ORCID Profile
0000-0001-9380-0418
Current Organisation
University of Aveiro
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Macromolecular and Materials Chemistry | Nanochemistry and Supramolecular Chemistry
Expanding Knowledge in the Chemical Sciences | Physical and Chemical Conditions of Water not elsewhere classified |
Publisher: Wiley
Date: 21-01-2022
Abstract: Using the chemical versatility of the benzo[ b ]thiophene motif, an extensive library of 24 (thio)urea receptors, with different binding properties and lipophilicities, was prepared and included α,α‐, α,β‐, β,β‐, β,γ‐, α,γ‐, and γ,γ‐benzo[ b ]thiophene positional isomers, as well as β‐ or γ‐benzo[ b ]thiophene‐based molecules decorated with aliphatic chains or aryl moieties with different fluorination degrees. 1 H NMR titrations, X‐ray crystallographic studies, and DFT calculations were used to study the chloride binding affinities between receptors and substrates. Experimental efflux studies suggested that the anion transmembrane transport activity is dependent on the receptors′ lipophilicity and hydrogen bonding ability. Moreover, LUV based assays indicated that anion efflux occurs mainly through an uniport mechanism. Further MD simulations showed that anion transport is highly dependent on the orientation and interactions of the receptors at the water/lipid interface.
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B915548A
Abstract: Sulfate templation has been used in the synthesis of a novel tris-urea-based triply interlocked capsule, whose structure has been verified by DOSY NMR, mass spectrometry and molecular modelling investigations.
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B609937H
Abstract: The binding properties of dioxadiaza- ([17](DBF)N2O2) and trioxadiaza- ([22](DBF)N2O3), macrocyclic ligands containing a rigid dibenzofuran group (DBF), to metal cations and structural studies of their metal complexes have been carried out. The protonation constants of these two ligands and the stability constants of their complexes with Ca2+, Ba2+, and Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+, were determined at 298.2 K in methanol-water (1:1, v/v), and at ionic strength 0.10 mol dm-3 in KNO3. The values of the protonation constants of both ligands are similar, indicating that no cavity size effect is observed. Only mononuclear complexes of these ligands with the alent metal ions studied were found, and their stability constants are lower than expected, especially for the complexes of the macrocycle with smaller cavity size. However, the Cd2+ complex with [17](DBF)N2O2 exhibits the highest value of stability constant for the whole series of metal ions studied, indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of all the metal ions studied, except copper(II), indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of the mentioned metal ions. The crystal structures of H2[17](DBF)N2O3(2+) (diprotonated form of the ligand) and of its cadmium complex were determined by X-ray diffraction. The Cd2+ ion fits exactly inside the macrocyclic cavity exhibiting coordination number eight by coordination to all the donor atoms of the ligand, and additionally to two oxygen atoms from one nitrate anion and one oxygen atom from a water molecule. The nickel(II) and copper(II) complexes with the two ligands were further studied by UV-vis-NIR and the copper(II) complexes also by EPR spectroscopic techniques in solution indicating square-pyramidal structures and suggesting that only one nitrogen and oxygen donors of the ligands are bound to the metal. However an additional weak interaction of the second nitrogen cannot be ruled out.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0DT00340A
Abstract: The hexaazamacrocycles [28](DBF)(2)N(6) {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminoethyleneiminoethylene]} and [32](DBF)(2)N(6) {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminopropyleneiminopropylene]} form stable dinuclear copper(ii) complexes suitable to behave as receptors for several anionic substrates. These two receptors were used to study the binding interactions with several substrates, such as imidazole (Him) and some carboxylates [benzoate (bz(-)), oxalate (ox(2-)), malonate (mal(2-)), phthalate (ph(2-)), isophthalate (iph(2-)), and terephthalate (tph(2-))] by spectrophotometric titrations and EPR spectroscopy in MeOH (or H(2)O):DMSO (1 : 1 v/v) solution. The largest association constant was found for ox(2-) with Cu(2)[32](DBF)(2)N(6)(4+), whereas for the aromatic dicarboxylate anions the binding constants follow the trend ph(2-) > iph(2-) > tph(2-), i.e. decrease with the increase of the distance of the two binding sites of the substrate. On the other hand, the large blue shift of 68 nm observed by addition of Him to Cu(2)[32](DBF)(2)N(6)(4+) points out for the formation of the bridged CuimCu cascade complex, indicating this receptor as a potential sensor for the detection and determination of imidazole in solution. The X-band EPR spectra of the Cu(2)[28](DBF)(2)N(6)(4+) and Cu(2)[32](DBF)(2)N(6)](4+) complexes and the cascade complexes with the substrates, performed in H(2)O:DMSO (1 : 1 v/v) at 5 to 15 K, showed that the CuCu distance is slightly larger than the one found in crystal state and that this distance increases when the substrate is accommodated between the two copper centres. The crystal structure of [Cu(2)[28](DBF)(2)N(6)(ph)(2)]·CH(3)OH was determined by X-ray diffraction and revealed the two copper centres bridged by two ph(2-) anions at a CuCu distance of 5.419(1) Å. Each copper centre is surrounded by three carboxylate oxygen atoms from two phthalate anions and three contiguous nitrogen atoms of the macrocycle in a pseudo octahedral coordination environment.
Publisher: Wiley
Date: 22-11-2013
Abstract: Three triazolium-based [2]rotaxanes containing different sized axle and macrocycle components were synthesised in good yields (40-57%) through chloride anion templation. The anion recognition properties of the interlocked receptor systems were investigated using (1)H NMR titration experiments: all three rotaxanes display impressive selectivities for halide anions over the more basic oxoanion acetate. The rotaxanes incorporating shorter, more rigid axle components with aryl-substituted triazolium groups display substantially higher anion binding affinities than those with longer, bis-alkyl-substituted heterocycles, which is attributed to the increased intercomponent preorganisation afforded by the smaller axle component. Computational DFT and molecular dynamics simulations composed of unconstrained and umbrella s ling simulations corroborate the experimental observations.
Publisher: American Chemical Society (ACS)
Date: 03-07-2012
DOI: 10.1021/JA302213R
Abstract: The synthesis and anion binding properties of a new family of fluorescent halogen bonding (XB) macrocyclic halo-imidazolium receptors are described. The receptors contain chloro-, bromo-, and iodo-imidazolium motifs incorporated into a cyclic structure using naphthalene spacer groups. The large size of the iodine atom substituents resulted in the isolation of anti and syn conformers of the iodo-imidazoliophane, whereas the chloro- and bromo-imidazoliophane analogues exhibit solution dynamic conformational behavior. The syn iodo-imidazoliophane isomer forms novel dimeric isostructural XB complexes of 2:2 stoichiometry with bromide and iodide anions in the solid state. Solution phase DOSY NMR experiments indicate iodide recognition takes place via cooperative convergent XB-iodide 1:1 stoichiometric binding in aqueous solvent mixtures. (1)H NMR and fluorescence spectroscopic titration experiments with a variety of anions in the competitive CD(3)OD/D(2)O (9:1) aqueous solvent mixture demonstrated the bromo- and syn iodo-imidazoliophane XB receptors to bind selectively iodide and bromide respectively, and sense these halide anions exclusively via a fluorescence response. The protic-, chloro-, and anti iodo-imidazoliophane receptors proved to be ineffectual anion complexants in this aqueous methanolic solvent mixture. Computational DFT and molecular dynamics simulations corroborate the experimental observations that bromo- and syn iodo-imidazoliophane XB receptors form stable cooperative convergent XB associations with bromide and iodide.
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B415718D
Abstract: Structural studies of metal complexes of five ditopic hexaazamacrocycles containing two pyridine rings ([n]py2N4 n= 18, 20, 22, 24 and 26) have been carried out. The synthesis of macrocycles [22]- to [26]-py2N4 are also reported. The protonation constants of the last three compounds and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, and Pb2+ were determined at 25 degrees C in 0.10 mol dm(-3) KNO3 in aqueous solution. Our results with [22]py2N4 show significant differences from those described previously, while [24]py2N4 has not been studied before and [26]py2N4 is a new compound. Mononuclear and dinuclear complexes of the alent metal ions studied with [22]- to [26]-py2N4 were found in solution. The stability constants for the ML complexes of the three ligands follow the Irving-Williams order: NiL2+ > ZnL2+ > PbL2+, however for the dinuclear complexes the values for Pb2+ complexes are higher than the corresponding values for the Ni2+ and the Zn2+ complexes. The X-ray single crystal structures of the supramolecular aggregates [Cu2([20]py2N4)(H2O)4][Cu(H2O)6](SO4)3 x 3H2O and [Cu(2)([20]py(2)N4)(CH3CN)4][Ni([20]py2N4)]2(ClO4)8 x H2O, which are composed of homodinuclear [Cu2([20]py2N4])(H2O)4]4+ and [Cu2([20]py2N4])(CH3CN))4]4+, and mononuclear species, [Cu(H2O)6]2+ and [Ni([20]py2N4)]2+, respectively, assembled by an extensive network of hydrogen bonds, are also reported. In both homodinuclear complexes the copper centres are located at the end of the macrocycle and display distorted square pyramidal coordination environments with the basal plane defined by three consecutive nitrogen donors and one solvent molecule, water in and acetonitrile in . The macrocycle adopts a concertina-type conformation leading to the formation of macrocyclic cavities with the two copper centres separated by intramolecular distances of 5.526(1) and 5.508(7) A in 1a and 2a, respectively. The mononuclear complex [Ni([20]py2N4])]2+ displays a distorted octahedral co-ordination environment with the macrocycle wrapping the metal centre in a helical shape. EPR spectroscopy of the copper complexes indicated the presence of mono- and dinuclear species.
Publisher: Wiley
Date: 28-10-2010
Abstract: A new, versatile chloride-anion-templating synthetic pathway is exploited for the preparation of a series of eight new [2]rotaxane host molecules, including the first sulfonamide interlocked system. (1)H NMR spectroscopic titration investigations demonstrate the rotaxanes' capability to selectively recognise the chloride anion in competitive aqueous solvent media. The interlocked host's halide binding affinity can be further enhanced and tuned through the attachment of electron-withdrawing substituents and by increasing its positive charge. A dicationic rotaxane selectively binds chloride in 35% water, wherein no evidence of oxoanion binding is observed. NMR spectroscopy, X-ray structural analysis and computational molecular dynamics simulations are used to account for rotaxane formation yields, anion binding strengths and selectivity trends.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2SC20041D
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1DT10887E
Abstract: A new [2]rotaxane host system containing nitro-isophthalamide macrocycle and polyether functionalised pyridinium axle components is prepared via clipping and stoppering synthetic methodologies using chloride anion templation. After removing the chloride anion template, (1)H NMR titration experiments reveal the unique interlocked host cavity to be highly selective for binding chloride and bromide in preference to basic oxoanions in competitive aqueous solvent mixtures. The rotaxane host system proved to be a superior anion complexant in comparison to the in idual macrocycle and axle components. The anion binding affinity of the novel rotaxane is also investigated via molecular dynamics simulations and in general the structural data obtained corroborates the experimental solution anion recognition behaviour.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3SM52140K
Abstract: The interaction of six tripodal synthetic chloride transmembrane transporters with a POPC bilayer was investigated by means of molecular dynamics simulations using the general Amber force field (GAFF) for the transporters and the LIPID11 force field for phospholipids. These transporters are structurally simple molecules, based on the tris(2-aminoethyl)amine scaffold, containing three thiourea binding units coupled with three n-butyl (1), phenyl (2), fluorophenyl (3), pentafluorophenyl (4), trifluoromethylphenyl (5), or bis(trifluoromethyl)phenyl (6) substituents. The passive diffusion of 1-6⊃ Cl(-) was evaluated with the complexes initially positioned either in the water phase or inside the bilayer. In the first scenario the chloride is released in the water solution before the synthetic molecules achieve the water-lipid interface and permeate the membrane. In the latter one, only when the chloride complex reaches the interface is the anion released to the water phase, with the transporter losing the initial ggg tripodal shape. Independently of the transporter used in the membrane system, the bilayer structure is preserved and the synthetic molecules interact with the POPC molecules at the phosphate headgroup level, via N-H···O hydrogen bonds. Overall, the molecular dynamics simulations' results indicate that the small tripodal molecules in this series have a low impact on the bilayer and are able to diffuse with chloride inside the lipid environment. Indeed, these are essential conditions for these molecules to promote the transmembrane transport as anion carriers, in agreement with experimental efflux data.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4OB00801D
Abstract: A [2]rotaxane incorporating the novel 3-amido-phenyl-triazolium motif exhibits unusually high selectivity for halide anions over larger more basic oxoanions. Computational studies offer insight into this selectivity preference.
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B617704B
Abstract: New dioxadiaza- and trioxadiaza-macrocycles containing one rigid dibenzofuran unit (DBF) and N-(2-aminoethyl) pendant arms were synthesized, N,N'-bis(2-aminoethyl)-[17](DBF)N(2)O(2) (L(1)) and N,N'-bis(2-aminoethyl)-[22](DBF)N(2)O(3) (L(2)), respectively. The binding properties of both macrocycles to metal ions and structural studies of their metal complexes were carried out. The protonation constants of both compounds and the stability constants of their complexes with Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+) were determined at 298.2 K, in aqueous solutions, and at ionic strength 0.10 mol dm(-3) in KNO(3). Mononuclear complexes with both ligands were formed, and dinuclear complexes were only found for L(2). The thermodynamic binding affinities of the metal complexes of L(2) are lower than those of L(1) as expected, but the Pb(2+) complexes of both macrocycles exhibit close stability constant values. On the other hand, the binding affinities of Cd(2+) and Pb(2+) for L(1) are very high, when compared to those of Co(2+), Ni(2+) and Zn(2+). These interesting properties were explained by the presence of the rigid DBF moiety in the backbone of the macrocycle and to the special match between the macrocyclic cavity size and the studied larger metal ions. To elucidate the adopted structures of complexes in solution, the nickel(II) and copper(II) complexes with both ligands were further studied by UV-vis-NIR spectroscopy in DMSO-H(2)O 1 : 1 (v/v) solution. The copper(II) complexes were also studied by EPR spectroscopy in the same mixture of solvents. The crystal structure of the copper complex of L(1) was also determined. The copper(II) displays an octahedral geometry, the four nitrogen atoms forming the equatorial plane and two oxygen atoms, one from the DBF unit and the other one from the ether oxygen, in axial positions. One of the ether oxygens of the macrocycle is out of the coordination sphere. Our results led us to suggest that this geometry is also adopted by the Co(2+) to Zn(2+) complexes, and only the larger Cd(2+) and Pb(2+) manage to form complexes with the involvement of all the oxygen atoms of the macrocyclic backbone.
Publisher: American Chemical Society (ACS)
Date: 18-05-2009
DOI: 10.1021/JO9005798
Abstract: A macrobicycle formed by a tetraoxadiaza macrocycle containing a dibenzofuran (DBF) spacer and an isophthalamide head unit, named DBF-bz, was used as receptor for anion recognition. The molecular structure of DBF-bz was established in solution by NMR and ESI-MS spectroscopies and in single crystal by X-ray diffraction analysis. The X-ray structure showed a water molecule encapsulated into the macrobicyclic cavity by four hydrogen bonds, two of them involving the two N-H amide binding sites and the oxygen of the water molecule (N-H...O hydrogen bonds) and the other two (O-H...N) involving the amine groups as hydrogen bonding acceptors. (1)H NMR temperature dependence studies demonstrated that the same structure exists in solution. The ability of this ditopic receptor to recognize alkali halide salts was evaluated by extraction studies followed by (1)H NMR and ESI-MS spectroscopies. The macrobicycle showed a capacity to extract halide salts from aqueous solutions into organic phases. The binding ability of this macrobicycle for halides was also quantitatively investigated using (1)H NMR titrations in CDCl(3) (and DMSO-d(6)) solution, and in acidic D(2)O solution. The largest binding association constant was found for the chloride anion and the completely protonated receptor. The results suggest that the diammonium-diamide unit of the receptor strongly bind the anionic substrate via multiple N-H...Cl(-) hydrogen bonds and electrostatic interactions. The binding trend follows the order Cl(-) > Br(-) > I(-) approximately F(-) established from the best fit between the size of the anion and the cavity size of the protonated macrobicycle. Molecular dynamics (MD) simulations of the DBF-bz in CHCl(3) solution allowed a detailed insight into the structural and binding properties of the receptor.
Publisher: Wiley
Date: 22-06-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C2SC21112B
Publisher: Elsevier BV
Date: 09-2006
Publisher: Wiley
Date: 12-09-2011
Publisher: Wiley
Date: 11-2005
Abstract: The host–guest binding interactions of the hexaazamacrocycle [26]py 2 N 4 , in its tetraprotonated form H 4 [26]py 2 N 4 4+ as well as in its dicopper( II ) complex [Cu 2 ([26]py 2 N 4 )(H 2 O) 4 ] 4+ , with dicarboxylate anions of different stereoelectronicrequirements, such as oxalate (ox 2– ), malonate (mal 2– ), succinate (suc 2– ), fumarate (fu 2– ) and maleate (ma 2– ), were evaluated. The association constants were determined using potentiometric methods in aqueous solution, at 298.0 K and 0.10 mol · dm –3 KCl. These values for the tetraprotonated ditopic receptor with the dicarboxylate anions revealed that the main species in solution corresponds to the formation of {H 4 [26]py 2 N 4 (A)} 2+ (pH ≈ 4–9), A being the substrate anion. The values determined are not especially high, but the receptor exhibits selectivity for the malonate anion. The study of the cascade complexes revealed several species in solution, involving mononuclear and dinuclear complexes, mainly protonated and hydrolysed species, as well as the expected complexes [Cu 2 ([26]py 2 N 4 )(A)(H 2 O) x ] 2+ or [Cu 2 ([26]py 2 N 4 )(A) 2 (H 2 O) y ]. Ox 2– and mal 2– form cascade complexes with only one anion, which will necessarily bridge the two copper atoms because of the symmetrical arrangement of the dinuclear complex. The two other studied anions, suc 2– and ma 2– , form species involving two substrate anions, although species with only one suc 2– anion were also found. UV/Vis and EPR spectroscopy have shown that the dicopper complex can operate as a sensor to detect and quantitatively determine oxalate spectrophotometrically because of the red shift of the maximum of the visible band observed by addition of ox 2– to an aqueous solution of the dinuclear copper complex. However the selectivity of [Cu 2 ([26]py 2 N 4 )(H 2 O) 4 ] 4+ as a receptor for ox 2– in the studied series is not sufficiently high to detect ox 2– spectrophotometrically in the presence of the other anions. Molecular dynamics simulations indicated that the H 4 [26]py 2 N 4 4+ receptor provides a large and flexible cavity to accommodate the studied anions. Molecular recognition is based in electrostatic interactions rather than in multiple hydrogen‐bonding interactions acting cooperatively. By contrast, the [Cu 2 ([26]py 2 N 4 )] 4+ receptor has a well‐shaped cavity with adequate size to uptake these anions as bridging ligands with formation of four Cu–O bonds. The ox 2– anion is encapsulated within the cascade complex while the remaining anions are located above the N 6 macrocyclic plane, suggesting a selective coordination behaviour of this receptor. In spite of our molecular simulation being carried out in gas phase, the modelling results are consistent with the solution studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CP02576B
Abstract: The anion carrier mechanism promoted by squaramide-based molecules has been elucidated by molecular dynamics and chloride efflux studies.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3SC51023A
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8SC05155K
Abstract: A series of fluorinated tripodal tris-thioureas function as highly active anion transporters across lipid bilayers and cell membranes.
Publisher: Springer Science and Business Media LLC
Date: 30-01-2017
DOI: 10.1038/NCHEM.2706
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2OB25934F
Abstract: Three tetra-triazole macrocycles were synthesized in good yields by the copper(i)-catalysed cycloaddition of bis-triazole azides and bis-alkynes. One of these was alkylated to give a cyclic tetra-triazolium receptor, which complexes anions strongly in competitive DMSO-water mixtures. In 1 : 1 DMSO-water, the tetracationic receptor exhibits a preference for the larger halides, bromide and iodide, with all halides associating more strongly than the oxoanion, acetate. The sulfate dianion is complexed far more strongly than any of the monobasic anions (K(a) > 10(4) M(-1)). Quantum mechanics/molecular mechanics simulations corroborate the experimentally determined anion binding selectivity trends.
Publisher: American Chemical Society (ACS)
Date: 18-03-2009
DOI: 10.1021/JA809905X
Abstract: The design, synthesis, structure, and anion-binding properties of the first indolocarbazole-containing interlocked structure are described. The novel [2]rotaxane molecular structure incorporates a neutral indolocarbazole-containing axle component which is encircled by a tetracationic macrocycle functionalized with an isophthalamide anion recognition motif. (1)H NMR and UV-visible spectroscopies and X-ray crystallography demonstrated the importance of pi-donor-acceptor, CH...pi, and electrostatic interactions in the assembly of pseudorotaxanes between the electron-deficient tetracationic macrocycle and a series of pi-electron-rich indolocarbazole derivatives. Subsequent urethane stoppering of one of these complexes afforded a [2]rotaxane, which was shown by (1)H NMR spectroscopic titration experiments to exhibit enhanced chloride and bromide anion recognition compared to its non-interlocked components. Computational molecular dynamics simulations provide further insight into the mechanism and structural nature of the anion recognition process, confirming it to involve cooperative hydrogen-bond donation from both macrocycle and indolocarbazole components of the rotaxane. The observed selectivity of the [2]rotaxane for chloride is interpreted in terms of its unique interlocked binding cavity, defined by the macrocycle isophthalamide and indolocarbazole N-H protons, which is complementary in size and shape to this halide guest.
Publisher: Wiley
Date: 27-12-2019
Abstract: The anion-binding and transport properties of an extensive library of thiophene-based molecules are reported. Seventeen bis-urea positional isomers, with different binding conformations and lipophilicities, have been synthesized by appending α- or β-thiophene or α-, β-, or γ-benzo[b]thiophene moieties to an ortho-phenylenediamine central core, yielding six subsets of positional isomers. Through
Publisher: Wiley
Date: 16-01-2012
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3OB41522H
Location: Portugal
Location: Portugal
Start Date: 2021
End Date: 2002
Funder: Australian Research Council
View Funded ActivityStart Date: 10-2021
End Date: 10-2025
Amount: $370,000.00
Funder: Australian Research Council
View Funded Activity