1) and k(r) = 100 s(-1), and that the unimolecular decomposition of the corresponding intermediate occurs with a rate constant of 2.2 s(-1). The rapid cis(+) → trans(+) isomerization of the electrogenerated cis-[W(CO)(2)(dpe)(2)](+), where dpe = 1,2-diphenylphosphinoethane, was examined to illustrate the effects of a simpler EC mechanism on the higher harmonics a rate constant of 280 s(-1) was determined. These results not only shed new light on the chemistry of these systems, but provide a clear demonstration that the higher harmonics of ac voltammetry provide mechanistic insights into coupled homogeneous processes far more detailed than those that are readily accessible with dc techniques.
Publisher: American Chemical Society (ACS)
Date: 03-1973
DOI: 10.1021/JA00786A017
Publisher: American Chemical Society (ACS)
Date: 05-1985
DOI: 10.1021/IC00204A036
Publisher: American Chemical Society (ACS)
Date: 07-1973
DOI: 10.1021/AC60330A004
Publisher: Elsevier BV
Date: 03-1993
Publisher: Elsevier BV
Date: 02-2017
Publisher: No publisher found
Date: 1998
DOI: 10.5517/CC3QVRD
Publisher: American Chemical Society (ACS)
Date: 1982
DOI: 10.1021/IC00131A023
Publisher: No publisher found
Date: 2007
DOI: 10.5517/CCPMC6V
Publisher: Wiley
Date: 1993
Publisher: Wiley
Date: 15-05-2012
Abstract: The layered crystal MoS(2) has been proposed as an alternative to noble metals as the electrocatalyst for the hydrogen evolution reaction (HER). However, the activity of this catalyst is limited by the number of available edge sites. It was previously shown that, by using an imidazolium ionic liquid as synthesis medium, nanometre-size crystal layers of MoS(2) can be prepared which exhibit a very high number of active edge sites as well as a de-layered morphology, both of which contribute to HER electrocatalytic activity. Herein, it is examined how to control these features synthetically by using a range of ionic liquids as synthesis media. Non-coordinating ILs with a planar heterocyclic cation produced MoS(2) with the de-layered morphology, which was subsequently shown to be highly advantageous for HER electrocatalytic activity. The results furthermore suggest that the crystallinity, and in turn the catalytic activity, of the MoS(2) layers can be improved by employing an IL with specific solvation properties. These results provide the basis for a synthetic strategy for increasing the HER electrocatalytic activity of MoS(2) by tuning its crystal properties, and thus improving its potential for use in hydrogen production technologies.
Publisher: CSIRO Publishing
Date: 2017
DOI: 10.1071/CH17187
Abstract: The transformation of cadmium 7,7,8,8-tetracyanoquinodimethane (TCNQ) into a cadmium terephthalate co-ordination polymer is reported, with the chemistry of this material elucidated using elemental analysis, X-ray photoelectron spectroscopy and synchrotron radiation single-crystal X-ray diffraction. A heptacoordinated CdII linear coordination polymer catena-poly[triaqua-(μ2-benzene-1,4-dicarboxylato-κO,O′)cadmium(ii)]hydrate (1) was isolated while attempting to recrystallize Cd(TCNQ)2. Density functional theory calculations for the oxidation of benzylic carbon attached to the cyano group provided evidence that the reaction pathway proposed herein is highly exergonic and thermodynamically plausible. This structure showed a distorted pentagonal bipyramidal geometry together with a symmetrical mononuclear unit in which each CdII ion is doubly bridged by a dicarboxylato anion. Owing to the softness and minute size of these crystals, this structure had to be elucidated using synchrotron radiation X-ray crystallography.
Publisher: American Chemical Society (ACS)
Date: 07-03-2012
DOI: 10.1021/LA205013N
Abstract: Graphene modified electrodes have been fabricated by electrodeposition from an aqueous graphene oxide solution onto conducting Pt, Au, glassy carbon, and indium tin dioxide substrates. Detailed investigations of the electrochemistry of the [Ru(NH(3))(6)](3+/2+) and [Fe(CN)(6)](3-/4-) and hydroquinone and uric acid oxidation processes have been undertaken at glassy carbon and graphene modified glassy carbon electrodes using transient cyclic voltammetry at a stationary electrode and near steady-state voltammetry at a rotating disk electrode. Comparisons of the data with simulation suggest that the transient voltammetric characteristics at graphene modified electrodes contain a significant contribution from thin layer and surface confined processes. Consequently, interpretations based solely on mass transport by semi-infinite linear diffusion may result in incorrect conclusions on the activity of the graphene modified electrode. In contrast, steady-state voltammetry at a rotating disk electrode affords a much simpler method for the evaluation of the performance of graphene modified electrode since the relative importance of the thin layer and surface confined processes are substantially diminished and mass transport is dominated by convection. Application of the rotated electrode approach with carbon nanotube modified electrodes also should lead to simplification of data analysis in this environment.
Publisher: American Chemical Society (ACS)
Date: 11-11-2003
DOI: 10.1021/AC034921E
Abstract: Conventional cyclic voltammetric studies on the oxidation of millimolar concentrations (mg masses) of trans-[Mn(CN)(CO)(2)[P(OPh)(3)](Ph(2)PCH(2)PPh(2))] (trans-Mn) dissolved in milliliter volumes of bulk ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM.PF(6)), give rise to a reversible [trans-Mn](0/+) process. In this study, it is shown that equally well-defined reversible voltammetry can be more economically obtained under microchemical ionic liquid conditions by employing a chemically modified electrode (microg quantities of trans-Mn adhered to a glassy carbon electrode covered with microliter volumes of water-immiscible BMIM.PF(6)) in contact with aqueous (0.1 M KPF(6)) electrolyte. The ability to obtain electrochemical data that are directly relatable to bulk ionic liquid media under these microchemical conditions is principally associated with the dissolution of electrogenerated solid [trans-Mn](+) in the layer of water-immiscible BMIM.PF(6) present at the electrode/ionic liquid/aqueous electrolyte interface. If the BMIM.PF(6) layer is sufficiently thick, mass transport of the dissolved species is governed by semi-infinite linear diffusion. Under these conditions, the voltammetric waveshape and position, but not the current magnitude are the same as those found when conventional bulk ionic liquid conditions are employed. In contrast, use of very thin layers produces voltammograms that exhibit the characteristics expected for a reversible process in which the mass transport process is predominantly governed by finite rather than semi-infinite diffusion. A theoretical model has been developed that describes the transformation from thick- to thin-layer type behavior as the thickness of the ionic liquid layer is decreased.
Publisher: American Chemical Society (ACS)
Date: 06-06-2014
DOI: 10.1021/JP501442H
Publisher: American Chemical Society (ACS)
Date: 20-09-2007
DOI: 10.1021/IC700796M
Abstract: [Ru(bpy)(2)(Mebpy-COOH)](PF(6))(2).3H(2)O (1), [Ru(phen)(2)(Mebpy-COOH)](ClO(4))(2).5H(2)O (2), [Ru(dppz)(2)(Mebpy-COOH)]Cl(2).9H(2)O (3), and [Ru(bpy)(dppz)(Mebpy-COOH)](PF(6))(2).5H(2)O (4) (bpy = 2,2'-bipyridine, Mebpy-COOH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid, phen = 1,10-phenanthroline, dppz = dipyrido[3,2,-a ',3-c]phenazine) have been synthesized and characterized spectroscopically and by microanalysis. The [Ru(Mebpy-COOH)(CO)(2)Cl(2)].H(2)O intermediate was prepared by reaction of the monocarboxylic acid ligand, Mebpy-COOH, with [Ru(CO)(2)Cl(2)](n), and the product was then reacted with either bpy, phen, or dppz in the presence of an excess of trimethylamine-N-oxide (Me(3)NO), as the decarbonylation agent, to generate 1, 2, and 3, respectively. For compound 4, [Ru(bpy)(CO)Cl(2)](2) was reacted with Mebpy-COOH to yield [Ru(bpy)(Mebpy-COOH)(CO)Cl](PF(6)).H(2)O as a mixture of two main geometric isomers. Chemical decarbonylation in the presence of dppz gave 4 also as a mixture of two isomers. Electrochemical and spectrophotometric studies indicated that complexes 1 and 2 were present as a mixture of protonated and deprotonated forms in acetonitrile solution because of water of solvation in the isolated solid products. The X-ray crystal structure determination on crystals of [Ru(bpy)2(MebpyCOO)][Ru(bpy)(2)(MebpyCOOH)](3)(PF(6))(7), 1a, and [Ru(phen)(2)(MebpyCOO)](ClO(4)).6H(2)O, 2a, obtained from solutions of 1 and 2, respectively, revealed that 1a consisted of a mixture of protonated and deprotonated forms of the complex in a 1:3 ratio and that 2a consisted of the deprotonated derivative of 2. A distorted octahedral geometry for the Ru(II) centers was found for both complexes. Upon excitation at 450 nm, MeCN solutions of the protonated complexes 1-4 were found to exhibit emission bands in the 635-655 nm range, whereas the corresponding emission maxima of their deprotonated forms were observed at lower wavelengths. Protonation/deprotonation effects were also observed in the luminescence and electrochemical behavior of complexes 1-4. Comprehensive electrochemical studies in acetonitrile show that the ruthenium centers on 1, 2, 3, and 4 are oxidized from Ru(II) to Ru(III) with reversible potentials at 917, 929, 1052, and 1005 mV vs Fc(0/+) (Fc = ferrocene), respectively. Complexes 1 and 2 also exhibit an irreversible oxidation process in acetonitrile, and all compounds undergo ligand-based reduction processes.
Publisher: Elsevier BV
Date: 05-1993
Publisher: American Chemical Society (ACS)
Date: 02-1980
DOI: 10.1021/AC50052A043
Publisher: American Chemical Society (ACS)
Date: 25-08-2010
DOI: 10.1021/AC101321A
Abstract: The recently synthesized ionic liquid (IL) 2-butylthiolonium bis(trifluoromethanesulfonyl)amide, [mimSBu][NTf(2)], has been used for the extraction of copper(II) from aqueous solution. The pH of the aqueous phase decreases upon addition of [mimSBu](+), which is attributed to partial release of the hydrogen attached to the N(3) nitrogen atom of the imidazolium ring. The presence of sparingly soluble water in [mimSBu][NTf(2)] also is required in solvent extraction studies to promote the incorporation of Cu(II) into the [mimSBu][NTf(2)] ionic liquid phase. The labile copper(II) system formed by interacting with both the water and the IL cation component has been characterized by cyclic voltammetry as well as UV-vis, Raman, and (1)H, (13)C, and (15)N NMR spectroscopies. The extraction process does not require the addition of a complexing agent or pH control of the aqueous phase. [mimSBu][NTf(2)] can be recovered from the labile copper-water-IL interacting system by washing with a strong acid. High selectivity of copper(II) extraction is achieved relative to that of other alent cobalt(II), iron(II), and nickel(II) transition-metal cations. The course of microextraction of Cu(2+) from aqueous media into the [mimSBu][NTf(2)] IL phase was monitored in situ by cyclic voltammetry using a well-defined process in which specific interaction with copper is believed to switch from the ionic liquid cation component, [mimSBu], to the [NTf(2)] anion during the course of electrochemical reduction from Cu(II) to Cu(I). The microextraction-voltammetry technique provides a fast and convenient method to determine whether an IL is able to extract electroactive metal ions from an aqueous solution.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3DT53161A
Abstract: Structures of the n-tetrabutylammonium salts of [SVM11O40](3-) (M = Mo, W) have been determined by X-ray crystallography and exhibit 3D networks with the V atom disordered over several sites. The cyclic voltammetric behavior of SVM11 in neutral and acidified acetonitrile solutions also has been investigated with respect to the V(V)/V(IV) couple. Results have been interpreted in conjunction with data provided by (51)V NMR spectroscopy on the oxidized V(V) form and by EPR spectroscopy on the reduced V(IV) form. Based on mechanistic details inferred from these studies, simulations of the cyclic voltammograms have been undertaken and results compared with experimental data in acidic media (two protonated forms) in order to provide estimates of equilibrium and kinetic parameters. For the V(V)/V(IV) couple in the series [XVM11O40](n-) (X = Si,Ge,P,As,S M = Mo,W), the reversible potentials in neutral acetonitrile linearly depend on the total charge of the vanadium-substituted polyoxometalates, similar to the dependence previously reported for the non-substituted parent Keggin polyoxometalates [XM12O40](m-).
Publisher: Elsevier BV
Date: 03-1997
Publisher: Elsevier BV
Date: 1983
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD77Q
Publisher: Wiley
Date: 11-10-2018
Publisher: Elsevier BV
Date: 2000
Publisher: CSIRO Publishing
Date: 1981
DOI: 10.1071/CH9811393
Abstract: Phosphorus-31, cadmium-113 and mercury-199 n.m.r. spectra have been recorded for a series of O,O-dialkyldithiophosphate (dtp) and dialkyldithiocarbamate (dtc) complexes of cadmium and mercury in dichloromethane solution. Both types of ligand are labile on the n.m.r. time scale at room temperature, although the exchange of dtc ligands can be slowed at low temperatures. .The complexes interact with tributylphosphine and tricyclohexylphosphine (pcy), but at room temperature the phosphines are also labile. At low temperatures, however, the phosphine exchange becomes slow on the n.m.r. time scale to allow identification of the adducts except for Cd(dtc)2 adducts with PBu3 which are still labile at -110°C. All the data indicate that cadmium has a lower affinity for phosphine than mercury and that dtc ligands are more strongly bound to the metals than dtp ligands.
Publisher: Elsevier BV
Date: 03-1986
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B504721H
Abstract: Recent developments associated with voltammetric studies in ionic liquid media have been critically reviewed. Initially, advantageous electrochemical properties of ionic liquids are summarised, as are limitations encountered by the presence of impurities and problems related to purification and recovery of ionic liquids. Subsequently, the use of IUPAC recommended ferrocene oxidation and cobalticenium reduction processes as potential reference scales in ionic liquids and the application of voltammetry of adhered solid and microchemical approaches to the measurement of formal potentials and kinetics of coupled first order chemical reactions are discussed. Finally, the possible use of volatile ionic liquids is considered as an alternative to use of the non-volatile ionic liquids media, presently emphasized in most studies.
Publisher: American Chemical Society (ACS)
Date: 11-06-1998
DOI: 10.1021/OM970897H
Publisher: American Chemical Society (ACS)
Date: 25-02-2014
DOI: 10.1021/IC500225V
Publisher: Elsevier BV
Date: 09-1993
Publisher: Elsevier BV
Date: 1985
Publisher: American Chemical Society (ACS)
Date: 18-07-2013
DOI: 10.1021/JA403555D
Abstract: Activation barriers to the electrochemical oxidation for the series PPh3-n(dipp)n (dipp = 2,6-diisopropylphenyl) in CH2Cl2/Bu4NPF6 were measured using large litude FT ac voltammetry. Increasing substitution across this series, which offers the widest range of steric requirements across any analogous series of triarylphosphines reported to date, increases the energetic barrier to electron transfer values of 18, 24, and 25 kJ mol(-1) were found for compounds with n = 1, 2, and 3, respectively. These values are significantly greater than those calculated for outer sphere activation barriers, with deviations between observed and calculated values increasing with the number of dipp ligands. This suggests that the steric congestion afforded by these bulky substituents imposes significant reorganizational energy on the electron transfer processes. This is the first investigation of the effect of sterics on the kinetics of heterogeneous electron transfer across a structurally homologous series. Increased alkyl substitution across the series also increases the chemical reversibility of the oxidations and decreases the oxidation peak potentials. As the compounds for which n = 1 and 2 are novel, the synthetic strategies employed in their preparation are described, along with their full spectroscopic, physical, and crystallographic characterization. Optimal synthesis when n = 1 is via a Grignard reagent, whereas when n = 2 an aryl copper reagent must be employed, as use of a Grignard results in reductive coupling. Chemical oxidation studies were performed to augment the electrochemical work the O, S, and Se oxidation products for the parent triarylphosphines for which n = 1 and 2 were isolated and characterized.
Publisher: American Chemical Society (ACS)
Date: 12-01-2022
DOI: 10.1021/ACS.ACCOUNTS.1C00617
Abstract: ConspectusElectrochemical reduction of the greenhouse gas CO
Publisher: Wiley
Date: 06-2023
Publisher: Wiley
Date: 06-2023
Abstract: The front cover artwork was done by Michelle Farrelly, a member of the Martin group at Monash University. The image represents a perspective of a cuvette in which the catalysis of the thiosulfate‐ferricyanide reaction was achieved by a TCNQF 4 ‐based redox reaction in aqueous solution. The primary method used to monitor these reactions was spectrophotometry. Read the full text of the Research Article at 10.1002/cphc.202200942 .
Publisher: American Chemical Society (ACS)
Date: 06-1985
DOI: 10.1021/IC00206A045
Publisher: Springer Berlin Heidelberg
Date: 30-09-2010
Publisher: Informa Healthcare
Date: 21-07-2006
Abstract: Cytochrome P450 (CYP) enzymes perform crucial functions in humans, including the metabolism of drugs and hormone synthesis. The catalytic reactions performed by these enzymes (typically monoxygenation) require the transfer of electrons. Thermodynamic and mechanistic detail of the electron transfer component of these catalytic processes has been obtained traditionally from potentiometric titrations. More recently, voltammetric approaches (that are inherently simpler and require less s le) have been used. This has been made possible by the creation of biocompatible electrode surfaces at which the P450 enzyme is confined and able to undergo physiologically relevant electron transfer processes. The continuing challenge has been to obtain an in vivo-like enzyme response, and to provide the basis for the creation of an artificial bioprocess in vitro. A powerful instrumental electrochemical method, employing Fourier-transformed large- litude ac voltammetry, offers the potential for greater insight and new opportunities to understand the nuances of the electron transfer process. This review highlights several recent advances in the electrochemistry of P450 enzymes rather than providing a comprehensive review of P450 electrochemistry.
Publisher: American Chemical Society (ACS)
Date: 02-1978
DOI: 10.1021/AC50024A014
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD78R
Publisher: Elsevier BV
Date: 09-1992
Publisher: Elsevier BV
Date: 10-1999
Publisher: American Chemical Society (ACS)
Date: 09-1977
DOI: 10.1021/IC50175A010
Publisher: Elsevier BV
Date: 06-2014
Publisher: American Chemical Society (ACS)
Date: 15-11-2011
DOI: 10.1021/JP2072793
Publisher: American Chemical Society (ACS)
Date: 03-1979
DOI: 10.1021/AC50039A005
Publisher: Elsevier BV
Date: 02-1989
Publisher: American Chemical Society (ACS)
Date: 28-11-2008
DOI: 10.1021/LA702511W
Abstract: A quartz crystal microbalance coupled with electrochemistry was used to examine the adsorption of azurin on a gold electrode modified with a self-assembled monolayer of octanethiol. Azurin adsorbed irreversibly to form a densely packed monolayer. The rate of azurin adsorption was related to the bulk concentration of azurin in solution within the concentration range studied. At a high azurin concentration (2.75 muM), adsorption was rapid with a stable adsorption maximum attained in 2-3 min. At a lower azurin solution concentration (0.35 muM), the time to reach a stable adsorption maximum was approximately 30 min. Interestingly, the maximum surface concentration attained for all solution concentrations studied by the QCM method was 25 +/- 1 pmol cm-2, close to that predicted for monolayer coverage. The dissipation was monitored during adsorption, and only small changes were detected, implying a rigid adsorption model, as needed when using the Sauerbrey equation. Cyclic voltammetric data were consistent with a one-electron, surface-confined CuII/CuI azurin process with fast electron-transfer kinetics. The electroactive surface concentration calculated using voltammetry was 7 +/- 1 pmol cm-2. The differences between the QCM and voltammetrically determined surface coverage values reflect, predominantly, the different measurement methods but imply that all surface-confined azurin is not electrochemically active on the time scale of cyclic voltammetry.
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCYHGSN
Publisher: The Electrochemical Society
Date: 09-1992
DOI: 10.1149/1.2221232
Publisher: American Chemical Society (ACS)
Date: 17-09-2005
DOI: 10.1021/JA050561W
Abstract: Use of the technique of scanning electrochemical microscopy (SECM) enables the surface of single crystals of 7,7',8,8'-tetracyanoquinodimethane (TCNQ) to be modified in a controlled manner to produce highly dense and micrometer sized regions of semiconducting phase I CuTCNQ nanorod crystals by a nucleation and growth mechanism. This method involves the localized reduction of solid TCNQ to TCNQ- by aqueous phase V(aq)2+ reductant generated at a SECM ultramicroelectrode tip by reduction of V(aq)3+, coupled with the incorporation and reduction of Cu(aq)2+ ions also present in the aqueous electrolyte. SECM parameters can be systematically varied to control the extent of surface modification and the packing density of the CuTCNQ crystals. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide evidence that the TCNQ to CuTCNQ solid-solid transformation is accompanied by a drastic localized crystal volume and morphology change achieved by fragmentation of the TCNQ crystal surface. Patterns of semiconducting CuTCNQ (phase I) nanorod shaped crystals have been characterized by SEM, AFM, and infrared (IR) techniques. A reaction scheme has been proposed for the interaction between the electrogenerated mediator V(aq)2+, Cu(aq)2+, and the TCNQ crystal in the nucleation and growth stages of phase I CuTCNQ formation.
Publisher: American Chemical Society (ACS)
Date: 03-1983
DOI: 10.1021/IC00148A030
Publisher: Royal Society of Chemistry (RSC)
Date: 1993
DOI: 10.1039/DT9930003641
Publisher: American Chemical Society (ACS)
Date: 03-1968
DOI: 10.1021/AC60259A010
Publisher: Elsevier BV
Date: 2010
Publisher: Wiley
Date: 05-1992
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2DT30558E
Abstract: The photochemistry of the Dawson-type [Bu(4)N](4)[S(2)Mo(18)O(62)] and [Bu(4)N](4)[S(2)W(18)O(62)] polyoxometalates in molecular solvents and [Bmim][BF(4)] and [Bmim][BF(6)] ionic liquids with water present as the electron donor is reported. Irradiation with UV (275-320 nm) or white (275-750 nm) light leads to reduction of the [S(2)Mo(18)O(62)](4-) anion and concomitant oxidation of water to give dioxygen and protons in all media examined. Oxygen gas also is rapidly evolved when solid [Bu(4)N](4)[S(2)Mo(18)O(62)] in contact with water is irradiated with light. In contrast, photoreduction of [S(2)W(18)O(62)](4-) is observed only in "wet" ionic liquids. Reactants and products associated with the photochemical reactions were monitored by a range of electrochemical methods. Substantial shifts in reversible potentials combined with modified structure of water introduced by water-IL interactions are hypothesised to facilitate photooxidation of water in ionic liquid environments. Intriguingly, whilst the polyoxotungstate is preferable as a photosensitizer, the molybdenum analogue is superior for photooxidation of water to dioxygen.
Publisher: American Chemical Society (ACS)
Date: 28-05-2013
DOI: 10.1021/AC400915Z
Abstract: Three highly aprotic bis(trifluoromethylsulfonyl)amide (NTf2(-)) based ionic liquids (ILs) containing the cations trihexyl(tetradecyl)phosphonium (P6,6,6,14(+)), N-butyl-N-methylpyrrolidinium (Pyrr4,1(+)), and (trimethylamine)(dimethylethylammine)dihydroborate ((N111)(N112)BH2(+)) have been examined as media for room temperature voltammetric detection of highly basic stilbene dianions electrochemically generated by the reduction of trans-stilbene (t-Stb) and its derivatives (4-methoxy-, 2-methoxy-, 4,4'-dimethyl-, and 4-chloromethyl-). Transient and steady-state data in the ILs were compared with results obtained in the molecular solvent acetonitrile. In all media examined, the t-Stb(0/•-) process is chemically and electrochemically reversible with a heterogeneous charge transfer rate constant in CH3CN of 1.5 cm s(-1), as determined by Fourier transformed AC voltammetry. However, further reduction to the dianion was always irreversible in this molecular but weakly acidic solvent. On the other hand, a substantial level of chemical reversibility for the reduction of t-Stb(•-) to t-Stb(2-) on the time scale of cyclic voltammetry is achieved when the concentration of trans-stilbene, [t-Stb], appreciably exceeds the concentration of adventitious water or other proton sources. In particular, these conditions are met when [t-Stb] ≥ 0.1 M in thoroughly dehydrated and purified ILs, while in the presence of CH3CN, t-Stb(2-) still suffers fast irreversible protonation under these stilbene concentration conditions. The E0/•-(0) values (vs Fc(0/+)) for substituted trans-stilbenes in acetonitrile and (N111)(N112)BH2-NTf2 do not differ substantially, nor do the E0/•-(0) and E•-/2-(0) differences or other aspects of the voltammetric behavior.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1GC15929A
Publisher: American Chemical Society (ACS)
Date: 09-02-2007
DOI: 10.1021/AC061859N
Abstract: The influence of uncompensated resistance (also called the IRu effect, where I is current and Ru is uncompensated resistance) and slow electrode kinetics have been assessed for the dc and first five ac harmonics derived from Fourier transformed large- litude ac voltammetry. Resistance and rate constant conditions emphasized correspond to those where separation of effects attributable to either parameter is essentially impossible under conditions of dc cyclic voltammetry. Results derived from simulations and experiments demonstrate that it is relatively easy to discriminate and quantify contributions from these two effects over a wide range of values using the fourth and fifth harmonic ac components derived from single large- litude ac voltammetric measurement. Furthermore, these ac components also are essentially devoid of background charging current. Concepts developed initially from simulations are confirmed by experimental studies on the following: (a) the oxidation of ferrocene, in moderately resistive CH3CN and highly resistive CH2Cl2 (represents ex les of IRu effect on a reversible electron-transfer process) (b) the reduction of a low 0.2 mM concentration of [Fe(CN)6]3- in the highly conductive 3 M KCl electrolyte media (case of slow kinetics with negligible IRu effect) (c) and reduction of a high 10 mM concentration of [Fe(CN)6]3- in less conductive aqueous 0.5 M KCl electrolyte media (ex le where the simultaneous effects of both IRu and slow kinetics need to be resolved).
Publisher: Elsevier BV
Date: 02-1977
Publisher: American Chemical Society (ACS)
Date: 11-1990
DOI: 10.1021/IC00348A016
Publisher: Elsevier BV
Date: 07-2008
Publisher: Wiley
Date: 08-1990
DOI: 10.1111/J.1432-1033.1990.TB19182.X
Abstract: The electrochemistry of the redox proteins, cytochrome c, cytochrome b5, plastocyanin and ferredoxin at modified gold electrodes has been examined on the basis that electron transfer takes place at electroactive sites which are microscopic in size. Using this model, it is now proposed that electrochemistry of these proteins occurs at suitably modified sites with fast rates at potentials near the standard redox potential. The microscopic model implies that redox proteins and enzymes take part in fast electron transfer at specific sites on the electrode, other sites being completely ineffective. This form of molecular recognition, i.e. the ability to discriminate between the different sites on an electrode surface, mimics homogeneous redox reactions wherein redox active proteins 'recognize' their biological partners in a very specific sense. Previously, protein electrochemistry has been interpreted via use of a macroscopic model in which the proteins are transported to the electrode surface by linear diffusion followed by quasi-reversible or irreversible electron transfer to the electrode surface. The microscopic model, which assumes that the movement of the protein occurs predominantly by radial diffusion to very small sites, would appear to explain the data more satisfactorily and be consistent with biologically important, homogeneous redox reactions which are known to be fast.
Publisher: Royal Society of Chemistry (RSC)
Date: 2001
DOI: 10.1039/B008682G
Publisher: CSIRO Publishing
Date: 2019
DOI: 10.1071/CH19175
Abstract: The reaction of [FeII(L•)2][BF4]2 with LiTCNQF4 results in the formation of [FeII(L•)2][TCNQF4•−]2·2CH3CN (1) (L• is the neutral aminoxyl radical ligand 4,4-dimethyl-2,2-di(2-pyridyl)oxazolidine-N-oxide TCNQF4 is 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane). Single-crystal X-ray diffraction Raman, Fourier-transform infrared (FTIR) and ultraviolet–visible spectroscopies and electrochemical studies are all consistent with the presence of a low-spin FeII ion, the neutral radical form (L•) of the ligand, and the radical anion TCNQF4•−. 1 is largely diamagnetic and the electrochemistry shows five well-resolved, diffusion-controlled, reversible one-electron processes.
Publisher: Wiley
Date: 25-09-2014
Publisher: American Chemical Society (ACS)
Date: 03-1974
DOI: 10.1021/IC50133A020
Publisher: American Chemical Society (ACS)
Date: 03-1984
DOI: 10.1021/IC00175A010
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCYHGRM
Publisher: American Chemical Society (ACS)
Date: 24-05-2013
DOI: 10.1021/JA4021155
Abstract: A family of dinuclear cobalt complexes with bridging bis(dioxolene) ligands derived from 3,3,3',3'-tetramethyl-1,1'-spirobis(indane-5,5',6,6'-tetrol) (spiroH4) and ancillary ligands based on tris(2-pyridylmethyl)amine (tpa) has been synthesized and characterized. The bis(dioxolene) bridging ligand is redox-active and accessible in the (spiro(cat-cat))(4-), (spiro(SQ-cat))(3-), and (spiro(SQ-SQ))(2-) forms, (cat = catecholate, SQ = semiquinonate). Variation of the ancillary ligand (Mentpa n = 0-3) by successive methylation of the 6-position of the pyridine rings influences the redox state of the complex, governing the distribution of electrons between the cobalt centers and the bridging ligands. Pure s les of salts of the complexes [Co2(spiro)(tpa)2](2+) (1), [Co2(spiro)(Metpa)2](2+) (2), [Co2(spiro)(Me2tpa)2](2+) (3), [Co2(spiro)(Me3tpa)2](2+) (4), [Co2(spiro)(tpa)2](3+) (5), and [Co2(spiro)(tpa)2](4+) (6) have been isolated, and 1, 4, and 6 have been characterized by single crystal X-ray diffraction. Studies in the solid and solution states using multiple techniques reveal temperature invariant redox states for 1, 2, and 4-6 and provide clear evidence for four different charge distributions: 1 and 2 are Co(III)-(spiro(cat-cat))-Co(III), 4 is Co(II)-(spiro(SQ-SQ))-Co(II), 5 is Co(III)-(spiro(SQ-cat))-Co(III), and 6 is Co(III)-(spiro(SQ-SQ))-Co(III). Of the six complexes, only 3 shows evidence of temperature dependence of the charge distribution, displaying a rare thermally induced two-step valence tautomeric transition from the Co(III)-(spiro(cat-cat))-Co(III) form to Co(II)-(spiro(SQ-cat))-Co(III) and then to Co(II)-(spiro(SQ-SQ))-Co(II) in both solid and solution states. This is the first time a two-step valence tautomeric (VT) transition has been observed in solution. Partial photoinduction of the VT transition is also possible in the solid. Magnetic and spectroscopic studies of 5 and 6 reveal that spiroconjugation of the bis(dioxolene) ligand allows electronic interaction across the spiro bridge, suggesting that thermally activated vibronic coupling between the two cobalt-dioxolene moieties plays a key role in the two-step transition evident for 3.
Publisher: American Chemical Society (ACS)
Date: 03-1997
DOI: 10.1021/IC961295D
Abstract: Reaction of Mn(CO)(5)X (X = Cl, Br) with Ph(2)P(CH(2))(2)P(Ph)(CH(2))(2)PPh(2) (P(2)P') in refluxing xylene led to the formation of isomerically pure cis,mer-Mn(CO)(2)(eta(3)-P(2)P')X. Cyclic voltammograms in dichloromethane (0.1 M Bu(4)NPF(6)) show a reversible one-electron oxidation (process 1, E(1/2) = 0.142 V) to give cis,mer-[Mn(CO)(2)(P(2)P')X](+). However, in acetone (0.1 M Bu(4)NPF(6)) at room temperature, process 1 is not reversible and an additional redox process 4 (E(1/2) = 0.048 V) is observed. Process 4 is not observed at low temperatures, and at higher temperatures in acetone it merges with process 1 and also a new reversible redox couple (process 5, E(1/2) = -0.411 V) appears. A combination of electrolyses, chemical oxidation, and subsequent reduction, coupled with IR and (31)P NMR spectroscopies and electrospray mass spectrometry (ESMS), is used to show that processes 1, 4, and 5 are all associated with redox and interconversion reactions of different isomers of Mn(CO)(2)(P(2)P')X and [Mn(CO)(2)(P(2)P')X](+). Other irreversible processes due to oxidation of the different isomers of [Mn(CO)(2)(P(2)P')X](+) are observed at very positive potentials. Reaction between Re(CO)(5)X and P(2)P' in refluxing mesitylene gives a soluble product and a small amount of precipitate. The major soluble product was identified as cis,mer-Re(CO)(2)(P(2)P')X, and the oxidative chemistry is similar to that of the manganese analogues. The precipitate consists of five compounds, one of which was cis,mer-Re(CO)(2)(P(2)P')X. The new compounds A-D were identified as follows: A is cis,mer-{Re(CO)(2)(P(2)P')X}(2), a dimeric species with bridging P(2)P' ligands. The spectroscopic data for B indicated that it was a form of cis,mer-Re(CO)(2)(P(2)P')X, but not the same as the major product. Compound C is cis,fac-Re(CO)(2)(P(2)P')X, and compound D was shown to be fac-[Re(CO)(3)(P(2)P')]X. The crystal structures of cis,mer-Re(CO)(2)(P(2)P')Cl(I) and cis,mer-Re(CO)(2)(P(2)P')Cl(II) show the compounds to be diastereoisomers with the same mer geometry of the P(2)P' ligand, which of necessity generates a cavity formed by three phenyl rings on one side of the rhenium atom. The coordination geometry of the two compounds differ only by the interchange of the mutually trans chloro and carbonyl ligands. In (I) the carbonyl ligand is within the cavity and in (II) the chloro ligand is within the cavity.
Publisher: Springer Berlin Heidelberg
Date: 2010
Publisher: Institute of Organic Chemistry & Biochemistry
Date: 2001
DOI: 10.1135/CCCC20010255
Abstract: We extend our earlier work on the numerical simulation of ac linear sweep voltammetry at macroelectrodes to the case of microdisc electrodes. This requires the solution of the underlying diffusional transport equations in two dimensions, rather than one, using a cylindrical coordinate system. We use the two-dimensional FIRM algorithm combined with a specially designed exponentially expanding mesh. We examine the ac response as a function of the frequency and litude of the ac signal, and as a function of the non-dimensional parameter p = ( nFa 2 v / RTD ) 1/2 , where a is electrode radius, v the sweep rate, and D the diffusion coefficient. Results are analysed using Fast Fourier Transform (FFT) methods. We are able to derive a range of conditions under which radial diffusion has only a minor effect on the ac response of the system. The analytical results available for macroelectrodes therefore carry through to the microelectrode case for many practical ranges of system parameters (electrode size, dc sweep rate and diffusion coefficient). Experimental results are given which show good agreement with the numerical simulations.
Publisher: Springer Science and Business Media LLC
Date: 12-07-2011
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD76P
Publisher: Elsevier BV
Date: 1984
Publisher: Royal Society of Chemistry (RSC)
Date: 2001
DOI: 10.1039/B006264M
Publisher: Elsevier BV
Date: 05-2014
Publisher: Elsevier BV
Date: 08-1984
Publisher: MDPI AG
Date: 10-09-2018
DOI: 10.3390/W10091219
Abstract: Legionella pneumophila is an increasingly recognized threat to public health via aerosol exposures with a variety of control measures including: water temperature/flow management and free chlorine used to reduce the risk of infection within healthcare centers. Despite these efforts, L. pneumophila often recolonizes plumbing systems after specific treatments, which prompted us to examine ultraviolet (UV) irradiation for a point-of-use, secondary control measure. Currently, there is no data on the efficacy of high ( nm) wavelength UV-C (100–280 nm) light inactivation of L. pneumophila with resuscitation of viable but non-culturable (VBNC) cells. We report for the first time L. pneumophila dose-responses for 268.6 nm and 288.6 nm UV-C, as compared to 256 nm, and demonstrate UV induced VBNC L. pneumophila remaining infectious to Acanthamoeba polyphaga during co-culture experiments. Findings were correlated to molecular-based activity assays to identify additional measures of L. pneumophila viability following UV disinfection compared to culture. A collection of viability markers may provide a more representative measure of risk compared to current culture-based detection, since UV-C irradiated L. pneumophila lose culturability, yet retain activity, increased ATP production, and the ability to be resuscitated by amoeba co-culture. This finding is significant as it identifies potential concern from VBNC cells following UV-C disinfection and the need for further research into the efficacy of UV inactivation as a point-of-use application for L. pneumophila control and management.
Publisher: American Chemical Society (ACS)
Date: 11-1981
DOI: 10.1021/JA00413A008
Publisher: American Chemical Society (ACS)
Date: 15-12-1990
DOI: 10.1021/AC00223A009
Publisher: American Chemical Society (ACS)
Date: 13-02-2017
DOI: 10.1021/ACS.ANALCHEM.6B03924
Abstract: Quantitative studies of electron transfer processes at electrode/electrolyte interfaces, originally developed for homogeneous liquid mercury or metallic electrodes, are difficult to adapt to the spatially heterogeneous nanostructured electrode materials that are now commonly used in modern electrochemistry. In this study, the impact of surface heterogeneity on Fourier-transformed alternating current voltammetry (FTACV) has been investigated theoretically under the simplest possible conditions where no overlap of diffusion layers occurs and where numerical simulations based on a 1D diffusion model are sufficient to describe the mass transport problem. Experimental data that meet these requirements can be obtained with the aqueous [Ru(NH
Publisher: Royal Society of Chemistry (RSC)
Date: 11-10-2001
DOI: 10.1039/B104636P
Publisher: American Chemical Society (ACS)
Date: 20-07-2011
DOI: 10.1021/LA2017819
Abstract: The higher harmonic components available from large- litude Fourier-transformed alternating current (FT-ac) voltammetry enable the surface active state of a copper electrode in basic media to be probed in much more detail than possible with previously used dc methods. In particular, the absence of capacitance background current allows low-level Faradaic current contributions of fast electron-transfer processes to be detected these are usually completely undetectable under conditions of dc cyclic voltammetry. Under high harmonic FT-ac voltammetric conditions, copper electrodes exhibit well-defined and reversible premonolayer oxidation responses at potentials within the double layer region in basic 1.0 M NaOH media. This process is attributed to oxidation of copper adatoms (Cu*) of low bulk metal lattice coordination numbers to surface-bonded, reactive hydrated oxide species. Of further interest is the observation that cathodic polarization in 1.0 M NaOH significantly enhances the current detected in each of the fundamental to sixth FT-ac harmonic components in the Cu*/Cu hydrous oxide electron-transfer process which enables the underlying electron transfer processes in the higher harmonics to be studied under conditions where the dc capacitance response is suppressed the results support the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis. The underlying quasi-reversible interfacial Cu*/Cu hydrous oxide process present under these conditions is shown to mediate the reduction of nitrate at a copper electrode, while the mediator for the hydrazine oxidation reaction appears to involve a different mediator or active state redox couple. Use of FT-ac voltammetry offers prospects for new insights into the nature of active sites and electrocatalysis at the electrode/solution interface of Group 11 metals in aqueous media.
Publisher: CSIRO Publishing
Date: 2004
DOI: 10.1071/CH04130
Abstract: Naphthalene diimides 1–4 having different N,N-disubstitution undergo single electron reduction processes either chemically or electrochemically to yield the corresponding radical anion in high yield. This study concentrates on 1, bearing pentyl side chains connected through the diimide nitrogens, and compares the results obtained against those bearing isopropyl, propargyl, and phenylalanyl side chains. Compound 1 exhibits mirror image absorption and fluorescence in the near-UV region in CH2Cl2 and dimethylformamide that is typical of monomeric N,N-dialkyl-substituted naphthalene diimides. In toluene, excimer-like emission is observed, which suggests ground-state complexes involving 1 are formed. X-Ray crystallography has been used to characterize 1 in the solid state. Cyclic voltammetry enables the reversible potentials for [NDI]0/– and [NDI]−/2– type processes to be measured. Bulk one-electron reduction of 1–4 is characterized by dramatic changes in the absorption and emission spectra. Additionally, highly structured EPR (electron paramagnetic resonance) signals from dimethylformamide solutions of the radical anions of 1–3 have been obtained and are consistent with coupling between the unpaired electron and the naphthalene diimide nitrogens and hydrogens and the NCH hydrogens of the appropriate side chains. The overall structure of the EPR spectrum is substituent-dependent. These changes in spectroscopic output upon an electronic input may be described as a simple ‘on/off’ switching mechanism with which to apply a ‘bottom-up’ approach to molecular device manufacture.
Publisher: American Chemical Society (ACS)
Date: 05-1987
DOI: 10.1021/IC00256A021
Publisher: The Polarographic Society of Japan
Date: 2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4DT03268C
Abstract: Cyclopalladated complexes containing the 2-C 6 F 4 PPh 2 fragment have been prepared and their electrochemical reduction behaviour investigated.
Publisher: American Chemical Society (ACS)
Date: 07-1998
DOI: 10.1021/IC971634I
Abstract: Structural, electrochemical, and EPR studies of binuclear copper(II) complexes of bis(pentadentate) ligands, obtained by attaching 2-pyridylmethyl arms to the four secondary nitrogens of bis(tacn) macrocycles linked by ethyl (tmpdtne, [Cu(2)(tmpdtne)](ClO(4))(4).2H(2)O 2), propyl (tmpdtnp, [Cu(2)(tmpdtnp)](ClO(4))(4) 3), butyl (tmpdtnb, [Cu(2)(tmpdtnb)](ClO(4))(4) 4), m-xylyl (tmpdtnm-X, [Cu(2)(tmpdtnm-X)](ClO(4))(4).2DMSO.2H(2)O, 5), and 2-propanol (tmpdtnp-OH, [Cu(2)(tmpdtnp-OH)](ClO(4))(4).2H(2)O, 6) bridges, are reported, together with further analysis of the mononuclear complex, [Cu(dmptacn)](ClO(4))(2) 1, dmptacn = 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane. Single-crystal X-ray diffraction studies established the molecular structure of 3 and the tetrakis(DMF) solvate of 4. Complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 13.867(3), b = 13.548(6), c = 28.055(4) Å, beta = 102.63(1) degrees, V= 5143(2) Å(3), and Z = 4. Refinement gave R = 0.085 and R(w) = 0.089 for 3696 observed reflections. 4 crystallizes in the triclinic space group &Pmacr (No. 2) with a = 11.775(4), b = 12.718(3), c = 13.201(3) Å, alpha = 61.25(2), beta = 75.99(3), gamma = 77.66(3) degrees, V = 1673(1) Å(3), and Z = 1. Refinement gave R = 0.072 and R(w) = 0.065 for 3876 observed reflections. In 4, the pentadentate compartments are oriented in an anti configuration, while in 3, constraints introduced by the propane bridging group result in a syn configuration. Both complexes exhibit distorted square pyramidal (SP) geometries about the Cu(II) centers with Cu-N(apical) approximately 2.25 Å and Cu-N(equatorial) approximately 2.0 Å. Molecular mechanics calculations have been carried out on these types of complexes for the first time in order to predict the solution structures of 5 and 6. The calculations revealed that the SP geometry is also preferred by these complexes and that there is little energy difference between the syn and anti configurations. Cyclic, square-wave, and steady-state voltammetric studies on 1-6 indicate that, on the time scale of the measurements, 1 undergoes a one-electron reduction to the Cu(I) state while 2-6 undergo an overall two-electron reduction to the binuclear Cu(I) complexes. For 2-4, a shift in reduction potential to more negative values with increasing Cu.Cu separation reflects the stabilization of the Cu(II) state while the two partially resolved reduction processes for 6 suggest that the alcohol group in the ligand backbone promotes a small level of interaction between copper centers.
Publisher: Elsevier BV
Date: 09-2011
Publisher: Elsevier BV
Date: 2015
Publisher: American Chemical Society (ACS)
Date: 19-09-2006
DOI: 10.1021/IC061081O
Abstract: A detailed study is reported of the influence of protons, metal cations, and media on the redox chemistry of lacunary anions [alpha-SiW11O39]8- and [alpha-PW11O39]7- of high formal negative charge. Each anion displayed a single chemically reversible one-electron reduction process in carefully dried aprotic CH3CN solution. This process was detected at very negative potentials just prior to the solvent limit. Addition of 0.3 equiv of acid gave rise to a new reduction process at considerably less negative potentials, which is attributed to formation of the protonated species [SiW11O38(OH)]7- and [PW11O38(OH)]6-. Voltammograms derived from simulations based on a double-square scheme are in excellent agreement with experiment. Previous data reported the presence of several processes in CH3CN and appear to have been influenced by the presence of protons and/or adventitious water. Not surprisingly, protonation reactions coupled to charge transfer contribute significantly to the voltammetry of these lacunary anions in buffered aqueous media over the pH range 2-6. A multi-square-scheme mechanism allowed the essential thermodynamic and kinetic features of this system to be captured and an assessment of the relative significance of possible in idual pathways. The high formal anionic charges of [SiW11O39]8- and [PW11O39]7- appear to provide highly basic reduced forms that are able to abstract protons from water to produce protonated species which are reduced at potentials more than a volt less negative than those for the processes [SiW11O39]8-/9- and [PW11O39]7-/8- found in dry aprotic media.
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTM7M8
Publisher: Institute of Organic Chemistry & Biochemistry
Date: 1991
DOI: 10.1135/CCCC19910192
Abstract: A microelectrode based detector system has been developed for measurement of steady state voltammetric curves in flowing solutions. Two microprocessors operating in parallel allow the direct transfer of collected data to a floppy diskette. Long term experiments can then be performed, with in idual voltammograms being rapidly obtained, recorded and stored. The system can be used with scan rates up to 10 V s -1 and with 1 mV resolution over a potential range of 2.5 V. When a 10 μm diameter micro-disk platinum electrode serves as the working electrode, rapid scan voltammetry (scan rate 1 to 10 V s -1 ) can be undertaken under steady state conditions for reversible processes with a flow rate in the range of 1 to 3 ml min -1 as evidenced by the observation of sigmoidal rather than the peak shaped curves obtained with previously described rapid scan systems. That is, complete voltammograms can be obtained with minimal distortion due to uncompensated resistance and charging current which is not the case when conventionally sized electrodes are used or when microelectrodes are used at excessively high scan rates where linear diffusion terms become important. The working microelectrodes were developed to suit a conventional thin-layer cell design and therefore permit ready adaptation to existing flow through electrochemical detection systems. The detection limits for the determination of ferrocene in methanol at flow rates up to 3 ml min -1 were 10 -6 mol dm -3 after background correction, and the response was found to be linear over the concentration range 10 -3 to 10 -6 mol dm -3 . Three-dimensional methods of data treatment and contour plots can be used to interpret results obtained from steady state or near steady state voltammograms of incompletely resolved chromatograms as demonstrated with range of biologically important compounds.
Publisher: American Chemical Society (ACS)
Date: 15-05-1995
DOI: 10.1021/AC00106A007
Publisher: American Chemical Society (ACS)
Date: 05-1992
DOI: 10.1021/AC00033A010
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B516281E
Abstract: The electrochemical properties of porphyrin-appended dendrimers containing 2-, 4-, 8-, 16-, 32- and 64-porphyrin macrocycles in their free-base and zinc(II) forms have been investigated. Both series gave diffusional based voltammetric responses in dichloromethane. There was minimal effect of dendrimer generation on the redox potentials. Multiple pi-cation and anion radicals as well as dications and dianions were formed on the surface of the dendrimers on oxidation or reduction as appropriate, with each cyclic voltammetric wave representing electron transfer to or from multiple non-interacting porphyrin sites. Electrostatic interactions in the higher generation dendrimers result in kinetic effects being observed for the highly charged species generated when each porphyrin unit is doubly or triply oxidised. The number of electrons transferred on reduction or oxidation of the dendrimers was evaluated using steady-state microelectrode voltammetry. For the lower generations of species a good correlation was observed between numbers of electrons transferred and number of porphyrin entities per molecule for the dendrimers containing 32 and 64 units, however, slight negative deviations were observed, possibly due to electrostatic interactions as the porphyrins become closer packed.
Publisher: American Chemical Society (ACS)
Date: 04-1987
DOI: 10.1021/JA00241A012
Publisher: Elsevier BV
Date: 08-1991
Publisher: Royal Society of Chemistry (RSC)
Date: 1999
DOI: 10.1039/A806905K
Publisher: Elsevier BV
Date: 1992
Publisher: American Chemical Society (ACS)
Date: 1996
DOI: 10.1021/JP9601173
Publisher: Elsevier BV
Date: 09-2016
DOI: 10.1016/J.JINORGBIO.2016.01.015
Abstract: The bulk oxidative electrolysis of a 2mM solution of trans-[Pt
Publisher: Elsevier BV
Date: 04-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP00095E
Abstract: The yield of electrocarboxylation of aromatic ketone depends on the imidazolium-based ionic liquid anion and the ketone substituent.
Publisher: American Chemical Society (ACS)
Date: 25-03-2006
DOI: 10.1021/AC051823F
Abstract: This paper describes an application of Fourier transform (FT) voltammetry that provides a quantitative evaluation of the electron-transfer kinetics of protein molecules attached to electrode surfaces. The potential waveform applied in these experiments consists of a large- litude square wave of frequency f superimposed onto the traditional triangular voltage used in dc cyclic voltammetry. The resultant current-time response, when Fourier transformed into the frequency domain, provides patterns of data at the even harmonic frequencies that arise from nonlinearity in the Faradaic response. These even harmonic contributions are ideally suited for kinetic evaluation of electron-transfer processes because they are highly selective to quasi-reversible behavior (insensitive to reversible or irreversible processes) and almost devoid of background charging current. Inverse FT methods can then be used to provide the wave shapes of the dc as well as the ac voltammetric components and other characteristics employed to detect the level of nonideality present relative to theoretical models based upon noninteracting surface-confined molecules. The new form of data evaluation has been applied to the electron-transfer properties of a typical biological electron carrier, the blue copper protein azurin, immobilized on polycrystalline gold electrodes modified with self-assembled monolayers of different length alkanethiols. Details of the electrode kinetics (rates of electron transfer, dispersion, and charge-transfer coefficients) as a function of alkanethiol, apparent surface coverage, and capacitance are all deduced from the square wave (FT-inverse FT) protocol, and the implications of these findings are considered.
Publisher: American Chemical Society (ACS)
Date: 07-1984
DOI: 10.1021/IC00183A026
Publisher: Elsevier BV
Date: 12-2009
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTM7L7
Publisher: American Chemical Society (ACS)
Date: 10-1974
DOI: 10.1021/AC60348A014
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT781B
Publisher: American Chemical Society (ACS)
Date: 09-1991
DOI: 10.1021/OM00055A059
Publisher: American Chemical Society (ACS)
Date: 09-1991
DOI: 10.1021/OM00055A058
Publisher: American Chemical Society (ACS)
Date: 02-1993
DOI: 10.1021/J100110A031
Publisher: American Chemical Society (ACS)
Date: 28-03-1998
DOI: 10.1021/JP972956A
Publisher: Elsevier BV
Date: 12-2001
Publisher: American Chemical Society (ACS)
Date: 22-01-1998
DOI: 10.1021/IC9714192
Publisher: Wiley
Date: 15-07-2016
Publisher: Elsevier BV
Date: 07-2013
Publisher: Elsevier BV
Date: 09-2020
Publisher: Wiley
Date: 05-07-2011
Abstract: Solid-state electrochemistry of a tetracyanoquinodimethane (TCNQ)-modified electrode in contact with a tetrapropylammonium cation (Pr(4)N(+)) electrolyte showed two electron-transfer steps to give Pr(4)N(TCNQ)(2) (1) and Pr(4)N(TCNQ) (2) rather than the traditional one-electron step to directly give Pr(4)N(TCNQ). Two thermodynamically stable Pr(4)N(+)-TCNQ stoichiometries, 1 and 2, were synthesized and characterized. The degree of charge transfer (ρ) calculated from the crystal structure is -0.5 for the TCNQ moieties in 1 and -1.0 for those in 2. Raman spectra for Pr(4)N(TCNQ)(2) show only one resonance for the extracyclic C=C stretching at 1423 cm(-1), which lies approximately midway between that of TCNQ at 1454 cm(-1) and TCNQ(-) at 1380 cm(-1). Both the magnetic susceptibility and EPR spectra are temperature-dependent, with a magnetic moment close to that for one unpaired electron per (TCNQ)(2) unit in 1, whereas 2 is almost diamagnetic. Pressed discs of both complexes show conductivity (1-2×10(-5) S cm(-1)) in the semiconductor range. For 1, the position of zero current for the steady-state voltammograms implies 50% of TCNQ(-) and 50% TCNQ(0) is present in solution, thereby supporting a dissociation of (TCNQ)(2)(-) in solution, but is indicative of only TCNQ(-) being present for 2.
Publisher: Elsevier BV
Date: 03-1989
Publisher: American Chemical Society (ACS)
Date: 08-1991
DOI: 10.1021/OM00054A021
Publisher: American Chemical Society (ACS)
Date: 18-05-2011
DOI: 10.1021/IC1016627
Abstract: Simple polyoxometalate anions are known to be photoreduced in molecular solvents in the presence of 2-propanol or benzyl alcohol. The use of ionic liquids (ILs) as the solvent is now reported to also allow the photooxidation of water to be achieved. In particular, the photochemistry of the classic Dawson polyoxometalate salt K(6)[P(2)W(18)O(62)] has been studied in detail when water is present in the aprotic IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) and the protic IL, diethanolamine hydrogen sulfate (DEAS). In these and other ILs, irradiation with white light (wavelength 275-750 nm) or UV light (wavelength 275-320 nm) leads to overall reduction of the [P(2)W(18)O(62)](6-) anion to [P(2)W(18)O(62)](7-) and concomitant oxidation of water to dioxygen and protons. The modified structure of bulk water present in ILs appears to facilitate its oxidation. Analogous results were obtained in aqueous solutions containing the protic IL as an electrolyte. The photoproducts (reduced polyoxometalate anion, dioxygen, and protons) were identified by, respectively, voltammetry, a Clark electrode, and monitoring of pH. The formal reversible potentials E(0)(F) for [P(2)W(18)O(62)](6-/7-/8-/9-/10-) couples are much more positive than in molecular solvents. The [P(2)W(18)O(62)](8-) and more reduced anions, if formed as intermediates, would efficiently reduce photoproducts H(+) or dioxygen to produce [P(2)W(18)O(62)](7-), rather than reform to [P(2)W(18)O(62)](6-). Thus, under photoirradiation conditions [P(2)W(18)O(62)](7-) acts as a kinetic sink so that in principle indirect splitting of water to produce dioxygen and dihydrogen can be achieved. The equivalent form of photooxidation does not occur in liquid water or in molecular solvents such as MeCN and MeCN/CH(2)Cl(2) containing added water, but does occur for solid K(6)[P(2)W(18)O(62)] in contact with water vapor.
Publisher: American Chemical Society (ACS)
Date: 16-09-2015
Publisher: American Chemical Society (ACS)
Date: 06-1975
DOI: 10.1021/IC50148A054
Publisher: Elsevier BV
Date: 04-1997
Publisher: American Chemical Society (ACS)
Date: 08-1980
DOI: 10.1021/AC50059A016
Publisher: American Chemical Society (ACS)
Date: 16-09-2010
DOI: 10.1021/LA102495T
Abstract: Advances in basic knowledge relevant to the pseudocapacitive and electrocatalytic properties of RuO(2) materials require a detailed understanding of the redox chemistry that occurs at the electrode interface. Although several redox processes have been identified via dc cyclic voltammograms derived from surface-confined RuO(2) materials, mechanistic details remain limited because the faradaic signals of interest are heavily masked by the background current. Here, it is shown that the underlying electron transfer reactions associated with the VI to II oxidation states of surface-confined RuO(2) materials in acidic medium are far more accessible in the background current free fourth and higher harmonic components available via large- litude Fourier transformed ac voltammetry. Enhanced resolution and sensitivity to both electron transfer and protonation processes and discrimination against solvent and background capacitance are achieved so that the Ru(V) to Ru(VI) process can be studied for the first time. Thus, kinetic and thermodynamic information relevant to each ruthenium redox level is readily deduced. The relative rate of electron transfer and the impact of protonation associated with Ru(VI) to Ru(II) redox processes are found to depend on the nature of the RuO(2) materials (extent of crystallinity and hydration) and concentration of sulfuric acid electrolyte. In the electrocatalytic oxidation of glucose in alkaline medium, access to the underlying electron transfer processes allows ready detection of the redox couple associated with the catalysis. Thus, application of an advanced ac electroanalytical technique is shown to provide the methodology for enhancing our understanding of the charge transfer processes of RuO(2), relevant to pseudocapacitance and electrocatalysis.
Publisher: Public Library of Science (PLoS)
Date: 20-11-2015
Publisher: American Chemical Society (ACS)
Date: 15-09-1988
DOI: 10.1021/AC00169A008
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B709602J
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTM7N9
Publisher: American Chemical Society (ACS)
Date: 02-1976
DOI: 10.1021/IC50156A041
Publisher: Elsevier BV
Date: 12-1991
Publisher: American Chemical Society (ACS)
Date: 24-07-2003
DOI: 10.1021/JA029348F
Abstract: Oxidative photocurrents measured upon irradiation by a 7-W visible light (wavelength 312-700 nm) demonstrated that the sulfo-polyoxometalate anion clusters [S2W18O62]4- (1a), [S2Mo18O62]4- (1b), and [SMo12O40]2- (2) may be activated photochemically to oxidize the organic substrates benzyl alcohol, ethanol, and (-)-menthol. In the case of catalytic photooxidation of benzyl alcohol to benzaldehyde in the presence of 1a, quantitative electrochemical methods have identified pathways for the oxidation of reduced forms of 1 generated during the catalysis. More generally, the oxidation pathways P(n+2)- + 2H+ Pn- + H2 and 2P(n+2)- + O2 + 4H+ 2Pn- + 2H2O have been evaluated by monitoring acidified acetonitrile solutions of the 2e(-)-reduced clusters by rotating disk electrode voltammetry under anaerobic and aerobic conditions, respectively. Neither of the reduced forms 1b(2e-) nor 2(2e-) reacted under these conditions. In contrast, 1a(2e-) was oxidized via both pathways, consistent with its more negative redox potential, with the rate of oxidation by air-oxygen being significantly faster than that by H+. The present work demonstrated that the crucial step necessary to oxidize reduced catalyst in photocatalytic reactions involving the anions studied may be achieved or accelerated by application of an external potential more positive than the first redox potential of the polyoxometalate anion. Voltammetric analysis revealed that this in situ electrolytic regeneration of the reduced catalyst is an option that leads to a viable photoelectrocatalytic pathway, even when the H+ and O2 pathways are not available.
Publisher: Canadian Science Publishing
Date: 2001
Publisher: American Chemical Society (ACS)
Date: 03-01-2003
DOI: 10.1021/AC025842Q
Abstract: The voltammetry of solid 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (ITF) at an electrode-microparticle-aqueous (electrolyte) interface generates characteristic current-potential profiles associated with solid-solid-phase transformations. During the reactions, electrolyte ions are included into the TCNQ (cations) and TTF (anions) lattice sites as part of the charge neutralization process. Consequently, electrolyte ion concentration is associated with the reversible potential of the TCNQ0/- and TTF0/+ reactions, making these processes candidates for the development of novel voltammetric cation and anion sensors, respectively. Electrode potential-analyte ion concentration dependence studies exhibited highly reproducible potential shifts of 45 (+/- 1) mV/decade change in ion analyte concentration for both the TCNQ cation sensor and the TTF anion sensor. When presented with mixed-analyte solutions, both ion-sensing systems exhibited a degree of ion selectivity. Ion selectivity trends may be modeled using equations based on a Nicolsky-type selectivity relationship, in accordance with the concept that these are the voltammetric analogies of potentiometric ion-selective membrane electrodes.
Publisher: American Chemical Society (ACS)
Date: 08-1985
DOI: 10.1021/J100263A031
Publisher: CSIRO Publishing
Date: 2017
DOI: 10.1071/CH17245
Abstract: The demand for catalysts that are highly active and stable for electron-transfer reactions has been boosted by the discovery that [Pt(NH3)4](TCNQF4)2 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) is an efficient catalyst. In this work, we prepare and characterize the two related [Pt(NH3)4]2+ complexes, [Pt(NH3)4](TCNQ)2·(DMF)2 (1) and [Pt(NH3)4](TCNQ)2 (2). Reaction of [Pt(NH3)4](NO3)2 with LiTCNQ in a mixed solvent (methanol/dimethylformamide, 4 : 1 v/v) gives [Pt(NH3)4](TCNQ)2·(DMF)2 (1), whereas the same reaction in water affords [Pt(NH3)4](TCNQ)2 (2). 2 has been previously reported. Both 1 and 2 have now been characterized by single-crystal X-ray crystallography, Fourier-transform (FT)IR, Raman and UV-vis spectroscopy, and electrochemistry. Structurally, in 1, the TCNQ1− anions form infinite stacks with a separation between adjacent anions within the stack alternating between 3.12 and 3.42 Å. The solvated structure 1 differs from the non-solvated form 2 in that pairs of TCNQ1− anions are clearly displaced from each other. The conductivities of pressed pellets of 1 and 2 are both in the semi-conducting range at room temperature. 2 can be electrochemically synthesized by reduction of a TCNQ-modified electrode in contact with an aqueous solution of [Pt(NH3)4](NO3)2 via a nucleation growth mechanism. Interestingly, we discovered that 1 and 2 are not catalysts for the ferricyanide and thiosulfate reaction. Li+ and tetraalkylammonium salts of TCNQ1−/2− and TCNQF41−/2− were tested for potential catalytic activity towards ferricyanide and thiosulfate. Only TCNQF41−/2− salts were active, suggesting that the dianion redox level needs to be accessible for efficient catalytic activity and explaining why 1 and 2 are not good catalysts. Importantly, the origin of the catalytic activity of the highly active [Pt(NH3)4](TCNQF4)2 catalyst is now understood, enabling other families of catalysts to be developed for important electron-transfer reactions.
Publisher: Wiley
Date: 14-06-2021
Abstract: Use of carefully designed computer supported parameterisation methods in voltammetric studies can provide highly robust and accurate methods for simultaneously quantifying the large number of parameters present in complex electrochemical reactions. In this study, a computer program has been developed to parameterise large litude AC voltammetric data using mathematical optimisation in combination with Bayesian inference algorithms for calculating posterior distributions of parameters and hence uncertainties in parameter values. The computer program has been applied to objective functions, relevant to total AC current, frequency domain data in the form of the power spectrum derived from Fourier transformation and multivariate based methods using the resolved harmonic data. The robustness of the objective functions have been confirmed and Bayesian inference methods have been validated using “noisy” synthetic and experimental data for the [Fe(CN) 6 ] 3−/4− reduction process in aqueous 3.0 M KCl electrolyte at a gold electrode. It was found that the harmonic based Bayesian inference methods outperformed other methods in parameterisation of the thermodynamics and electrode kinetics of the close to reversible [Fe(CN) 6 ] 3−/4− process due to their ability to compensate for non‐ideality in the modelling and the superior parameter sensitivities available in the higher harmonics. The computer supported and heuristic methods were compared. Their advantages and limitations are discussed.
Publisher: Royal Society of Chemistry (RSC)
Date: 04-02-2003
DOI: 10.1039/B210815A
Publisher: American Chemical Society (ACS)
Date: 11-1975
DOI: 10.1021/AC60363A022
Publisher: Elsevier BV
Date: 07-1997
Publisher: American Chemical Society (ACS)
Date: 04-1977
DOI: 10.1021/IC50170A023
Publisher: American Chemical Society (ACS)
Date: 09-1976
DOI: 10.1021/AC50005A052
Publisher: Springer Science and Business Media LLC
Date: 24-02-2022
Publisher: F1000 Research Ltd
Date: 05-03-2018
DOI: 10.12688/F1000RESEARCH.12684.1
Abstract: Adult neurogenesis occurs in the dentate gyrus in the mammalian hippoc us. These new neurons arise from neural precursor cells named radial glia-like cells, which are situated in the subgranular zone of the dentate gyrus. Here, we review the emerging topic of precursor heterogeneity in the adult subgranular zone. We also discuss how this heterogeneity may be established during development and focus on the embryonic origin of the dentate gyrus and radial glia-like stem cells. Finally, we discuss recently developed single-cell techniques, which we believe will be critical to comprehensively investigate adult neural stem cell origin and heterogeneity.
Publisher: American Chemical Society (ACS)
Date: 17-05-2008
DOI: 10.1021/AC0715221
Abstract: An analytical evaluation of the higher ac harmonic components derived from large litude Fourier transformed voltammetry is provided for the reversible oxidation of ferrocenemethanol (FcMeOH) and oxidation of uric acid by an EEC mechanism in a pH 7.4 phosphate buffer at a glassy carbon (GC) electrode. The small background current in the analytically optimal fifth harmonic is predominantly attributed to faradaic current associated with the presence of electroactive functional groups on the GC electrode surface, rather than to capacitive current which dominates the background in the dc, and the initial three ac harmonics. The detection limits for the dc and the first to fifth harmonic ac components are 1.9, 5.89, 2.1, 2.5, 0.8, and 0.5 microM for FcMeOH, respectively, using a sine wave modulation of 100 mV at 21.46 Hz and a dc sweep rate of 111.76 mV s (-1). Analytical performance then progressively deteriorates in the sixth and higher harmonics. For the determination of uric acid, the capacitive background current was enhanced and the reproducibility lowered by the presence of surface active uric acid, but the rapid overall 2e (-) rather than 1e (-) electron transfer process gives rise to a significantly enhanced fifth harmonic faradaic current which enabled a detection limit of 0.3 microM to be achieved which is similar to that reported using chemically modified electrodes. Resolution of overlapping voltammetric signals for a mixture of uric acid and dopamine is also achieved using higher fourth or fifth harmonic components, under very low background current conditions. The use of higher fourth and fifth harmonics exhibiting highly favorable faradaic to background (noise) current ratios should therefore be considered in analytical applications under circumstances where the electron transfer rate is fast.
Publisher: American Chemical Society (ACS)
Date: 16-12-2009
DOI: 10.1021/AC801732G
Abstract: The level of edge plane defect sites present in highly ordered pyrolytic graphite (HOPG) electrodes has been evaluated via analysis of dc, ac fundamental, and higher-order ac harmonics available from a single large- litude Fourier transformed (FT) ac voltammetric experiment. Deliberate introduction of a low level of edge plane defect was achieved by polishing, with a higher level being introduced via electrochemical pretreatment. Kinetics regimes associated with fast electron transfer on the edge plane defect sites and slow electron transfer on the basal plane surface are resolved under ac conditions when using the surface-sensitive [Fe(CN)(6)](3-/4-) redox probe. However, because of their insensitivity to slow electron transfer, higher-order ac faradaic harmonics almost exclusively detect only the much faster processes that emanate from edge plane defect sites. Thus, detection of fourth- and higher-order ac Faradaic harmonic components that are devoid of background capacitive current is possible at freshly cleaved HOPG in the region near the reversible potential for the [Fe(CN)(6)](3-/4-) process. Under these circumstances, dc cyclic voltammograms exhibit only reduction and oxidation peaks separated by more than 1 V. The fundamental ac harmonic provides detailed information on the capacitive current, which increases with the level of edge plane defect sites. Apparent charge transfer rate constants also can be derived from peak-to-peak separations obtained from the dc aperiodic component. Estimates of the percentage of edge plane defect sites based on ac higher harmonics, capacitance, and dc aperiodic component that are available from a single experiment have been compared. The edge plane defect levels deduced from capacitance (fundamental harmonic ac component) and higher harmonic Faradaic currents are considered to be more reliable than estimations based on apparent rate constants derived from the dc aperiodic component or conventional dc cyclic voltammogram.
Publisher: Wiley
Date: 13-12-2021
Abstract: The oxidation of thiosulfate has been of interest for more than a century, including the famous oscillating iodine clock reaction. From a thermodynamic perspective, calculations based on the reversible potentials reveal that both neutral TCNQF 4 0 (2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane) or its radical anion (TCNQF 4 1− ) can oxidize thiosulfate to tetrathionate to form TCNQF 4 2− . The reaction of S 2 O 3 2− with TCNQF 4 0 in a 2:1 or greater concentration ratio occurs in a step‐wise fashion to initially (and rapidly) form S 4 O 6 2− and TCNQF 4 1− (reaction 1), followed by a slow step involving the oxidation of residual S 2 O 3 2− by TCNQF 4 1− to give more S 4 O 6 2− and TCNQF 4 2− (reaction 2). Thus, this reaction occurs in two, temporally well‐resolved, steps with dramatically different kinetics. If S 2 O 3 2− and TCNQF 4 1− are mixed in a 1 : 1 ratio, then S 4 O 6 2− and TCNQF 4 2− are formed quantitatively on the same (hours) timescale, as for the second (slow) step described above. There is no evidence of further oxidation of S 4 O 6 2− to SO 4 2− . A slight increase in the rate of reaction 2 was observed in the presence of Bu 4 NPF 6 and attributed to ion‐pairing effects. Interestingly, during voltammetric experiments, if the Pt counter electrode is not separated from the reaction solution via a salt bridge, reaction 2 is catalyzed. The rates of reaction 2 have been studied over a wide range of conditions. Intriguingly, the mechanisms are dependent on whether S 2 O 3 2− or TCNQF 4 1− (much faster) are in excess. With S 2 O 3 2− in excess, the rate of reaction is first‐order in both S 2 O 3 2− and TCNQF 4 1− . With TCNQF 4 1− in excess, the reaction is more complicated with indications of Li + catalysis through electrostatic shielding of the TCNQF 4 1− and/or S 2 O 3 2− reactants. The large difference in rate of reaction of TCNQF 4 0 /S 2 O 3 2− (rapid) compared with TCNQF 4 1− /S 2 O 3 2− (sluggish) is in part attributable to the much larger driving force in the former case. All experimental studies were undertaken in the mixed solvent system, acetonitrile (MeCN) containing 5 % water, v/v (95 % MeCN : 5 % water) where all the reactants and products are soluble and stable. Voltammetric analysis using steady‐state (microdisc) or transient cyclic voltammetry (macrodisc) with electrolyte (Bu 4 NPF 6 ) and UV‐visible spectrophotometry with or without electrolyte were used to monitor the time dependence and establish the identity of the products.
Publisher: American Chemical Society (ACS)
Date: 20-09-2001
DOI: 10.1021/JP0103878
Publisher: American Chemical Society (ACS)
Date: 31-07-2008
DOI: 10.1021/AC702531F
Abstract: The ability of the technique of large- litude Fourier transformed (FT) ac voltammetry to facilitate the quantitative evaluation of electrode processes involving electron transfer and catalytically coupled chemical reactions has been evaluated. Predictions derived on the basis of detailed simulations imply that the rate of electron transfer is crucial, as confirmed by studies on the ferrocenemethanol (FcMeOH)-mediated electrocatalytic oxidation of ascorbic acid. Thus, at glassy carbon, gold, and boron-doped diamond electrodes, the introduction of the coupled electrocatalytic reaction, while producing significantly enhanced dc currents, does not affect the ac harmonics. This outcome is as expected if the FcMeOH (0/+) process remains fully reversible in the presence of ascorbic acid. In contrast, the ac harmonic components available from FT-ac voltammetry are predicted to be highly sensitive to the homogeneous kinetics when an electrocatalytic reaction is coupled to a quasi-reversible electron-transfer process. The required quasi-reversible scenario is available at an indium tin oxide electrode. Consequently, reversible potential, heterogeneous charge-transfer rate constant, and charge-transfer coefficient values of 0.19 V vs Ag/AgCl, 0.006 cm s (-1) and 0.55, respectively, along with a second-order homogeneous chemical rate constant of 2500 M (-1) s (-1) for the rate-determining step in the catalytic reaction were determined by comparison of simulated responses and experimental voltammograms derived from the dc and first to fourth ac harmonic components generated at an indium tin oxide electrode. The theoretical concepts derived for large- litude FT ac voltammetry are believed to be applicable to a wide range of important solution-based mediated electrocatalytic reactions.
Publisher: Elsevier BV
Date: 08-1999
Publisher: Elsevier BV
Date: 1984
Publisher: American Chemical Society (ACS)
Date: 09-1976
DOI: 10.1021/IC50163A004
Publisher: The Electrochemical Society
Date: 2008
DOI: 10.1149/1.2936177
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A704850E
Publisher: Elsevier BV
Date: 06-1982
Publisher: Elsevier BV
Date: 02-1990
Publisher: Elsevier BV
Date: 10-1991
Publisher: American Chemical Society (ACS)
Date: 18-02-2009
DOI: 10.1021/IC802213V
Abstract: Electrochemical studies of the salts [cat](4)[Pt(2)(mu-pop)(4)] (cat(+) = Bu(4)N(+) or PPN(+) [Ph(3)P=N=PPh(3)](+) pop = pyrophosphite, [P(2)O(5)H(2)](2-)) have been carried out in dichloromethane. In agreement with published studies of K(4)[Pt(2)(mu-pop)(4)] in water and [Ph(4)As](4)[Pt(2)(mu-pop)(4)] in acetonitrile, the [Pt(2)(mu-pop)(4)](4-) anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt(2)(mu-pop)(4)](3-). However, in the more weakly coordinating solvent dichloromethane, [Pt(2)(mu-pop)(4)](3-) appears to undergo oligomerization instead of solvent-induced disproportionation thus the overall process remains a one-electron reaction rather than an overall two-electron oxidative addition process, even under long time-scale, bulk electrolysis conditions. Chemical oxidation of [cat](4)[Pt(2)(mu-pop)(4)] with [NO][BF(4)] or AgBF(4) gives mainly a dark, insoluble, ill-defined solid that appears to contain Pt(III) according to X-ray photoelectron spectroscopy (XPS). In the case of [NO][BF(4)], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat](3)[Pt(2)(mu-pop)(4)(NO)]. The X-ray structure of the PPN(+) salt shows the anion to consist of the usual lantern-shaped Pt(2)(mu-pop)(4) framework with an unusually large Pt-Pt separation [2.8375(6) A] one of the platinum atoms carries a bent nitrosyl group [r(N-O) = 1.111(15) A angle(Pt-N-O) = 118.1(12) degrees] occupying an axial position. The nitrosyl group migrates rapidly on the (31)P NMR time-scale between the metal atoms at room temperature but the motion is slow enough at 183 K that the expected two pairs of inequivalent phosphorus nuclei can be observed. The X-ray photoelectron (XP) spectrum of the nitrosyl-containing anion confirms the presence of two inequivalent platinum atoms whose 4f(7/2) binding energies are in the ranges expected for Pt(II) and Pt(III) an alternative interpretation is that the second platinum atom has a formal oxidation number of +4 and that its binding energy is modified by the strongly sigma-donating NO(-) ligand. Reduction of [Pt(2)(mu-pop)(4)X(2)](4-) (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt(2)(mu-pop)(4)](4-), as is the case in more strongly coordinating solvents.
Publisher: American Chemical Society (ACS)
Date: 05-12-2001
DOI: 10.1021/IC991310P
Abstract: Isolation of a soluble [NHex4]+ salt has allowed a detailed electrochemical study of the anion alpha-[SMo12O40]2- to be undertaken. Four reversible one-electron-reduction processes are observed in CH2Cl2 solution. Controlled potential electrolysis led to isolation of tetraalkylammonium salts of the one-electron-reduced anion alpha-[SMo12O40]3- and the two-electron-reduced anion alpha-[SMo12O40].4- [SMo12O40]3- is stable to disproportionation in dry solvents (Kdis = 10(-7.4). EPR and magnetic susceptibility data indicate that [SMo12O40]3- is a simple paramagnet (S = 1/2) while [SMo12O40]4- is paramagnetic with the mu eff values decreasing at low temperatures. Solutions of the two-electron-reduced species are EPR silent, but microcrystalline powders show very weak signals. The crystal structure of alpha-[NBu4]3[SMo12O40] has been determined (triclinic P1 a = 13.840(3) A b = 15.587(4) A c = 19.370(3) A alpha = 94.82(2) degrees beta = 93.10(1) degrees gamma = 91.05(2) degrees Z = 2). There is disorder around the C2 axis of the central SO4(2-) tetrahedron. In the presence of aqueous HClO4 (0.045 M) in thf/H2O or MeCN/H2O (98/2 v/v), [SMo12O40]2- exhibits five two-electron-reduction processes. Under these conditions, [SMo12O40]3- protonates and disproportionates into [SMo12O40]2- and the (2e-, 2H+)-reduced anion [H2SMo12O40]2-.
Publisher: American Chemical Society (ACS)
Date: 27-12-2013
DOI: 10.1021/AC3029135
Abstract: Electroanalytical protocols executed under quiescent conditions generally require that the analyte medium be stirred (or agitated) between repetitions to ensure reestablishment of identical initial conditions in the vicinity of the electrode surface. The present work examines what happens when experimental conditions preclude stirring. We consider two general schemes: Scheme 1 where the potential is stepped from E(start) to E(step) to oxidize the initially present reduced redox moiety, A, to B under diffusion control (i.e., [A](x=0) = 0) for 0 ≤ t ≤ τ(1) followed by a second potential step from E(step) back to E(start) and continuing for τ(1) < t ≤ τ(2) during which time species B is reduced back to the initially present species A under diffusion control (i.e., [B](x=0) = 0) and Scheme 2 where the potential is again stepped from E(start) to E(step) to oxidize A to B under diffusion control for 0 ≤ t ≤ τ(1) followed by a second potential step from E(step) back to E(start) and continuing for τ(1) < t ≤ τ(2) during which there is no electron transfer i.e., the electrochemical conversion of B to A (or vice versa) does not occur, and the electrode is effectively at open circuit for time τ(1) < t ≤ τ(2). We define a recovery parameter which specifies the concentration of A at distance (D(A)τ(1))(1/2) from the electrode as a function of the recovery-time ratio τ(2)/τ(1) and the operative Scheme (J). We show that for any given level of recovery τ(2)/τ(1) for Scheme 2 is much larger than for Scheme 1.
Publisher: Elsevier BV
Date: 05-1978
Publisher: American Chemical Society (ACS)
Date: 08-10-2013
DOI: 10.1021/IC401748Y
Abstract: Voltammetric studies of the Ru-containing polyoxometalate water oxidation molecular catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2](10-) ([1(γ-SiW10O36)2](10-) where 1 represents the {Ru4O4(OH)2(H2O)4} core and 1(0) stands for its initial form with all ruthenium centers in the oxidation state IV) have been carried out in aqueous media over a wide range of pH (2-12 using Britton-Robinson buffer) and ionic strength. Well-defined voltammograms in buffered media are only obtained when Frumkin double layer effects are suppressed by the presence of a sufficient concentration of additional supporting electrolyte (LiNO3, NaNO3, KNO3, Ca(NO3)2, Mg(NO3)2, MgSO4, or Na2SO4). A combination of data derived from dc cyclic, rotating disk electrode, and Fourier transformed large litude ac voltammetry allow the assignment of two processes related to reduction of the framework and the complete series of Ru(III/IV) and Ru(IV/V) redox processes and also provide their reversible potentials. Analysis of these data reveals that K(+) has a significantly stronger interaction with 1(1) (the number inside bracket stands for the number of electrons removed from 1(0)) than found for the other cations investigated, and hence its presence significantly alters the pH dependence of the 1(0)/1(1) reversible potential. Comparison of experimental data with theory developed in terms of equilibrium constants for process 1(0)/1(1) reveals that both H(+) and K(+) interact competitively with both 1(0) and 1(1). Importantly, reversible potential data reveal that (i) proton transfer does not necessarily need to be coupled to all electron transfer steps to achieve catalytic oxidation of water, (ii) the four-electron oxidized form, 1(4), is capable of oxidizing water under all conditions studied, and (iii) under some conditions, the three-electron oxidized form, 1(3), also exhibits considerable catalytic activity.
Publisher: CSIRO Publishing
Date: 2017
DOI: 10.1071/CH17241
Abstract: Voltammetric quantification of the electrode kinetics for the quasi-reversible reaction requires detailed experiment–theory comparisons. Ideally, predicted data derived from the theoretical model are fitted to the experimental data by adjusting the reversible potential (E0), heterogeneous electron transfer rate constant at E0 (k0), and charge transfer coefficient α, with mass-transport and other parameters exactly known. However, parameters relevant to mass transport that include electrode area (A), diffusion coefficient (D), and concentration (c), are usually subject to some uncertainty. Herein, we examine the consequences of having different combinations of errors present in A, D, and c in the estimation of E0, k0, and α on the basis of the a.c. (alternating current) voltammetric experiment–theory comparisons facilitated by the use of a computer-assisted parameter optimisation algorithm. In most cases, experimentally reasonable errors ( %) in the mass-transport parameters do not introduce significant errors in recovered E0, k0, and α values. However, a pernicious situation may emerge when a slight overestimation of A, D or c is included in the model and results in erroneous identification of a reversible redox process as a quasi-reversible one with a report of apparently quantifiable kinetic parameters k0 and α.
Publisher: American Chemical Society (ACS)
Date: 12-1968
DOI: 10.1021/AC50158A026
Publisher: American Chemical Society (ACS)
Date: 23-10-2007
DOI: 10.1021/CM070780B
Publisher: Wiley
Date: 02-2022
Abstract: Pd is an attractive electrocatalyst for the conversion of CO 2 to CO. Herein, we report the synthesis of ultrathin Pd nanosheets with a (111) exposed facet which enables CO evolution to be achieved in a CO 2 saturated 0.1 m KHCO 3 solution in a conventional H‐cell with a faradaic efficiency of 74±4 % at −0.75 V vs RHE and a partial current density (calculated based on the geometric area) of −0.65 mA cm −2 . Further, to reduce the cost, Cu was introduced into the Pd nanosheets to form Cu x Pd y bimetallic alloy nanosheets with (111) exposed planes. The composition of the Cu x Pd y alloy played a significant role in determining the nature of the nanosheet structure and the product selectivity. When 50 % of the Pd was replaced by Cu, competitive CO evolution could still be achieved relative to use of purely Pd nanosheets with 57±5 % of CO achieved at −0.85 V vs RHE and a partial current density of −0.9 mA cm −2 . Under flow‐cell conditions with a higher CO 2 mass transport rate, CuPd nanosheets exhibited enhanced current densities in the range of −5 mA cm −2 to −35 mA cm −2 but with a negligible change in faradaic efficiencies irrespective of the applied potential in a 1.0 m KHCO 3 medium. The use of a 1.0 m KOH solution further improved the catalytic performance generating 71±3 % of CO with a partial current density of −58±2 mA cm −2 at a low potential of −0.6 V vs RHE. Post electrolysis characterization revealed structural transformations occurred during electrolysis that impacted the product selectivity of some catalysts.
Publisher: Springer Science and Business Media LLC
Date: 20-07-2009
DOI: 10.1038/NN.2371
Publisher: Royal Society of Chemistry (RSC)
Date: 1992
DOI: 10.1039/AP9922900132
Publisher: American Chemical Society (ACS)
Date: 02-1995
DOI: 10.1021/J100007A045
Publisher: American Chemical Society (ACS)
Date: 12-02-2008
DOI: 10.1021/LA702454K
Abstract: Polycrystalline gold electrodes of the kind that are routinely used in analysis and catalysis in aqueous media are often regarded as exhibiting relatively simple double-layer charging/discharging and monolayer oxide formation/removal in the positive potential region. Application of the large litude Fourier transformed alternating current (FT-ac) voltammetric technique that allows the faradaic current contribution of fast electron-transfer processes to be emphasized in the higher harmonic components has revealed the presence of well-defined faradaic (premonolayer oxidation) processes at positive potentials in the double-layer region in acidic and basic media which are enhanced by electrochemical activation. These underlying quasi-reversible interfacial electron-transfer processes may mediate the course of electrocatalytic oxidation reactions of hydrazine, ethylene glycol, and glucose on gold electrodes in aqueous media. The observed responses support key assumptions associated with the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis.
Publisher: The Electrochemical Society
Date: 2005
DOI: 10.1149/1.1955047
Publisher: American Chemical Society (ACS)
Date: 31-10-2011
DOI: 10.1021/IC201911F
Abstract: A series of Ru(II)-peptide nucleic acid (PNA)-like monomers, [Ru(bpy)(2)(dpq-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(dpq-L-PNA-OH)](2+) (M2), [Ru(bpy)(2)(dppz-L-PNA-OH)](2+) (M3), and [Ru(phen)(2)(dppz-L-PNA-OH)](2+) (M4) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dpq-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl)methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-a:2',3'-c]phenazine-11-carboxamido)hexanamido)acetic acid, dppz-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl) methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-f:2',3'-h]quinoxaline-2-carboxamido)acetic acid) have been synthesized and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, and elemental analysis. As is typical for Ru(II)-tris(diimine) complexes, acetonitrile solutions of these complexes (M1-M4) show MLCT transitions in the 443-455 nm region and emission maxima at 618, 613, 658, and 660 nm, respectively, upon photoexcitation at 450 nm. Changes in the ligand environment around the Ru(II) center are reflected in the luminescence and electrochemical response obtained from these monomers. The emission intensity and quantum yield for M1 and M2 were found to be higher than for M3 and M4. Electrochemical studies in acetonitrile show the Ru(II)-PNA monomers to undergo a one-electron redox process associated with Ru(II) to Ru(III) oxidation. A positive shift was observed in the reversible redox potentials for M1-M4 (962, 951, 936, and 938 mV, respectively, vs Fc(0/+) (Fc = ferrocene)) in comparison with [Ru(bpy)(3)](2+) (888 mV vs Fc(0/+)). The ability of the Ru(II)-PNA monomers to generate electrochemiluminescence (ECL) was assessed in acetonitrile solutions containing tripropylamine (TPA) as a coreactant. Intense ECL signals were observed with emission maxima for M1-M4 at 622, 616, 673, and 675 nm, respectively. At an applied potential sufficiently positive to oxidize the ruthenium center, the integrated intensity for ECL from the PNA monomers was found to vary in the order M1 (62%) > M3 (60%) > M4 (46%) > M2 (44%) with respect to [Ru(bpy)(3)](2+) (100%). These findings indicate that such Ru(II)-PNA bioconjugates could be investigated as multimodal labels for biosensing applications.
Publisher: Elsevier BV
Date: 08-2000
Publisher: American Chemical Society (ACS)
Date: 12-1989
DOI: 10.1021/JA00208A008
Publisher: American Chemical Society (ACS)
Date: 04-1990
DOI: 10.1021/OM00118A051
Publisher: American Chemical Society (ACS)
Date: 15-05-2004
DOI: 10.1021/AC049744B
Abstract: Significant advantages of Fourier transformed large- litude ac higher (second to eighth) harmonics relative to responses obtained with conventional small- litude ac or dc cyclic voltammetric methods have been demonstrated with respect to (i) the suppression of capacitive background currents, (ii) the separation of the reversible reduction of [Ru(NH(3))(6)](3+) from the overlapping irreversible oxygen reduction process under conditions where aerobic oxygen remains present in the electrochemical cell, and (iii) the kinetic resolution of the reversible [Ru(NH(3))(6)](3+/2+) process in mixtures of [Fe(CN)(6)](3-) and [Ru(NH(3))(6)](3+) at appropriately treated boron-doped diamond electrodes, even when highly unfavorable [Fe(CN)(6)](3-) to [Ru(NH(3))(6)](3+) concentration ratios are employed. Theoretical support for the basis of kinetic discrimination in large- litude higher harmonic ac cyclic voltammetry is provided.
Publisher: Elsevier BV
Date: 05-1989
Publisher: Elsevier BV
Date: 11-1970
Publisher: Wiley
Date: 30-09-2013
Publisher: American Chemical Society (ACS)
Date: 03-1972
DOI: 10.1021/AC60311A040
Publisher: American Chemical Society (ACS)
Date: 12-1985
DOI: 10.1021/AC00291A007
Publisher: Royal Society of Chemistry (RSC)
Date: 1998
DOI: 10.1039/A800494C
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3DT50505G
Abstract: Uncatalysed 1,3-dipolar cycloaddition reactions between two phosphaalkynes, P≡CR (R = Bu(t) or Me), and a series of di-, tri- and poly-azido precursor compounds have given very high yields of a range of triazaphosphole substituted systems. These comprise the 1,1'-bis(triazaphosphole)ferrocenes, [Fe{C5H4(N3PCR)}2], the tris(triazaphosphole)cyclohexane, cis-1,3,5-C6H9(N3PCBu(t))3, and the poly(allyltriazaphosphole)s, {C3H5(N3PCR)}∞. Electrochemical studies on the 1,1'-bis(triazaphosphole)ferrocenes reveal the compounds to undergo reversible 1-electron oxidation processes, at significantly more positive potentials than ferrocene itself. Attempts to chemically oxidise one 1,1'-bis(triazaphosphole)ferrocene with a silver salt, Ag[Al{OC(CF3)3}4] were not successful, and led to the formation of a silver coordination complex, [{Fe[μ-C5H4(N3PCBu(t))]2(μ-Ag)}2][Al{OC(CF3)3}4]2, thereby demonstrating the potential the reported triazaphosphole substituted systems possess as novel ligands in coordination chemistry.
Publisher: American Chemical Society (ACS)
Date: 04-03-1998
DOI: 10.1021/AC9703616
Abstract: Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state: Co(II) + 2dmgH(2) ⇌ (solution) [Co(II)(dmgH)(2)] + 2H(+) [Co(II)(dmgH)(2)] + Hg ⇌ (electrode) [Co(II)(dmgH)(2)](ads)Hg and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.
Publisher: Wiley
Date: 02-2006
Publisher: Elsevier BV
Date: 09-1970
Publisher: American Chemical Society (ACS)
Date: 14-03-2017
DOI: 10.1021/ACS.INORGCHEM.6B03046
Abstract: The structure of the Keggin-type β-[PW
Publisher: Elsevier BV
Date: 06-1995
Publisher: Wiley
Date: 31-10-2019
Publisher: Elsevier BV
Date: 10-2016
Publisher: American Chemical Society (ACS)
Date: 09-1974
DOI: 10.1021/AC60347A020
Publisher: American Chemical Society (ACS)
Date: 09-1974
DOI: 10.1021/AC60347A024
Publisher: Elsevier BV
Date: 10-2013
Publisher: Elsevier BV
Date: 03-2012
Publisher: Elsevier BV
Date: 05-1978
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B705991D
Abstract: The electrochemistry of the Dawson-like sulfite polyoxometalate anion alpha-[Mo18O54(SO3)2]6-, derived from the TEAH6{alpha-[Mo18O54(SO3)2]} salt (TEAH+ is the triethanolammonium cation pKa=7.8), has been investigated in aqueous media using cyclic and rotated disk voltammetry at glassy carbon electrodes and bulk electrolysis, with a focus on the pH-dependence for oxidation to alpha-[Mo18O54(SO3)2]4-. In buffered media at pH>or=4, the cyclic voltammetric response for alpha-[Mo18O54(SO3)2]6- reveals two partially resolved one-electron oxidation processes corresponding to the sequential generation of alpha-[Mo18O54(SO3)2]5- and alpha-[Mo18O54(SO3)2]4-. At lower pH, using electrolytes containing sulfuric acid, the two waves coalesce but the in idual apparent E0' reversible formal potential values for the two processes can be extracted down to pH 2 by assuming that reversible protonation accompanies fast electron transfer. The results for 2<or=pH<or=8 are well described by the double-square scheme mechanism: [FORMULAS: SEE TEXT] where A, B and C correspond to species alpha-[Mo18O54(SO3)2]4-, alpha-[Mo18O54(SO3)2]5- and alpha-[Mo18O54(SO3)2]6- respectively. The following thermodynamic values could be deduced: E=-0.009 V vs. Fc+/Fc E=-0.125 V vs. Fc+/Fc and KC=1.5x10(-5) M values for KA, KB, E and E could not be determined. Protonated alpha-[HMo18O54(SO3)2]5-, deduced to be the major species present at pH<4, is highly stable in aqueous media. In contrast, alpha-[Mo18O54(SO3)2]6-, which is dominant at higher pH values, slowly decomposes. Data considered in the context of acid-base properties of both the TEAH+ cation and alpha-[HMo18O54(SO3)2]5- anion imply that the TEAH+ cation is important in the isolation of (TEAH)6{alpha-[Mo18O54(SO3)2]}. Cyclic and rotating disk electrode voltammetries demonstrate that at least 8 electrons also can be easily added to the [Mo18O54(SO3)2]4- framework in acidic media. The existence of the electron transfer series alpha-[Mo18O54(SO3)2]4-/5-/6-/7-/8- was confirmed by cyclic voltammetric studies of water insoluble [Pn4N]4{alpha-[Mo18O54(SO3)2]} adhered to a glassy carbon electrode in contact with an aqueous 0.1 M Et4NCl electrolyte.
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A700168A
Publisher: Elsevier BV
Date: 1991
Publisher: Elsevier BV
Date: 06-1981
Publisher: American Chemical Society (ACS)
Date: 02-1972
DOI: 10.1021/AC60310A021
Publisher: Elsevier BV
Date: 04-1995
Publisher: Royal Society of Chemistry (RSC)
Date: 2199
DOI: 10.1039/AN9941901051
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCYBSRS
Publisher: No publisher found
Date: 2009
DOI: 10.5517/CCS3LWB
Publisher: Royal Society of Chemistry (RSC)
Date: 1994
DOI: 10.1039/AN9941901057
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CCN69RW
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4RA16588H
Abstract: The chemistry of oxidized forms of TTF in acidified CH 3 CN has been established using electrochemical and spectroscopic techniques.
Publisher: American Chemical Society (ACS)
Date: 11-1983
DOI: 10.1021/IC00165A015
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCYTP6M
Publisher: American Chemical Society (ACS)
Date: 09-1982
DOI: 10.1021/AC00248A011
Publisher: American Chemical Society (ACS)
Date: 03-1988
DOI: 10.1021/JA00215A017
Publisher: American Chemical Society (ACS)
Date: 09-1982
DOI: 10.1021/AC00248A012
Publisher: Elsevier BV
Date: 02-1978
Publisher: American Chemical Society (ACS)
Date: 14-06-2005
DOI: 10.1021/IC050032T
Abstract: The electrochemical reduction of tetrabutylammonium salts of isostructural pairs of polyoxometalates [Bu4N]2[M6O19], [Bu4N]4[alpha-SiM12O40], and [Bu4N]4[alpha-S2M18O62] (M = Mo or W) has been investigated at glassy carbon electrodes in dissolved and surface-confined states in ionic liquids and other media. In the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)], between two and six reversible one-electron-transfer processes were detected. Detailed studies on the process [alpha-S2W18O62](4-/5-) in a range of ionic liquids, water, and conventional organic solvents (containing 0.1 M electrolyte) suggest that the polarity of the medium plays a key role in the determination of the reversible potential. Reduction processes involving very highly charged [alpha-S2W18O62](8-/9-/10-) species are strongly influenced by the purity of the medium.
Publisher: Elsevier BV
Date: 04-1988
Publisher: American Chemical Society (ACS)
Date: 1989
DOI: 10.1021/IC00300A013
Publisher: Royal Society of Chemistry (RSC)
Date: 2003
DOI: 10.1039/B309078G
Abstract: The voltammetry of 7,7,8,8-tetracyanoquinodimethane (TCNQ) at an electrode-microparticle-aqueous (electrolye) interface has been proposed as a cation sensor on the basis that changes in electrolyte cation (analyte) concentrations result in reproducible shifts in the TCNQ0/- reversible potential. In order to probe the ion selective nature of the TCNQ sensor, the voltammetric response towards a series of tetraalkylammonium cations of variable size and hydrophobicity were studied. Both the thermodynamics (reversible potential) and kinetics (voltammetric peak separation) of the TCNQ0/- system were strongly dependant on the identity of the R4N+ cation. The reversible potential responded in a Nernstian manner to changes in cation concentration. When presented with mixed-analyte solutions, the TCNQ system exhibited Nicolsky type (or competitive) form of selectivity. However, the selectivity coefficients found in the present study were far greater than previously reported with group I cations. The order obtained for the tetraalkylammonium series indicates that ion selectivity is predominantly based on analyte solvation thermodyanics rather than a specific ionophore mechanism.
Publisher: American Chemical Society (ACS)
Date: 10-1977
DOI: 10.1021/AC50020A042
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCYBSQR
Publisher: Elsevier BV
Date: 02-1994
Publisher: American Chemical Society (ACS)
Date: 07-1980
DOI: 10.1021/AC50058A039
Publisher: American Chemical Society (ACS)
Date: 30-10-2003
DOI: 10.1021/IC0206802
Abstract: The photophysical properties of acetonitrile solutions of [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) are described. We discuss evidence for ion cluster formation in solution and the observation that despite the strong donor ability of the excited state of [Ru(bpy)(3)](2+) and its inherent photolability, adducts with [S(2)Mo(18)O(62)](4-) were photostable. Photophysical studies suggest that the quenching of the [Ru(bpy)(3)](2+) excited state by [S(2)Mo(18)O(62)](4-) occurs via a static mechanism and that binding is largely electrostatic in nature. Evidence is provided from difference spectroscopy and luminescence excitation spectroscopy for good electronic communication between [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) with the presence of a novel, luminescent, inter-ion charge-transfer transition. The identity of the transition is confirmed by resonance Raman spectroscopy.
Publisher: American Chemical Society (ACS)
Date: 10-1977
DOI: 10.1021/AC50020A041
Publisher: American Chemical Society (ACS)
Date: 1995
DOI: 10.1021/OM00001A012
Publisher: Elsevier BV
Date: 02-1987
Publisher: Wiley
Date: 07-11-2006
Abstract: The synthesis, isolation and structural characterization of the sulfite polyoxomolybdate clusters alpha-(D(3h))(C(20)H(44)N)(4){alpha-[Mo(18)O(54)(SO(3))(2)]}CH(3)CN and beta-(D(3d))(C(20)H(44)N)(4){beta-[Mo(18)O(54)(SO(3))(2)]}CH(3)CN is presented. Voltammetric studies in acetonitrile (0.1 M Hx(4)NClO(4), Hx(4)N=tetra-n-hexylammonium) reveal the presence of an extensive series of six one-electron reduction processes for both isomers. Under conditions of bulk electrolysis, the initial [Mo(18)O(54)(SO(3))(2)](4-/5-) and [Mo(18)O(54)(SO(3))(2)](5-/6-) processes produce stable [Mo(18)O(54)(SO(3))(2)](5-) and [Mo(18)O(54)(SO(3))(2)](6-) species, respectively, and the same reduced species may be produced by photochemical reduction. Spectroelectrochemical data imply that retention of structural form results upon reduction, so that both alpha and beta isomers are available at each of the 4-, 5-, and 6-redox levels. However, the alpha isomer is the thermodynamically favored species in both the one- and two-electron-reduced states, with beta-->alpha isomerization being detected in both cases on long time scales (days). EPR spectra also imply that increasing localization of the unpaired electron occurs over the alpha- and beta-[Mo(18)O(54)(SO(3))(2)](5-) frameworks as the temperature approaches 2 K where the EPR spectra show orthorhombic symmetry with different g and hyperfine values for the alpha and beta isomers. Theoretical studies support the observation that it is easier to reduce the alpha cluster than the beta form and also provide insight into the driving force for beta-->alpha isomerization in the reduced state. Data are compared with that obtained for the well studied alpha-[Mo(18)O(54)(SO(4))(2))](4-) sulfate cluster.
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CCYTP5L
Publisher: Elsevier BV
Date: 05-1996
Publisher: Elsevier BV
Date: 02-1971
Publisher: American Chemical Society (ACS)
Date: 08-04-2008
DOI: 10.1021/JP7107279
Publisher: Wiley
Date: 1997
Publisher: American Chemical Society (ACS)
Date: 19-11-2004
DOI: 10.1021/IC049043X
Abstract: Comparative studies on the voltammetric reduction of the alpha and gamma isomers of Dawson [S(2)W(18)O(62)](4)(-) and alpha, beta, and gamma forms of Keggin [SiW(12)O(40)](4)(-) polyoxometalate anions have been undertaken. For the six reversible one-electron [S(2)W(18)O(62)](4)(-)(/5)(-)(/6)(-)(/7)(-)(/8)(-)(/9)(-)(/10)(-) processes in acetonitrile, reversible potentials (E(0)(')) were found to be independent of isomeric form within experimental error (+/-5 mV). However, because both the alpha and gamma* isomers of [Bu(4)N](4)[S(2)W(18)O(62)] are insoluble in water, solid-state voltammetric studies with microcrystals adhered to electrode surfaces in contact with aqueous Et(4)NCl and Bu(4)NCl electrolyte media were also possible. Although no isomeric distinction was again detected in the solid-state studies, it was found that reduction of adhered solid by four or more electron equivalents led to rapid dissolution. When Et(4)NCl was the electrolyte, this dissolution process coupled with potential cycling experiments enabled conventional solution-phase data to be obtained in water for the analogous six one-electron reduction steps previously detected in acetonitrile. A strong medium effect attributed to Lewis acidity effects was apparent upon comparison with E(0)(') data obtained in water and acetonitrile. In contrast, with the [SiW(12)O(40)](4)(-) system, E(0)(') values for the [SiW(12)O(40)](4)(-)(/5)(-)(/6)(-)(/7)(-) processes in acetonitrile exhibited a larger (about 70 mV) dependence on isomeric form, and the isomerization step, [gamma-SiW(12)O(40)](6)(-)--> [alpha-SiW(12)O(40)](6)(-), was detected on the voltammetric time scale. The influence of isomeric form on reversible potential data is considered in terms of structural and charge density differences exhibited in the [S(2)W(18)O(62)](4)(-) and [SiW(12)O(40)](4)(-) systems studied in this paper and published data available on the alpha, beta, gamma, and gamma isomers of [As(2)W(18)O(62)](6)(-) and [P(2)W(18)O(62)](6)(-) Dawson anions and Keggin systems.
Publisher: Wiley
Date: 18-09-2015
Abstract: Cyclohexanone, a model compound chosen to conveniently represent small oxygenates present in the aqueous phase of biomass hydrothermal upgrading streams, was hydrogenated in the presence of electrodeposited iron(0) using aqueous formic or sulfuric acid as a hydrogen donor. Under these conditions, zero-valent iron is consumed stoichiometrically and serves as both a formic acid decomposition site and a hydrogen transfer agent. However, the resulting iron(II) can be used to continuously regenerate iron(0) when a potential is applied to the glassy carbon working electrode. Controlled potential electrolysis experiments show a 17% conversion of cyclohexanone (over 1000 seconds) to cyclohexanol with >80% efficiency of iron deposition from an iron(II) sulfate solution containing formic or sulfuric acid. In the absence of electrodeposited iron, formation of cyclohexanol could not be detected.
Publisher: The Electrochemical Society
Date: 2001
DOI: 10.1149/1.1342181
Publisher: American Chemical Society (ACS)
Date: 09-03-2007
DOI: 10.1021/IC062022D
Abstract: 1-n-Butyl-3-methylimidazolium (bmim) salts of [alpha-SiM12O40]4- and [alpha-S2M18O62]4- (M = Mo, W) were synthesized and characterized. In sharp contrast to the multiple one-electron diffusion-controlled reduction processes expected in solution at a glassy carbon electrode, reduction of these salts beyond the one-electron level in CH3CN (0.1 M [bmim][PF6]) led to rapid precipitation of arrays of microdroplets or microcrystals onto the surface. Upon oxidation these arrays dissolved on the electrochemical time scale, resulting in voltammograms displaying both diffusion-controlled and surface-confined behavior. These novel observations appear to be related to the ability of the [bmim]+ cations and polyoxometalate anions to form ion clusters in solution and to the lower solubilities of the reduced salts.
Publisher: No publisher found
Date: 2000
DOI: 10.5517/CC4SVB2
Publisher: American Chemical Society (ACS)
Date: 26-05-2009
DOI: 10.1021/JA8092295
Abstract: Unexpected nonadditivity of currents encountered in the electrochemistry of mixtures of ferrocene (Fc) and cobaltocenium cation (Cc(+)) as the PF(6)(-) salt has been investigated by direct current (dc) and Fourier-transformed alternating current (ac) cyclic voltammetry in two aprotic (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate) and three protic (triethylammonium formate, bis(2-hydroxyethyl)ammonium acetate, and triethylammonium acetate) ionic liquids (ILs). The voltammetry of the in idual Fc(0/+) and Cc(+/0) couples always exhibits near-Nernstian behavior at glassy carbon and gold electrodes. As expected for an ideal process, the reversible formal potentials and diffusion coefficients at 23 +/- 1 degrees C in each IL determined from measurement on in idual Fc and Cc(+) solutions were found to be independent of electrode material, concentration, and technique used for the measurement. However, when Fc and Cc(+) were simultaneously present, the dc and ac peak currents per unit concentration for the Fc(0/+) and Cc(+/0) processes were found to be significantly enhanced in both aprotic and protic ILs. Thus, the apparent diffusion coefficient values calculated for Fc and Cc(+) were respectively found to be about 25 and 35% larger than those determined in idually in the aprotic ILs. A similar change in the Fc(0/+) mass transport characteristics was observed upon addition of tetrabutylammonium hexafluorophosphate (Bu(4)NPF(6)), and the double layer capacitance also varied in distinctly different ways when Fc and Cc(+) were present in idually or in mixtures. Importantly, the nonadditivity of Faradaic current is not associated with a change in viscosity or from electron exchange as found when some solutes are added to ILs. The observation that the (1)H NMR T(1) relaxation times for the proton resonance in Cc(+) also are modified in mixed systems implies that specific interaction with aggregates of the constituent IL ionic species giving rise to subtle structural changes plays an important role in modifying the mass transport, double layer characteristics, and dynamics when solutes of interest in this study are added to ILs. Analogous voltammetric changes were not observed in studies in organic solvent media containing 0.1 M added supporting electrolyte. Implications of the nonadditivity of Faradaic and capacitance terms in ILs are considered.
Publisher: Elsevier BV
Date: 05-2000
Publisher: American Chemical Society (ACS)
Date: 07-1985
DOI: 10.1021/AC00285A050
Abstract: Long-distance cell-cell communication is essential for organ development and function. Whereas neurons communicate at long distances by transferring signals at sites of direct contact (i.e., at synapses), it has been presumed that the only way other cell types signal is by dispersing signals through extracellular fluid--indirectly. Recent evidence from Drosophila suggests that non-neuronal cells also exchange signaling proteins at sites of direct contact, even when long distances separate the cells. We review here contact-mediated signaling in neurons and discuss how this signaling mechanism is shared by other cell types.
Publisher: Elsevier BV
Date: 07-1995
Publisher: Elsevier BV
Date: 1979
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CCN69PT
Publisher: Wiley
Date: 27-02-2013
Publisher: The Electrochemical Society
Date: 1972
DOI: 10.1149/1.2403988
Publisher: American Chemical Society (ACS)
Date: 23-05-2019
DOI: 10.1021/ACS.LANGMUIR.9B01028
Abstract: Many drugs have intracellular or membrane-associated targets, thus understanding their interaction with the cell membrane is of value in drug development. Cell-free tools used to predict membrane interactions should replicate the molecular organization of the membrane. Microcavity array-supported lipid bilayer (MSLB) platforms are versatile biophysical models of the cell membrane that combine liposome-like membrane fluidity with stability and addressability. We used an MSLB herein to interrogate drug-membrane interactions across seven drugs from different classes, including nonsteroidal anti-inflammatories: ibuprofen (Ibu) and diclofenac (Dic) antibiotics: rif icin (Rif), levofloxacin (Levo), and pefloxacin (Pef) and bisphosphonates: alendronate (Ale) and clodronate (Clo). Fluorescence lifetime correlation spectroscopy (FLCS) and electrochemical impedance spectroscopy (EIS) were used to evaluate the impact of drug on 1,2-dioleyl- sn-glycerophosphocholine and binary bilayers over physiologically relevant drug concentrations. Although FLCS data revealed Ibu, Levo, Pef, Ale, and Clo had no impact on lipid lateral mobility, EIS, which is more sensitive to membrane structural change, indicated modest but significant decreases to membrane resistivity consistent with adsorption but weak penetration of drugs at the membrane. Ale and Clo, evaluated at pH 5.25, did not impact the impedance of the membrane except at concentrations exceeding 4 mM. Conversely, Dic and Rif dramatically altered bilayer fluidity, suggesting their translocation through the bilayer, and EIS data showed that resistivity of the membrane decreased substantially with increasing drug concentration. Capacitance changes to the bilayer in most cases were insignificant. Using a Langmuir-Freundlich model to fit the EIS data, we propose R
Publisher: American Chemical Society (ACS)
Date: 29-03-2007
DOI: 10.1021/IC062067E
Abstract: The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr4N)4{alpha-[W18O54(SO3)2]}.2CH3CN and the one-electron reduced form (Pr4N)5{alpha-[W18O54(SO3)2]}.2CH3CN has been achieved. alpha-[W18O54(SO3)2]5- was obtained as a Pr4N+ salt by reducing the "Trojan Horse" [W18O56(SO3)2(H2O)2]8- cluster via a template orientation transformation. Acetonitrile solutions of pure alpha-[W18O54(SO3)2]5- also were prepared electrochemically by one-electron bulk reductive electrolysis of alpha-[W18O54(SO3)2]4-. Cyclic voltammetry of alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5- in CH3CN (0.1 M Hx4NClO4) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten-oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH3CN exhibit the expected sign and magnitude of the steady-state limiting current values for the alpha-[W18O54(SO3)2]4-/5-/6- series and confirm the existence of a stable one-electron reduced species, alpha-[W18O54(SO3)2]5-. Employment of the Randles-Sevcik (cyclic voltammetry) and Levich (rotating disk electrode) equations at a glassy carbon electrode (d=3 mm) enable diffusion coefficient values of 3.7 and 3.8x10(-6) cm2 s-1 to be obtained for alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-, respectively. The tungsten polyoxometalates are highly photoactive, since measurable photocurrents and color changes are detected for both species upon irradiation with white light. EPR spectra obtained from both acetonitrile solution and solid s les, down to temperatures as low as 2.3 K, of the chemically and electrochemically prepared one-electron reduced species provided evidence that the unpaired electron in alpha-[W18O54(SO3)2]5- is delocalized over a number of atoms in the polyoxometalate structure, even at very low temperatures.
Publisher: CSIRO Publishing
Date: 2012
DOI: 10.1071/CH12183
Abstract: Complex mixtures of cation : anion stoichometries often result from the syntheses of tetracyanoquinodimethane (TCNQ) salts, and often these cannot be easily separated. In this study, the reaction of N,N-dimethyl-d-proline-methylester (Pro(CH3)3+) with LiTCNQ resulted in a mixture of crystals. Hand selection and characterisation of each crystal type by X-ray, infrared, Raman and electrochemistry has provided two stoichometries, 1 : 1 [Pro(CH3)3TCNQ] and 2 : 3 ([(Pro(CH3)3)2(TCNQ)3]). A detailed comparison of these structures is provided. The electrochemical method provides an exceptionally sensitive method of distinguishing differences in stoichiometry. The room temperature conductivity of the mixture is 3.1 × 10–2 S cm–1, which lies in the semiconducting range.
Publisher: Royal Society of Chemistry (RSC)
Date: 1992
DOI: 10.1039/AN9921701845
Publisher: American Chemical Society (ACS)
Date: 07-1970
DOI: 10.1021/AC60290A032
Publisher: American Chemical Society (ACS)
Date: 03-1972
DOI: 10.1021/AC60311A011
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CCN69QV
Publisher: Elsevier BV
Date: 08-1999
Publisher: Wiley
Date: 20-04-2012
Publisher: American Chemical Society (ACS)
Date: 22-02-2012
DOI: 10.1021/AC2030514
Abstract: The chemistry and electrochemistry of TCNQ (7,7,8,8-tetracyanoquinodimethane), TCNQ(•-), TCNQ(2-), and H(2)TCNQ in acetonitrile (0.1 M Bu(4)NPF(6)) solution containing trifluoroacetic acid (TFA) has been studied by transient and steady-state voltammetric methods with the interrelationship between the redox and the acid-base chemistry being supported by simulations of the cyclic voltammograms. In the absence of acid, TCNQ and its anions undergo two electrochemically and chemically reversible one-electron processes. However, in the presence of TFA, the voltammetry is considerably more complex. The TCNQ(2-) dianion is protonated to form HTCNQ(-), which is oxidized to HTCNQ(•), and H(2)TCNQ which is electroinactive over the potential range of -1.0 to +1.0 V versus Ag/Ag(+). The monoreduced TCNQ(•-) radical anion is weakly protonated to give HTCNQ(•), which disproportionates to TCNQ and H(2)TCNQ. In acetonitrile, H(2)TCNQ deprotonates slowly, whereas in N,N-dimethylformamide or tetrahydrofuran, rapid deprotonation occurs to yield HTCNQ(-) as the major species. H(2)TCNQ is fully deprotonated to the TCNQ(2-) dianion in the presence of an excess concentration of the weak base, CH(3)COOLi. Differences in the redox and acid-base chemistry relative to the fluorinated derivative TCNQF(4) are discussed in terms of structural and electronic factors.
Publisher: American Chemical Society (ACS)
Date: 10-1984
DOI: 10.1021/AC00276A025
Publisher: Royal Society of Chemistry (RSC)
Date: 1999
DOI: 10.1039/A900088G
Publisher: American Chemical Society (ACS)
Date: 26-09-2000
DOI: 10.1021/IC0000294
Abstract: The reactions of M(CO)5X (M = Mn, Re X = Cl, Br) with (Ph2PCH2)3CCH3 (P3) and (Ph2P(CH2)2)3P (P3P') are investigated, and the products are characterized by IR, NMR (31P and 13C), and electrospray mass spectrometric (ESMS) techniques. With P3, the major products are fac-M(CO)3(eta 2-P3)X (syn and anti isomers) and cis,fac-M(CO)2(eta 3-P3)X, and with P3P', the major product for each metal is cis,mer-M(CO)2(eta 3-P3P')X, but cis-[M(CO)2(eta 4-P3P')]X and fac-[Re(CO)3(eta 3-P3P')]X are also characterized. Addition of MeI to those complexes containing pendant phosphine groups produces the corresponding phosphonium cations without affecting the remainder of the molecule. On the voltammetric time scale, electrochemical oxidation of cis,fac-Mn(CO)2(eta 3-P3)X yields the corresponding 17e cation cis,fac-[Mn(CO)2(eta 3-P3)X]+, but on the longer time scale of exhaustive electrolysis or chemical oxidation, the product is fac-[Mn(CO)3(eta 3-P3)]+. In contrast, the rhenium cation cis,fac-[Re(CO)2(eta 3-P3)X]+ is stable on the synthetic time scale, but upon oxidation of cis,fac-Re(CO)2(eta 3-P3)X with NOBF4, the final product is the 18e [Re(CO)(NO)(eta 3-P3)X]+. cis,mer-Mn(CO)2(eta 3-P3P')X is reversibly oxidized to cis,mer-[Mn(CO)2(eta 3-P3P')X]+ on the voltammetric time scale, but on the longer synthetic time scale, the product isomerizes to trans-[Mn(CO)2(eta 3-P3P')X]+, which can be reduced to trans-Mn(CO)2(eta 3-P3P')X. Upon voltammetric oxidation, the corresponding rhenium complexes show an initial irreversible response associated with the pendant phosphine group prior to the reversible oxidation of the metal on the synthetic time scale spectroscopic data indicate formation of cis,mer-Re(CO)2(eta 3-P3P'O)X. The complex cis,mer-[Re(CO)2(eta 3-P3P'Me)X]+ shows only the reversible metal oxidation response. ESMS data are obtained directly for the methylated cationic complexes, and neutral complexes are either oxidized or adducted with sodium ions to produce cationic species.
Publisher: Elsevier BV
Date: 1976
Publisher: American Chemical Society (ACS)
Date: 13-07-2009
DOI: 10.1021/IC900729D
Abstract: Seven new di-, tri-, tetra-, and hexanuclear iron complexes that incorporate a polydentate Schiff base and variously substituted catecholate ligands have been synthesized from the trinuclear precursor [Fe(3)(OAc)(3)(L)(3)] (1), where LH(2) = 2-[[(2-hydroxyethyl)imino]phenylmethyl]-phenol. These were isolated as the compounds [Fe(3)(OAc)(Cat)(L)(3)] (2), [Fe(6)(OAc)(2)(Cat)(4)(L)(4)] (3), [Fe(4)(3,5-DBCat)(2)(L)(4)] (4), [Bu(4)N][Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)] (5a, 5(-) is the complex monoanion [Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)](-)), [Fe(4)(OAc)(3,5-DBCat)(3)(3,5-DBSQ)(L)(2)] (6), [Fe(2)(Cl(4)Cat)(2)(L)(LH(2))(H(2)O)] (7), and [Et(3)NH](2)[Fe(2)(Cl(4)Cat)(2)(L)(2)] (8a, 8(2-) is the complex dianion [Fe(2)(Cl(4)Cat)(2)(L)(2)](2-)), where CatH(2) = catechol 3,5-DBCatH(2) = 3,5-di-tert-butyl-catechol 3,5-DBSQH = 3,5-di-tert-butyl-semiquinone, and Cl(4)CatH(2) = tetrachlorocatechol. While compounds 2-4, 5a, 7, and 8a were obtained by directly treating 1 with the appropriate catechol, compound 6 was synthesized by chemical oxidation of 5a. These compounds have been characterized by single crystal X-ray diffraction, infrared and UV-visible spectroscopy, voltammetry, UV-visible spectroelectrochemistry, and magnetic susceptibility and magnetization measurements. An electrochemical study of the three tetranuclear complexes (4, 5(-), and 6) reveals multiple reversible redox processes due to the o-dioxolene ligands, in addition to reductive processes corresponding to the reduction of the iron(III) centers to iron(II). A voltammetric study of the progress of the chemical oxidation of compound 5a, together with a spectroelectrochemical study of the analogous electrochemical oxidation, indicates that there are two isomeric forms of the one-electron oxidized product. A relatively short-lived neutral species (5) that possesses the same ligand arrangement as complex 5(-) is the kinetic product of both chemical and electrochemical oxidation. After several hours, this species undergoes a significant structural rearrangement to convert to complex 6, which appears to be largely driven by the preference for the 3,5-DBSQ(-) ligand to bind in a non-bridging mode. Variable temperature magnetic susceptibility measurements for compounds 3, 4, 5a, 6, 7, and 8a reveal behavior dominated by pairwise antiferromagnetic exchange interactions, giving rise to a poorly isolated S = 0 ground state spin for compound 3, well-isolated S = 0 ground state spins for complexes 4, 5(-), 7 and 8(2-), and a well-isolated S = 1/2 ground state spin for complex 6. The ground state spin values were confirmed by low temperature variable field magnetization measurements. The thermal variation of the magnetic susceptibility for compounds 3, 4, 5a, 6, 7, and 8a were fitted and/or simulated using the appropriate Hamiltonians to derive J values that are consistent with magnetostructural correlations that have been reported previously for alkoxo-bridged ferric complexes.
Publisher: Elsevier BV
Date: 09-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 1996
DOI: 10.1039/FT9969203925
Publisher: Elsevier BV
Date: 03-1995
Publisher: The Electrochemical Society
Date: 02-1994
DOI: 10.1149/1.2054722
Publisher: American Chemical Society (ACS)
Date: 23-06-2017
Publisher: American Chemical Society (ACS)
Date: 11-1984
DOI: 10.1021/AC00277A030
Publisher: American Chemical Society (ACS)
Date: 15-10-2009
DOI: 10.1021/JA9063519
Abstract: Electrocrystallization of nanocubes, nanorods, nanowires, and crystalline thin films of silver-tetracyanoquinodimethane (AgTCNQ) onto glassy carbon, indium tin oxide, and platinum electrodes can be achieved from ionic liquids containing dissolved TCNQ and Ag(I) salts. In conventional molecular organic solvents, such as acetonitrile, the reduction of TCNQ and Ag(+) occurs at almost the same potential. In contrast, the different thermodynamics that apply to the room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF(4)), give rise to a large potential separation in the two processes, which enables electrocrystallization of AgTCNQ to be undertaken via two distinctly different, potential-dependent mechanisms. Cyclic and microelectrode voltammetric, chrono erometric, together with microscopic and spectroscopic techniques reveal that AgTCNQ nanostuctures of controlled morphology, size, density, and uniformity can be achieved by tuning the electrocrystallization parameters such as potential, stoichiometric ratio of Ag(+) and TCNQ, and their concentrations, time, and ionic liquid viscosity by altering the water content. In the potential range of -0.1 to 0.3 V vs Fc(0/+) (Fc = ferrocene), electrocrystallization occurs when Ag is deposited at electrode defect sites via a progressive nucleation and 3-D growth mechanism followed by reaction with TCNQ to produce structures ranging from nanocubes to nanowires. At higher stoichiometric concentrations of Ag(+) and more negative potentials (<-0.1 V vs Fc(0/+)), extremely thin crystalline films could be obtained via overpotential deposition. Infrared and Raman spectroscopy, elemental analysis, together with X-ray diffraction and scanning electron microscopy all confirm the formation of highly pure AgTCNQ nanomaterials, which exhibit differences in morphology but not phase. The study highlights the capability of the electrocrystallization method to precisely control the morphology of nanomaterials, and also the unprecedented opportunities provided by using ionic liquids as the medium for preparation of technologically important metal-TCNQ charge transfer complexes.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC34687G
Abstract: Crystalline (PMePh(3))(2)[Cd(2)(dhbq)(3)], (dhbq(2-) = deprotonated 2,5-dihydroxybenzoquinone, H(2)dhbq), attached to electrode surfaces, survives repeated cycles of reduction followed by re-oxidation when placed in contact with aqueous electrolyte media. The results afford encouragement that a range of coordination networks containing redox active connecting ligands and/or redox active metal centres may be reducible or oxidisable in the solid state.
Publisher: American Chemical Society (ACS)
Date: 11-1984
DOI: 10.1021/AC00277A031
Abstract: Short-term wind speed forecasting for Colonia Eulacio, Soriano Department, Uruguay, is performed by applying an artificial neural network (ANN) technique to the hourly time series representative of the site. To train the ANN and validate the technique, data for one year are collected by one tower, with anemometers installed at heights of 101.8, 81.8, 25.7, and 10.0 m. Different ANN configurations are applied for each site and height then, a quantitative analysis is conducted, and the statistical results are evaluated to select the configuration that best predicts the real data. This method has lower computational costs than other techniques, such as numerical modelling. For integrating wind power into existing grid systems, accurate short-term wind speed forecasting is fundamental. Therefore, the proposed short-term wind speed forecasting method is an important scientific contribution for reliable large-scale wind power forecasting and integration in Uruguay. The results of the short-term wind speed forecasting showed good accuracy at all the anemometer heights tested, suggesting that the method is a powerful tool that can help the Administración Nacional de Usinas y Transmissiones Eléctricas manage the national energy supply.
Publisher: American Chemical Society (ACS)
Date: 11-1969
DOI: 10.1021/AC60282A025
Publisher: American Chemical Society (ACS)
Date: 08-1984
DOI: 10.1021/IC00186A034
Publisher: American Chemical Society (ACS)
Date: 07-06-2007
DOI: 10.1021/IC070243T
Abstract: The previously unknown radical anions of unsaturated E2N4S2 ring systems (E=RC, R2NC, R2P) can be generated voltammetrically by the one-electron reduction of the neutral species and, despite half-lives on the order of a few seconds, have been unambiguously characterized by electron paramagnetic resonance (EPR) spectroelectrochemistry using a highly sensitive in situ electrolysis cell. Cyclic voltammetric studies using a glassy-carbon working electrode in CH3CN and CH2Cl2 with [nBu4N][PF6] as the supporting electrolyte gave reversible formal potentials for the [E2N4S2]0/- process in the range of -1.25 to -1.77 V and irreversible peak potentials for oxidation in the range of 0.66 to 1.60 V (vs the Fc+/0 couple Fc=ferrocene). Reduction of the neutral compound undergoes an electrochemically reversible one-electron transfer, followed by the decay of the anion to an unknown species via a first-order (chemical) reaction pathway. The values of the first-order rate constant, kf, for the decay of all the radical anions in CH2Cl2 have been estimated from the decay of the EPR signals for (X-C6H4CN2S)2*-, where X=4-OCH3 (kf=0.04 s(-1)), 4-CH3 (kf=0.02 s(-1)), 4-H (kf=0.08 s(-1)), 4-Cl (kf=0.05 s(-1)), 4-CF3 (kf=0.05 s(-1)), or 3-CF3 (kf=0.07 s(-1)), and for [(CH3)3CCN2S]2*- (kf=0.02 s(-1)), [(CH3)2NCN2S]2*- (kf=0.05 s(-1)), and [(C6H5)2PN2S]2*- (kf=0.7 s(-1)). Values of kf for X=4-H and for [(CH3)2NCN2S]2*- were also determined from the cyclic voltammetric responses (in CH2Cl2) and were both found to be 0.05 s(-1). Possible pathways for the first-order anion decomposition that are consistent with the experimental observations are discussed. Density functional theory calculations at the UB3LYP/6-31G(d) level of theory predict the structures of the radical anions as either planar (D2h) or folded (C2v) species the calculated hyperfine coupling constants are in excellent agreement with experimental results. Linear correlations were observed between the voltammetrically determined potentials and both the orbital energies and Hammett coefficients for the neutral aryl-substituted rings.
Publisher: American Chemical Society (ACS)
Date: 28-06-2000
DOI: 10.1021/IC000178M
Publisher: Elsevier BV
Date: 03-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9EE00018F
Abstract: Twisted bismuth nanowire (BiNW) with abundant crystal lattice dislocations is a highly active electrocatalyst for CO 2 reduction to formate at low overpotential.
Publisher: Elsevier BV
Date: 07-1988
Publisher: American Chemical Society (ACS)
Date: 03-1981
DOI: 10.1021/IC50217A024
Publisher: Elsevier BV
Date: 09-2005
Publisher: Elsevier
Date: 1999
Publisher: Elsevier BV
Date: 1986
Publisher: CSIRO Publishing
Date: 2002
DOI: 10.1071/CH02141
Publisher: Springer Science and Business Media LLC
Date: 19-11-2011
Publisher: Elsevier BV
Date: 07-1987
Publisher: American Chemical Society (ACS)
Date: 04-1972
DOI: 10.1021/AC60312A024
Publisher: American Chemical Society (ACS)
Date: 04-1972
DOI: 10.1021/AC60312A021
Publisher: American Chemical Society (ACS)
Date: 15-07-1987
DOI: 10.1021/AC00141A024
Publisher: Wiley
Date: 06-11-2014
Publisher: American Chemical Society (ACS)
Date: 10-1976
DOI: 10.1021/AC50006A010
Publisher: American Chemical Society (ACS)
Date: 21-04-2015
DOI: 10.1021/IC503027G
Abstract: A closo-type 11-vertex osmaborane [1-(η(6)-pcym)-1-OsB10H10] (pcym = para-cymene) has been synthesized and characterized by single-crystal X-ray diffraction and elemental analysis, as well as by (11)B and (1)H NMR, UV-visible, and mass spectrometry. The redox chemistry has been probed by dc and Fourier transformed ac voltammetry and bulk reductive electrolysis in CH3CN (0.10 M (n-Bu)4NPF6) and by voltammetry in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (Pyrr1,4-NTf2), which allows the oxidative chemistry of the osmaborane to be studied. A single-crystal X-ray diffraction analysis has shown that [1-(η(6)-pcym)-1-OsB10H10] is isostructural with other metallaborane compounds of this type. In CH3CN (0.10 M (n-Bu)4NPF6), [1-(η(6)-pcym)-1-OsB10H10] undergoes two well-resolved one-electron reduction processes with reversible potentials separated by ca. 0.63-0.64 V. Analysis based on a comparison of experimental and simulated ac voltammetric data shows that the heterogeneous electron transfer rate constant (k(0)) for the first reduction process is larger than that for the second step at GC, Pt, and Au electrodes. k(0) values for both processes are also larger at GC than metal electrodes and depend on the electrode pretreatment, implying that reductions involve specific interaction with the electrode surface. EPR spectra derived from the product formed by one-electron reduction of [1-(η(6)-pcym)-1-OsB10H10] in CH3CN (0.10 M (n-Bu)4NPF6) and electron orbital data derived from the DFT calculations are used to establish that the formal oxidation state of the metal center of the original unreduced compound is Os(II). On this basis it is concluded that the metal atom in [1-(η(6)-pcym)-1-OsB10H10] and related metallaboranes makes a 3-orbital 2-electron contribution to the borane cluster. Oxidation of [1-(η(6)-pcym)-1-OsB10H10] coupled to fast chemical transformation was observed at 1.6 V vs ferrocene(0/+) in Pyrr1,4-NTf2. A reaction scheme for the oxidation involving formation of [1-(η(6)-pcym)-1-OsB10H10](+), which rearranges to an unknown electroactive derivative, is proposed, and simulations of the voltammograms are provided.
Publisher: American Chemical Society (ACS)
Date: 03-1997
DOI: 10.1021/AC960846E
Abstract: Piperonyl butoxide may be reversibly oxidized in acetonitrile at a glassy carbon electrode to a cation radical under short time scale voltammetric conditions, e.g., cyclic voltammetry when the potential scan rate is above 500 mV s(-)(1). During longer time domain experiments, the cation radical decays in a rate-limiting heterolytic bond cleavage step and subsequent transfer of a second electron at the potential of the first process. Additionally, a second oxidation process develops at more positive potentials. One product isolated from the initial oxidation process in an almost quantitative yield, under controlled potential electrolysis conditions, is 6-n-propyl-1,3-benzodioxole-5-carboxaldehyde. This carboxaldehyde is oxidized at the same positive applied potential as the second oxidation process observed in long time domain voltammetric experiments with piperonyl butoxide. The limit of detection for piperonyl butoxide in acetonitrile, using differential pulse voltammetry at a glassy carbon electrode, is 1.6 × 10(-)(6) M (3σ), with a limit of determination of 4.1 × 10(-)(6) M (10σ). Piperonyl butoxide was selectively determined using differential pulse voltammetry with a concentration of 5.11 ± 0.02 g L(-)(1) in a commercial insecticide formulation containing pyrethrins. This result is in good agreement with the manufacturer's stated concentration of 5.07 g L(-)(1). The s le preparation requires only simple dilution of the formulation in an acetonitrile/dichloromethane (95:5) solvent mixture.
Publisher: American Chemical Society (ACS)
Date: 02-1975
DOI: 10.1021/IC50144A011
Publisher: No publisher found
Date: 2005
DOI: 10.5517/CC91GSK
Publisher: Elsevier BV
Date: 2011
Publisher: American Chemical Society (ACS)
Date: 24-07-2012
DOI: 10.1021/AC3017554
Abstract: The flow rate dependencies of the aperiodic direct current (dc) and fundamental to eighth alternating current (ac) harmonic components derived from large- litude Fourier transformed ac (FT-ac) voltammetry have been evaluated in a microfluidic flow cell containing a 25 μm gold microband electrode. For the oxidation of ferrocenemethanol ([FcMeOH]/[FcMeOH](+) process) in aqueous 0.1 M KNO(3) electrolyte, standard "Levich-like" dc behavior is observed for the aperiodic dc component, which enables the diffusion coefficient for FcMeOH to be obtained. In experimental studies, the first and second ac harmonic components contain contributions from the double layer capacitance current, thereby allowing details of the non-Faradaic current to be established. In contrast, the higher order harmonics and dc aperiodic component are essentially devoid of double layer capacitance contributions allowing the faradaic current dependence on flow rate to be studied. Significantly, flow rate independent data conforming to linear diffusion controlled theory are found in the sixth and higher ac harmonics at a frequency of 15 Hz and for all ac harmonics at a frequency of ≥ 90 Hz. Analysis of FT-ac voltammograms by theory based on stationary microband or planar electrode configurations confirms that stationary microband and planar electrode configurations and experimental data all converge for the higher order harmonics and establishes that the electrode kinetics are very fast (≥1 cms(-1)). The ability to locate, from a single experiment, a dc Faradaic component displaying Levich behavior, fundamental and second harmonics that contain details of the double layer capacitance, and Faradaic ac higher order harmonic currents that are devoid of capacitance, independent of the volume flow rate and also conform closely to mass transport by planar diffusion, provides enhanced flexibility in mass transport and electrode kinetic analysis and in understanding the performance of hydrodynamic electrochemical cells and reactors.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0DT00882F
Abstract: Four salts have been isolated combining the triarylmethane dye cations pararosaniline (PR(+)) and crystal violet (CV(+)) with the hexametalates [M(6)O(19)](2-) (M = Mo, W). A new hexatungstic acid H(2)[W(6)O(19)]·4dma (dma = dimethylacetamide) was isolated and is a useful synthon for hexatungstate salts. Single-crystal X-ray diffraction confirmed the presence of PR(+) and [Mo(6)O(19)](2-) ions in [PR](2)[Mo(6)O(19)]·6dmf (dmf = dimethylformamide). A number of charge-assisted hydrogen bonds N-H···O exist between the cation -NH(2) functions and the anion oxygen atoms. Comparative cyclic voltammetry of salts [A]Cl (A = PR, CV), [Bu(4)N](2)[M(6)O(19)](2-) and A(2)[M(6)O(19)] was established in MeCN and Me(2)SO solutions and of solids in contact with the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [emim][tfsa]. In the molecular solvents, the reversible potential for the process [Mo(6)O(19)](2-/3-) is less negative than the first reduction processes of the dye cations. In contrast, that for [W(6)O(19)](2-/3-) is more negative. Spectro-electrochemistry and bulk electrolysis experiments reveal significantly different pathways in the two cases. In contrast, in the [emim][tfsa] medium, a positive shift in reduction potential of at least 400 mV is seen for the anion processes but relatively little change for the dye cation processes. This means that initial reduction of the anions always precedes that of the dyes, providing significant simplification of the complex voltammetric data. Chemically modified electrodes can be used in the ionic liquid because of slow dissolution kinetics. However, reduced anion salts dissolve rapidly, allowing dissolved phase electrochemistry to be examined. The electrochemistries of the oxidized salts A(2)[M(6)O(19)] are essentially those of the in idual ions, although low level interaction of A(+) with reduced anions [M(6)O(19)](3-,4-) is evident. The work establishes protocols for synthesis and handling of intensely absorbing and relatively insoluble salts which can now be applied to systems containing more complex polyoxometalate anions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4RA08038F
Abstract: The chemistry of TTF 0/+/2+ and HTTF + in acetonitrile/water uses different reaction pathways e.g. illumination of TTF + oxidises water to O 2 .
Publisher: American Chemical Society (ACS)
Date: 08-1988
DOI: 10.1021/JA00224A010
Publisher: No publisher found
Date: 2009
DOI: 10.5517/CCS3LT8
Publisher: American Chemical Society (ACS)
Date: 11-1986
DOI: 10.1021/OM00142A023
Publisher: Wiley
Date: 09-03-2018
Abstract: The reaction of [Fe
Publisher: Springer Science and Business Media LLC
Date: 11-07-1997
Publisher: Wiley
Date: 30-07-2010
Abstract: The [Fc-bis{Zn(II)(TACN)(Py)}] complex, comprising two Zn(II)(TACN) ligands (Fc=ferrocene Py=pyrene TACN=1,4,7-triazacyclononane) bearing fluorescent pyrene chromophores linked by an electrochemically active ferrocene molecule has been synthesised in high yield through a multistep procedure. In the absence of the polyphosphate guest molecules, very weak excimer emission was observed, indicating that the two pyrene-bearing Zn(II)(TACN) units are arranged in a trans-like configuration with respect to the ferrocene bridging unit. Binding of a variety of polyphosphate anionic guests (PPi and nucleotides di- and triphosphate) promotes the interaction between pyrene units and results in an enhancement in excimer emission. Investigations of phosphate binding by (31)P NMR spectroscopy, fluorescence and electrochemical techniques confirmed a 1:1 stoichiometry for the binding of PPi and nucleotide polyphosphate anions to the bis(Zn(II)(TACN)) moiety of [Fc-bis{Zn(II)(TACN)(Py)}] and indicated that binding induces a trans to cis configuration rearrangement of the bis(Zn(II)(TACN)) complexes that is responsible for the enhancement of the pyrene excimer emission. Pyrophosphate was concluded to have the strongest affinity to [Fc-bis{Zn(II)(TACN)(Py)}] among the anions tested based on a six-fold fluorescence enhancement and 0.1 V negative shift in the potential of the ferrocene/ferrocenium couple. The binding constant for a variety of polyphosphate anions was determined from the change in the intensity of pyrene excimer emission with polyphosphate concentration, measured at 475 nm in CH(3)CN/Tris-HCl (1:9) buffer solution (10.0 mM, pH 7.4). These measurements confirmed that pyrophosphate binds more strongly (K(b)=(4.45+/-0.41) x 10(6) M(-1)) than the other nucleotide di- and triphosphates (K(b)=1-50 x 10(5) M(-1)) tested.
Publisher: American Chemical Society (ACS)
Date: 30-04-2013
DOI: 10.1021/OM4002318
Publisher: American Chemical Society (ACS)
Date: 05-1989
DOI: 10.1021/ES00063A016
Publisher: American Chemical Society (ACS)
Date: 20-07-2016
Publisher: Walter de Gruyter GmbH
Date: 1990
Publisher: American Chemical Society (ACS)
Date: 10-1975
DOI: 10.1021/AC60362A045
Publisher: Elsevier BV
Date: 2005
Publisher: Elsevier BV
Date: 08-1985
Publisher: American Chemical Society (ACS)
Date: 07-1974
DOI: 10.1021/IC50137A015
Publisher: American Chemical Society (ACS)
Date: 11-1976
DOI: 10.1021/AC50007A041
Publisher: Wiley
Date: 15-03-2012
Abstract: The reduction of benzophenone was investigated in five different ionic liquids by using transient cyclic voltammetry, near steady-state voltammetry, and numerical simulation. Two reversible, well-resolved one-electron-reduction processes were observed in dry (≤20 ppm water, ca. 1 mM)) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpyrd][NTf(2)]) and 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide ([Bmpipd][NTf(2)]), which did not contain any readily available proton source. Upon addition of water, the second process became chemically irreversible and shifted to a more positive potential by approximately 600 mV moreover, the two reduction processes merged into a single two-electron proton-coupled process when about 0.6 M H(2)O was present. This large dependence of potential on water content, which was not observed in molecular solvents (electrolyte), was explained by a reaction mechanism that incorporated protonation and hydrogen-bonding interactions of the benzophenone dianion with as many as seven water molecules. In the three imidazolium-based ionic liquids used herein, the first benzophenone-reduction process was again reversible, whilst the second reduction process became chemically irreversible owing to the availability of the C2-H imidazolium protons in these ionic liquids. The reversible potentials for benzophenone reduction were remarkably independent of the identity of the ionic liquids, thereby implying either weak interactions with the ionic liquids or relatively insignificant differences in the levels of ion-pairing. Thus, the magnitude of the separation of the potentials of the reversible first and irreversible second reduction processes mainly reflected the proton availability from either the ionic liquid itself or from adventitious water. Consequently, voltammetric reduction of benzophenone provides a sensitive tool for the determination of proton availability in ionic liquids.
Publisher: Wiley
Date: 04-02-2019
Publisher: Wiley
Date: 03-09-2018
Abstract: Two‐dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few‐layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO 2 reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co‐existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier‐transformed alternating current voltammetry (FTacV) are attributed to CO 2 reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO 2 .− is the rate determining step for bismuth catalysed CO 2 reduction.
Publisher: Elsevier BV
Date: 11-1973
DOI: 10.1016/0039-9140(73)80075-X
Abstract: One disadvantage of conventional d.c. polarography as an analytical method has always been its relative slowness. The possibility of simplifying and speeding up analyses by avoiding the necessity for removal of oxygen is demonstrated under suitable conditions with current-s led d.c., pulse and a.c. polarography. In particular it is shown that high-frequency phase-selective a.c. polarography gives considerable discrimination against the oxygen electrode process in some aqueous media. Under these conditions, the high-frequency a.c. technique can be combined with the method of short drop-time, fast scan-rate rapid a.c. polarography to provide a most attractive method of routine analysis. Polarographic analysis in non-aqueous media without removal of oxygen is also discussed.
Publisher: American Chemical Society (ACS)
Date: 12-1986
DOI: 10.1021/OM00143A027
Publisher: No publisher found
Date: 2003
DOI: 10.5517/CC4MXRD
Publisher: American Chemical Society (ACS)
Date: 07-0010
DOI: 10.1021/OM00109A022
Publisher: No publisher found
Date: 2009
DOI: 10.5517/CCS3LV9
Publisher: American Chemical Society (ACS)
Date: 22-02-2016
DOI: 10.1021/JACS.5B11408
Abstract: Highly efficient electrocatalytic oxidation of ethanol and methanol has been achieved using the ruthenium-containing polyoxometalate molecular catalyst, [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2](10-) ([1(γ-SiW10O36)2](10-)). Voltammetric studies with dissolved and surface-confined forms of [1(γ-SiW10O36)2](10-) suggest that the oxidized forms of 1 can act as active catalysts for alcohol oxidation in both aqueous (over a wide pH range covering acidic, neutral, and alkaline) and alcohol media. Under these conditions, the initial form of 1 also exhibits considerable reactivity, especially in neutral solution containing 1.0 M NaNO3. To identify the oxidation products, preparative scale bulk electrolysis experiments were undertaken. The products detected by NMR, gas chromatography (GC), and GC-mass spectrometry from oxidation of ethanol are 1,1-diethoxyethane and ethyl acetate formed from condensation of acetaldehyde or acetic acid with excess ethanol. Similarly, the oxidation of methanol generates formaldehyde and formic acid which then condense with methanol to form dimethoxymethane and methyl formate, respectively. These results demonstrate that electrocatalytic oxidation of ethanol and methanol occurs via two- and four-electron oxidation processes to yield aldehydes and acids. The total faradaic efficiencies of electrocatalytic oxidation of both alcohols exceed 94%. The numbers of aldehyde and acid products per catalyst were also calculated and compared with the literature reported values. The results suggest that 1 is one of the most active molecular electrocatalysts for methanol and ethanol oxidation.
Publisher: American Chemical Society (ACS)
Date: 25-05-2011
DOI: 10.1021/JP2021787
Abstract: Heterogeneous charge transfer rate constants (k°) for the oxidation of ferrocene, Fc (k° = 0.21 cm s(-1) at 20 °C), and the reduction of the cobaltocenium cation, Cc(+) (k° = 0.12 cm s(-1) at 18 °C), in CH(2)Cl(2) (0.5 M Bu(4)NPF(6)) at a glassy carbon (GC) electrode were determined as a function of temperature using the higher harmonic components available in Fourier transformed large litude ac voltammetry. The measured k° values lie at the upper end of the analytically useful range available for the acquisition of meaningful kinetic data for these very fast (i.e., close to reversible) processes. Measurements of the kinetics are facilitated by the ac technique because contributions resulting from uncompensated resistance and slow electrode kinetics, both of which also vary with temperature, can be distinguished via their different contributions to in idual harmonics. Values of k° measured over the temperature range of -18 to +20 °C for the Fc(0/+) and Cc(+/0) processes gave linear Arrhenius plots yielding free energies of activation (ΔG(‡)) estimates of 17.0 and 18.0 kJ mol(-1), respectively, in excellent agreement with theoretical values derived from Marcus theory. An analogous temperature dependence is indicated in a study of the Fc(0/+) process in acetonitrile (0.1 M Bu(4)NPF(6)), but the greater k° value evident makes the temperature dependence of these parameters more difficult to quantify as departures from reversibility are minimal, even in the higher harmonics.
Publisher: American Chemical Society (ACS)
Date: 11-1974
DOI: 10.1021/AC60349A026
Publisher: Springer Science and Business Media LLC
Date: 25-11-1997
Publisher: American Chemical Society (ACS)
Date: 19-06-2019
Publisher: Elsevier BV
Date: 07-2001
Publisher: American Chemical Society (ACS)
Date: 06-1985
DOI: 10.1021/AC00284A046
Abstract: The authors investigated the utility of an intravascular magnetic resonance (MR) contrast agent, poly-L-lysine-gadolinium diethylenetriaminepentaacetic acid (DTPA), for differentiating acutely ischemic from normally perfused myocardium with first-pass MR imaging. Hypoperfused regions, identified with microspheres, on the first-pass images displayed significantly decreased signal intensities compared with normally perfused myocardium (P < .0007). Estimates of regional myocardial blood content, obtained by measuring the ratio of areas under the signal intensity-versus-time curves in tissue regions and the left ventricular chamber, averaged 0.12 mL/g +/- 0.04 (n = 35), compared with a value of 0.11 mL/g +/- 0.05 measured with radiolabeled albumin in the same tissue regions. To obtain MR estimates of regional myocardial blood flow, in situ calibration curves were used to transform first-pass intensity-time curves into content-time curves for analysis with a multiple-pathway, axially distributed model. Flow estimates, obtained by automated parameter optimization, averaged 1.2 mL/min/g +/- 0.5 (n = 29), compared with 1.3 mL/min/g +/- 0.3 obtained with tracer microspheres in the same tissue specimens at the same time. The results represent a combination of T1-weighted first-pass imaging, intravascular relaxation agents, and a spatially distributed perfusion model to obtain absolute regional myocardial blood flow and volume.
Publisher: Springer International Publishing
Date: 2015
Publisher: American Chemical Society (ACS)
Date: 11-1974
DOI: 10.1021/AC60349A021
Publisher: CSIRO Publishing
Date: 2014
DOI: 10.1071/CH14390
Abstract: The mononuclear oxazolidine nitroxide complex [MnII(L•)2](ClO4)2 (1) (L•, 4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide) has been synthesized and investigated using single-crystal X-ray diffraction, variable-temperature magnetic susceptibility measurements, and electrochemistry. The structural analysis reveals bond lengths compatible with a linear L•–MnII–L• arrangement where the ligands are in the neutral ligand form and the central MnII ion is high spin (S = 5/2). Although analysis of the variable-temperature magnetic susceptibility data suggests a strong antiferromagnetic metal–radical interaction, the radical–radical intramolecular interaction could not be determined unambiguously from such fits. The resultant isolated S = 3/2 ground state is confirmed by low-temperature magnetization versus field measurements. Electrochemical studies reveal similar square schemes and redox intermediates to the previously reported analogues [FeII(L•)2][BF4]2 and [CoII(L•)2][NO3]2.
Publisher: American Chemical Society (ACS)
Date: 02-12-2016
DOI: 10.1021/JACS.6B10304
Abstract: Detection and quantification of redox transformations involved in water oxidation electrocatalysis is often not possible using conventional techniques. Herein, use of large litude Fourier transformed ac voltammetry and comprehensive analysis of the higher harmonics has enabled us to access the redox processes responsible for catalysis. An examination of the voltammetric data for water oxidation in borate buffered solutions (pH 9.2) at electrodes functionalized with systematically varied low loadings of cobalt (CoO
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCWD7FX
Publisher: Wiley
Date: 15-08-2018
Publisher: American Chemical Society (ACS)
Date: 08-2000
DOI: 10.1021/JP0017442
Publisher: American Chemical Society (ACS)
Date: 07-1976
DOI: 10.1021/AC50002A044
Publisher: No publisher found
Date: 2013
DOI: 10.5517/CC6SYJF
Publisher: American Chemical Society (ACS)
Date: 04-1988
DOI: 10.1021/JO00244A027
Publisher: Elsevier BV
Date: 12-2013
Publisher: American Chemical Society (ACS)
Date: 07-1981
DOI: 10.1021/AC00231A018
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX0V
Publisher: Springer Science and Business Media LLC
Date: 23-12-2009
Publisher: Springer Science and Business Media LLC
Date: 16-04-2013
Publisher: Springer Science and Business Media LLC
Date: 24-10-2014
Publisher: The Electrochemical Society
Date: 29-11-2013
DOI: 10.1149/2.016302JES
Publisher: Elsevier BV
Date: 1995
Publisher: American Chemical Society (ACS)
Date: 12-08-2006
DOI: 10.1021/CM060852J
Publisher: IEEE
Date: 02-2010
Publisher: American Chemical Society (ACS)
Date: 05-1988
DOI: 10.1021/IC00283A008
Publisher: Wiley
Date: 11-01-2011
Publisher: Elsevier BV
Date: 12-1986
Publisher: Elsevier BV
Date: 08-1971
Publisher: Elsevier BV
Date: 09-1992
Publisher: Elsevier BV
Date: 05-2006
Publisher: Elsevier BV
Date: 12-2022
Publisher: American Chemical Society (ACS)
Date: 11-1997
DOI: 10.1021/OM970468J
Publisher: American Chemical Society (ACS)
Date: 1977
DOI: 10.1021/IC50167A033
Publisher: Elsevier BV
Date: 11-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B605663F
Abstract: Voltammetric, photo-physical and photo-electrochemical properties of the Dawson polyoxometalate anions alpha-[S(2)M(18)O(62)](4-) (M = Mo, W) are presented, both in the presence and absence of a series of [Ru(II)L(n)](+/2+) cations [L(n) = (bpy)(3), (bpy)(2)(Im)(2), (bpy)(2)(dpq), (bpy)(2)(box) and (biq)(2)(box)]. Electrochemical processes for both the anion and Ru(II/III) couples were detected in solutions of the salts [Ru(II)L(n)](2)[S(2)M(18)O(62)] in dimethylformamide (0.1 M Bu(4)NPF(6)) by both cyclic and hydrodynamic voltammetries. Responses were also detected when the solid salts were adhered to the surface of a glassy carbon electrode in contact with an electrolyte in which they are insoluble (CH(3)CN 0.1M Bu(4)NPF(6)). Photolysis experiments were performed on solutions of the salts [R(4)N](4)[S(2)M(18)O(62)] (R = n-butyl or n-hexyl) and [Ru(II)L(n)](2)[S(2)M(18)O(62)] at 355 and 420 nm in dimethylformamide and acetonitrile in the presence and absence of benzyl alcohol (10% v/v). When associated with [Ru(bpy)(3)](2+), the molybdate anion exhibited a large increase in the quantum yield for photo-reduction at 420 nm. The quantum yield for the tungstate analogue was lower but the experiments again provided clear evidence for sensitization of the photo-reduction reaction in the visible spectral region. The origin of this sensitization is ascribed to the new optical transition observed around 480 nm in static ion clusters {[Ru(bpy)(3)][S(2)M(18)O(62)]}(2-) and {[Ru(bpy)(3)](2)[S(2)M(18)O(62)]} present in solution. Measurable photocurrents resulted from irradiation of solutions of the anions with white light in the presence of the electron donor dimethylformamide. Evidence is also presented for possible quencher-fluorophore interactions in the presence of certain [Ru(II)L(n)](+) cations.
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX1W
Publisher: Elsevier BV
Date: 1984
Publisher: American Chemical Society (ACS)
Date: 10-11-2019
Publisher: American Chemical Society (ACS)
Date: 11-02-2000
DOI: 10.1021/IC9814470
Abstract: Structural, electrochemical, ESR, and H2O2 reactivity studies are reported for [Mn(dmptacn)Cl]ClO4 (1, dmptacn = 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane) and binuclear complexes of bis(pentadentate) ligands, generated by attaching 2-pyridylmethyl arms to each secondary nitrogen in bis(1,4,7-triazacyclononane) macrocycles and linked by ethyl (tmpdtne, [Mn2(tmpdtne)Cl2](ClO4)2.2DMF, 2), propyl (tmpdtnp, [Mn2(tmpdtnp)Cl2](ClO4)2.3H2O, 3), butyl (tmpdtnb, [Mn2(tmpdtnb)Cl2](ClO4)2.DMF.2H2O, 4), m-xylyl (tmpdtn-m-X, [Mn2(tmpdtn-m-X)-Cl2](ClO4)2, 5) and 2-propanol (tmpdtnp-OH, [Mn2(tmpdtnp-OH)Cl2](ClO4)2, 6) groups. 1 crystallizes in the orthorhombic space group P2(1)2(1)2(1) (No. 19) with a = 7.959(7) A, b = 12.30(1) A, and c = 21.72(2) A 2, in the monoclinic space group P2(1)/c (No. 14) with a = 11.455(4) A, b = 15.037(6) A, c = 15.887(4) A, and beta = 96.48(2) degrees 3, in the monoclinic space group P2(1)/c (No. 14) with a = 13.334(2) A, b = 19.926(2) A, c = 18.799(1) A, and beta = 104.328(8) degrees and [Mn2(tmpdtnb)Cl2](ClO4)2.4DMF.3H2O (4'), in the monoclinic space group P2(1)/n (No. 14) with a = 13.361(3) A, b = 16.807(5) A, c = 14.339(4) A, and beta = 111.14(2) degrees. Significant distortion of the Mn(II) geometry is evident from the angle subtended by the five-membered chelate (ca. 75 degrees) and the angles spanned by trans donor atoms ( MnIIMnIII-->MnIII2] and then to the MnIV state [MnIII2-->MnIIIMnIV-->MnIV2]. For 2, the second oxidation process was partially resolved into two 1e- oxidation processes under the conditions of square-wave voltammetry. In the case of 6, initial oxidation to the MnIII2 state occurs in two overlapping 1e- processes as was found for 2-5, but this complex then undergoes two further clearly separated 1e- oxidation processes to the MnIIIMnIV state at +0.89 V and the MnIV2 state at +1.33 V (vs Fc/Fc+). This behavior is attributed to formation of an alkoxo-bridged complex. Complexes 1-6 were found to catalyze the disproportionation of H2O2. Addition of H2O2 to 2 generated an oxo-bridged mixed-valent MnIIIMnIV intermediate with a characteristic 16-line ESR signal.
Publisher: American Chemical Society (ACS)
Date: 15-04-2019
Publisher: American Chemical Society (ACS)
Date: 04-1976
DOI: 10.1021/AC60368A034
Publisher: CSIRO Publishing
Date: 2012
DOI: 10.1071/CH11361
Abstract: The in situ electrocrystallization of zinc tetracyanoquinodimethane (TCNQ) has been explored using synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) at potentials in the region of the cyclic voltammetric peak where reduction of TCNQ to TCNQ– occurs at a Pt electrode in acetonitrile (0.1 M [NBu4][PF6]) solution containing Zn(NO3)2·6H2O. The in situ SR-GIXRD data along with ex situ IR and Raman spectroscopy results all confirmed the formation of the kinetically favoured phase of Zn[TCNQ]2(H2O)2 as the product.
Publisher: Royal Society of Chemistry (RSC)
Date: 1988
DOI: 10.1039/DT9880002379
Publisher: No publisher found
Date: 2000
DOI: 10.5517/CC4SV91
Publisher: Elsevier BV
Date: 06-1997
Publisher: Elsevier BV
Date: 08-1984
Publisher: Wiley
Date: 30-04-2009
Publisher: MDPI AG
Date: 09-2023
Publisher: American Chemical Society (ACS)
Date: 14-04-2010
DOI: 10.1021/AC100378G
Abstract: Physicochemical changes and substantially modified electrochemical behavior have been reported when ionic liquids are degassed with nitrogen. In conventional experiments in aqueous and organic media, degassing with N(2) is commonly used to remove the electroactive dissolved oxygen. However, in hydrophilic ionic liquid media, degassing with N(2) removes not only the dissolved oxygen but also a significant amount of the adventitious water present. Given the low viscosity of water, this in turn leads to a dramatic change of the viscosity of the degassed ionic liquid and hence mass transport properties that influence voltammetric responses. In the widely used and relatively viscous room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF(4)) containing the redox probe tetracyanoquinodimethane (TCNQ) and 9% (v/v) deliberately added water, 1 h degassing with very dry N(2) under benchtop conditions results in a dramatic decrease of the TCNQ reduction current obtained under steady-state conditions at a 1 mum diameter microdisc electrode. This is reflected by a change of diffusion coefficient of TCNQ (D(TCNQ)) from 2.6 x 10(-7) to 4.6 x 10(-8) cm(2) s(-1). Karl Fischer titration measurements show that almost complete removal of the deliberately added 9% water is achieved by degassing under benchtop conditions. However, displacement of oxygen by nitrogen in the ionic liquid solution results in the decrease of electrochemical reduction current by 6%, implying that dissolved gases need not be inert with respect to solvent properties. Oxygen removal by placing the BMIMBF(4) ionic liquid in a nitrogen-filled glovebox or in a vacuum cell also simultaneously leads to removal of water and alteration of voltammetric data. This study highlights that (i) important physicochemical differences may arise upon addition or removal of a solute from viscous ionic liquids (ii) degassing with dry nitrogen removes water as well as oxygen from ionic liquids, which may have implications on the viscosity and structure of the medium (iii) particular caution must be exercised when deoxygenation is applied in ionic liquid media as part of the protocol used in electrochemical experiments to remove oxygen (iv) gases such as oxygen, argon, and nitrogen dissolved in ionic liquids need not be innocent with respect to the properties of an ionic liquid. The use of vacuum based techniques to eliminate all volatile solutes, including water and oxygen, is advocated.
Publisher: American Chemical Society (ACS)
Date: 16-04-2008
DOI: 10.1021/AC8002227
Abstract: Voltammetric behavior at gold electrodes in aqueous media is known to be strongly dependent on electrode polishing and history. In this study, an electrode array consisting of 100 nominally identical and in idually addressable gold disks electrodes, each with a radius of 127 microm, has been fabricated. The ability to analyze both in idual electrode and total array performance enables microscopic aspects of the overall voltammetric response arising from variable levels of inhomogeneity in each electrode to be identified. The array configuration was initially employed with the reversible and hence relatively surface insensitive [Ru(NH 3) 6] (3+/2+) reaction and then with the more highly surface sensitive quasi-reversible [Fe(CN) 6] (3-/4-) process. In both these cases, the reactants and products are solution soluble and, at a scan rate of 50 mV s (-1), each electrode in the array is assumed to behave independently, since no evidence of overlapping of the diffusion layers was detected. As would be expected, the variability of the in idual electrodes' responses was significantly larger than found for the summed electrode behavior. In the case of cytochrome c voltammetry at a 4,4'-dipyridyl disulfide modified electrode, a far greater dependence on electrode history and electrode heterogeneity was detected. In this case, voltammograms derived from in idual electrodes in the gold array electrode exhibit shape variations ranging from peak to sigmoidal. However, again the total response was always found to be well-defined. This voltammetry is consistent with a microscopic model of heterogeneity where some parts of each chemically modified electrode surface are electroactive while other parts are less active. The findings are consistent with the common existence of electrode heterogeneity in cyclic voltammetric responses at gold electrodes, that are normally difficult to detect, but fundamentally important, as electrode nonuniformity can give rise to subtle forms of kinetic and other forms of dispersion.
Publisher: American Chemical Society (ACS)
Date: 10-1975
DOI: 10.1021/IC50152A046
Publisher: American Chemical Society (ACS)
Date: 16-02-2012
DOI: 10.1021/IC202761W
Abstract: The feasibility of devising a solid support mediated approach to multimodal Ru(II)-peptide nucleic acid (PNA) oligomers is explored. Three Ru(II)-PNA-like monomers, [Ru(bpy)(2)(Cpp-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(Cpp-L-PNA-OH)](2+) (M2), and [Ru(dppz)(2)(Cpp-L-PNA-OH)](2+) (M3) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine, Cpp-L-PNA-OH = [2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycine), have been synthesized as building blocks for Ru(II)-PNA oligomers and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. As a proof of principle, M1 was incorporated on the solid phase within the PNA sequences H-g-c-a-a-t-a-a-a-a-Lys-NH(2) (PNA1) and H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-lys-NH(2) (PNA4) to give PNA2 (H-g-c-a-a-t-a-a-a-a-M1-lys-NH(2)) and PNA3 (H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-M1-lys-NH(2)), respectively. The two Ru(II)-PNA oligomers, PNA2 and PNA3, displayed a metal to ligand charge transfer (MLCT) transition band centered around 445 nm and an emission maximum at about 680 nm following 450 nm excitation in aqueous solutions (10 mM PBS, pH 7.4). The absorption and emission response of the duplexes formed with the cDNA strand (DNA: 5'-T-T-T-T-T-T-T-A-T-T-G-C-T-T-T-3') showed no major variations, suggesting that the electronic properties of the Ru(II) complexes are largely unaffected by hybridization. The thermal stability of the PNA·DNA duplexes, as evaluated from UV melting experiments, is enhanced compared to the corresponding nonmetalated duplexes. The melting temperature (T(m)) was almost 8 °C higher for PNA2·DNA duplex, and 4 °C for PNA3·DNA duplex, with the stabilization attributed to the electrostatic interaction between the cationic residues (Ru(II) unit and positively charged lysine/arginine) and the polyanionic DNA backbone. In presence of tripropylamine (TPA) as co-reactant, PNA2, PNA3, PNA2·DNA and PNA3·DNA displayed strong electrochemiluminescence (ECL) signals even at submicromolar concentrations. Importantly, the combination of spectrochemical, thermal and ECL properties possessed by the Ru(II)-PNA sequences offer an elegant approach for the design of highly sensitive multimodal biosensing tools.
Publisher: Portland Press Ltd.
Date: 03-1953
DOI: 10.1042/BJ0530642
Publisher: Elsevier BV
Date: 07-1998
Publisher: Elsevier BV
Date: 02-1987
Publisher: American Chemical Society (ACS)
Date: 26-02-2016
DOI: 10.1021/ACS.ANALCHEM.5B04715
Abstract: Scanning electrochemical microscopy (SECM) is a powerful tool that enables quantitative measurements of fast electron transfer (ET) kinetics when coupled with modeling predictions from finite-element simulations. However, the advent of nanoscale and nanogap electrode geometries that have an intrinsically high surface area-to-solution volume ratio realizes the need for more rigorous data analysis procedures, as surface effects such as adsorption may play an important role. The oxidation of ferrocenylmethyl trimethylammonium (FcTMA(+)) at highly oriented pyrolytic graphite (HOPG) is used as a model system to demonstrate the effects of reversible reactant adsorption on the SECM response. Furthermore, the adsorption of FcTMA(2+) species onto glass, which is often used to encapsulate ultramicroelectrodes employed in SECM, is also found to be important and affects the voltammetric tip response in a nanogap geometry. If a researcher is unaware of such effects (which may not be readily apparent in slow to moderate scan voltammetry) and analyzes SECM data assuming simple ET kinetics at the substrate and an inert insulator support around the tip, the result is the incorrect assignment of tip-substrate heights, kinetics, and thermodynamic parameters. Thus, SECM kinetic measurements, particularly in a nanogap configuration where the ET kinetics are often very fast (only just distinguishable from reversible), require that such effects are fully characterized. This is possible by expanding the number of experimental variables, including the voltammetric scan rate and concentration of redox species, among others.
Publisher: No publisher found
Date: 2000
DOI: 10.5517/CC4SV7Z
Publisher: American Chemical Society (ACS)
Date: 08-1982
DOI: 10.1021/AC00246A027
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX2X
Publisher: American Chemical Society (ACS)
Date: 05-11-1998
DOI: 10.1021/JP9828437
Publisher: Elsevier BV
Date: 03-1986
Publisher: American Chemical Society (ACS)
Date: 23-06-2017
Publisher: No publisher found
Date: 2000
DOI: 10.5517/CC4SV80
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX50
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CP01608D
Abstract: Graphene–cobalt nanocomposite modified electrodes fabricated using a facile electrochemical co-deposition method exhibit high water oxidation efficiency in alkaline media.
Publisher: Elsevier BV
Date: 09-1993
Publisher: Institute of Organic Chemistry & Biochemistry
Date: 1993
DOI: 10.1135/CCCC19932769
Abstract: Voltammetry is an important electrochemical technique which is used extensively to solve problems in many areas of chemistry. Since the method is based on the use of current-potential-time curves, voltammetric instrumentation is highly suited to computer based forms of technology. In this article, an overview of existing hardware and software that have been used to facilitate improvements in computer based voltammetric instrumentation is provided. it is concluded on the basis of this survey that developments to date in the use of computer based technology have been conservative relative to those in spectroscopic forms of instrumentation. Consequently, it is postulated that a new generation of more "intelligent" voltammetric instruments would become available immediately if the full power of presently available digital hardware and software were to be implemented as has been the case with some other forms of instrumentation.
Publisher: Elsevier BV
Date: 08-1995
Publisher: No publisher found
Date: 2011
DOI: 10.1039/C1JM10114E
Publisher: Wiley
Date: 04-04-2017
Publisher: Springer Science and Business Media LLC
Date: 07-09-2014
Publisher: Elsevier BV
Date: 1998
Publisher: American Chemical Society (ACS)
Date: 14-05-2004
DOI: 10.1021/OM034388T
Publisher: Elsevier BV
Date: 05-1974
Publisher: American Chemical Society (ACS)
Date: 10-03-2009
DOI: 10.1021/JA806893T
Abstract: The synthesis of exceptionally long semiconducting silver tetracyanoquinodimethane (AgTCNQ) nanowires has been achieved in the room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF(4)) by photochemical reduction of TCNQ to TCNQ(-), coupled with use of benzyl alcohol as the sacrificial electron donor. The presence of Ag(I) in the ionic liquid allows formation of mm length AgTCNQ nanowires onto both conducting and insulating surfaces, via a nucleation and diffusion-controlled growth mechanism. Remarkably, photocrystallization also can be achieved using adventitious or deliberately added water present in the ionic liquid as the sacrificial electron donor. In this case, oxidation of water produces O(2) as the counter reaction in the photoreduction of TCNQ. In contrast, irradiation in "dried" ionic liquids fails to induce any detectable photochemistry. Molecular structural differences, relative to the situation encountered in more conventional solvent media, are believed to account for the more favorable kinetics available for oxidization of water in ionic liquids. Water assisted photocrystallization in viscous BMIMBF(4) where diffusion rate are slow leads to slow growth of AgTCNQ, thereby allowing easy manipulation of AgTCNQ morphology from small nanoparticles to extremely long single nanowires by tuning the irradiation and ripening time. Infrared and Raman spectroscopic data, elemental analysis, and scanning electron microscopic images all confirm the formation of highly pure AgTCNQ nanomaterials. This study highlights the significant role that water present as an adventitious impurity may play in photochemical studies in ionic liquids and also suggests that ionic liquids may provide a favorable environment for photochemically based water splitting.
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX3Y
Publisher: American Chemical Society (ACS)
Date: 19-12-2019
DOI: 10.1021/ACS.ANALCHEM.8B04238
Abstract: Recently, we introduced the use of techniques drawn from Bayesian statistics to recover kinetic and thermodynamic parameters from voltammetric data and were able to show that the technique of large litude ac voltammetry yielded significantly more accurate parameter values than the equivalent dc approach. In this paper, we build on this work to show that this approach allows us, for the first time, to separate the effects of random experimental noise and inherent system variability in voltammetric experiments. We analyze ten repeated experimental data sets for the [Fe(CN)
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX61
Publisher: Wiley
Date: 03-2009
Publisher: American Chemical Society (ACS)
Date: 08-1989
DOI: 10.1021/J100354A041
Publisher: American Chemical Society (ACS)
Date: 10-1975
DOI: 10.1021/IC50152A021
Publisher: American Chemical Society (ACS)
Date: 12-11-2012
DOI: 10.1021/IC302045M
Abstract: The charge-transfer material TTF-SV(IV)Mo(11)O(40) (TTF = tetrathiafulvalene) was prepared by a spontaneous redox reaction between TTF and the vanadium-substituted polyoxometalate (n-Bu(4)N)(3)[SV(V)Mo(11)O(40)] in both solution and solid state phases. Single crystal X-ray diffraction gave the stoichiometry TTF(4)[SVMo(11)O(40)]·2H(2)O·2CH(2)Cl(2), with the single V atom positionally disordered with eight Mo atoms over the whole α-Keggin polyanion [SVMo(11)O(40)](4-). Raman spectra support the 1+ charge assigned to the oxidized TTF deduced from bond lengths, and elemental and voltammetric analysis also are consistent with this formulation. Scanning electron microscopy images showed a rod-type morphology for the new charge-transfer material. The conductivity of the solid at room temperature is in the semiconducting range. The TTF and (n-Bu(4)N)(3)[SV(V)Mo(11)O(40)] solids also undergo a rapid interfacial reaction, as is the case with TTF and TCNQ (TCNQ = tetracyanoquinodimethane) solids. EPR spectra at temperatures down to 2.6 K confirm the presence of two paramagnetic species, V(IV) and the oxidized TTF radical. Spectral evidence shows that the TTF-SV(IV)Mo(11)O(40) materials prepared from either solution or solid state reactions are equivalent. The newly isolated TTF-SV(IV)Mo(11)O(40) material represents a new class of TTF-polyoxometalate compound having dual electrical and magnetic functionality derived from both the cationic and anionic components.
Publisher: American Chemical Society (ACS)
Date: 30-06-2000
DOI: 10.1021/AC000020J
Abstract: Because of its presumed ideal reversible behavior, the oxidation of ferrocene is widely used in cyclic voltammetric studies in highly resistive organic solvents as a means of reference electrode potential calibration. In this study, it is shown that a good estimate of the uncompensated resistance value, needed for reference potential correction and also frequently an input parameter in simulation of the theory, can be obtained simultaneously with the ferrocene reference potential measurement using a simple analysis based on the semiintegral. Application to cyclic voltammetric oxidation of ferrocene in dichloromethane (0.1 M NBu4PF6), under conditions where uncompensated resistances of approximately 2.5 komega are encountered, is used to illustrate the fidelity of the semiintegral method of analysis. Inclusion of this estimated resistance value as the input parameter in a commercially available digital simulation package confirms that the oxidation of ferrocene in dichloromethane represents a close-to-ideal diffusion-controlled reversible process. However, use of the semiintegral method of data analysis also enables detection of subtle forms of nonideality encountered with the ferrocene oxidation process in other media where kinetically controlled adsorption of the ferricenium cation may occur.
Publisher: Elsevier BV
Date: 1986
Publisher: American Chemical Society (ACS)
Date: 15-11-2013
DOI: 10.1021/AC402150Y
Publisher: American Chemical Society (ACS)
Date: 03-1986
DOI: 10.1021/IC00227A006
Publisher: Elsevier BV
Date: 02-1984
Publisher: American Chemical Society (ACS)
Date: 07-1983
DOI: 10.1021/IC00156A017
Publisher: American Chemical Society (ACS)
Date: 09-04-1999
DOI: 10.1021/IC980796R
Abstract: The electrochemical oxidation of cis,mer-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Br] (dpm = Ph(2)PCH(2)PPh(2)), or (cis,mer)(0),()()has been examined in dichloromethane (0.1 M Bu(4)NPF(6)) by voltammetric, bulk electrolytic, in situ and ex situ spectroelectrochemical and simulation techniques. On the voltammetric time scale at 20 degrees C, the neutral 18-electron cis,mer Mn(I) species is oxidized to the corresponding 17-electron cation which at slow scan rates isomerizes to the trans cation. Simulations are consistent with a rate constant of 3.1 +/- 0.3 s(-1) for this isomerization process. Monitoring the reaction by in situ IR spectroscopy at low-temperature enables the identification of the nu(CO) bands of all four species ((cis,mer)(0) (cis,mer)(+) (trans)(0) (trans)(+)) in the resultant square reaction scheme that is operative under these thin layer electrolysis conditions. Additionally, 17-electron cis,fac-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Br](+) and its 18-electron (cis,fac)(0) counterpart, generated by a redox-induced catalytic isomerization reaction, are detected and characterized by IR spectroscopy (nu(CO)). Room-temperature bulk oxidative electrolysis experiments reveal that the trans cation, generated in bulk solution from the (cis,mer)(+) and (cis,fac)(+) isomers, slowly ejects bromide with a rate constant of 1.6 x 10(-3) s(-1) to form trans-[Mn(CO)(2)(eta(2)-dpm)(2)](+). The equivalent voltammetry in acetonitrile is complicated by an additional competing kinetic step which is attributed to reaction of this cation with the solvent. However, the major product formed upon oxidation at room temperature is still the trans cation. Less detailed studies on the oxidation of cis,mer-[Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Cl] only show significant differences under conditions of bulk electrolysis after trans-[Mn(CO)(2)(eta(2)-dpm)(2)](2+) is formed via expulsion of Cl(-).
Publisher: American Chemical Society (ACS)
Date: 07-02-2007
DOI: 10.1021/IC061902P
Abstract: A cyclen derivative bearing a ferrocenyl arm (L) and a series of its ZnII complexes [ZnL(OH2)][ClO4]2 (C1), [ZnL(OH)][ClO4] (C2), and [ZnL(Cl)][ClO4].CH3CN (C3) (cyclen = 1,4,7,10-tetraazacyclododecane, L = 1-(ferrocenemethyl)-1,4,7,10-tetraazacyclododecane) have been prepared and characterized spectroscopically. An X-ray structure determination confirmed the formation of complex C1 and revealed that the coordinated water participates in hydrogen bonding with the perchlorate counter ions. The pKa value for deprotonation of the water molecule determined by potentiometric titration was found to be 7.36 +/- 0.09 at 25 degrees C and I = 0.1 (KNO3). The possibility of using complex C1 as a potential sensor for thymine derivatives in aqueous solution has been examined. Shifts in the 1H and 13C NMR resonances showed the binding occurred with thymine (T) and two thymine derivatives, thymidine (dT) and thymidine 5'-monophosphate (TMP2-). Significant shifts of the nuC=O and nuC=C vibrations of the thymine derivatives were also observed via IR spectroscopy upon complexation with the receptor. The thymine adduct, [ZnL(thymine anion)][ClO4].2H2O (C4), has been crystallized and characterized. The X-ray structure of C4 confirmed the thymine binding to the receptor, and the short Zn-N(thymine) distance of 1.975(5) A indicated clearly that the ferrocenyl arm does not affect the complexation of the DNA base. In contrast to the large spectral changes, electrochemical studies showed a small shift of the reversible potential of the redox couple Fc+/Fc (Fc = ferrocene) and subtle changes in voltammetry upon the addition of an excess of dT, TMP2-, and guanine (dG) at physiological pH, indicating the level of interaction is similar in both Fc and Fc+ forms.
Publisher: No publisher found
Date: 2004
DOI: 10.5517/CC7QX4Z
Publisher: American Chemical Society (ACS)
Date: 10-1993
DOI: 10.1021/JA00074A021
Publisher: Elsevier BV
Date: 04-2009
Publisher: Wiley
Date: 19-04-2023
Abstract: Published data suggest that sparingly soluble metal complexes of , where n=0, 1, 2, 4, can act as heterogeneous catalysts for the kinetically very slow ‐ / reaction in aqueous solution. This study shows that the coordination polymer , participates as a homogeneous catalyst via an extremely small concentration of dissolved . This finding suggests that the generally accepted mechanism of catalysis by based solids needs to be revisited to ascertain the role of homogeneous pathways. In the present study, UV‐visible spectrophotometry was used to examine the catalysis of the aqueous redox reaction of (1.0 mM) with (100 mM) in the presence of (i) a precursor catalyst, (ii) the catalyst, , as the water soluble Li + salt and (iii) . A homogeneous reaction scheme that utilises the couple is provided. In the case of derived from highly soluble , quantitative conversion of 1.0 mM to 0.50 mM occurs with complete reduction of to being rapidly accelerated by sub‐micomolar concentrations of . generated in the catalytic cycle, reacts with to reform and produce . Along with the rapid catalytic reaction, the sluggish competing reaction between and occurs to give , which is protonated to , along with a trace amount of . On addition of the precursor catalyst, , rapid reduction with occurs to form – the active catalyst. added to water is shown to be sufficiently soluble to provide adequate to act as the catalyst for the ‐ / reaction.
Publisher: Royal Society of Chemistry (RSC)
Date: 1979
DOI: 10.1039/DT9790001891
Publisher: Elsevier BV
Date: 05-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B607290A
Publisher: Royal Society of Chemistry (RSC)
Date: 1998
DOI: 10.1039/A806084C
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4RA14392B
Abstract: High reactivity of anodized gold allows electroless deposition of active IrO x nanoparticles. With its highly stable electrocatalytic activity for OER, the method is the simplest yet developed.
Publisher: American Chemical Society (ACS)
Date: 1990
DOI: 10.1021/AC00200A006
Abstract: The incorporation of platinum disk microelectrodes of various radii (2.5-50 microns) in a well-jet flow cell offers reduced limits of detection for the determination of copper in urine by flow injection analysis compared with standard methods based on a conventional sized glassy carbon disk macroelectrode (radius 1.5 mm), in a thin-layer cell. The radius of the platinum disk microelectrode was found to be critical with respect to both the limit of detection and flow rate dependence. An optimal radius value of 28 microns was found with detection limits increasing with both larger and smaller electrode radii. In contrast, as theoretically expected, a diminished flow rate dependence was observed the smaller the radii of the platinum disk microelectrodes. S le cleanup and preparation is conveniently achieved by the use of Sep-Pak cartridges and formation of a copper dithiocarbamate complex. The metal complex is easily oxidized at platinum disk microelectrodes in acetonitrile, which was the solvent used in the flow injection method of analysis.
Publisher: American Chemical Society (ACS)
Date: 15-07-1989
DOI: 10.1021/AC00189A006
Publisher: American Chemical Society (ACS)
Date: 1990
DOI: 10.1021/AC00200A008
Publisher: Wiley
Date: 15-09-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 1974
DOI: 10.1039/DT9740000773
Publisher: Elsevier BV
Date: 1984
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CP23819E
Abstract: The theory for large litude Fourier transformed ac voltammetry at a rotating disc electrode is described. Resolution of time domain data into dc and ac harmonic components reveals that the mass transport for the dc component is controlled by convective-diffusion, while the background free higher order harmonic components are flow rate insensitive and mainly governed by linear diffusion. Thus, remarkable versatility is available Levich behaviour of the dc component limiting current provides diffusion coefficient values and access to higher harmonics allows fast electrode kinetics to be probed. Two series of experiments (dc and ac voltammetry) have been required to extract these parameters here large litude ac voltammetry with RDE methodology is used to demonstrate that kinetics and diffusion coefficient information can be extracted from a single experiment. To demonstrate the power of this approach, theoretical and experimental comparisons of data obtained for the reversible [Ru(NH(3))(6)](3+/2+) and quasi-reversible [Fe(CN)(6)](3-/4-) electron transfer processes are presented over a wide range of electrode rotation rates and with different concentrations and electrode materials. Excellent agreement of experimental and simulated data is achieved, which allows parameters such as electron transfer rate, diffusion coefficient, uncompensated resistance and others to be determined using a strategically applied approach that takes into account the different levels of sensitivity of each parameter to the dc or the ac harmonic.
Publisher: American Chemical Society (ACS)
Date: 30-08-2019
DOI: 10.1021/ACS.ANALCHEM.9B01891
Abstract: At present, electrochemical mechanisms are most commonly identified subjectively based on the experience of the researcher. This subjectivity is reflected in bias to particular mechanisms as well as lack of quantifiable confidence in the chosen mechanism compared to potential alternative mechanisms. In this paper we demonstrate that a deep neural network trained to recognize dc cyclic voltammograms for three commonly encountered mechanisms provides correct classifications within 5 ms without the problem of subjectivity. To mimic experimental data, the impact of noise, uncompensated resistance, and dependence on scan rate, factors that are relevant to practical studies, has also been investigated. Outcomes with two experimental data sets are also presented.
Publisher: Elsevier BV
Date: 10-2015
Publisher: American Chemical Society (ACS)
Date: 15-11-1993
DOI: 10.1021/AC00070A014
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3DT50233C
Abstract: The cyclic voltammetric behavior of [FeIIICl(salen)] complexes has been investigated in CH3CN and compared to that obtained with [CoII(salen)] analogues. Details of the mechanism associated with iron- and cobalt-salen complex reduction in the presence of the lithium cation have been elucidated by comparison of simulated and experimental voltammograms. Electrogenerated [FeICl(salen)]²⁻ and [FeICl(salophen)]²⁻ complexes catalyze the dehalogenation of halo-alkyl compounds as is the case with [CoI(salen)]⁻ complexes, even in the presence of the lithium cation which allows the reduction to occur at a less negative potential.
Publisher: American Chemical Society (ACS)
Date: 02-1977
DOI: 10.1021/IC50168A036
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3AY40769A
Publisher: Proceedings of the National Academy of Sciences
Date: 11-11-2015
Abstract: The mononuclear Mo enzymes are ubiquitous throughout life, and the notion that their activity arises from Mo(VI/V/IV) redox cycling is a central dogma of bioinorganic chemistry. We prove that YedY, a structurally simple mononuclear Mo enzyme, operates via a strikingly different mechanism: the catalytically active state is generated from addition of three electrons and three protons to the Mo(V) form of the enzyme, suggesting for the first time (to our knowledge) that organic-ligand–based electron transfer reactions at the pyranopterin play a role in catalysis. We showcase Fourier-transformed alternating-current voltammetry as a technique with powerful utility in metalloenzyme studies, allowing the simultaneous measurement of redox catalysis and the underlying electron transfer reactions.
Publisher: Springer Science and Business Media LLC
Date: 29-05-2020
Publisher: Oxford University Press (OUP)
Date: 18-12-2017
DOI: 10.1111/JAM.13631
Abstract: Globally, sustainable provision of high-quality safe water is a major challenge of the 21st century. Various chemical and biological monitoring analytics are presently utilized to guarantee the availability of high-quality water. However, these techniques still face some challenges including high costs, complex design and onsite and online limitations. The recent technology of using microbial fuel cell (MFC)-based biosensors holds outstanding potential for the rapid and real-time monitoring of water source quality. MFCs have the advantages of simplicity in design and efficiency for onsite sensing. Even though some sensing applications of MFCs were previously studied, e.g. biochemical oxygen demand sensor, recently numerous research groups around the world have presented new practical applications of this technique, which combine multidisciplinary scientific knowledge in materials science, microbiology and electrochemistry fields. This review presents the most updated research on the utilization of MFCs as potential biosensors for monitoring water quality and considers the range of potentially toxic analytes that have so far been detected using this methodology. The advantages of MFCs over established technology are also considered as well as future work required to establish their routine use.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP50690H
Abstract: Aluminium electrodeposition is demonstrated from a thermally degraded ionic liquid solution. NMR and voltammetric analyses established that Al(3+) reduction was remarkably similar to that in non-degraded IL solutions suggesting that the electroactive metal-containing species was unaffected by heat treatment. Electron microscopy revealed a significant grain refinement of the deposited metal.
Publisher: Elsevier BV
Date: 03-2001
Publisher: No publisher found
Date: 2005
DOI: 10.5517/CC7ZT66
Publisher: American Chemical Society (ACS)
Date: 10-03-2014
DOI: 10.1021/JP500786J
Abstract: Electrochemical reduction of cis-stilbene occurs by two well-resolved one-electron reduction steps in acetonitrile with (n-Bu)4NPF6 as the supporting electrolyte and in N-butyl-N-methylpyrrolidinium (Pyrr1,4(+)) and (trimethylamine)(dimethylethylamine)-dihydroborate bis(trifluoromethylsulfonyl)amide (NTf2(-)) ionic liquids (ILs). Mechanistic details of the electroreduction have been probed by dc and Fourier transformed ac voltammetry, simulation of the voltammetry, bulk electrolysis, and EPR spectroscopy. The first one-electron reduction induces fast cis to trans isomerization in CH3CN and ILs, most likely occurring via disproportionation of cis-stilbene radical anions and fast transformation of the cis-dianion to the trans-configuration. The second reduction process is chemically irreversible in CH3CN due to protonation of the dianion but chemically reversible in highly aprotic ILs under high cis-stilbene concentration conditions. Increase of the (n-Bu)4NPF6 supporting electrolyte concentration (0.01-1.0 M) in CH3CN induces substantial positive shifts in the potentials for reduction of cis-stilbene, consistent with strong ion pairing of the anion radical and dianion with (n-Bu)4N(+). However, protection by ion pairing against protonation of the stilbene dianions or electrochemically induced cis-trans-stilbene isomerization is not achieved. Differences in electrode kinetics and reversible potentials for cis-stilbene(0/•-) and trans-stilbene(0/•-) processes are less pronounced in the Pyrr1,4-NTf2 ionic liquid than in the molecular solvent acetonitrile.
Publisher: Elsevier BV
Date: 04-1987
Publisher: American Chemical Society (ACS)
Date: 26-07-2017
DOI: 10.1021/JACS.7B03611
Publisher: Elsevier BV
Date: 1989
Publisher: American Chemical Society (ACS)
Date: 18-09-2017
DOI: 10.1021/ACS.ANALCHEM.7B01224
Abstract: Two zeolitic imidazolate frameworks, ZIF-67 and ZIF-8, were interrogated for their redox properties using Fourier transformed alternating current voltammetry, which revealed that the 2-methylimidazolate ligand is responsible for multiple redox transformations. Further insight was gained by employing discrete tetrahedral complexes, [M(DMIM)
Publisher: American Chemical Society (ACS)
Date: 31-03-2014
DOI: 10.1021/IC402980T
Abstract: Electron-transfer-facilitated dissolution, ion insertion, and desorption associated with an MMX-type quasi-one-dimensional iodide-bridged dinuclear Pt complex (MMX chain) have been investigated for the first time. K2(NC3N)[Pt2(pop)4I]·4H2O (1) (NC3N(2+) = (H3NC3H6NH3)(2+) pop = P2H2O5(2-)) is a semiconductor with a three-dimensional coordination-bond and hydrogen-bond network included in the chain. The cyclic voltammetry of 1 was studied by using 1-modified electrodes in contact with acetonitrile solutions containing electrolyte. The chemical reversibility for oxidation of 1 depended on the electrolyte cation size, with large cations such as tetrabutylammonium (Bu4N(+)) being too large to penetrate the pores formed by the loss of K(+) and NC3N(2+) upon oxidation. The potential for reduction of 1 decreased as the cation size increased. The presence of the acid induced additional well-defined processes but with gradual solid dissolution, attributed to the breaking of the coordination-bond networks.
Publisher: American Chemical Society (ACS)
Date: 06-2002
DOI: 10.1021/AC015729K
Abstract: Reference potential scales are not generally available in ionic liquids. Consequently, comparison of data with those obtained in conventional solvent (electrolyte) media is not possible. The process [Co(Cp)2](+/0) (Co(Cp)2 = cobaltocene) has been studied at gold, glassy carbon and platinum macrodisk electrodes to test the feasibility of using this redox couple as a voltammetric reference standard in the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]). A reversible, one-electron reduction process was observed, and the measured reversible potential versus a silver quasi-reference electrode was independent of the working electrode material, the concentration, and the scan rate. Ferrocene, the other traditionally used reference compound, is poorly soluble in this ionic liquid. However, the solution-phase voltammetry of ethylferrocene could be readily studied in [bmim][PF6], and a reversible oxidation process was observed. A reversible potential of +1285 +/- 5 mV versus the [Co(Cp)2](+/0) reference potential scale was obtained, and this value is comparable with that obtained in CH3CN (0.1 M Bu4NPF6) when referenced to the same potential scale. Ferrocene, decamethylferrocence, 1,1'-dimethylferrocene, 1,1'-diacetylferrocene, and ferrocenecarboxaldehyde were adhered to the working electrode surface and immersed in [bmim][PF6]. In each case, solid-state voltammetry provided well-defined, reversible one-electron oxidation processes that had the appearance of being diffusion controlled, with charge neutralization occurring via the ionic liquid. Reversible potentials of the solid-state processes referenced against the [Co(Cp)2](+/0) scale were similar to solution-phase values obtained in CH3CN (0.1 M Bu4NPF6).
Publisher: Elsevier BV
Date: 05-1988
Publisher: Elsevier BV
Date: 05-2016
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.ACA.2013.04.036
Abstract: Phosphomolybdate, H3PMo12O40, (PMo12)-doped-poly(3,4-ethylenedioxythiophene) (PEDOT) coated gold nanoparticles have been synthesized in aqueous solution by reduction of AuCl4(-) using hydroxymethyl EDOT as a reducing agent in the presence of polystyrene sulfonate and PMo12. The resulting PMo12-doped-PEDOT stabilized Au nanoparticles are water soluble and have been characterized by UV-visible spectroscopy, scanning electron microscopy and electrochemistry. Glassy carbon electrodes modified with these Au nanoparticles show excellent stability and catalytic activity towards the reduction of bromate in an aqueous electrolyte solution containing 10mM H2SO4 and 0.1M Na2SO4.
Publisher: The Electrochemical Society
Date: 1970
DOI: 10.1149/1.2407755
Publisher: American Chemical Society (ACS)
Date: 23-04-2012
DOI: 10.1021/IC2027412
Abstract: The synthesis and characterization of microtubes of SiMoW(11) Keggin polyoxometalates containing either an Mo(V) or Mo(VI) atom is reported. The introduction of a Mo atom into the Keggin-type tungstosilicate microtubes endows them with new properties. The Mo-substituted microtubes may exert both W and Mo functionalities in electrocatalytic reactions and in the immobilization of noble metal nanoparticles. The degree of reduction of the Mo component in the SiMoW(11) microtubes is controllable simply by tuning the amount of reductant present in the mother liquor. Mo-substituted Keggin tungstosilicate microtubes in their reduced state are more stable than the all-tungsten Keggin tungstosilicate heteropoly blue microtubes.
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CC678C1
Publisher: Wiley
Date: 23-09-2011
Publisher: Elsevier BV
Date: 02-1987
Publisher: Elsevier BV
Date: 12-2001
Publisher: American Chemical Society (ACS)
Date: 12-2021
Publisher: American Chemical Society (ACS)
Date: 07-07-2014
DOI: 10.1021/IC500878W
Abstract: The water insoluble complex Rb4[Ru(II)(bpy)3]5[{Ru(III)4O4(OH)2(H2O)4}(γ-SiW10O36)2], ([Ru(II)bpy]5[Ru(III)4POM]), was synthesized from Rb8K2[{Ru(IV)4O4(OH)2(H2O)4}(γ-SiW10O36)2] and used for electrocatalytic water oxidation under both thin- and thick-film electrode conditions. Results demonstrate that the [Ru(II)bpy]5[Ru(III)4POM] modified electrode enables efficient water oxidation to be achieved at neutral pH using thin-film conditions, with [Ru(bpy)3](3+)([Ru(III)bpy]) acting as the electron transfer mediator and [Ru(V)4POM] as the species releasing O2. The rotating ring disc electrode (RRDE) method was used to quantitatively determine the turnover frequency (TOF) of the catalyst, and a value of 0.35 s(-1) was obtained at a low overpotential of 0.49 V (1.10 V vs Ag/AgCl) at pH 7.0. The postulated mechanism for the mediator enhanced catalytic water process in a pH 7 buffer containing 0.1 M LiClO4 as an additional electrolyte includes the following reactions (ion transfer for maintaining charge neutrality is omitted for simplicity): [Ru(II)bpy]5[Ru(III)4POM] → [Ru(III)bpy]5[Ru(V)4POM] + 13 e(-) and [Ru(III)bpy]5[Ru(V)4POM] + 2H2O → [Ru(III)bpy]5[Ru(IV)4POM] + O2 + 4H(+). The voltammetry of related water insoluble [Ru(II)bpy]2[S2M18O62] (M = W and Mo) and [Fe(II)Phen]x[Ru(III)4POM] materials has also been studied, and the lack of electrocatalytic water oxidation in these cases supports the hypothesis that [Ru(III)bpy] is the electron transfer mediator and [Ru(V)4POM] is the species responsible for oxygen evolution.
Publisher: Elsevier BV
Date: 1983
Publisher: Wiley
Date: 28-01-2010
Abstract: The recent literature is surveyed to explore the nature of voltammetry in room temperature ionic liquids. The extent of similarities with conventional electrochemical solvents is reported and some surprising differences are noted.
Publisher: Elsevier BV
Date: 2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2NR03539A
Abstract: Alloying is efficient for tuning product selectivity of copper in electrochemical reduction of CO 2 . Different alloying strategies and their impacts on product formation paths, the key challenges and future directions of the field have been reviewed.
Publisher: American Chemical Society (ACS)
Date: 08-1981
DOI: 10.1021/AC00232A022
Publisher: American Chemical Society (ACS)
Date: 12-1989
DOI: 10.1021/IC00324A017
Publisher: Elsevier BV
Date: 04-1975
Publisher: Wiley
Date: 12-12-2018
Abstract: The reaction of Mn(BF
Publisher: American Chemical Society (ACS)
Date: 03-1975
DOI: 10.1021/AC60353A022
Publisher: American Chemical Society (ACS)
Date: 02-1987
DOI: 10.1021/OM00145A024
Publisher: American Chemical Society (ACS)
Date: 03-2001
DOI: 10.1021/JA003966J
Abstract: Solid-state voltammetry, spectroscopy, and microscopy studies have been used to probe the proton and electron conductivity within a self-assembled cocrystal, HQBpt. This crystallographically defined material contains 3,5-bis(pyridin-2-yl)-1,2,4-triazole, HBpt, dimers that are pi-stacked and hydrogen bonded to 1,4-hydroquinone, H(2)Q, in a herringbone arrangement. When deposited onto platinum microelectrodes, the cocrystal exhibits a well-defined voltammetric response corresponding to oxidation of H(2)Q to the quinone, Q, across a wide range of voltammetric time scales, electrolyte compositions, and pH values. Scanning electron microscopy reveals that redox cycling in aqueous perchlorate solutions in which the pH is systematically varied from 1 to 7 triggers electrocrystallization and the extensive formation of rodlike crystals. Fast scan rate voltammetry reveals that the homogeneous charge transport diffusion coefficient, D(app), is independent of the perchlorate concentration for 0.1 < [ClO(4)(-)] < 1.0 M (pH 6.6) at 3.14 +/- 0.11 x 10(-)(9) cm(2) s(-)(1). Moreover, D(app) is independent of the perchloric acid concentration for concentrations greater than approximately 2.0 M, maintaining a value of 4.81 +/- 0.07 x 10(-)(8) cm(2) s(-)(1). The observation that D(app) is independent of the supporting electrolyte suggests that the rate-determining step for homogeneous charge transport is not the availability of charge-compensating counterions or protons, but the dynamics of electron self-exchange between H(2)Q and Q. We have used the Dahms-Ruff formalism to determine electron self-exchange rate constants which are 2.84 +/- 0.22 x 10(9) and 9.69 +/- 0.73 x 10(10) M(-)(1) s(-)(1) for pH values greater than approximately 2.0 and less than -0.3, respectively. Significantly, these values are more than 2 orders of magnitude larger that those found for benzoquinone self-exchange reactions in aqueous solution. These results indicate that hydrogen bonds play an important role in supporting rapid electron transfer. The increase in D(app) between pH 1.0 and -0.3 is associated with protonation of the HBpt moieties, which triggers a reversible change in the material's structure.
Publisher: The Electrochemical Society
Date: 1970
DOI: 10.1149/1.2407321
Publisher: Elsevier BV
Date: 06-1997
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT787J
Publisher: American Chemical Society (ACS)
Date: 02-07-2009
DOI: 10.1021/IC9006982
Abstract: The bioinspired Mn-oxo cubane complex, [Mn(4)O(4)L(6)](+) 1b(+) (L = (p-MeO-Ph)(2)PO(2)), is a model of the photosynthetic O(2)-evolving complex. It is able to electro-oxidize water at 1.00 V (vs Ag/AgCl) under illumination by UV-visible light when suspended in a proton-conducting membrane (Nafion) coated onto a conducting electrode. Electrochemical measurements, and UV-visible, NMR, and EPR spectroscopies are interpreted to indicate that 1b(+) is the dominant electro-active species in the Nafion, both before and after catalytic cycling, and thus correlates closely with activity. The observation of a possible intermediate and free phosphinate ligand within the Nafion suggests a catalytic mechanism involving photolytic disruption of a phosphinate ligand, followed by O(2) formation, and subsequent reassembly of the cubane structure. Several factors that influence catalytic turnover such as the applied potential, illumination wavelength, and energy have been examined in respect of attaining optimum catalytic activity. Catalytic turnover frequencies of 20-270 molecules O(2) h(-1) catalyst(-1) at an overpotential of 0.38 V plus light (275-750 nm) and turnovers numbers >1000 molecules O(2) catalyst(-1) are observed. The 1b(+)-Nafion system is among the most active and durable molecular water oxidation catalysts known.
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CC678D2
Publisher: American Chemical Society (ACS)
Date: 16-11-2010
DOI: 10.1021/JO101449Q
Abstract: The alkylation reaction of 2-mercapto-1-methylimidazole 1b with 2-chloroacetonitrile and 2-chloropropionitrile produced S-alkyl methimazole chlorides 2a and 2b which were subjected to anion metathesis with lithium bis(trifluoromethanesulfonyl)amide, LiNTf(2), to afford nitrile functionalized methimazole-based room temperature ionic liquids 3a and 3b in 94% and 89% yields, respectively. Ionic liquids 3a and 3b have reasonably wide electrochemical windows. The efficient extraction of Ag(+) from aqueous media into 3a and 3b is also reported.
Publisher: Elsevier BV
Date: 2012
Publisher: American Chemical Society (ACS)
Date: 1990
DOI: 10.1021/IC00327A027
Publisher: Wiley
Date: 03-05-2016
Publisher: Elsevier BV
Date: 04-1972
Publisher: American Chemical Society (ACS)
Date: 28-02-2012
DOI: 10.1021/AC2031173
Abstract: An electrochemical method based on cathodic stripping voltammetry at a gold electrode has been developed for the determination of water in ionic liquids. The technique has been applied to two aprotic ionic liquids, (1-butyl-3-ethylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate), and two protic ionic liquids, (bis(2-hydroxyethyl)ammonium acetate and triethylammonium acetate). When water is present in an ionic liquid, electrooxidation of a gold electrode forms gold oxides. Thus, application of an anodic potential scan or holding the potential of the electrode at a very positive value leads to accumulation of an oxide film. On applying a cathodic potential scan, a sensitive stripping peak is produced as a result of the reduction of gold oxide back to gold. The magnitude of the peak current generated from the stripping process is a function of the water concentration in an ionic liquid. The method requires no addition of reagents and can be used for the sensitive and in situ determination of water present in small volumes of ionic liquids. Importantly, the method allows the determination of water in the carboxylic acid-based ionic liquids, such as acetate-based protic ionic liquids, where the widely used Karl Fischer titration method suffering from an esterification side reaction which generates water as a side product.
Publisher: Elsevier BV
Date: 05-2010
Publisher: American Chemical Society (ACS)
Date: 10-2014
DOI: 10.1021/IC501431C
Abstract: Both conventional solution-phase and direct solid-solid redox reactions between tetrathiafulvalene (TTF) and the vanadium-substituted polyoxometalate (n-Bu4N)3[SV(V)W11O40] give rise to microcrystalline or powdered semiconducting charge transfer solid material. A single-crystal X-ray structure derived from growing crystals from a MeCN-CH2Cl2 solution-phase redox reaction gives a stoichiometry of TTF4[SVW11O40]·2H2O·2CH2Cl2 and reveals that there are two crystallographically different TTF cation moieties based on (TTF2)(2+) dimers. While the color and morphology of the microcrystalline or powdered TTF4[SVW11O40] differ from the single crystals prepared for structural analysis, all materials are spectroscopically (infrared (IR), Raman with respect to the TTF bands, and electron paramagnetic resonance (EPR)) indistinguishable. Raman spectra suggest that the charge transfer is unevenly distributed across the (TTF2)(2+) dimers, which is postulated to give rise to enhanced mixed-valence features. Structural, spectral, and other properties, such as conductivity, are compared with results available on the recently published molybdenum TTF4[SVMo11O40]·2H2O·2CH2Cl2 analogue, where the charge distribution is uniform on all TTF cations. In both ex les, the position of the V atom is located over several sites. Elemental analysis and voltammetric data also are consistent with the formulations deduced from structural and spectroscopic studies. The conductivity at room temperature is in the semiconducting range, but significantly greater than that for the Mo analogue. EPR spectra at temperatures down to the liquid helium regime confirm the presence of paramagnetic V(IV) and paramagnetic oxidized TTF. The newly isolated TTF-SV(IV)W11O40 material also has magnetic functionality derived from the cationic and anionic components.
Publisher: American Chemical Society (ACS)
Date: 29-07-2011
DOI: 10.1021/AC201373D
Abstract: The electrochemistry of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF(4)), [TCNQF(4)](•-), and [TCNQF(4)](2-) have been studied in acetonitrile (0.1 M [Bu(4)N][ClO(4)]). Transient and steady-state voltammetric techniques have been utilized to monitor the generation of [TCNQF(4)](•-) and [TCNQF(4)](2-) anions as well as their reactions with trifluoroacetic acid (TFA). In the absence of TFA, the reduction of TCNQF(4) occurs via two, diffusion controlled, chemically and electrochemically reversible, one-electron processes where the reversible formal potentials are 0.31 and -0.22 V vs Ag/Ag(+). Unlike the TCNQ analogues, both [TCNQF(4)](•-) and [TCNQF(4)](2-) are persistent when generated via bulk electrolysis even under aerobic conditions. Voltammetric and UV-vis data revealed that although the parent TCNQF(4) does not react with TFA, the electrochemically generated radical anion and dianion undergo facile protonation to yield [HTCNQF(4)](•), [HTCNQF(4)](-) and H(2)TCNQF(4) respectively. The voltammetry can be simulated to give a complete thermodynamic and kinetic description of the complex, coupled redox and acid-base chemistry. The data indicate dramatically different equilibrium and rate constants for the protonation of [TCNQF(4)](•-) (K(eq) = 3.9 × 10(-6), k(f) = 1.0 × 10(-3) M(-1) s(-1)) and [TCNQF(4)](2-) (K(eq) = 3.0 × 10(3), k(f) = 1.0 × 10(10) M(-1) s(-1)) in the presence of TFA.
Publisher: Springer International Publishing
Date: 2015
Publisher: American Chemical Society (ACS)
Date: 03-1986
DOI: 10.1021/IC00226A008
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B822167G
Abstract: Based on studies with microcrystals of [Ru(bpy)(3)](2)[alpha-W(18)O(54)(SO(3))(2)] adhered to an electrode surface in contact with the ionic liquids [BMIM][PF(6)] and [BMIM][BF(4)], it has been found that a series of well defined monoelectronic reduction processes associated with the tungsten-oxo cage of the [alpha-W(18)O(54)(SO(3))(2)](4-) species are observed at much less negative potentials than found in conventional organic solvents. Furthermore, since the potentials of the [Ru(bpy)(3)](2+) 2,2'-bipyridyl ligand based reduction processes are not strongly medium dependent, ionic liquid investigations allowed the characterisation of the [Ru(bpy)(3)](2)[alpha-W(18)O(54)(SO(3))(2)] complex without extensive overlap of the ligand based reductions from the [Ru(bpy)(3)](2+) cation and the [W(18)O(54)(SO(3))(2)](4-) anions. In the case of the Mo analogues, [alpha and beta-Mo(18)O(54)(SO(3))(2)](4-), the much higher reactivity of the reduced forms precluded access to well defined monoelectronic reversible steps at negative potentials in all media examined, even though reduction is far easier and hence availability of extensively reduced species should be simpler, in a thermodynamic sense.
Publisher: Royal Society of Chemistry (RSC)
Date: 1996
DOI: 10.1039/AN9962100357
Publisher: Springer Science and Business Media LLC
Date: 07-2018
Publisher: Elsevier BV
Date: 02-1974
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT786H
Publisher: Elsevier BV
Date: 10-2012
DOI: 10.1016/J.JINORGBIO.2012.07.016
Abstract: The putative platinum(IV) anticancer drugs, [Pt{((R)NCH(2))(2)}(py)(2)XY] (X,Y=Cl, R=p-HC(6)F(4) (1a), C(6)F(5) (1b) X,Y=OH, R=p-HC(6)F(4) (2) X=Cl, Y=OH, R=p-HC(6)F(4) (3), py = pyridine) have been prepared by oxidation of the Pt(II) anticancer drugs [Pt{((R)NCH(2))(2)}(py)(2)] (R=p-HC(6)F(4) (4a) or C(6)F(5) (4b)) with PhICl(2) (1a,b), H(2)O(2) (2) and PhICl(2)/Bu(4)NOH (3). NMR spectroscopy and the X-ray crystal structures of 1b, 2 and 3 show that they have octahedral stereochemistry with the X,Y ligands in the trans-position. The net two electron electrochemical reduction of 1a, 2 and 3 has been studied by voltammetric, spectroelectrochemical and bulk electrolysis techniques in acetonitrile. NMR and other data reveal that reduction of 1a gives pure 4a via the elimination of both axial chloride ligands. In the case of 2, one end of the diamide ligand is protonated and the resulting -NH(p-HC(6)F(4)) group dissociated giving a [Pt{N(p-HC(6)F(4))CH(2)CH(2)NH(p-HC(6)F(4))}] arrangement, one pyridine ligand is lost and a hydroxide ion retained in the coordination sphere. Intriguingly, in the case of reduction of 3, a 50% mixture of the reduction products of pure 1a and 2 is formed. The relative ease of reduction is 1>3>2. Testing of 1a, 2 and 3 against L1210 and L1210(DDP) (DDP = cis-diamine-dichloroplatinum(II)) mouse leukaemia cells shows all to be cytotoxic with IC(50) values of 1.0-3.5 μM. 2 and 3 are active in vivo against AHDJ/PC6 tumor line when delivered in peanut oil despite being hard to reduce electrochemically, and notably are more active than 4a delivered in this medium whilst comparable with 4a delivered in saline/Tween.
Publisher: American Chemical Society (ACS)
Date: 09-1970
DOI: 10.1021/AC60293A028
Publisher: American Chemical Society (ACS)
Date: 09-1970
DOI: 10.1021/AC60293A027
Publisher: Elsevier BV
Date: 1990
Publisher: Wiley
Date: 04-1992
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B512263E
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/DT9950001917
Publisher: Elsevier BV
Date: 11-1973
Publisher: Springer Science and Business Media LLC
Date: 27-09-2008
Publisher: Elsevier BV
Date: 12-1997
Publisher: Wiley
Date: 05-1997
Publisher: Royal Society of Chemistry (RSC)
Date: 1993
DOI: 10.1039/AN9931800973
Abstract: Electrochemical reduction of H2O2 at pyrolytic graphite disc electrodes of radius 2.5 mm occurs at readily accessible potentials (600 mV versus the standard hydrogen electrode) in the presence of yeast cytochrome c peroxidase. Introduction of the enzyme into the electrolyte solution initiates large changes in the ellipsometric angles measured for the electrode-solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electrochemical activity. Over the same time course, linear-sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type waveform. It is proposed that the time-dependent behaviour may be rationalized by use of a microscopic model for substrate mass transport, in which the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules. A voltammetric theory based on treating the adsorbed redox enzymes as an expanding array of microelectrodes is in excellent agreement with experiment.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC17431F
Abstract: Thin films of polyoxometalates that are sensitized with a Ru(II) metallopolymer generate significant photocurrents in the presence of benzyl alcohol and visible light. Significantly, the photocurrent generated by the tungstate based adduct, α-[P(2)W(18)O(62)](6-), is approximately seven fold larger than that found for the Dawson polyoxomolybdate α-[S(2)Mo(18)O(62)](4-).
Publisher: Wiley
Date: 24-05-2018
Publisher: American Chemical Society (ACS)
Date: 1985
DOI: 10.1021/LA00061A018
Publisher: Wiley
Date: 25-09-2012
Publisher: American Chemical Society (ACS)
Date: 06-1979
DOI: 10.1021/IC50196A001
Publisher: No publisher found
Date: 2006
DOI: 10.5517/CC678F3
Publisher: American Chemical Society (ACS)
Date: 03-1997
DOI: 10.1021/JO961492U
Publisher: The Electrochemical Society
Date: 03-1995
DOI: 10.1149/1.2048548
Publisher: Informa UK Limited
Date: 06-12-2017
Publisher: Elsevier BV
Date: 03-1986
Publisher: Elsevier BV
Date: 06-1994
Publisher: Elsevier BV
Date: 10-2013
DOI: 10.1016/J.ACA.2013.07.035
Abstract: Nanoparticles with desirable properties not exhibited by the bulk material can be readily synthesized because of rapid technological developments in the fields of materials science and nanotechnology. In particular their highly attractive electrochemical properties and electrocatalytic activity have facilitated achievement of the high level of signal lification needed for the development of ultrasensitive electrochemical affinity biosensors for the detection of proteins and DNA. This review article explains the basic principles of nanoparticle based electrochemical biosensors, highlights the recent advances in the development of nanoparticle based signal lification strategies, and provides a critical assessment of the likely drawbacks associated with each strategy. Finally, future perspectives for achieving advanced signal simplification in nanoparticles based biosensors are considered.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3RA40397A
Publisher: Walter de Gruyter GmbH
Date: 28-02-1997
Publisher: Springer Science and Business Media LLC
Date: 07-03-2008
Publisher: The Electrochemical Society
Date: 1972
DOI: 10.1149/1.2404032
Publisher: Elsevier BV
Date: 08-2012
Publisher: Wiley
Date: 09-03-2018
Publisher: Elsevier BV
Date: 09-1999
Publisher: American Chemical Society (ACS)
Date: 11-02-2000
DOI: 10.1021/JP9925942
Publisher: American Chemical Society (ACS)
Date: 31-08-1999
DOI: 10.1021/JA9908974
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1FD00050K
Abstract: Deep neural networks applied to three cycle voltammograms showed significant advantages in classifying difficult simulated E, EC 1 st and EC 2 nd processes.
Publisher: Elsevier BV
Date: 1971
Publisher: Elsevier BV
Date: 04-2003
Publisher: Elsevier BV
Date: 12-2005
Publisher: American Chemical Society (ACS)
Date: 18-06-2013
DOI: 10.1021/IC400565H
Publisher: American Chemical Society (ACS)
Date: 07-1979
DOI: 10.1021/IC50197A052
Publisher: American Chemical Society (ACS)
Date: 09-03-2005
DOI: 10.1021/IC048660I
Abstract: Detailed electrochemical studies in dichloromethane (0.1 M Bu4NPF6) on the oxidation of the half-lantern [Pt2(kappa2As,C-C6H3-5-Me-2-AsPh2)2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)2] (1) and full-lantern [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4] (2) complexes reveal the presence of an exceptionally stable dinuclear Pt cation 2+. Thus, oxidation of 1 occurs on the voltammetric time scale via a ladder-square scheme to give 2+, whereas 2 is directly converted to 2+. Electrochemically informed chemical synthesis enabled the isolation of solid [2+][BF4-] to be achieved. Single-crystal X-ray structural analysis showed that 2+ also has a lantern structure but with a shorter separation between the Pt centers [2.7069(3) A (2+), 2.8955(4) A (2)]. EPR spectra of 2+ provide unequivocal evidence for axial symmetry of the complex and are noteworthy because of an exceptionally large, nearly isotropic hyperfine coupling constant of about 0.1 cm(-1). Spectroscopic data support the conclusion that the unpaired electron in the 2+ cation is distributed equally between the two Pt nuclei and imply that oxidation of 2 to 2+ leads to the establishment of the metal-to-metal hemibond. Results of extended Huckel molecular orbital and density functional calculations on 2 and 2+ lead to the conclusions that s, p, dz2 mixing of orbitals contributes to the large EPR Pt hyperfine coupling and also that the structural adjustments that occur upon removal of an electron from 2 are driven by the metal-metal bonding character present in 2+.
Publisher: American Chemical Society (ACS)
Date: 03-05-2003
DOI: 10.1021/AC026329F
Abstract: The voltammetry of ferrocene (Fc) and Fc+ in the room-temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM x PF6) has been studied when solid is adhered to glassy carbon or platinum disk electrodes. Due to the slow dissolution kinetics and small diffusion coefficients in the viscous BMIM x PF6 ionic liquid, it is possible to obtain voltammograms of adhered Fc or Fc+ solid that are essentially indistinguishable (except for the current magnitude) from the reversible solution-phase Fc(0/+) process widely employed to provide a reference potential scale. However, the nature of the voltammetry obtained from the adhered solid is governed by the thickness (mass of the solid) of the particle layer. The mechanism proposed to explain the equivalence to solution-phase data involves dissolution at the particle/ionic liquid interface and is supported by electrochemical quartz microbalance measurements and a numerical simulation. Extensive studies on other redox-active solids suggest that voltammograms of solid particles adhered to the electrode surface in contact with ionic liquids frequently exhibit classical behavior associated with solution-phase diffusion-controlled voltammetry. Consequently, the method of adhering microparticles onto an electrode surface can frequently provide an efficient method of establishing ionic liquid solution-phase redox data using extremely small quantities of solid.
Publisher: The Electrochemical Society
Date: 1971
DOI: 10.1149/1.2407790
Publisher: American Chemical Society (ACS)
Date: 24-02-2005
DOI: 10.1021/JA973164X
Publisher: American Chemical Society (ACS)
Date: 04-1978
DOI: 10.1021/IC50182A043
Publisher: American Chemical Society (ACS)
Date: 08-02-2001
DOI: 10.1021/JP002768B
Publisher: American Chemical Society (ACS)
Date: 08-10-2005
DOI: 10.1021/JP0528459
Abstract: The one-electron reduction of [alpha(2)-Fe(III)(OH(2))P(2)W(17)O(61)](7-) at a glassy carbon electrode was investigated using cyclic and rotating-disk-electrode voltammetry in buffered and unbuffered aqueous solutions over the pH range 3.45-7.50 with an ionic strength of approximately 0.6 M maintained. The behavior is well-described by a square-scheme mechanism P + e(-) Q (E(1)(0/) = -0.275 V, k(1)(0/) = 0.008 cm s(-1), and alpha(1) = 1/2), PH(+) + e(-) QH(+) (E(2)(0/) = -0.036 V, k(2)(0/) = 0.014 cm s(-1), and alpha(2) = 1/2), PH(+) P + H(+) (K(P) = 3.02 x 10(-6) M), and QH(+) Q + H(+) (K(Q) = 2.35 x 10(-10) M), where P, Q, PH(+), and QH(+) correspond to [alpha(2)-Fe(III)(OH)P(2)W(17)O(61)](8-), [alpha(2)-Fe(II)(OH)P(2)W(17)O(61)](9-), [alpha(2)-Fe(III)(OH(2))P(2)W(17)O(61)](7-), and [alpha(2)-Fe(II)(OH(2))P(2)W(17)O(61)](8-), respectively E(1)(0)' and E(2)(0)' are the formal potentials, k(1)(0)' and k(2)(0)' are the formal (standard) rate constants, and K(P) and K(Q) are the acid dissociation constants for the relevant reactions. The analysis for the buffered media is based on the approach of Laviron who demonstrated that a square scheme with fully reversible protonations, reversible or quasi reversible electron transfers with the assumption that alpha(1) = alpha(2), can be well-described by the behavior of a simple redox couple, ox + e(-) red, whose formal potential, E(app)(0)', and standard rate constant, k(app)(0)', are straightforwardly derived functions of pH, as are the values of E(1)(0)', k(1)(0)', E(2)(0)', k(2)(0)', and K(P) (only three of the four thermodynamic parameters in a square scheme can be specified). It was assumed that alpha(app) = 1/2, and the simulation program DigiSim was used to determine the values of E(app)(0)' and k(app)(0)', which are required to describe the cyclic voltammograms obtained in buffered media in the pH range from 3.45 to 7.52 (buffer-related reactions which effect general acid-base catalysis are included in the simulations). DigiSim simulations of cyclic voltammograms obtained in unbuffered media yielded the values of E(1)(0)' and k(1)(0)' K(Q) was then directly computed from thermodynamic constraints. These simulations included additional reactions between the redox species and H(2)O. The value of the diffusion coefficient of the [alpha(2)-Fe(III)(OH(2))P(2)W(17)O(61)](7-), 2.92 x 10(-6) cm(2) s(-1), was determined using DigiSim simulations of voltammograms at a rotating disk electrode in buffered and unbuffered media at pH 3.45. The diffusion coefficients of all redox species were assumed to be identical. When the pH is greater than 6, instability of P (i.e., [alpha(2)-Fe(III)(OH)P(2)W(17)O(61)](8-)) led to the loss of the reactant and precluded lengthy experimentation.
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT783D
Publisher: CSIRO Publishing
Date: 1988
DOI: 10.1071/CH9881389
Abstract: The chemistry of higher valent ruthenium(IV) complexes has attracted considerable attention because of its possible relevance in catalytic processes and the fact that analogous iron complexes may be biologically important. In this work a range of RuII (N4)(X)(Y) complexes (N4 = nitrogen-based macrocycle or related ligand X, Y = axial ligands) has been prepared. It is shown that the presence of macrocyclic type ligands and suitable axial ligands leads to readily accessible six coordinate formally ruthenium(IV) complexes on the voltammetric time scale as ascertained by studies at platinum, gold, glassy carbon and mercury electrodes. Thus, dimethylgloxime complexes RuII ( dmgH )2(PPh3)2 and other complexes containing non- oxidizable macrocyclic type ligands readily undergo two chemically and electrochemically reversible one-electron oxidation processes to produce six coordinate ruthenium(III) and ruthenium(IV) complexes. The ruthenium(III) species are moderately stable on the synthetic time scale at ordinary temperature, whereas -78°C is required to generate low concentrations of the formally ruthenium(IV) complexes with a limited range of complexes. When the axial phosphine ligands are replaced by nitrogen and oxygen donors (N-methylimidazole , dimethyl sulfoxide , pyridine, etc.), the stability of the six-coordinate ruthenium(IV) complexes are significantly lowered as evidenced by the more complex voltammetry for the ruthenium(III)/(IV) oxidation process. Similarly, replacement of the (N4) macrocyclic type system by (N-O)2 (e.g. quinolin-8-ol as ligand ) lowers the stability of the ruthenium(IV) complexes. When the macrocyclic type ligand can itself be oxidized (e.g. benzoquinone dioxime as a ligand) four electrons can be transferred reversibly. In this case the oxidation processes are not readily assigned in terms of formal oxidation states although ruthenium(IV) still appears to be an accessible oxidation state. Electrochemical oxidation of the iron complexes, Fe( dmgH)2(P(Obu)3)2 and Fe(Pc)(P( OBu ),3)2 (Pc = phthalocyanine ), also produces two reversible one-electron oxidation processes, confirming that information derived from the more kinetically inert ruthenium systems may be applied to related iron systems on the voltammetric time scale and that macrocyclic type ligands stabilize both high oxidation state formally ruthenium(IV) and iron(IV) oxidation states.
Publisher: Springer Science and Business Media LLC
Date: 24-07-2013
Publisher: The Electrochemical Society
Date: 2009
DOI: 10.1149/1.3232246
Publisher: American Chemical Society (ACS)
Date: 17-06-2020
Publisher: American Chemical Society (ACS)
Date: 12-12-2001
DOI: 10.1021/JP0128022
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTX7PM
Publisher: No publisher found
Date: 2002
DOI: 10.5517/CC5TGL0
Publisher: American Chemical Society (ACS)
Date: 06-1981
DOI: 10.1021/AC00230A021
Publisher: Elsevier BV
Date: 06-1997
Publisher: Royal Society of Chemistry (RSC)
Date: 1991
DOI: 10.1039/AN9911600257
Publisher: American Chemical Society (ACS)
Date: 06-1997
DOI: 10.1021/IC961480R
Abstract: Detailed voltammetric studies are reported of the reduction of alpha-[S(2)Mo(18)O(62)](4)(-) at glassy carbon and platinum macro- and microdisk electrodes (stationary and rotated) in acetonitrile and in 95/5 acetonitrile/water mixtures containing 0.02 M perchloric acid. Experiments at -30 degrees C and at short time scales in acetonitrile detect eight one-electron processes in the potential range 0.1 to -2.7 V versus Fc(+)/Fc (Fc = ferrocene). The eight processes fall into four pairs. The differences in potential within each pair are remarkably constant (0.26 +/- 0.02 V), as are the separations between adjacent pairs (0.60 +/- 0.06 V). This periodicity is consistent with spin-paired [Mo(V)O](2)(&mgr -O) fragments providing a significant contribution to the overall superexchange stabilization. The influence of the following chemical reactions (primarily protonation by trace water) increases with the number of electrons added, although the five-electron reduced species [S(2)Mo(18)O(62)](9)(-) has a significant lifetime on the voltammetric time scale. In the presence of aqueous acid and at short time scales, eight chemically reversible processes are observed in the range 0 to -1.5 V in which two, two, two, two, four, four, two, and eight electrons, respectively, are transferred. The four pairs of one-electron processes found in acetonitrile occur as the first four overall two-electron reduction steps, separated by about 0.1, 0.2, and 0.3 V, respectively. Addition of a further 10 electrons occurs in a range of 0.3 V only and results in an 18-electron reduced species, stable on the voltammetric time scale. This corresponds to formal reduction of all Mo(VI) centers in alpha-[S(2)Mo(18)O(62)](4)(-) to Mo(V). The species is able to accept a further eight electrons in a series of unresolved processes.
Publisher: Wiley
Date: 16-05-2008
Publisher: Elsevier BV
Date: 03-1983
Publisher: American Chemical Society (ACS)
Date: 03-1995
DOI: 10.1021/IC00111A016
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCTM7PB
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT782C
Publisher: American Chemical Society (ACS)
Date: 07-1985
DOI: 10.1021/IC00210A006
Publisher: Wiley
Date: 21-12-2017
Abstract: In a natural geochemical cycle, manganese-oxide minerals (MnO
Publisher: American Chemical Society (ACS)
Date: 06-08-2015
DOI: 10.1021/ACS.ANALCHEM.5B01667
Abstract: The concept of using an internal reversible reference process as a calibration in the determination of fast electrode kinetics has been developed and applied with the technique of Fourier transformed large litude ac voltammetry to minimize the influence of errors arising from uncertainties in parameters such as electrode area (A), concentration (C), diffusion coefficient (D), and uncompensated resistance (Ru). Since kinetic parameters (electron transfer rate constant, k(0), and electron transfer coefficient, α) are irrelevant in the voltammetric characterization of a reversible reaction, parameters such as A, C, D, and Ru can be calibrated using the reversible process prior to quantification of the electrode kinetics associated with the fast quasi-reversible process. If required, new values of parameters derived from the calibration exercise can be used for the final determination of k(0) and α associated with the process of interest through theory-experimental comparison exercises. Reference to the reversible process is of greatest significance in diminishing the potentially large impact of systematic errors on the measurement of electrode kinetics near the reversible limit. Application of this method is demonstrated with respect to the oxidation of tetrathiafulvalene (TTF), where the TTF(0/•+) process is used as a reversible internal reference for the measurement of the quasi-reversible kinetics of the TTF(•+/2+) process. The more generalized concept is demonstrated by use of the Fc(0/+) (Fc = ferrocene) reversible process as an internal reference for measurement of the kinetics of the Cc(+/0) (Cc(+) = cobaltocenium) process. Via the internal reversible reference approach, a k(0) value of 0.55 cm s(-1) was obtained for the TTF(•+/2+) process at a glassy carbon electrode and 2.7 cm s(-1) for the Cc(+/0) one at a carbon fiber microelectrode in acetonitrile (0.1 M Bu4NPF6).
Publisher: American Chemical Society (ACS)
Date: 23-07-2009
DOI: 10.1021/JP9046769
Abstract: The preparation and characterization of a series of ionic liquids based on S-alkyl thiolonium, S-alkyl thiotetrazolium, or S-alkyl thiobenzolium cations coupled with bis(trifluoromethanesulfonyl)amide, trifluoromethanesulfonate, alkyl phosphate, chloride, and hexafluorophosphate anions are reported. All are liquid at room temperature, except the chloride salt, which has a melting point of 92 degrees C. The electrochemical characteristics of this class of ionic liquid have been determined by cyclic voltammetry. Potential windows of the ionic liquids have been obtained at glassy carbon, platinum, and gold electrodes and found to be the largest at glassy carbon, but are limited by oxidation of the thioether-functionalized cation. The voltammetry of IUPAC reference potential scale systems, ferrocene/ferrocenium, cobaltocenium/cobaltocene, and decamethylferrocene/decamethylferrocenium have been evaluated, with the last being most widely applicable. Nonadditivity of Faradaic current is found in the voltammograms of decamethylferrocene in the presence of ferrocene and cobaltocenium. Diffusion coefficient, viscosity, ionic conductivity, double layer capacitance, and other physical properties have also been measured. The dependence of the diffusion coefficient vs viscosity follows the Stokes-Einstein relationship. The properties of the ionic liquids are compared with the related imidazolium family of ionic liquids.
Publisher: American Chemical Society (ACS)
Date: 11-04-2008
DOI: 10.1021/JO702511V
Abstract: The alkylation reaction of 2-mercapto-1-methylimidazole 1a with iodoethane and chlorobutane produced S-alkylmethimazole halides 2a and 2b which were subjected to anion metathesis with two different metal salts (MA) to afford methimazole-based room-temperature ionic liquids 3a, 3b, and 3c in 82%, 85%, and 87% yields, respectively. S-Alkylation giving 2a and 2b suggests that methimazole reacts through the thione tautomer.
Publisher: Elsevier BV
Date: 06-2002
Publisher: Royal Society of Chemistry (RSC)
Date: 1990
DOI: 10.1039/AN9901501569
Abstract: The extremely sensitive catalytic hydrogen ion reduction wave observed after the formation of a platinum-formazone complex at a mercury electrode in a hydrazine-formaldehyde-H2SO4 medium has been utilised to determine platinum voltammetrically in well characterised platinum inorganic complexes (oxidation states O, II and IV) and in biological, geological and water s les. Experimental conditions have been optimised and s le-treatment procedures for various matrices have been critically evaluated for the quantification of platinum by the standard additions method. The determination of platinum in geological s les by this method has been compared with an inductively coupled plasma mass spectrometric method. Both conventional and portable field-based instrumentation have been used in the studies, and the possibility of developing a field-based method for the determination of platinum has been investigated. Despite the inherent sensitivity of the method, which enables concentrations down to 0.01 p.p.b. to be detected in simple matrices, natural levels in water and biological materials, where matrix effects suppress the voltammetric response, are often below the detection limit.
Publisher: Royal Society of Chemistry (RSC)
Date: 1999
DOI: 10.1039/A906920H
Publisher: American Chemical Society (ACS)
Date: 02-04-2009
DOI: 10.1021/JP9015849
Publisher: Wiley
Date: 05-06-2013
Publisher: The Electrochemical Society
Date: 03-2022
Abstract: Nuclear energy represents an important option for generating largely clean CO 2 -free electricity. Zirconium is a fission product in the nuclear reaction that needs to be extracted from irradiated fuels used in Gen-IV molten salt reactors. The present investigation addresses the electrochemical reduction of solution soluble Zr 4+ (soln) to surface confined Zr o (s−c) at a molybdenum electrode in a LiF—CaF 2 eutectic molten salt at 840 °C using DC cyclic, square-wave and AC voltammetry. Cyclic voltammograms simulated by the reaction scheme: Zr 4+ (soln) + 4e − → Zr o (soln) Zr o (soln) ↔ Zr* (s−c) Zr* (s−c) → Zr 4+ * (s−c) + 4e − Zr 4+ * (s−c) → Zr 4+ (soln) Zr* (s−c) + Zr 4+ (soln) ↔ 2Zr 2+ (soln) Zr 2+ (soln) ↔ Zr 2+ * (s−c) and Zr 2+ * (s−c) → Zr 4+ * (s−c) + 2e − provided excellent agreement with experimental data over the scan rate range of 50 to 500 mV s −1 . The interpretation of the simulation is that the reduction of Zr 4+ (soln) to Zr o (metal) takes place via a transiently soluble Zr o (soln) in an overall 4-electron essentially reversible diffusion-controlled process having a reversible formal potential (E o f ) of −1.22 V (vs Pt). A minor oxidation process observed at −0.455 V (vs Pt) on the reversing the potential scan direction is simulated via the reaction step Zr (s−c) + Zr 4+ (soln) ↔ 2Zr 2+ (s−c) followed by Zr 2+ (s−c) → Zr 4+ (sol) + 2e − . The sharply rising initial component where reduction of Zr 4+ (sol) commences, contains evidence of a nucleation-growth mechanism associated with the electrocrystallisation of zirconium metal. This initial rapid growth of current is not fully accommodated in the simulations, but all features found beyond the peak potential are supported by the theory. A comparison with theory based on a direct reduction of Zr 4+ (soln) to the metallic state having unit activity is provided. It is proposed that an analogous mechanism applies at a Ni electrode, except that a Ni-Zr alloy formation occurs instead of Zr metal.
Publisher: Springer Science and Business Media LLC
Date: 15-10-2008
Publisher: Elsevier BV
Date: 08-1992
Publisher: Elsevier BV
Date: 02-2008
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT785G
Publisher: Wiley
Date: 21-04-2015
Publisher: American Chemical Society (ACS)
Date: 11-1988
DOI: 10.1021/AC00172A026
Publisher: Royal Society of Chemistry (RSC)
Date: 1997
DOI: 10.1039/A702632C
Abstract: The gold AuIII + 3e(-)-->Au0 reduction and Au0-->AuIII + 3e- oxidation stripping processes in dilute aqua regia electrolyte (0.1 M HCl + 0.32 M HNO3) were examined at platinum, rhodium, iridium, gold and glassy carbon disk electrodes. After ascertaining that the preferred material was platinum, the effect of electrode size was evaluated by using nine different platinum disk electrodes having diameters ranging from 2 to 2000 microns. The optimum analytical response was obtained with a 50 microns diameter platinum disk electrode. With this electrode diameter, a sharp symmetrical gold stripping peak was obtained and the deposition process occurred predominantly under conditions of radial diffusion so that stirring of the solution was not required. In contrast, larger sized platinum electrodes produced a broader, asymmetric stripping response for the gold oxidation peak, whereas electrodes of smaller diameter provided poorer signal-to-noise ratios. The limit of detection and limit of quantification were calculated to be 4.4 x 10(-7) M (86 ppb) and 13.1 x 10(-7) M (258 ppb), respectively, at the 50 microns diameter platinum disk electrode under conditions of linear sweep stripping voltammetry at a scan rate of 200 mV s-1 and a 140 s deposition time. The optimum electrode gave a very well defined gold oxidation signal with negligible background current when applied to the determination of gold in a gold ore s le.
Publisher: No publisher found
Date: 2012
DOI: 10.5517/CCTX7RP
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TA00023A
Abstract: An urchin-like sulphide-derived bismuth electrocatalyst was synthesised for CO 2 reduction and a maximum of 84.0% faradaic efficiency for formate formation was achieved. The origin of the activity of the sulphide-derived bismuth catalyst was explored and its defect-rich structure was responsible for the high formate selectivity.
Publisher: American Chemical Society (ACS)
Date: 05-1983
DOI: 10.1021/IC00153A017
Publisher: No publisher found
Date: 2011
DOI: 10.5517/CCSF17G
Publisher: American Chemical Society (ACS)
Date: 07-1983
DOI: 10.1021/J100237A012
Publisher: American Chemical Society (ACS)
Date: 02-2010
DOI: 10.1021/IC9025238
Abstract: The oxidative electrochemistry of [CpFe(CO)(2)](2), 1 (Cp = [eta(5)-C(5)H(5)](-)), was examined in detail in ionic liquids (ILs) composed of ions of widely varying Lewis acid-base properties. Cyclic voltammetric responses were strongly dependent on the nucleophilic properties of the IL anion, but all observations are consistent with the initial formation of 1(+) followed by attack from the IL anion. In [NTf(2)](-)-based ILs ([NTf(2)](-) = bis(trifluoromethylsulfonyl)amide), the process shows nearly ideal chemical reversibility as the reaction between 1(+) and [NTf(2)](-) is very slow. This is highly significant, as 1(+) is known to be highly susceptible to nucleophilic attack and its stability indicates a remarkable lack of coordinating ability of these ILs. In 1-methyl-3-butylimidazolium hexafluorophosphate, [bmim][PF(6)], the oxidation of 1 is still largely reversible, but there is more pronounced evidence of [PF(6)](-) coordination. In contrast, 1 exhibits an irreversible two-electron oxidation process in a dicyanamide-based IL. This overall oxidation process is thought to proceed via an ECE mechanism, details of which are presented. Rate constants were estimated by fitting the experimental data to digital simulations of the proposed mechanism. The use of [NTf(2)](-)-based ILs as a supporting electrolyte in CH(2)Cl(2) was examined by using this solvent/electrolyte as a medium in which to perform bulk electrolyses of 1 and 1*, the permethylated analogue [Cp*Fe(CO)(2)](2) (Cp* = [eta(5)-C(5)(CH(3))(5)](-)). These cleanly yielded the corresponding binuclear radical-cation species, 1(+) and 1*(+), which were subsequently characterized by electron paramagnetic resonance (EPR) spectroscopy. In addition to the above oxidation studies, the reduction of 1 was studied in each of the ILs differences in cathodic peak potentials are attributed, in part, to ion-pairing effects. This study illustrates the wide range of electrochemical environments available with ILs and demonstrates their utility for the investigation of the redox properties of metal carbonyls and other organometallic compounds.
Publisher: American Chemical Society (ACS)
Date: 04-2002
DOI: 10.1021/LA00060A046
Publisher: No publisher found
Date: 2010
DOI: 10.5517/CCT784F
Publisher: American Chemical Society (ACS)
Date: 07-1984
DOI: 10.1021/AC00272A007
No related grants have been discovered for Alan Bond.