ORCID Profile
0000-0003-2525-3162
Current Organisation
University of Wollongong
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Structural Chemistry and Spectroscopy | Physical Chemistry (Incl. Structural) | Analytical Spectrometry | Reaction Kinetics and Dynamics | Physical Chemistry not elsewhere classified | Chemical Thermodynamics and Energetics | Chemical Thermodynamics And Energetics | Structural Chemistry | Chemical Spectroscopy | Free Radical Chemistry | Food Chemistry and Molecular Gastronomy (excl. Wine) | Physical Organic Chemistry | Structural Biology (incl. Macromolecular Modelling) | Industrial Chemistry | Analytical Chemistry | Organic Chemistry | Bioinorganic Chemistry | Chemotherapy | Inorganic Geochemistry | Medical Biochemistry and Metabolomics | Chemical Engineering not elsewhere classified | Soil Chemistry (excl. Carbon Sequestration Science) | Crop and Pasture Biochemistry and Physiology | Medical Biochemistry: Proteins and Peptides (incl. Medical Proteomics) | Medical Biochemistry: Lipids | Medical Biochemistry: Inorganic Elements and Compounds | Analytical Biochemistry | Atomic and Molecular Physics
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Medical and Health Sciences | Atmospheric Processes and Dynamics | Management of Liquid Waste from Mineral Resource Activities (excl. Water) | Management of Solid Waste from Mineral Resource Activities | Inorganic Industrial Chemicals | Chemical sciences | Renewable energy not elsewhere classified (e.g. geothermal) | Mining and Extraction of Precious (Noble) Metal Ores | Occupational Health | Expanding Knowledge in History and Archaeology | Energy Transformation not elsewhere classified | Urban and Industrial Air Quality | Energy Conservation and Efficiency in Transport | Paints | Human Pharmaceutical Treatments (e.g. Antibiotics) | Expanding Knowledge in the Environmental Sciences | Expanding Knowledge in the Earth Sciences | Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering | Scientific Instruments | Expanding Knowledge in the Agricultural and Veterinary Sciences | Expanding Knowledge in the Biological Sciences |
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Publications
Reaction of the C2H Radical with 1-Butyne (C4H6): Low-Temperature Kinetics and Isomer-Specific Product Detection
Publisher: American Chemical Society (ACS)
Date: 08-02-2010
DOI: 10.1021/JP911132R
Abstract: The rate coefficient for the reaction of the ethynyl radical (C(2)H) with 1-butyne (H-C[triple bond]C-CH(2)-CH(3)) is measured in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by laser photolysis of acetylene (C(2)H(2)) at 193 nm and detected via chemiluminescence (C(2)H + O(2) --> CH (A(2)Delta) + CO(2)). The rate coefficients are measured over the temperature range of 74-295 K. The C(2)H + 1-butyne reaction exhibits no barrier and occurs with rate constants close to the collision limit. The temperature-dependent rate coefficients can be fit within experimental uncertainties by the expression k = (2.4 +/- 0.5) x 10(-10)(T/295 K)(-(0.04+/-0.03)) cm(3) molecule(-1) s(-1). Reaction products are detected at room temperature (295 K) and 533 Pa using a multiplexed photoionization mass spectrometer (MPIMS) coupled to the tunable vacuum ultraviolet synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. Two product channels are identified for this reaction: m/z = 64 (C(5)H(4)) and m/z = 78 (C(6)H(6)) corresponding to the CH(3)-loss and H-loss channels, respectively. Photoionization efficiency (PIE) curves are used to analyze the isomeric composition of both product channels. The C(5)H(4) products are found to be exclusively linear isomers composed of ethynylallene and methyldiacetylene in a 4:1 ratio. In contrast, the C(6)H(6) product channel includes two cyclic isomers, fulvene 18(+/-5)% and 3,4-dimethylenecyclobut-1-ene (DMCB) 32(+/-8)%, as well as three linear isomers, 2-ethynyl-1,3-butadiene 8(+/-5)%, 3,4-hexadiene-1-yne 28(+/-8)%, and 1,3-hexadiyne 14(+/-5)%. Within experimental uncertainties, we do not see appreciable amounts of benzene and an upper limit of 10% is estimated. Diacetylene (C(4)H(2)) formation via the C(2)H(5)-loss channel is also thermodynamically possible but cannot be observed due to experimental limitations. The implications of these results for modeling of planetary atmospheres, especially of Saturn's largest moon Titan and the relationships to combustion reactions, are discussed.
Gas phase reactions of iodide and bromide anions with ozone: evidence for stepwise and reversible reactions
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0CP01498B
Abstract: Ion-trap mass spectrometry maps the discrete steps in the reaction of I − and Br − with gaseous ozone.
Comment on the Ionization Energy of B2F4
Publisher: American Chemical Society (ACS)
Date: 28-08-2012
DOI: 10.1021/JP306150U
Direct Observation of Photodissociation Products from Phenylperoxyl Radicals Isolated in the Gas Phase
Publisher: American Chemical Society (ACS)
Date: 07-06-2013
DOI: 10.1021/JA402610S
Abstract: Gas phase peroxyl radicals are central to our chemical understanding of combustion and atmospheric processes and are typically characterized by strong absorption in the UV (λ(max) ≈ 240 nm). The analogous maximum absorption feature for arylperoxyl radicals is predicted to shift to the visible but has not previously been characterized nor have any photoproducts arising from this transition been identified. Here we describe the controlled synthesis and isolation in vacuo of an array of charge-substituted phenylperoxyl radicals at room temperature, including the 4-(N,N,N-trimethylammonium)methyl phenylperoxyl radical cation (4-Me3N([+])CH2-C6H4OO(•)), using linear ion-trap mass spectrometry. Photodissociation mass spectra obtained at wavelengths ranging from 310 to 500 nm reveal two major photoproduct channels corresponding to homolysis of aryl-OO and arylO-O bonds resulting in loss of O2 and O, respectively. Combining the photodissociation yields across this spectral window produces a broad (FWHM ≈ 60 nm) but clearly resolved feature centered at λ(max) = 403 nm (3.08 eV). The influence of the charge-tag identity and its proximity to the radical site are investigated and demonstrate no effect on the identity of the two dominant photoproduct channels. Electronic structure calculations have located the vertical B ← X transition of these substituted phenylperoxyl radicals within the experimental uncertainty and further predict the analogous transition for unsubstituted phenylperoxyl radical (C6H5OO(•)) to be 457 nm (2.71 eV), nearly 45 nm shorter than previous estimates and in good agreement with recent computational values.
Ultraviolet and vacuum ultraviolet photo-processing of protonated benzonitrile (C6H5CNH+)
Publisher: EDP Sciences
Date: 2022
DOI: 10.1051/0004-6361/202142206
Abstract: Context. The recent detection in pre-stellar sources of cyano-substituted and pure hydrocarbon cycles has emphasized the importance of aromatic chemistry in the earliest stages of star formation. Ultraviolet (UV) and vacuum-UV (VUV) radiation is ubiquitous in space and thus the photo-processing of small cyclic ions may open a window onto rich chemical networks and lead to the formation of larger aromatics in space. Aims. The aim is to investigate the fate of protonated benzonitrile species after UV and VUV photoexcitation and the subsequent potential impact on stellar and interstellar chemistry. Methods. Protonated benzonitrile was isolated in a linear ion trap prior to irradiation with UV and VUV radiation (4.5–13.6 eV) from the DESIRS beamline at synchrotron SOLEIL. The study was extended down to 3.5 eV using a cryogenic Paul ion trap coupled to an OPO laser at the PIIM laboratory. Photodissociation action spectra were obtained by monitoring the photofragment yields as a function of photon energy. Results. The UV/VUV photodissociation action spectra of protonated benzonitrile show structured bands from 3.8 to 9 eV. The primary dissociation channel of protonated benzonitrile corresponds to HCN/HNC loss and formation of the phenylium cation (C 6 H 5 + ) whereas at high energies, a minor channel is observed that correlates with HC 3 N loss and formation of C 4 H 5 + . Conclusions. The UV and VUV photodestruction of protonated benzonitrile leads to the formation of a highly reactive cationic species, C 6 H 5 + , predicted to be an important precursor of larger aromatic molecules in space, such as polycyclic aromatic hydrocarbons. The inclusion of C 6 H 5 + – a precursor of benzene and, by extension, of benzonitrile – as the result of formation via the photodissociation of protonated benzonitrile in current astrochemical models could improve the predicted abundance of benzonitrile, which is currently underestimated.
Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus , with comparisons to other Scombroidei
Publisher: Wiley
Date: 17-12-2018
DOI: 10.1002/JMOR.20919
Abstract: Atlantic Cutlassfish, Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger-shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro-CT scanning to study 92 specimens of T. lepturus from the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement in T. lepturus depending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement in T. lepturus to 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions.
Infrared Laser Desorption of Hydroquinone from a Water−Ethanol Liquid Beam
Publisher: American Chemical Society (ACS)
Date: 19-07-2003
DOI: 10.1021/JP022248B
Structural elucidation of hydroxy fatty acids by photodissociation mass spectrometry with photolabile derivatives
Publisher: Wiley
Date: 13-03-2020
DOI: 10.1002/RCM.8741
Mass Spectrometry Imaging of Lipids Using MALDI Coupled with Plasma-Based Post-Ionization on a Trapped Ion Mobility Mass Spectrometer
Publisher: American Chemical Society (ACS)
Date: 06-12-2022
Protonation Isomer Specific Ion–Molecule Radical Reactions
Publisher: American Chemical Society (ACS)
Date: 20-06-2023
DOI: 10.1021/JACS.3C02552
Direct Observation of para-Xylylene as the Decomposition Product of the meta-Xylyl Radical Using VUV Synchrotron Radiation
Publisher: American Chemical Society (ACS)
Date: 22-07-2013
DOI: 10.1021/JZ401207Z
Enhanced Sensitivity Using MALDI Imaging Coupled with Laser Postionization (MALDI-2) for Pharmaceutical Research
Publisher: American Chemical Society (ACS)
Date: 29-07-2019
Chemically activated reactions on the C7 H5 energy surface: Propargyl + diacetylene, i-C5 H3 + acetylene, and n-C5 H3 + acetylene
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CP20112C
Abstract: This study uses computational chemistry and statistical reaction rate theory to investigate the chemically activated reaction of diacetylene (butadiyne, C(4)H(2)) with the propargyl radical (C˙H(2)CCH) and the reaction of acetylene (C(2)H(2)) with the i-C(5)H(3) (CH(2)CCCC˙H) and n-C(5)H(3) (CHCC˙HCCH) radicals. A detailed G3SX-level C(7)H(5) energy surface demonstrates that the C(3)H(3) + C(4)H(2) and C(5)H(3) + C(2)H(2) addition reactions proceed with moderate barriers, on the order of 10 to 15 kcal mol(-1), and form activated open-chain C(7)H(5) species that can isomerize to the fulvenallenyl radical with the highest barrier still significantly below the entrance channel energy. Higher-energy pathways are available leading to other C(7)H(5) isomers and to a number of C(7)H(4) species + H. Rate constants in the large multiple-well (15) multiple-channel (30) chemically activated system are obtained from a stochastic solution of the one-dimensional master equation, with RRKM theory for microcanonical rate constants. The dominant products of the C(4)H(2) + C(3)H(3) reaction at combustion-relevant temperatures and pressures are i-C(5)H(3) + C(2)H(2) and CH(2)CCHCCCCH + H, along with several quenched C(7)H(5) intermediate species below 1500 K. The major products in the n-C(5)H(3) + C(2)H(2) reaction are i-C(5)H(3) + C(2)H(2) and a number of C(7)H(4) species + H, with C(7)H(5) radical stabilization at lower temperatures. The i-C(5)H(3) + C(2)H(2) reaction predominantly leads to C(7)H(4) + H and to stabilized C(7)H(5) products. The title reactions may play an important role in polycyclic aromatic hydrocarbon (PAH) formation in combustion systems. The C(7)H(5) potential energy surface developed here also provides insight into several other important reacting gas-phase systems relevant to combustion and astrochemistry, including C(2)H + the C(3)H(4) isomers propyne and allene, benzyne + CH, benzene + C((3)P), and C(7)H(5) radical decomposition, for which some preliminary analysis is presented.
Pyrolysis of fulvenallene (C7H6) and fulvenallenyl (C7H5): Theoretical kinetics and experimental product detection
Publisher: Elsevier BV
Date: 12-2011
Ultraviolet photodissociation action spectroscopy of gas-phase protonated quinoline and isoquinoline cations
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP02035B
Abstract: Gas-phase two-photon UV action spectra of protonated quinoline and isoquinoline cations are reported revealing two broad, vibrationally-structured electronic bands and multiple photoproduct channels.
The combination of laser photodissociation, action spectroscopy, and mass spectrometry to identify and separate isomers
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CC02101C
Abstract: The separation and detection of isomers remains a challenge for many areas of mass spectrometry. This article highlights laser photodissociation and ion mobility strategies that have been recently deployed to meet this challenge with focus on small molecule isomers including protonation isomers, structural isomers, conformation isomers and new studies emerging on chiral isomers. Laser techniques span UV and visible laser photodissociation, time-resolved pump-probe schemes and application of laser hole-burning arrangements to assign isomers within selected ion populations. Also surveyed are applications of ion mobility strategies to separate isomers followed by laser spectroscopic techniques to assign the separated ions. Ultimately, with ongoing refinement in hardware and methods, there are clear pathways forward for laser and mass spectrometry techniques to make decisive breakthroughs in understanding how isomeric details affect biological processes, physiology and disease.
Photo and Collision Induced Isomerization of a Cyclic Retinal Derivative: An Ion Mobility Study
Publisher: American Chemical Society (ACS)
Date: 08-06-2016
DOI: 10.1007/S13361-016-1427-8
Abstract: A cationic degradation product, formed in solution from retinal Schiff base (RSB), is examined in the gas phase using ion mobility spectrometry, photoisomerization action spectroscopy, and collision induced dissociation (CID). The degradation product is found to be N-n-butyl-2-(β-ionylidene)-4-methylpyridinium (BIP) produced through 6π electrocyclization of RSB followed by protonation and loss of dihydrogen. Ion mobility measurements show that BIP exists as trans and cis isomers that can be interconverted through buffer gas collisions and by exposure to light, with a maximum response at λ = 420 nm.Graphical Abstract.
Observation of nondegenerate cavity modes for a distorted polystyrene microsphere
Publisher: Optica Publishing Group
Date: 15-07-2006
DOI: 10.1364/OL.31.002211
Abstract: Nondegenerate azimuthal morphology-dependent resonances are observed for a distorted, fluorescently labeled polystyrene microsphere levitated in a quadrupole ion trap. Modeling the in idual resonances by using perturbation theory allows a determination of quadrupole and octupole distortion parameters. The particle's shape changes slowly over the course of the measurement and eventually becomes spherical. The morphological changes are facilitated by laser heating of the particle above the polystyrene glass transition temperature. We demonstrate a method of transforming a trapped particle to a sphere and rendering its azimuthal modes degenerate.
Drop-on-demand microdroplet generation: A very stable platform for single-droplet experimentation
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6RA08472A
Abstract: This paper reports the performance of drop-on-demand piezo-activated microdroplet generation, investigated using microdroplet cavity enhanced fluorescence spectroscopy.
Preparation of an ion with the highest calculated proton affinity: ortho-diethynylbenzene dianion
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6SC01726F
Abstract: Owing to the increased proton affinity that results from additional negative charges, multiply-charged anions are shown as a route to preparing powerful ‘superbases’.
Reactivity Trends in the Gas-Phase Addition of Acetylene to the N-Protonated Aryl Radical Cations of Pyridine, Aniline, and Benzonitrile
Publisher: American Chemical Society (ACS)
Date: 14-01-2021
Selective Mass Spectrometry Imaging of Aromatic Antioxidants Using Sequential Matrix‐Assisted Laser Desorption and Resonant Photoionisation
Publisher: Wiley
Date: 04-12-2021
Abstract: Matrix‐assisted laser/desorption ionisation‐mass spectrometry imaging (MALDI‐MSI) enables label‐free imaging of biomolecules in biological tissues. However, many molecules remain undetected due to their poor ionisation efficiencies. These poor ionisation efficiencies practically limit spatial resolution. Herein, we address this challenge for aromatic antioxidants by reporting an innovative approach involving sequential matrix‐assisted laser desorption and two‐photon ionisation of desorbed neutrals. It is shown that ion yields increase with reduced s ling areas obtained using sub‐threshold primarily laser fluence. This counterintuitive observation could arise from a reduction in radical/ion neutralisation reactions within the sparse plume and/or favorable molecular desorption under low fluence conditions. The utility of this approach is demonstrated for imaging tocopherols and ubiquinols in mouse brain and prostate cancer tissue. This can pave the way for improved sensitivity in MSI experiments at cellular and sub‐cellular resolutions.
Product Detection of the CH Radical Reaction with Acetaldehyde
Publisher: American Chemical Society (ACS)
Date: 31-01-2012
DOI: 10.1021/JP2113126
Abstract: The reaction of the methylidyne radical (CH) with acetaldehyde (CH(3)CHO) is studied at room temperature and at a pressure of 4 Torr (533.3 Pa) using a multiplexed photoionization mass spectrometer coupled to the tunable vacuum ultraviolet synchrotron radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory. The CH radicals are generated by 248 nm multiphoton photolysis of CHBr(3) and react with acetaldehyde in an excess of helium and nitrogen gas flow. Five reaction exit channels are observed corresponding to elimination of methylene (CH(2)), elimination of a formyl radical (HCO), elimination of carbon monoxide (CO), elimination of a methyl radical (CH(3)), and elimination of a hydrogen atom. Analysis of the photoionization yields versus photon energy for the reaction of CH and CD radicals with acetaldehyde and CH radical with partially deuterated acetaldehyde (CD(3)CHO) provides fine details about the reaction mechanism. The CH(2) elimination channel is found to preferentially form the acetyl radical by removal of the aldehydic hydrogen. The insertion of the CH radical into a C-H bond of the methyl group of acetaldehyde is likely to lead to a C(3)H(5)O reaction intermediate that can isomerize by β-hydrogen transfer of the aldehydic hydrogen atom and dissociate to form acrolein + H or ketene + CH(3), which are observed directly. Cycloaddition of the radical onto the carbonyl group is likely to lead to the formation of the observed products, methylketene, methyleneoxirane, and acrolein.
Branching Fractions of the CN + C3H6 Reaction Using Synchrotron Photoionization Mass Spectrometry: Evidence for the 3-Cyanopropene Product
Publisher: American Chemical Society (ACS)
Date: 28-10-2011
DOI: 10.1021/JP208496R
Abstract: The gas-phase CN + propene reaction is investigated using synchrotron photoionization mass spectrometry (SPIMS) over the 9.8-11.5 eV photon energy range. Experiments are conducted at room temperature in 4 Torr of He buffer gas. The CN + propene addition reaction produces two distinct product mass channels, C(3)H(3)N and C(4)H(5)N, corresponding to CH(3) and H elimination, respectively. The CH(3) and H elimination channels are measured to have branching fractions of 0.59 ± 0.15 and 0.41 ± 0.10, respectively. The absolute photoionization cross sections between 9.8 and 11.5 eV are measured for the three considered H-elimination coproducts: 1-, 2-, and 3-cyanopropene. Based on fits using the experimentally measured photoionization spectra for the C(4)H(5)N mass channel and contrary to the previous study (Int. J. Mass. Spectrom.2009, 280, 113-118), where it was concluded that 3-cyanopropene was not a significant product, the new data suggests 3-cyanopropene is produced in significant quantity along with 1-cyanopropene, with isomer branching fractions from this mass channel of 0.50 ± 0.12 and 0.50 ± 0.24, respectively. However, similarities between the 1-, 2-, and 3-cyanopropene photoionization spectra make an unequivocal assignment difficult based solely on photoionization spectra. The CN + CH(2)CHCD(3) reaction is studied and shows, in addition to the H-elimination product signal, a D-elimination product channel (m/z 69, consistent with CH(2)CHCD(2)CN), providing further evidence for the formation of the 3-cyanopropene reaction product.
Dissociation of proton-bound complexes reveals geometry and arrangement of double bonds in unsaturated lipids
Publisher: Elsevier BV
Date: 11-2015
Does Addition of NO2 to Carbon-Centered Radicals Yield RONO or RNO2? An Investigation Using Distonic Radical Ions
Publisher: American Chemical Society (ACS)
Date: 23-02-2013
DOI: 10.1007/S13361-012-0549-X
Abstract: Nitrogen dioxide is used as a "radical scavenger" to probe the position of carbon-centered radicals within complex radical ions in the gas phase. As with analogous neutral radical reactions, this addition results in formation of an [M + NO2](+) adduct, but the structural identity of this species remains ambiguous. Specifically, the question remains: do such adducts have a nitro- (RNO2) or nitrosoxy- (RONO) moiety, or are both isomers present in the adduct population? In order to elucidate the products of such reactions, we have prepared and isolated three distonic phenyl radical cations and observed their reactions with nitrogen dioxide in the gas phase by ion-trap mass spectrometry. In each case, stabilized [M + NO2](+) adduct ions are observed and isolated. The structure of these adducts is probed by collision-induced dissociation and ultraviolet photodissociation action spectroscopy and a comparison made to the analogous spectra of authentic nitro- and nitrosoxy-benzenes. We demonstrate unequivocally that for the phenyl radical cations studied here, all stabilized [M + NO2](+) adducts are exclusively nitrobenzenes. Electronic structure calculations support these mass spectrometric observations and suggest that, under low-pressure conditions, the nitrosoxy-isomer is unlikely to be isolated from the reaction of an alkyl or aryl radical with NO2. The combined experimental and theoretical results lead to the prediction that stabilization of the nitrosoxy-isomer will only be possible for systems wherein the energy required for dissociation of the RO-NO bond (or other low energy fragmentation channels) rises close to, or above, the energy of the separated reactants.
Solvent-Mediated Proton-Transfer Catalysis of the Gas-Phase Isomerization of Ciprofloxacin Protomers
Publisher: American Chemical Society (ACS)
Date: 11-01-2022
Abstract: Understanding how neutral molecules become protonated during positive-ion electrospray ionization (ESI) mass spectrometry is critically important to ensure analytes can be efficiently ionized, detected, and unambiguously identified. The ESI solvent is one of several parameters that can alter the dominant site of protonation in polyfunctional molecules and thus, in turn, can significantly change the collision-induced dissociation (CID) mass spectra relied upon for compound identification. Ciprofloxacin─a common fluoroquinolone antibiotic─is one such ex le whereby positive-ion ESI can result in gas-phase [M + H]
Photodissociation of TEMPO-modified peptides: new approaches to radical-directed dissociation of biomolecules
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3CP54825B
Abstract: Radical-directed dissociation of gas phase ions is emerging as a powerful and complementary alternative to traditional tandem mass spectrometric techniques for biomolecular structural analysis. Previous studies have identified that coupling of 2-[(2,2,6,6-tetramethylpiperidin-1-oxyl)methyl]benzoic acid (TEMPO-Bz) to the N-terminus of a peptide introduces a labile oxygen-carbon bond that can be selectively activated upon collisional activation to produce a radical ion. Here we demonstrate that structurally-defined peptide radical ions can also be generated upon UV laser photodissociation of the same TEMPO-Bz derivatives in a linear ion-trap mass spectrometer. When subjected to further mass spectrometric analyses, the radical ions formed by a single laser pulse undergo identical dissociations as those formed by collisional activation of the same precursor ion, and can thus be used to derive molecular structure. Mapping the initial radical formation process as a function of photon energy by photodissociation action spectroscopy reveals that photoproduct formation is selective but occurs only in modest yield across the wavelength range (300-220 nm), with the photoproduct yield maximised between 235 and 225 nm. Based on the analysis of a set of model compounds, structural modifications to the TEMPO-Bz derivative are suggested to optimise radical photoproduct yield. Future development of such probes offers the advantage of increased sensitivity and selectivity for radical-directed dissociation.
Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP53690D
Abstract: The reactions of distonic 4-(N,N,N-trimethylammonium)-2-methylphenyl and 5-(N,N,N-trimethylammonium)-2-methylphenyl radical cations (m/z 149) with O2 are studied in the gas phase using ion-trap mass spectrometry. Photodissociation (PD) of halogenated precursors gives rise to the target distonic charge-tagged methylphenyl radical whereas collision-induced dissociation (CID) is found to produce unreactive radical ions. The PD generated distonic radicals, however, react rapidly with O2 to form [M + O2]˙(+) and [M + O2- OH]˙(+) ions, detected at m/z 181 and m/z 164, respectively. Quantum chemical calculations using G3SX(MP3) and M06-2X theories are deployed to examine key decomposition pathways of the 5-(N,N,N-trimethylammonium)-2-methylphenylperoxyl radical and rationalise the observed product ions. The prevailing product mechanism involves a 1,5-H shift in the peroxyl radical forming a QOOH-type intermediate that subsequently eliminates ˙OH to yield charge-tagged 2-quinone methide. Our study suggests that the analogous process should occur for the neutral methylphenyl + O2 reaction, thus serving as a plausible source of ˙OH radicals in combustion environments.
Reactions of a distonic peroxyl radical anion influenced by SOMO–HOMO conversion: an example of anion-directed channel switching
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9CP05989J
Abstract: Deprotonation of a remote site in a peroxyl radical energetically buries the singly occupied molecular orbital, suppressing radical-driven oxidation and promoting reactions involving the anion site.
Unimolecular reaction chemistry of a charge-tagged beta-hydroxyperoxyl radical
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CP02981J
Abstract: The study of unimolecular isomerization and decomposition of a charge-tagged β-hydroxyperoxyl radical anion ˙CH 2 C(OH)(CH 3 )CH 2 C(O)O − using mass spectrometry, quantum mechanical calculations and master equation kinetic simulations.
Introduction of a Fixed-Charge, Photolabile Derivative for Enhanced Structural Elucidation of Fatty Acids
Publisher: American Chemical Society (ACS)
Date: 12-07-2019
DOI: 10.1021/ACS.ANALCHEM.9B01566
Abstract: Fatty acids are a structurally erse category of lipids with a myriad of biochemical functions, which includes their role as building blocks of more complex lipids (e.g., glycerophospholipids and triacylglycerols). Increasingly, the analysis of fatty acids is undertaken using liquid chromatography-mass spectrometry (LC-MS), due to its versatility in the detection of lipids across a wide range of concentrations and ersity of molecular structures and masses. Previous work has shown that fixed-charge pyridinium derivatives are effective in enhancing the detection of fatty acids in LC-MS workflows. Herein, we describe the development of two novel pyridinium fixed-charged derivatization reagents that incorporate a photolabile aryl iodide that is selectively activated by laser irradiation inside the mass spectrometer. Photodissociation mass spectra of fatty acids conjugated to 1-(3-(aminomethyl)-4-iodophenyl)pyridin-1-ium (4-I-AMPP
Isolation and characterization of charge-tagged phenylperoxyl radicals in the gas phase: direct evidence for products and pathways in low temperature benzene oxidation
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CP43507A
Abstract: The phenylperoxyl radical has long been accepted as a critical intermediate in the oxidation of benzene and an archetype for arylperoxyl radicals in combustion and atmospheric chemistry. Despite being central to many contemporary mechanisms underpinning these chemistries, reports of the direct detection or isolation of phenylperoxyl radicals are rare and there is little experimental evidence connecting this intermediate with expected product channels. We have prepared and isolated two charge-tagged phenyl radical models in the gas phase [i.e., 4-(N,N,N-trimethylammonium)phenyl radical cation and 4-carboxylatophenyl radical anion] and observed their reactions with dioxygen by ion-trap mass spectrometry. Measured reaction rates show good agreement with prior reports for the neutral system (k(2)[(Me(3)N(+))C(6)H(4)˙ + O(2)] = 2.8 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 4.9% k(2)[((-)O(2)C)C(6)H(4)˙ + O(2)] = 5.4 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 9.2%) and the resulting mass spectra provide unequivocal evidence for the formation of phenylperoxyl radicals. Collisional activation of isolated phenylperoxyl radicals reveals unimolecular decomposition by three pathways: (i) loss of dioxygen to reform the initial phenyl radical (ii) loss of atomic oxygen yielding a phenoxyl radical and (iii) ejection of the formyl radical to give cyclopentadienone. Stable isotope labeling confirms these assignments. Quantum chemical calculations for both charge-tagged and neutral phenylperoxyl radicals confirm that loss of formyl radical is accessible both thermodynamically and entropically and competitive with direct loss of both hydrogen atom and carbon dioxide.
Rapid differentiation of isomeric lipids by photodissociation mass spectrometry of fatty acid derivatives
Publisher: Wiley
Date: 18-02-2013
DOI: 10.1002/RCM.6503
Abstract: Both traditional electron ionization and electrospray ionization tandem mass spectrometry have demonstrated limitations in the unambiguous identification of fatty acids. In the former case, high electron energies lead to extensive dissociation of the radical cations from which little specific structural information can be obtained. In the latter, conventional collision-induced dissociation (CID) of even-electron ions provides little intra-chain fragmentation and thus few structural diagnostics. New approaches that harness the desirable features of both methods, namely radical-driven dissociation with discrete energy deposition, are thus required. Herein we describe the derivatization of a structurally erse suite of fatty acids as 4-iodobenzyl esters (FAIBE). Electrospray ionization of these derivatives in the presence of sodium acetate yields abundant [M + Na](+) ions that can be mass-selected and subjected to laser irradiation (λ = 266 nm) on a modified linear ion-trap mass spectrometer. Photodissociation (PD) of the FAIBE derivatives yields abundant radical cations by loss of atomic iodine and in several cases selective dissociation of activated carbon-carbon bonds (e.g., at allylic positions) are also observed. Subsequent CID of the [M + Na - I](•+) radical cations yields radical-directed dissociation (RDD) mass spectra that reveal extensive carbon-carbon bond dissociation without scrambling of molecular information. Both PD and RDD spectra obtained from derivatized fatty acids provide a wealth of structural information including the position(s) of unsaturation, chain-branching and hydroxylation. The structural information obtained by this approach, in particular the ability to rapidly differentiate isomeric lipids, represents a useful addition to the lipidomics tool box.
Electrostatically Tuning the Photodissociation of the Irgacure 2959 Photoinitiator in the Gas Phase by Cation Binding
Publisher: American Chemical Society (ACS)
Date: 11-01-2021
DOI: 10.1021/JACS.0C11978
An intermediate band dye-sensitised solar cell using triplet–triplet annihilation
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP04825G
Abstract: A new mechanism of charge photogeneration is demonstrated for the first time, based on organic molecular structures.
Accelerating Ozonolysis Reactions Using Supplemental RF-Activation of Ions in a Linear Ion Trap Mass Spectrometer
Publisher: American Chemical Society (ACS)
Date: 24-02-2022
DOI: 10.1021/ACS.ANALCHEM.1C04915
Abstract: Gas-phase ion-molecule reactions provide structural insights across a range of analytical applications. A hindrance to the wider use of ion-molecule reactions is that they are relatively slow compared to other ion activation modalities and can thereby impose a bottleneck on the time required to analyze each s le. Here we describe a method for accelerating the rate of ion-molecule reactions involving ozone, implemented by supplementary RF-activation of mass-selected ions within a linear ion trap. Reaction rate accelerations between 15-fold (for ozonolysis of alkenes in ionised lipids) and 90-fold (for ozonation of halide anions) are observed compared to thermal conditions. These enhanced reaction rates with ozone increase s le throughput, aligning the reaction time with the overall duty cycle of the mass spectrometer. We demonstrate that the acceleration is due to the supplementary RF-activation surmounting the activation barrier energy of the entrance channel of the ion-molecule reaction. This rate acceleration is subsequently shown to aid identification of new, low abundance lipid isomers and enables an equivalent increase in the number of lipid species that can be analyzed.
Next-generation derivatization reagents optimized for enhanced product ion formation in photodissociation-mass spectrometry of fatty acids
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0AN01840F
Abstract: Next-generation derivatives for photodissociation-mass spectrometry for fatty acids generating photoproduct yields of up to 97% at 266 nm.
Mass spectrometry-directed structure elucidation and total synthesis of ultra-long chain (O-acyl)-ω-hydroxy fatty acids
Publisher: Elsevier BV
Date: 08-2018
DOI: 10.1194/JLR.M086702
Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics
Publisher: American Chemical Society (ACS)
Date: 31-12-2009
DOI: 10.1021/JP909633A
Abstract: Low-temperature rate coefficients are measured for the CN + benzene and CN + toluene reactions using the pulsed Laval nozzle expansion technique coupled with laser-induced fluorescence detection. The CN + benzene reaction rate coefficient at 105, 165, and 295 K is found to be relatively constant over this temperature range, (3.9-4.9) x 10(-10) cm(3) molecule(-1) s(-1). These rapid kinetics, along with the observed negligible temperature dependence, are consistent with a barrierless reaction entrance channel and reaction efficiencies approaching unity. The CN + toluene reaction is measured to have a rate coefficient of 1.3 x 10(-10) cm(3) molecule(-1) s(-1) at 105 K. At room temperature, nonexponential decay profiles are observed for this reaction that may suggest significant back-dissociation of intermediate complexes. In separate experiments, the products of these reactions are probed at room temperature using synchrotron VUV photoionization mass spectrometry. For CN + benzene, cyanobenzene (C(6)H(5)CN) is the only product recorded with no detectable evidence for a C(6)H(5) + HCN product channel. In the case of CN + toluene, cyanotoluene (NCC(6)H(4)CH(3)) constitutes the only detected product. It is not possible to differentiate among the ortho, meta, and para isomers of cyanotoluene because of their similar ionization energies and the approximately 40 meV photon energy resolution of the experiment. There is no significant detection of benzyl radicals (C(6)H(5)CH(2)) that would suggest a H-abstraction or a HCN elimination channel is prominent at these conditions. As both reactions are measured to be rapid at 105 K, appearing to have barrierless entrance channels, it follows that they will proceed efficiently at the temperatures of Saturn's moon Titan ( approximately 100 K) and are also likely to proceed at the temperature of interstellar clouds (10-20 K).
Direct Observation of the Gas-Phase Criegee Intermediate (CH2OO)
Publisher: American Chemical Society (ACS)
Date: 15-08-2008
DOI: 10.1021/JA804165Q
Abstract: Carbonyl oxide species play a key role in tropospheric oxidation of organic molecules and in low-temperature combustion processes. In the late 1940s, Criegee first postulated the participation of carbonyl oxides, now often called "Criegee intermediates," in ozonolysis of alkenes. However, despite decades of effort, no gas phase Criegee intermediate has before been observed. As a result, knowledge of gas phase carbonyl oxide reactions has heretofore been inferred by indirect means, with derived rate coefficients spanning orders of magnitude. We have directly detected the primary Criegee intermediate, formaldehyde oxide (CH2OO), in the chlorine-initiated gas-phase oxidation of dimethyl sulfoxide (DMSO). This work not only establishes that the Criegee intermediate is formed in DMSO oxidation also but opens the possibility for explicit kinetics studies on this critical atmospheric species.
Radical Generation from the Gas-Phase Activation of Ionized Lipid Ozonides
Publisher: American Chemical Society (ACS)
Date: 08-05-2017
Direct Detection of a Persistent Carbonyloxyl Radical in the Gas Phase
Publisher: Wiley
Date: 14-07-2013
Characterisation of the ionic products arising from electron photodetachment of simple dicarboxylate dianions
Publisher: Elsevier BV
Date: 10-2013
Gas-Phase Oxidation of the Protonated Uracil-5-yl Radical Cation
Publisher: American Chemical Society (ACS)
Date: 17-01-2018
Abstract: This study targets the kinetics and product detection of the gas-phase oxidation reaction of the protonated 5-dehydrouracil (uracil-5-yl) distonic radical cation using ion-trap mass spectrometry. Protonated 5-dehydrouracil radical ions (5-dehydrouracilH
Electrostatically Tuning the Photodissociation of the Irgacure 2959 Photoinitiator in the Gas Phase by Cation Binding
Publisher: American Chemical Society (ACS)
Date: 17-11-2020
DOI: 10.26434/CHEMRXIV.13239488.V1
Abstract: Our paper reports a combined experimental and computational investigation of the electrostatic tuning of Irgacure 2959, a Norrish-type I photoinitiator, in the presence of bound cations (H + , Li + , Na + , K + , Zn 2+ , Ca 2+ and Mg2+). Laser photodissociation action spectroscopy is deployed to acquire photodissociation spectra of mass- selected cation complexes. Quantum chemical calculations (TD-DFT and SCS-CC2) reveal that the cations are acting as point charges such that shifts of the key ππ* and nπ* states can be modelled as perturbations by an oriented electric field (OEF). The model agrees with the experimental photodissociation action spectra.
Calibration of a quadrupole ion trap for particle mass spectrometry
Publisher: Elsevier BV
Date: 05-2007
Isomer-Specific Product Detection of Gas-Phase Xylyl Radical Rearrangement and Decomposition Using VUV Synchrotron Photoionization
Publisher: American Chemical Society (ACS)
Date: 10-04-2014
DOI: 10.1021/JP501117N
Abstract: Xylyl radicals are intermediates in combustion processes since their parent molecules, xylenes, are present as fuel additives. In this study we report on the photoelectron spectra of the three isomeric xylyl radicals and the subsequent decomposition reactions of the o-xylyl radical, generated in a tubular reactor and probed by mass selected threshold photoelectron spectroscopy and VUV synchrotron radiation. Franck-Condon simulations are applied to augment the assignment of elusive species. Below 1000 K, o-xylyl radicals decompose by hydrogen atom loss to form closed-shell o-xylylene, which equilibrates with benzocyclobutene. At higher temperatures relevant to combustion engines, o-xylylene generates styrene in a multistep rearrangement, whereas the p-xylylene isomer is thermally stable, a key point of difference in the combustion of these two isomeric fuels. Another striking result is that all three xylyl isomers can generate p-xylylene upon decomposition. In addition to C8H8 isomers, phenylacetylene and traces of benzocyclobutadiene are observed and identified as further reaction products of o-xylylene, while there is also some preliminary evidence for benzene and benzyne formation. The experimental results reported here are complemented by a comprehensive theoretical C8H8 potential energy surface, which together with the spectroscopic assignments can explain the complex high-temperature chemistry of o-xylyl radicals.
Picosecond excited-state lifetimes of protonated indazole and benzimidazole: The role of the N–N bond
Publisher: AIP Publishing
Date: 08-11-2021
DOI: 10.1063/5.0071847
Abstract: Certain chemical groups give rise to characteristic excited-state deactivation mechanisms. Here, we target the role of a protonated N–N chemical group in the excited-state deactivation of protonated indazole by comparison to its isomer that lacks this group, protonated benzimidazole. Gas-phase protonated indazole and protonated benzimidazole ions are investigated at room temperature using picosecond laser pump–probe photodissociation experiments in a linear ion-trap. Excited state lifetimes are measured across a range of pump energies (4.0–5.4 eV). The 1ππ* lifetimes of protonated indazole range from 390 ± 70 ps using 4.0 eV pump energy to ≤18 ps using 4.6 eV pump energy. The 1ππ* lifetimes of protonated benzimidazole are systematically longer, ranging from 3700 ± 1100 ps at 4.6 eV pump energy to 400 ± 200 ps at 5.4 eV. Based on these experimental results and accompanying quantum chemical calculations and potential energy surfaces, the shorter lifetimes of protonated indazole are attributed to πσ* state mediated elongation of the protonated N–N bond.
Ultraviolet Photodissociation of the N-Methylpyridinium Ion: Action Spectroscopy and Product Characterization
Publisher: American Chemical Society (ACS)
Date: 15-10-2013
DOI: 10.1021/JP4075515
Abstract: The ultraviolet photodissociation of gas-phase N-methylpyridinium ions is studied at room temperature using laser photodissociation mass spectrometry and structurally diagnostic ion-molecule reaction kinetics. The C5H5N-CH3(+) (m/z 94), C5H5N-CD3(+) (m/z 97), and C5D5N-CH3(+)(m/z 99) isotopologues are investigated, and it is shown that the N-methylpyridinium ion photodissociates by the loss of methane in the 36,000 - 43,000 cm(-1) (280 - 230 nm) region. The dissociation likely occurs on the ground state surface following internal conversion from the S1 state. For each isotopologue, by monitoring the photofragmentation yield as a function of photon wavenumber, a broad vibronically featured band is recorded with origin (0-0) transitions assigned at 38 130, 38 140 and 38 320 cm(-1) for C5H5N-CH3(+) C5H5N-CD3+ and C5D5N-CH3(+), respectively. With the aid of quantum chemical calculations (CASSCF(6,6)/aug-cc-pVDZ), most of the observed vibronic detail is assigned to two in-plane ring deformation modes. Finally, using ion-molecule reactions, the methane coproduct at m/z 78 is confirmed as a 2-pyridinylium ion.
Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C002135K
Abstract: The reaction of the ground state methylidyne radical CH (X(2)Pi) with pyrrole (C(4)H(5)N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 363 K, at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr(3)) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C(5)H(5)N) is identified as the product of the reaction and resolved from (79)Br atoms, and the result is consistent with CH addition to pyrrole followed by H-elimination. The photoionization efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C(5)H(4)DN and identified as deuterated pyridine (d-pyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as gas-phase combustion processes, are discussed.
Isomer-specific product detection of CN radical reactions with ethene and propene by tunable VUV photoionization mass spectrometry
Publisher: Elsevier BV
Date: 02-2009
BIOPHYSCHEM2011: A joint meeting of the Australian society for biophysics and the RACI physical chemistry division
Publisher: CSIRO Publishing
Date: 2012
DOI: 10.1071/CH12213
Experimental evidence for long-range stabilizing and destabilizing interactions between charge and radical sites in distonic ions
Publisher: Elsevier BV
Date: 2019
Product detection study of the gas-phase oxidation of methylphenyl radicals using synchrotron photoionisation mass spectrometry
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CP01935A
Abstract: Reactions of ortho and meta -methylphenyl radicals with oxygen form products that depend acutely on the position of the methyl group.
Formation of dimethylketene and methacrolein by reaction of the CH radical with acetone
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP43829E
Abstract: The reaction of the methylidyne radical (CH) with acetone ((CH(3))(2)C[double bond, length as m-dash]O) is studied at room temperature and at a pressure of 4 Torr (533.3 Pa) using a multiplexed photoionization mass spectrometer coupled to the tunable vacuum ultraviolet synchrotron radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory. The CH radicals are generated by 248 nm multiphoton photolysis of bromoform and react with acetone in an excess of helium and nitrogen gas flow. The main observed reaction exit channel is elimination of a hydrogen atom to form C(4)H(6)O isomers. Analysis of photoionization spectra identifies dimethylketene and methacrolein as the only H-elimination products. The best fit to the data gives branching ratios of 0.68 ± 0.14 for methacrolein and 0.32 ± 0.07 for dimethylketene. A methylketene spectrum measured here is used to reanalyze the photoionization spectrum obtained at m/z = 56 for the CH + acetaldehyde reaction, (Goulay et al., J. Phys. Chem. A, 2012, 116, 6091) yielding new H-loss branching ratios of 0.61 ± 0.12 for acrolein and 0.39 ± 0.08 for methylketene. The contribution from methyleneoxirane to the reaction product distribution is revised to be negligible. Coupled with additional product detection for the CD + acetone reaction, these observations pave the way for development of general set of reaction mechanisms for the addition of CH to compounds containing an acetyl subgroup.
Are the three hydroxyphenyl radical isomers created equal? – The role of the phenoxy radical –
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP05346C
Abstract: Hydroxyphenyl radicals (˙C 6 H 4 –OH) rearrange in a heated micro tubular reactor to phenoxy (C 6 H 5 –O˙) radicals, which subsequently decompose to yield cyclopentadienyl and CO.
A Photoreactor-Interfaced Mass Spectrometer: An Online Platform to Monitor Photochemical Reactions
Publisher: American Chemical Society (ACS)
Date: 13-10-2023
Barrierless Reactions of Three Benzonitrile Radical Cations with Ethylene
Publisher: CSIRO Publishing
Date: 2020
DOI: 10.1071/CH19606
Abstract: Reactions of three protonated benzonitrile radical cations with ethylene are investigated. Product branching ratios and reaction kinetics, measured using ion-trap mass spectrometry, are reported and mechanisms are developed with support from quantum chemical calculations. Reactions proceed via pre-reactive van der Waals complexes with no energy barrier (above the reactant energy) and form radical addition and addition–elimination product ions. Rate coefficients are 4-dehydrobenzonitrilium: 1.72±0.01×10−11 cm3 molecule−1 s−1, 3-dehydrobenzonitrilium: 1.85±0.01×10−11 cm3 molecule−1 s−1, and 2-dehydrobenzonitrilium: 5.96±0.06×10−11 cm3 molecule−1 s−1 (with±50% absolute uncertainty). A ring-closure mechanism involving the protonated nitrile substituent is proposed for the 2-dehydrobenzonitrilium case and suggests favourable formation of the protonated indenimine cation.
Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry
Publisher: American Chemical Society (ACS)
Date: 18-07-2013
DOI: 10.1021/JP404965K
Abstract: The CH(X(2)Π) + propene reaction is studied in the gas phase at 298 K and 4 Torr (533.3 Pa) using VUV synchrotron photoionization mass spectrometry. The dominant product channel is the formation of C4H6 (m/z 54) + H. By fitting experimental photoionization spectra to measured spectra of known C4H6 isomers, the following relative branching fractions are obtained: 1,3-butadiene (0.63 ± 0.13), 1,2-butadiene (0.25 ± 0.05), and 1-butyne (0.12 ± 0.03) with no detectable contribution from 2-butyne. The CD + propene reaction is also studied and two product channels are observed that correspond to C4H6 (m/z 54) + D and C4H5D (m/z 55) + H, formed at a ratio of 0.4 (m/z 54) to 1.0 (m/z 55). The D elimination channel forms almost exclusively 1,2-butadiene (0.97 ± 0.20) whereas the H elimination channel leads to the formation of deuterated 1,3-butadiene (0.89 ± 0.18) and 1-butyne (0.11 ± 0.02) photoionization spectra of undeuterated species are used in the fitting of the measured m/z 55 (C4H5D) spectrum. The results are generally consistent with a CH cycloaddition mechanism to the C═C bond of propene, forming 1-methylallyl followed by elimination of a H atom via several competing processes. The direct detection of 1,3-butadiene as a reaction product is an important validation of molecular weight growth schemes implicating the CH + propene reaction, for ex le, those reported recently for the formation of benzene in the interstellar medium (Jones , B. M. Proc. Natl. Acad. Sci. U.S.A. 2011 , 108 , 452 - 457).
UV Photodissociation Action Spectroscopy of Haloanilinium Ions in a Linear Quadrupole Ion Trap Mass Spectrometer
Publisher: American Chemical Society (ACS)
Date: 23-04-2013
DOI: 10.1007/S13361-013-0615-Z
Abstract: UV-vis photodissociation action spectroscopy is becoming increasingly prevalent because of advances in, and commercial availability of, ion trapping technologies and tunable laser sources. This study outlines in detail an instrumental arrangement, combining a commercial ion-trap mass spectrometer and tunable nanosecond pulsed laser source, for performing fully automated photodissociation action spectroscopy on gas-phase ions. The components of the instrumentation are outlined, including the optical and electronic interfacing, in addition to the control software for automating the experiment and performing online analysis of the spectra. To demonstrate the utility of this ensemble, the photodissociation action spectra of 4-chloroanilinium, 4-bromoanilinium, and 4-iodoanilinium cations are presented and discussed. Multiple photoproducts are detected in each case and the photoproduct yields are followed as a function of laser wavelength. It is shown that the wavelength-dependent partitioning of the halide loss, H loss, and NH3 loss channels can be broadly rationalized in terms of the relative carbon-halide bond dissociation energies and processes of energy redistribution. The photodissociation action spectrum of (phenyl)Ag2 (+) is compared with a literature spectrum as a further benchmark.
Meet the Associate Editors: Adam Trevitt
Publisher: Wiley
Date: 25-12-2018
DOI: 10.1002/RCM.8329
Laser-initiated iodine radical chemistry in single microdroplets
Publisher: Elsevier BV
Date: 11-2012
Gas-Phase Internal Proton-Transfer of Protonated para-Aminobenzoic Acid Catalyzed by One Methanol Molecule
Publisher: American Chemical Society (ACS)
Date: 08-06-2023
Reaction of ionised steryl esters with ozone in the gas phase
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.CHEMPHYSLIP.2018.12.013
Abstract: Cholesterol is an ubiquitous membrane lipid, that also serves as a precursor to many steroid hormones. The 5,6 carbon-carbon double bond on the tetracyclic carbon backbone of cholesterol is an attractive target for ozone with the reaction giving rise to a wide range of possibly bioactive molecules. Despite this, little is known about the ozonolysis of cholesterol esters, which often possess an additional double bond(s) on the fatty acyl chain. Understanding the intrinsic gas phase reaction of ozone with the two disparate double bond positions on cholesteryl esters can inform our understanding of these processes in vivo, particularly reactions occurring at the air-water interface (e.g., tear film lipid layer) and on the surfaces of the body where these cholesterol and cholesteryl esters may be present (e.g., sebum). In the present work we describe the gas phase ozonolysis of lithium and sodium cations formed from three steryl esters: two isomeric for double bond position (cholestanyl oleate and cholesteryl stearate), and a third with carbon-carbon double bonds present in both the sterol ring system and fatty acyl chain (cholesteryl oleate). We confirm the enhanced reactivity of the endocyclic carbon-carbon double bond with ozone over double bonds present in the acyl chain, and elucidate competitive interactions between the two double bond positions during ozonolysis. Elucidation of the mechanisms underlying this interaction is important for both understanding these processes in vivo and for deploying ozonolysis chemistry in analytical strategies for lipidomics.
Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1CP20784A
Abstract: α-Carboxylate radical anions are potential reactive intermediates in the free radical oxidation of biological molecules (e.g., fatty acids, peptides and proteins). We have synthesised well-defined α-carboxylate radical anions in the gas phase by UV laser photolysis of halogenated precursors in an ion-trap mass spectrometer. Reactions of isolated acetate (˙CH(2)CO(2)(-)) and 1-carboxylatobutyl (CH(3)CH(2)CH(2)˙CHCO(2)(-)) radical anions with dioxygen yield carbonate (CO(3)˙(-)) radical anions and this chemistry is shown to be a hallmark of oxidation in simple and alkyl-substituted cross-conjugated species. Previous solution phase studies have shown that C(α)-radicals in peptides, formed from free radical damage, combine with dioxygen to form peroxyl radicals that subsequently decompose into imine and keto acid products. Here, we demonstrate that a novel alternative pathway exists for two α-carboxylate C(α)-radical anions: the acetylglycinate radical anion (CH(3)C(O)NH˙CHCO(2)(-)) and the model peptide radical anion, YGGFG˙(-). Reaction of these radical anions with dioxygen results in concerted loss of carbon dioxide and hydroxyl radical. The reaction of the acetylglycinate radical anion with dioxygen reveals a two-stage process involving a slow, followed by a fast kinetic regime. Computational modelling suggests the reversible formation of the C(α) peroxyl radical facilitates proton transfer from the amide to the carboxylate group, a process reminiscent of, but distinctive from, classical proton-transfer catalysis. Interestingly, inclusion of this isomerization step in the RRKM/ME modelling of a G3SX level potential energy surface enables recapitulation of the experimentally observed two-stage kinetics.
Products of the Benzene + O(3P) Reaction
Publisher: American Chemical Society (ACS)
Date: 25-01-2010
DOI: 10.1021/JP9114145
Abstract: The gas-phase reaction of benzene with O((3)P) is of considerable interest for modeling of aromatic oxidation, and also because there exist fundamental questions concerning the prominence of intersystem crossing in the reaction. While its overall rate constant has been studied extensively, there are still significant uncertainties in the product distribution. The reaction proceeds mainly through the addition of the O atom to benzene, forming an initial triplet diradical adduct, which can either dissociate to form the phenoxy radical and H atom or undergo intersystem crossing onto a singlet surface, followed by a multiplicity of internal isomerizations, leading to several possible reaction products. In this work, we examined the product branching ratios of the reaction between benzene and O((3)P) over the temperature range 300-1000 K and pressure range 1-10 Torr. The reactions were initiated by pulsed-laser photolysis of NO(2) in the presence of benzene and helium buffer in a slow-flow reactor, and reaction products were identified by using the multiplexed chemical kinetics photoionization mass spectrometer operating at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory. Phenol and phenoxy radical were detected and quantified. Cyclopentadiene and cyclopentadienyl radical were directly identified for the first time. Finally, ab initio calculations and master equation/RRKM modeling were used to reproduce the experimental branching ratios, yielding pressure-dependent rate expressions for the reaction channels, including phenoxy + H, phenol, cyclopentadiene + CO, which are proposed for kinetic modeling of benzene oxidation.
Comparing Positively and Negatively Charged Distonic Radical Ions in Phenylperoxyl Forming Reactions
Publisher: American Chemical Society (ACS)
Date: 04-06-2018
DOI: 10.1007/S13361-018-1988-9
Abstract: In the gas phase, arylperoxyl forming reactions play a significant role in low-temperature combustion and atmospheric processing of volatile organic compounds. We have previously demonstrated the application of charge-tagged phenyl radicals to explore the outcomes of these reactions using ion trap mass spectrometry. Here, we present a side-by-side comparison of rates and product distributions from the reaction of positively and negatively charge tagged phenyl radicals with dioxygen. The negatively charged distonic radical ions are found to react with significantly greater efficiency than their positively charged analogues. The product distributions of the anion reactions favor products of phenylperoxyl radical decomposition (e.g., phenoxyl radicals and cyclopentadienone), while the comparable fixed-charge cations yield the stabilized phenylperoxyl radical. Electronic structure calculations rationalize these differences as arising from the influence of the charged moiety on the energetics of rate-determining transition states and reaction intermediates within the phenylperoxyl reaction manifold and predict that this influence could extend to intra-molecular charge-radical separations of up to 14.5 Å. Experimental observations of reactions of the novel 4-(1-carboxylatoadamantyl)phenyl radical anion confirm that the influence of the charge on both rate and product distribution can be modulated by increasing the rigidly imposed separation between charge and radical sites. These findings provide a generalizable framework for predicting the influence of charged groups on polarizable radicals in gas phase distonic radical ions. Graphical Abstract.
Concerted HO2 Elimination from alpha-Aminoalkylperoxyl Free Radicals: Experimental and Theoretical Evidence from the Gas-Phase NH2 center dot CHCO2- + O-2 Reaction
Publisher: American Chemical Society (ACS)
Date: 07-03-2012
DOI: 10.1021/JZ300118K
Abstract: We have investigated the gas-phase reaction of the α-aminoacetate (glycyl) radical anion (NH2(•)CHCO2(-)) with O2 using ion trap mass spectrometry, quantum chemistry, and statistical reaction rate theory. This radical is found to undergo a remarkably rapid reaction with O2 to form the hydroperoxyl radical (HO2(•)) and an even-electron imine (NHCHCO2(-)), with experiments and master equation simulations revealing that reaction proceeds at the ion-molecule collision rate. This reaction is facilitated by a low-energy concerted HO2(•) elimination mechanism in the NH2CH(OO(•))CO2(-) peroxyl radical. These findings can explain the widely observed free-radical-mediated oxidation of simple amino acids to amides plus α-keto acids (their imine hydrolysis products). This work also suggests that imines will be the main intermediates in the atmospheric oxidation of primary and secondary amines, including amine carbon capture solvents such as 2-aminoethanol (commonly known as monoethanolamine, or MEA), in a process that avoids the ozone-promoting conversion of (•)NO to (•)NO2 commonly encountered in peroxyl radical chemistry.
Selecting and identifying gas-phase protonation isomers of nicotineH+ using combined laser, ion mobility and mass spectrometry techniques
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8FD00212F
Abstract: Protonation isomers of gas-phase nicotineH + are separated and assigned using a combination of FAIMS and UV photodissociation action spectroscopy.
Rapid profiling of laser-induced photochemistry in single microdroplets using mass spectrometry
Publisher: American Chemical Society (ACS)
Date: 26-02-2014
DOI: 10.1021/AC403976Q
Abstract: Rapid assessment of laser-induced photochemistry in single microdroplets is afforded by on-demand microdroplet generation coupled to a commercial ion-trap mass spectrometer. Single microdroplets (diameter ∼50 μm, 65 pL) fall on a steel needle held at +2 kV where they subsequently form a spray that is directed toward the inlet of an ion-trap mass spectrometer. It is demonstrated that single microdroplet mass spectra are recordable, one at a time, for methanol droplets containing 100 μM 4-iodoaniline. Extending on this, to probe laser-initiated photochemistry in single picoliter volumes, a UV laser pulse is timed to intercept the droplet before hitting the needle. Comparison of laser-on and laser-off mass spectra reveals the laser-initiated photochemical products. We demonstrate the technique by following UV laser initiated chemistry in methanol droplets containing 4-iodoaniline and 3-(iodomethyl)-N,N,N-trimethylbenzenamine and reveal numerous products within a few hundred single droplet experiments over several minutes. This technique allows for rapid detection of laser-initiated photochemistry in single picoliter volumes.
Actinic Wavelength Action Spectroscopy of the IO– Reaction Intermediate
Publisher: American Chemical Society (ACS)
Date: 08-12-2021
DOI: 10.1021/ACS.JPCLETT.1C03456
Abstract: Iodinate anions are important in the chemistry of the atmosphere where they are implicated in ozone depletion and particle formation. The atmospheric chemistry of iodine is a complex overlay of neutral-neutral, ion-neutral, and photochemical processes, where many of the reactions and intermediates remain poorly characterized. This study targets the visible spectroscopy and photostability of the gas-phase hypoiodite anion (IO
Discrimination between Protonation Isomers of Quinazoline by Ion Mobility and UV-Photodissociation Action Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 05-05-2001
Five vs. six membered-ring PAH products from reaction of o-methylphenyl radical and two C3H4 isomers
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1CP01764K
Abstract: Gas-phase o -methylphenyl reactions with propyne and allene form PAHs: with preferences for either six–six or five–six bicyclic products.
Modelling reaction kinetics of distonic radical ions: a systematic investigation of phenyl-type radical addition to unsaturated hydrocarbons
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2FD00045H
Abstract: We measure second-order rate coefficients for a suite of radical-ion reactions involving unsaturated hydrocarbons (C 2 H 2 and C 2 H 4 ), and report our efforts to develop an accurate modelling framework using a Rice–Ramsperger–Kassel–Marcus theory Master Equation approach.
Reactivity Trends in the Gas Phase Addition of Acetylene to N-protonated Aryl Radical Cations
Publisher: American Chemical Society (ACS)
Date: 13-10-2020
DOI: 10.26434/CHEMRXIV.13078334.V1
Abstract: A key step in gas-phase polycyclic aromatic hydrocarbon (PAH) formation involves the addition of acetylene (or other alkyne) to σ-type aromatic radicals, with successive additions yielding more complex PAHs. A similar process can happen for N- containing aromatics. In cold diffuse environments, such as the interstellar medium, rates of radical addition may be enhanced when the σ-type radical is charged. This paper investigates the gas-phase ion-molecule reactions of acetylene with nine aromatic distonic σ-type radical cations derived from pyridinium (Pyr), anilinium (Anl) and benzonitrilium (Bzn) ions. Three isomers are studied in each case (radical sites at the ortho, meta and para positions). Using a room temperature ion trap, second-order rate coefficients, product branching ratios and reaction efficiencies are reported.
Coalescence of levitated polystyrene microspheres
Publisher: Elsevier BV
Date: 05-2009
Ultraviolet photodissociation action spectroscopy of the N-pyridinium cation.
Publisher: AIP Publishing
Date: 05-01-2015
DOI: 10.1063/1.4904267
Abstract: The S1←S0 electronic transition of the N-pyridinium ion (C5H5NH+) is investigated using ultraviolet photodissociation (PD) spectroscopy of the bare ion and also the N2-tagged complex. Gas-phase N-pyridinium ions photodissociate by the loss of molecular hydrogen (H2) in the photon energy range 37 000–45 000 cm−1 with structurally diagnostic ion-molecule reactions identifying the 2-pyridinylium ion as the exclusive co-product. The photodissociation action spectra reveal vibronic details that, with the aid of electronic structure calculations, support the proposal that dissociation occurs through an intramolecular rearrangement on the ground electronic state following internal conversion. Quantum chemical calculations are used to analyze the measured spectra. Most of the vibronic features are attributed to progressions of totally symmetric ring deformation modes and out-of-plane modes active in the isomerization of the planar excited state towards the non-planar excited state global minimum.
Five vs Six Membered-Ring PAH Products from Reaction of o- Methylphenyl Radical and two C3H4 Isomers
Publisher: American Chemical Society (ACS)
Date: 06-05-2021
DOI: 10.26434/CHEMRXIV.14538516.V1
Abstract: Using VUV synchrotron photoionization mass spectrometry, quantum chemistry and RRKM kinetic modeling, our paper identifies the products formed when a substituted aromatic free radical (ortho- methylphenyl) reacts with two C3H4 isomers found in flames – propyne and allene.Both reactions form polycyclic aromatic hydrocarbons but profound structural differences result from the nature of the C3H4 isomer. The allene case favors the formation of six-six bicyclic rings (graphitic), while the formation of new five-six membered bicylics dominate for the propyne case. These conclusions are rigorously supported by experiments, calculations and kinetic modelling.
Highly efficient gas-phase reactivity of protonated pyridine radicals with propene
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP06644A
Abstract: Reaction of the three dehydro- N -pyridinium radical cation isomers with propene is highly efficient. Vinylpyridinium is the major product.
Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: a combined neutral and distonic radical study
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP02953H
Abstract: The o -hydroxyphenyl radical reacts with O 2 to form o -benzoquinone + OH and cyclopentadienone is assigned as a secondary product.
Molecular Weight Growth in the Gas-Phase Reactions of Dehydroanilinium Radical Cations with Propene
Publisher: American Chemical Society (ACS)
Date: 19-09-2019
Abstract: Protonated aniline-one of the simplest nitrogen-bearing aromatic molecules-is speculated to be present within Titan's atmosphere, where it could play a role in molecular weight growth chemistry. To investigate this possibility, this paper examines the reactions of propene with distonic radical cations derived from protonated aniline. The reaction kinetics, products, and branching ratios of these distonic radical cations (i.e., 2-, 3-, and 4-dehydroanilinium radical cations) are measured in the gas phase using ion-trap mass spectrometry, and calculations (M06-2
Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H<inf>3</inf>CCC) with small alkenes and alkynes
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP02589C
Abstract: Reaction of 1-propynyl radical with propyne and propene yields primarily methyl loss over hydrogen elimination. The implications of this result on molecular weight growth in Titan's atmosphere are discussed.
Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons
Publisher: American Chemical Society (ACS)
Date: 05-01-2009
DOI: 10.1021/JA804200V
Abstract: The reactions of the methylidyne radical (CH) with ethylene, acetylene, allene, and methylacetylene are studied at room temperature using tunable vacuum ultraviolet (VUV) photoionization and time-resolved mass spectrometry. The CH radicals are prepared by 248 nm multiphoton photolysis of CHBr(3) at 298 K and react with the selected hydrocarbon in a helium gas flow. Analysis of photoionization efficiency versus VUV photon wavelength permits isomer-specific detection of the reaction products and allows estimation of the reaction product branching ratios. The reactions proceed by either CH insertion or addition followed by H atom elimination from the intermediate adduct. In the CH + C(2)H(4) reaction the C(3)H(5) intermediate decays by H atom loss to yield 70(+/-8)% allene, 30(+/-8)% methylacetylene, and less than 10% cyclopropene, in agreement with previous RRKM results. In the CH + acetylene reaction, detection of mainly the cyclic C(3)H(2) isomer is contrary to a previous RRKM calculations that predicted linear triplet propargylene to be 90% of the total H-atom coproducts. High-level CBS-APNO quantum calculations and RRKM calculations for the CH + C(2)H(2) reaction presented in this manuscript predict a higher contribution of the cyclic C(3)H(2) (27.0%) versus triplet propargylene (63.5%) than earlier predictions. Extensive calculations on the C(3)H(3) and C(3)H(2)D system combined with experimental isotope ratios for the CD + C(2)H(2) reaction indicate that H-atom-assisted isomerization in the present experiments is responsible for the remaining discrepancy between the new RRKM calculations and the experimental results. Cyclic isomers are also found to represent 30(+/-6)% of the detected products in the case of CH + methylacetylene, together with 33(+/-6)% 1,2,3-butatriene and 37(+/-6)% vinylacetylene. The CH + allene reaction gives 23(+/-5)% 1,2,3-butatriene and 77(+/-5)% vinylacetylene, whereas cyclic isomers are produced below the detection limit in this reaction. The reaction exit channels deduced by comparing the product distributions for the aforementioned reactions are discussed in detail.
Laser Photodissociation Action Spectroscopy for the Wavelength-Dependent Evaluation of Photoligation Reactions
Publisher: American Chemical Society (ACS)
Date: 21-05-2021
Isomer Specific Product Detection in the Reaction of CH with Acrolein
Publisher: American Chemical Society (ACS)
Date: 22-10-2013
DOI: 10.1021/JP407428V
Abstract: The products formed in the reaction between the methylidene radical (CH) and acrolein (CH2═CHCHO) are probed at 4 Torr and 298 K employing tunable vacuum-ultraviolet synchrotron light and multiplexed photoionization mass-spectrometry. The data suggest a principal exit channel of H loss from the adduct to yield C4H4O, accounting for (78 ± 10)% of the products. Examination of the photoionization spectra measured upon reaction of both CH and CD with acrolein reveals that the isomeric composition of the C4H4O product is (60 ± 12)% 1,3-butadienal and (17 ± 10)% furan. The remaining 23% of the possible C4H4O products cannot be accurately distinguished without more reliable photoionization spectra of the possible product isomers but most likely involves oxygenated butyne species. In addition, C2H2O and C3H4 are detected, which account for (14 ± 10)% and (8 +10, -8)% of the products, respectively. The C2H2O photoionization spectrum matches that of ketene and the C3H4 signal is composed of (24 ± 14)% allene and (76 ± 22)% propyne, with an upper limit of 8% placed on the cyclopropene contribution. The reactive potential energy surface is also investigated computationally, and specific rate coefficients are calculated with RRKM theory. These calculations predict overall branching fractions for 1,3-butadienal and furan of 27% and 12%, respectively, in agreement with the experimental results. In contrast, the calculations predict a prominent CO + 2-methylvinyl product channel that is at most a minor channel according to the experimental results. Studies with the CD radical strongly suggest that the title reaction proceeds predominantly via cycloaddition of the radical onto the C═O bond of acrolein, with cycloaddition to the C═C bond being the second most probable reactive mechanism.
Differentiation of complex lipid isomers by radical-directed dissociation mass spectrometry
Publisher: American Chemical Society (ACS)
Date: 22-08-2012
DOI: 10.1021/AC301652A
Abstract: Contemporary lipidomics protocols are dependent on conventional tandem mass spectrometry for lipid identification. This approach is extremely powerful for determining lipid class and identifying the number of carbons and the degree of unsaturation of any acyl-chain substituents. Such analyses are however, blind to isomeric variants arising from different carbon-carbon bonding motifs within these chains including double bond position, chain branching, and cyclic structures. This limitation arises from the fact that conventional, low energy collision-induced dissociation of even-electron lipid ions does not give rise to product ions from intrachain fragmentation of the fatty acyl moieties. To overcome this limitation, we have applied radical-directed dissociation (RDD) to the study of lipids for the first time. In this approach, bifunctional molecules that contain a photocaged radical initiator and a lipid-adducting group, such as 4-iodoaniline and 4-iodobenzoic acid, are used to form noncovalent complexes (i.e., adduct ions) with a lipid during electrospray ionization. Laser irradiation of these complexes at UV wavelengths (266 nm) cleaves the carbon-iodine bond to liberate a highly reactive phenyl radical. Subsequent activation of the nascent radical ions results in RDD with significant intrachain fragmentation of acyl moieties. This approach provides diagnostic fragments that are associated with the double bond position and the positions of chain-branching in glycerophospholipids, sphingomyelins and triacylglycerols and thus can be used to differentiate isomeric lipids differing only in such motifs. RDD is demonstrated for well-defined lipid standards and also reveals lipid structural ersity in olive oil and human very-low density lipoprotein.
Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP06389B
Abstract: Gas-phase radical reactions of CN and CH with small hydrocarbons are overviewed with emphasis on isomer-resolved product detection.
Ultraviolet Action Spectroscopy of Iodine Labeled Peptides and Proteins in the Gas Phase
Publisher: American Chemical Society (ACS)
Date: 20-08-2012
DOI: 10.1021/JP305470J
Abstract: Structural investigations of large biomolecules in the gas phase are challenging. Herein, it is reported that action spectroscopy taking advantage of facile carbon-iodine bond dissociation can be used to examine the structures of large molecules, including whole proteins. Iodotyrosine serves as the active chromophore, which yields distinctive spectra depending on the solvation of the side chain by the remainder of the molecule. Isolation of the chromophore yields a double featured peak at ~290 nm, which becomes a single peak with increasing solvation. Deprotonation of the side chain also leads to reduced apparent intensity and broadening of the action spectrum. The method can be successfully applied to both negatively and positively charged ions in various charge states, although electron detachment becomes a competitive channel for multiply charged anions. In all other cases, loss of iodine is by far the dominant channel which leads to high sensitivity and simple data analysis. The action spectra for iodotyrosine, the iodinated peptides KGYDAKA, DAYLDAG, and the small protein ubiquitin are reported in various charge states.
Photoelectron Spectrum and Energetics of the meta-Xylylene Diradical.
Publisher: American Chemical Society (ACS)
Date: 10-10-2017
DOI: 10.1021/JACS.7B06714
Abstract: The meta-xylylene diradical m-C
UV photodissociation action spectra of protonated formylpyridines
Publisher: AIP Publishing
Date: 07-10-2022
DOI: 10.1063/5.0113107
Abstract: The first ππ* transition for protonated 2-, 3-, and 4-formylpyridine (FPH
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University Of California, Berkeley
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