Guy Bouchoux
Paris Sud XI University, Chemistry, Emeritus
Extensive exploration of the potential energy surfaces of protonated Nα-acetylhistidine hydrated by 0 to 3 molecules of water was performed. The methodology combined hierarchical and genealogical (Darwin family tree) approaches using... more
Extensive exploration of the potential energy surfaces of protonated Nα-acetylhistidine hydrated by 0 to 3 molecules of water was performed. The methodology combined hierarchical and genealogical (Darwin family tree) approaches using polarizable AMOEBA force field and M06 functional. It is demonstrated that this mixed approach allows recovering a number of conformers larger than when using any one of the two methods alone. Hydration enthalpies of protonated Nα-acetylhistidine and of model compounds have been computed using higher theoretical methods, up to the G4MP2 procedure. Excellent agreement with experiment is observed for successive hydration of methylamonium and imidazolium cations using MP2/6-311++G(2d,2p)//M06/6-311++G(d,p) and G4MP2 methods, thereby validating the theory levels used for hydrated protonated Nα-acetylhistidine. It is found that first hydration enthalpy of protonated Nα-acetylhistidine is ca. 10 kJ.mol-1 lower than that of imidazolium, a result explained by t...
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A microcanonical analysis of the thermokinetic method is performed using statistical rate calculations based on orbiting transition state theory in order to model a proton transfer process: MH(+) + B(i) -->... more
A microcanonical analysis of the thermokinetic method is performed using statistical rate calculations based on orbiting transition state theory in order to model a proton transfer process: MH(+) + B(i) --> M + B(i)H(+). The reaction efficiency is calculated as a function of the difference in zero point energy of reactants and products. Several models of reactions were investigated in order to simulate situations where the base of interest M exhibits loss of entropy upon protonation of up to approximately 40 J mol(-1) K(-1). It is shown that the standard thermokinetic method would predict correct 298 K gas phase basicities, GB(298)(M), even for polydentate molecules M, if experiments are conducted at this temperature. Proton affinity, PA(298)(M), and protonation entropy may be obtained by the thermokinetic method only in special circumstances such as, for example, experiments conducted at various temperatures.
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ABSTRACT An experimental and theoretical study of the protonation of representative dicarbonyl compounds M = 2,3-butanedione (biacetyl), 1, 2,4-pentanedione (acetylacetone), 2, 2,5-hexanedione (acetonylacetone), 3, and... more
ABSTRACT An experimental and theoretical study of the protonation of representative dicarbonyl compounds M = 2,3-butanedione (biacetyl), 1, 2,4-pentanedione (acetylacetone), 2, 2,5-hexanedione (acetonylacetone), 3, and methyl-acetoacetate, 4 has been carried out. The experimental proton affinities and protonation entropies have been obtained by the extended kinetic method using the orthogonal distance regression (ODR) treatment. Theoretical proton affinities are calculated at the G2MP2 level of theory while protonation entropies were estimated after a detailed treatment of the internal rotations. The data show that protonation of 1 and 2 is associated with negligible protonation entropies while significant negative values are obtained for molecules 3 and 4. Protonation of 2,3-butanedione, 1a, is associated with a tautomerisation inside the proton transfer complex thus leading to protonated 2-hydroxy-butenone, 1bH+. Protonation thermochemistry of 2,4-pentanedione 2 may be simply rationalized by the protonation of its most stable tautomer, the 4-hydroxy-3-pentene-2-one, 2b, to give its most stable protonated form 2bH+ stabilized by a strong intramolecular hydrogen bond. Protonation of 2,5-hexanedione 3a most probably produces a cyclic structure stabilized by a covalent bonding, 3aHc+. The structure of neutral methyl acetoacetate 4 sampled during protonation in mass spectrometry experiments appears to be its diketonic form 4a; its protonation leading to an internally hydrogen bonded stabilized structure 4aH+.
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ABSTRACT Using a combination of tandem mass spectrometry methodologies, collisional activation of fast (8 keV) or slow (20-30 eV) ion beams, neutralization-reionization and ion-molecule reactions, it is shown that thiosulfoxides X2S=S (X... more
ABSTRACT Using a combination of tandem mass spectrometry methodologies, collisional activation of fast (8 keV) or slow (20-30 eV) ion beams, neutralization-reionization and ion-molecule reactions, it is shown that thiosulfoxides X2S=S (X = H, CH3, C2H5) are stable in the gas phase as radical cations as well as neutral molecules, The absence of isomerization into the more conventional disulfane structure, XSSX, is firmly demonstrated by ion-molecule reactions of the isomeric ions with methyl isocyanide and by collisional activation of "survivor" ions generated in neutralization-reionization experiments. All the mass spectral data have been recorded with a single hybrid mass spectrometer of sectors-quadrupole-sectors configuration. Molecular orbital calculations demonstrate that ionized thiosulfoxides and disulfanes are local minima on the MP2/6-31G* potential energy surface. The disulfane structures are found to be the most stable species by 91, 65 and 59 kJ/mol for X = H, CH3 and C2H5, respectively. Heat of formation values of 1000, 810 and 760 kJ/mol are estimated for X2SS.+ ions (X = H, CH3 and C2H5, respectively). (C) 2000 Elsevier Science B.V.
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The generation of carbene radical cations (R C R·+) and related ions in the gas phase using various mass spectrometric techniques is critically reviewed. Their reactions as well as their thermochemical properties obtained either... more
The generation of carbene radical cations (R C R·+) and related ions in the gas phase using various mass spectrometric techniques is critically reviewed. Their reactions as well as their thermochemical properties obtained either experimentally or from ab initio quantum ...
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ABSTRACT Ion-molecule reactions between ionized carbonyl compounds or ionized enols with t-butyl nitrite allow a clear-cut distinction to be made between both these isomeric structures. The most relevant difference between the observed... more
ABSTRACT Ion-molecule reactions between ionized carbonyl compounds or ionized enols with t-butyl nitrite allow a clear-cut distinction to be made between both these isomeric structures. The most relevant difference between the observed reactions is the formal substitution of a hydrogen atom by nitric oxide in the enol ions. Collisional activation experiments on the product ions are interpreted in terms of alpha-nitroso carbonyl structures. However, a quantum chemical investigation at the B3LYP/6-311++G(d,p) level of theory shows that ionized alpha-nitroso carbonyl and vinyl nitrite structures may isomerize provided they contain ca 60 kj mol(-1) of internal energy. It is, therefore, possible that both structures are generated in the substitution reaction.
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Quantum chemistry calculations using composite G3B3, G3MP2B3 and CBS-QB3 methods were performed for benzaldehyde, 1, tropone, 2, ortho-quinone methide, 3, para-quinone methide, 4, their protonated forms 1H+–4H+ and the isomeric... more
Quantum chemistry calculations using composite G3B3, G3MP2B3 and CBS-QB3 methods were performed for benzaldehyde, 1, tropone, 2, ortho-quinone methide, 3, para-quinone methide, 4, their protonated forms 1H+–4H+ and the isomeric meta-hydroxybenzyl cation 5H+. The G3B3 298K heats of formation values obtained in this work are: −39, 61, 52, 39, 661, 679, 699, 680 and 733kJmol−1 for 1–4, 1H+–5H+, respectively. At
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... GUY BOUCHOUX et MARCEL FBTIZON Laboratoire de StBrBochimie, Universite de Paris-Sud, Centre d'Orsay, 91405 Orsay, France ... d'activation dans les approximations de Rabinovitch et Vestal Les approximations de Vestal et de... more
... GUY BOUCHOUX et MARCEL FBTIZON Laboratoire de StBrBochimie, Universite de Paris-Sud, Centre d'Orsay, 91405 Orsay, France ... d'activation dans les approximations de Rabinovitch et Vestal Les approximations de Vestal et de Rabinovitch conduisent 21 basse Cnergie B ...
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Ab initio molecular orbital calculations were carried out to determine the activation energy of the methane loss from the dimethyloxonium cation. At the approximate MP4SDTQ/6-311 + +G(2df,2p) + ZPE level based on... more
Ab initio molecular orbital calculations were carried out to determine the activation energy of the methane loss from the dimethyloxonium cation. At the approximate MP4SDTQ/6-311 + +G(2df,2p) + ZPE level based on MP2/6-31G(d,p)-geometries, the energy barrier is calculated to be 267 ± 15 kJ mol-1.
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Page 1. Organic Mass Spectrometry. 1976. Vol. 11. pp. 712 to 721. @ Heyden & Son Limited. Printed in Northern Ireland REARRANGEMENTS 1,3 EN SERIE HETEROCYCLIQUE. VI-FRAGMENTATION, EN SPECTROMETRIE ...
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... and Jeanine TortajadaS Dtpartement de Chimie, Groupe Masse-Chimie Thiorique, Ecole Polytechnique, 91 128 Palaiseau Cedex, France Jacques Dagaut ... The bond dissociation energies of primary, secondary and tertiary CH bonds were taken... more
... and Jeanine TortajadaS Dtpartement de Chimie, Groupe Masse-Chimie Thiorique, Ecole Polytechnique, 91 128 Palaiseau Cedex, France Jacques Dagaut ... The bond dissociation energies of primary, secondary and tertiary CH bonds were taken equal to 410,397 and 389 kJ mol ...
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The proton affinity, PA, and protonation entropy, Delta(p)S degree, of glycine (Gly), 1, aspartic acid (Asp), 2, asparagine (Asn), 3, histidine (His), 4, lysine (Lys), 5, glutamic acid (Glu), 6, and glutamine (Gln), 7, have been... more
The proton affinity, PA, and protonation entropy, Delta(p)S degree, of glycine (Gly), 1, aspartic acid (Asp), 2, asparagine (Asn), 3, histidine (His), 4, lysine (Lys), 5, glutamic acid (Glu), 6, and glutamine (Gln), 7, have been reinvestigated by the extended kinetic method, using the "isothermal point" method and the orthogonal distance regression, ODR, technique. The proton affinity values of a-aminoacids bearing a basic residue (PA = 926.8; 965.2; 996.0; 993.9; 981.8 and 988.1 kJ.mol(-1) for 2-7, respectively) show significant deviation from the tabulated values. As expected from the effect of a strong intramolecular hydrogen bond in the protonated forms of these peculiar aminoacids, negative protonation entropies are detected (Delta(p)S degree = 36; 43; 37; 29; 95 and 55 J mol(-1) K(-1) for for 27 respectively).
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The proton affinities of 2(5H)-furanone, 1 (836 kJ/mol), 5,6-dihydro-2H-pyran-2-one, 2 (862 kJ/mol), cyclopentenone, 3 (857 kJ/mol), and cyclohexenone, 4 (863 kJ/mol), have been measured by Fourier transform ion cyclotron resonance... more
The proton affinities of 2(5H)-furanone, 1 (836 kJ/mol), 5,6-dihydro-2H-pyran-2-one, 2 (862 kJ/mol), cyclopentenone, 3 (857 kJ/mol), and cyclohexenone, 4 (863 kJ/mol), have been measured by Fourier transform ion cyclotron resonance techniques. A comparison is made with (reexamined) data concerning saturated cyclic and unsaturated aliphatic analogs. Three general observations are made. First, the basicity is found to increase with the size of the ring. Second, unsaturated lactones are more basic than their corresponding aliphatic unsaturated esters. Third, unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated cyclic ketones are more basic than their saturated analogs. All these experimental findings have been rationalized by means of ab initio calculations up to the G2(MP2,SVP) level. The basicity trends along the series are the result of two main factors: t...
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The gas-phase basicities of a representative set of hydroxy- and methoxycarbonyl compounds (hydroxyacetone, 1, 3-hydroxybutanone, 2, 3-hydroxy-3-methylbutanone, 3, 1-hydroxy-2-butanone, 4, 4-hydroxy-2-butanone, 5, 5-hydroxy-2-pentanone,... more
The gas-phase basicities of a representative set of hydroxy- and methoxycarbonyl compounds (hydroxyacetone, 1, 3-hydroxybutanone, 2, 3-hydroxy-3-methylbutanone, 3, 1-hydroxy-2-butanone, 4, 4-hydroxy-2-butanone, 5, 5-hydroxy-2-pentanone, 6, methoxyacetone, 7, 3-methoxy-2-butanone, 8, 4-methoxy-2-butanone, 9, and 5-methoxy-2-pentanone, 10) were experimentally determined by the equilibrium method using Fourier transform ion cyclotron resonance and high-pressure mass spectrometry techniques. The latter method allows the measurement of proton transfer equilibrium constants at various temperatures and thus the estimate of both the proton affinities and the protonation entropies of the relevant species. Quantum chemical calculations at the G3 and the B3LYP/6-311+G(3df,2p)//6-31G(d) levels of theory were undertaken in order to find the most stable structures of the neutrals 1-10 and their protonated forms. Conformational and vibrational analyses have been done with the aim of obtaining a th...
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The proton affinities of 2(5H)-furanone, 1 (836 kJ/mol), 5,6-dihydro-2H-pyran-2-one, 2 (862 kJ/mol), cyclopentenone, 3 (857 kJ/mol), and cyclohexenone, 4 (863 kJ/mol), have been measured by Fourier transform ion cyclotron resonance... more
The proton affinities of 2(5H)-furanone, 1 (836 kJ/mol), 5,6-dihydro-2H-pyran-2-one, 2 (862 kJ/mol), cyclopentenone, 3 (857 kJ/mol), and cyclohexenone, 4 (863 kJ/mol), have been measured by Fourier transform ion cyclotron resonance techniques. A comparison is made with (reexamined) data concerning saturated cyclic and unsaturated aliphatic analogs. Three general observations are made. First, the basicity is found to increase with the size of the ring. Second, unsaturated lactones are more basic than their corresponding aliphatic unsaturated esters. Third, unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated cyclic ketones are more basic than their saturated analogs. All these experimental findings have been rationalized by means of ab initio calculations up to the G2(MP2,SVP) level. The basicity trends along the series are the result of two main factors: the different hybridization pattern of the carbonyl carbon as the size of the ring changes and, in the case of lactones, the nonbonding interaction between the proton attached to the carbonyl group and the ether-like oxygen which contributes to the enhanced stability of the protonated form. For unsaturated ketones the C=C double bond participates fully in the change in charge distribution induced by the protonation, while for unsaturated lactones the existence of an oxygen atom within the ring impedes this shift of the electron density.
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The complexes [L(5)Fe(II)Cl]BPh(4) and [L(5)Fe(II)(H(2)O)](BPh(4))(2) (L(5) =... more
The complexes [L(5)Fe(II)Cl]BPh(4) and [L(5)Fe(II)(H(2)O)](BPh(4))(2) (L(5) = N,N,N'-tris(2-pyridylmethyl)-N'-methyl-ethane-1,2-diamine) have been isolated. Bernal et al. (Bernal, J.; et al. J. Chem. Soc., Dalton Trans. 1995, 3667-3675) have prepared this ligand and the corresponding complex [L(5)Fe(II)Cl]PF(6). We obtained the structural data of [L(5)Fe(II)Cl]BPh(4) by X-ray diffraction. It crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 17.645(7) Å, b = 16.077(6) Å, c = 13.934(5) Å, V = 3953(3) Å(3), and Z = 4. It presents Fe(II)-N bond lengths close to 2.2 Å, typical of high-spin Fe(II). In solution the [L(5)Fe(II)(H(2)O)](BPh(4))(2) complex showed a dependence of spin state upon the nature of the solvent. It was high spin in acetone and changed to low spin in acetonitrile. This was detected by UV-vis spectroscopy and by (1)H NMR. Bernal et al. (ibidem) showed that these complexes in the presence of an excess of H(2)O(2) give a purple species, very likely the [L(5)Fe(III)(OOH)](2+) derivative, with spectroscopic signatures analogous to those of "activated bleomycin". The formation of [L(5)Fe(III)(OOH)](2+) is confirmed here by electrospray ionization mass spectrometry. We found that a L(5)/Fe system gave single-strand breaks on plasmid DNA in the presence of either a reducing agent (ascorbate) and air or oxidants (H(2)O(2), KHSO(5), MMPP) at 0.1 &mgr;M concentration. The methyl group in L(5) was substituted by a (CH(2))(5)N(CH(3))(3)(+) group in order to get higher affinity with DNA. The corresponding ligand L(5)(+) was used to prepare the complexes [L(5)(+)Fe(II)Cl]Y(2) (Y = BPh(4)(-), PF(6)(-), ClO(4)(-)) and [L(5)(+)Fe(II)Br](PF(6))(2). The crystal structure of [L(5)(+)Fe(II)Cl](ClO(4))(2) was solved. It crystallizes in the monoclinic space group P2(1)/a with a = 14.691(2) Å, b = 13.545(2) Å, c = 17.430(2) Å, beta = 93.43(1) degrees, V = 3462(1) Å(3), and Z = 4. The Fe(II)-ligand distances are similar to those of [L(5)Fe(II)Cl]BPh(4). At the relatively low concentration of 0.01 &mgr;M, [L(5)(+)Fe(II)Br](2+) promoted DNA breaks. The reaction was not inhibited by hydroxyl radical scavengers. The reaction might involve a nondiffusible oxygen reactive species, either a coordinated hydroperoxide or a high-valent metal-oxo entity.
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The chemistry leading to the competitive eliminations of H, CH(3), and OCOCH(3) from adducts of ionized methyl benzoate and neutral methyl isocyanide has been explored using density functional theory molecular orbital calculations. The... more
The chemistry leading to the competitive eliminations of H, CH(3), and OCOCH(3) from adducts of ionized methyl benzoate and neutral methyl isocyanide has been explored using density functional theory molecular orbital calculations. The energies of the various reactants and transition structures were estimated at the B3LYP/6-31+G(d,p) level of theory. Nucleophilic aromatic substitution is proposed to account for the H and OCOCH(3) eliminations. The corresponding sigma-complex intermediates, B(1ipso) and B(1ortho), are stable species lying in deep energy wells situated 70 and 120 kJ/mol, respectively, below the reactants, ionized methyl benzoate and methyl isocyanide. The latter complex, B(1ortho), may be also at the origin of a multistep rearrangement involving hydrogen migrations and methyl elimination from the original methoxy group of the benzoate moiety.
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ABSTRACT The proton affinities of 1,2-ethane diol (1), 1,3-propane diol (2), and 1,4-butane diol (3) were calculated by ab initio molecular orbital calculations at the G2(MP2) level. The values (PA(1) = 795.3, PA(2) = 851.5, and PA(3) =... more
ABSTRACT The proton affinities of 1,2-ethane diol (1), 1,3-propane diol (2), and 1,4-butane diol (3) were calculated by ab initio molecular orbital calculations at the G2(MP2) level. The values (PA(1) = 795.3, PA(2) = 851.5, and PA(3) = 882.4 kJ·mol-1) are in agreement with recent determinations using the kinetic method but at variance with previous results obtained from equilibrium constant measurements. Entropy differences, ΔpS°(M) = S°(MH+) − S°(M) (M = 1−3), were estimated by explicitly considering the rotational barriers of the torsional modes in both the neutral and the protonated molecules, M. Absolute values of calculated ΔpS° (−5, −22, and −32 J·mol-1·K-1 for M = 1, 2, and 3, respectively) are lower than that presently available in the literature. Combining the calculated PA(M) and ΔpS°(M) leads to gas-phase basicities GB(M) equal to 761.4, 812.4, and 840.4 kJ·mol-1 for M = 1, 2, and 3, respectively.
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The present paper reports the first experimental and theoretical results concerning the reaction of [1, 3-butadiene]+ radical cation, 1, with neutral acetylene C2H2, 2. Experiments conducted in the gas phase and under low pressure in an... more
The present paper reports the first experimental and theoretical results concerning the reaction of [1, 3-butadiene]+ radical cation, 1, with neutral acetylene C2H2, 2. Experiments conducted in the gas phase and under low pressure in an FT-ICR mass spectrometer ...
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Di-n-butyl sulfate (DNBS) has been studied by electrospray (ESI) and chemical (CI) ionization mass spectrometry. The use of methanol as solvent in electrospray ionization allows observation of relatively abundant [DNBS + CH(3)OH + H](+)... more
Di-n-butyl sulfate (DNBS) has been studied by electrospray (ESI) and chemical (CI) ionization mass spectrometry. The use of methanol as solvent in electrospray ionization allows observation of relatively abundant [DNBS + CH(3)OH + H](+) ions (m/z 243) which upon collision dissociate to [DNBS + H](+) ions (m/z 211). In both ESI and CI experiments, it is found that [DNBS + H](+) ions lead to m/z 113 daughter ions. The composition of this m/z 113 fragment ion and its mechanism of formation have been established by high resolution measurements and CID-MIKE experiments. An 'internal substitution' reaction involving an ion-neutral intermediate is proposed to explain the formation of a [C(8)H(17)](+) ion (m/z 113) by loss of a H(2)SO(4) molecule. Finally, a LC/ESI-MS/MS quantification method is proposed in which a detection limit of di-n-butyl sulfate in the ppm range is obtained. It is suggested that the quantification method might be extended to higher dialkyl sulfates. Copyright 2000 John Wiley & Sons, Ltd.
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... Raymond Houriet and Eric Rolli Institut de Chimie Physique, EPFL, CH 1015 Lausanne, Switzerland ... 9, Academic Press, New York (1979); (b) R. Walder and JL Franklin, Int. J. Mass Spectrom. /on Phys. 36,85 (1980); (c) CT Moylan and J.... more
... Raymond Houriet and Eric Rolli Institut de Chimie Physique, EPFL, CH 1015 Lausanne, Switzerland ... 9, Academic Press, New York (1979); (b) R. Walder and JL Franklin, Int. J. Mass Spectrom. /on Phys. 36,85 (1980); (c) CT Moylan and J. I. Brauman, Ann. Rev. fhys. Chem. ...