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Proton Transfer Reaction (proton + transfer_reaction)

Distribution by Scientific Domains

Chemistry	93%

Distribution within Chemistry

General & Introductory Chemistry	27%
Computational Chemistry & Molecular Modeling	21%
Mass Spectrometry	13%

Selected Abstracts

Theoretical Studies on Proton Transfer Reactions of 8-Hydroxyquinoline Monomers and Dimers

CHINESE JOURNAL OF CHEMISTRY, Issue 6 2006
Ji-Yang Zhao
Abstract Density functional theory (DFT) of quantum chemistry method was employed to investigate proton transfer reactions of 8-hydroxyquinoline (8-HQ) monomers and dimers. By studying the potential energy curves of the isomerization, the most possible reaction pathway was found. The total energy of 8-hydroxyquinoline was lower than that of quinolin-8(1H)-one, whereas the order was reversed in dimers. The findings explained the contrary experimental phenomena. The minimum reaction barrier of intramolecular proton transfer was 47.3 kJ/mol while that in dimer was only 25.7 kJ/mol. Hence it is obvious that proton transfer reactions of 8-HQ monomer have a considerable rate but it is easier to proceed for 8-HQ dimer than monomers. It implied that the hydrogen bond played an important role in depressing the activation energy of reaction. The mechanism of the tautomerization was discussed on the basis of theoretical results. [source]

Behaviour of [PdH(dppe)2]X (X=CF3SO3,, SbF6,, BF4,) as Proton or Hydride Donor: Relevance to Catalysis

CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2004
Michele Aresta Prof.
Abstract The synthesis, characterization and properties of [PdH(dppe)2]+CF3SO3,,0.125,THF (1; dppe=1,2-bis(diphenylphosphanyl)ethane) and its SbF6, (1,) and BF4, (1,,) analogues, the missing members of the [MH(dppe)2]+X, (M=Ni, Pd, Pt) family, are described. The Pd hydrides are not stable in solution and can react as proton or hydride donors with formation of dihydrogen, [Pd(dppe)2]2+ and [Pd(dppe)2]. Complexes 1,1,, react with carbocations and carbanions by transferring a hydride and a proton, respectively. Such H, or H+ transfer occurs also towards unsaturated compounds, for example, hydrogenation of a CC double bond. Accordingly, 1 can hydrogenate methyl acrylate to methyl propionate. Complex 1,, is an effective (hourly turnover frequency=16) and very selective (100,%) catalyst for the hydrogenation of cyclohexen-2-one to cyclohexanone with dihydrogen under mild conditions. Density functional calculations coupled with a dielectric continuum model were carried out to compute the energetics of the hydride/proton transfer reactions, which were used to rationalize some of the experimental findings. Theory provides strong support for the thermodynamic and kinetic viability of a tetracoordinate Pd complex as an intermediate in the reactions. [source]

Influence of carbonation on aroma release from liquid systems using an artificial throat and a proton transfer reaction,mass spectrometric technique (PTR,MS)

FLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2009
Maria Ángeles Pozo-Bayón
Abstract To determine whether carbonation affects aroma release from liquid systems, carbonated and non-carbonated flavoured model systems were prepared and volatile release was determined under static (equilibrium) and dynamic conditions. A model flavour system was added as a single compound or as a mixture of the six aroma compounds used in this study. Volatile release under dynamic conditions involved using a home-made device simulating an artificial throat, coupled to a proton transfer mass spectrometer (PTR,MS). The results showed that carbonation increased the release of most of the aroma compounds in both static and in dynamic testing conditions. The extent of this effect depended, however, on the physicochemical characteristics of the aroma compounds (the most volatile and most hydrophobic compounds were affected more). Release was also increased if the aroma compounds were added as a mixture rather than as individual compounds. CO2 appears to be a key factor responsible for the enhanced release of flavourings from carbonated liquid systems. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Theoretical study of CH,O hydrogen bond in proton transfer reaction of glycine

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2006
P. Selvarengan
Abstract Density functional theory (DFT) calculations are used to study the strength of the CH,O H-bond in the proton transfer reaction of glycine. Comparison has been made between four proton transfer reactions (ZW1, ZW2, ZW3, SCRFZW) in glycine. The structural parameters of the zwitterionic, transition, and neutral states of glycine are strongly perturbed when the proton transfer takes place. It has been found that the interaction of water molecule at the side chain of glycine is high in the transition state, whereas it is low in the zwitterionic and neutral states. This strongest multiple hydrogen bond interaction in the transition state reduces the barrier for the proton transfer reaction. The natural bond orbital analysis have also been carried out for the ZW2 reaction path, it has been concluded that the amount of charge transfer between the neighboring atoms will decide the strength of H-bond. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

Nitric Acid Dissociation at an Aqueous Surface: Occurrence and Mechanism

ISRAEL JOURNAL OF CHEMISTRY, Issue 2 2009
Shuzhi Wang
Here we briefly review some highlights of our recent work on the acid dissociation of nitric acid HNO3 at an aqueous surface, a proton transfer reaction of interest not only from a fundamental perspective, but also in connection with heterogeneous chemistry in a wide range of atmospheric contexts. Two types of studies of the potential acid dissociation are discussed, quantum chemical reaction path calculations to assess the reaction free energy and Car-Parrinello molecular dynamics simulations to assess the reaction feasibility. We discuss the agreement and disagreement between the predictions of these two calculations as a function of the initial location of the HNO3 molecule, ranging from a positioning on top of the aqueous surface to one several water layers below the surface. Special attention is given to the four key water solvent motions found to be necessary for the proton transfer reaction to occur. Finally, an Eigen cation, rather than a Zundel cation, is in all cases found to be predominant next to the nitrate ion in contact ion pairs produced in the acid dissociation. This predominance remains, although diminished, for solvent-separated ion pairs. [source]

Implementation of an adaptive umbrella sampling method for the calculation of multidimensional potential of mean force of chemical reactions in solution

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2003
Ramkumar Rajamani
Abstract We describe the implementation of an adaptive umbrella sampling method, making use of the weighted histogram analysis method, for computing multidimensional potential of mean force for chemical reaction in solution. The approach is illustrated by investigating the effect of aqueous solution on the free energy surface for the proton transfer reaction of [H3N,H,NH3]+ using a combined quantum mechanical and molecular mechanical AM1/TIP3P potential. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1775,1781, 2003 [source]

Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxides

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2003
David Rondeau
Abstract Organic peroxides such as the cumene hydroperoxide I (Mr = 152 u), the di- tert -butyl peroxide II (Mr = 146 u) and the tert -butyl peroxybenzoate III (Mr = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water,methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (,50 °C) and probe temperature (70,200 °C). The mass spectra of these compounds show the formation of (i) an [M + H]+ ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH3OH2]+ ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH3OH2+, i.e. thermochemical parameters () and two kinetic factors such as the capture constant of the initial stable ion,dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Electron transfer dissociation in the hexapole collision cell of a hybrid quadrupole-hexapole Fourier transform ion cyclotron resonance mass spectrometer

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2008
Desmond A. Kaplan
Electron transfer dissociation (ETD) of proteins is demonstrated in a hybrid quadrupole-hexapole Fourier transform ion cyclotron resonance mass spectrometer (Qh-FTICRMS). Analyte ions are selected in the mass analyzing quadrupole, accumulated in the hexapole linear ion trap, reacted with fluoranthene reagent anions, and then analyzed via an FTICR mass analyzer. The hexapole trap allows for a broad fragment ion mass range and a high ion storage capacity. Using a 3,T FTICRMS, resolutions of 60,000 were achieved with mass accuracies averaging below 1.4,ppm. The high resolution, high mass accuracy ETD spectra provided by FTICR obviates the need for proton transfer reaction (PTR) charge state reduction of ETD product ions when analyzing proteins or large peptides. This is demonstrated with the ETD of ubiquitin and apomyoglobin yielding sequence coverages of 37 and 20%, respectively. We believe this represents the first reported successful combination of ETD and a FTICRMS. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Theoretical study of CH,O hydrogen bond in proton transfer reaction of glycine

Solvent effects on glycine II.

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2004
Water-assisted tautomerization
Abstract The water-assisted tautomerization of glycine has been investigated at the B3LYP/6-31+G** level using supermolecules containing up to six water molecules as well as considering a 1:1 glycine,water complex embedded in a continuum. The conformations of the tautomers in this mechanism do not display an intramolecular H bond, instead the functional groups are bridged by a water molecule. The replacement of the intramolecular H bond by the bridging water reduces the polarity of the NH bond in the zwitterion and increases that of the OH bond in the neutral, stabilizing the zwitterion. Both the charge transfer effects and electrostatic interactions stabilize the nonintramolecularly H-bonded zwitterion conformer over the intramolecularly hydrogen bonded one. The nonintramolecularly H-bonded neutral is favored only by charge transfer effects. Although there is no strong evidence whether the intramolecularly hydrogen bonded or non hydrogen bonded structures are favored in the bulk solution represented as a dielectric continuum, it is likely that the latter species are more stable. The free energy of activation of the water-assisted mechanism is higher than the intramolecular proton transfer channel. However, when the presumably higher conformational energy of the zwitterion reacting in the intramolecular mechanism is taken into account, both mechanisms are observed to compete. The various conformers of the neutral glycine may form via multiple proton transfer reactions through several water molecules instead of a conformational rearrangement. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 690,703, 2004 [source]

The nitro anomaly and Brønsted ,nuc values in SN2 reactions on chlorine,

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2002
Linoam Eliad
Abstract The kinetics of chlorine transfer reactions between N -chlorosuccinimide (NCS) and four carbon nucleophiles (the conjugated bases of phenyldinitromethane, Meldrum's acid, phenylmalononitrile and phenylnitro-methane) in water were determined. A plot of log k for the SN2 reactions vs the pKa of the first three conjugated acids of the nucleophiles gave a straight line with a slope (,nuc) of 1.8. The data point for the mononitro derivative, phenylnitromethane, deviates negatively from the line by 6.7 log units. This deviation is typical of proton transfer reactions and was recently shown to occur also in SN2 reactions on bromine. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Gas-phase basicities of polyfunctional molecules.

MASS SPECTROMETRY REVIEWS, Issue 6 2007
Part 1: Theory, methods
Abstract The experimental and theoretical methods of determination of gas-phase basicities, proton affinities and protonation entropies are presented in a tutorial form. Particularities and limitations of these methods when applied to polyfunctional molecules are emphasized. Structural effects during the protonation process in the gas-phase and their consequences on the corresponding thermochemistry are reviewed and classified. The role of the nature of the basic site (protonation on non-bonded electron pairs or on ,-electron systems) and of substituent effects (electrostatic and resonance) are first examined. Then, linear correlations observed between gas-phase basicities and ionization energies or substituent constants are recalled. Hydrogen bonding plays a special part in proton transfer reactions and in the protonation characteristics of polyfunctional molecules. A survey of the main properties of intermolecular and intramolecular hydrogen bonding in both neutral and protonated species is proposed. Consequences on the protonation thermochemistry, particularly of polyfunctional molecules are discussed. Finally, chemical reactions which may potentially occur inside protonated clusters during the measurement of gas-phase basicities or inside a protonated polyfunctional molecule is examined. Examples of bond dissociations with hydride or alkyl migrations, proton transport catalysis, tautomerization, cyclization, ring opening and nucleophilic substitution are presented to illustrate the potentially complex chemistry that may accompany the protonation of polyfunctional molecules. © 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:775,835, 2007 [source]

Dynamic Study of Excited State Hydrogen-bonded Complexes of Harmane in Cyclohexane,Toluene Mixtures,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2002
Carmen Carmona
ABSTRACT Photoinduced proton transfer reactions of harmane or 1-methyl-9H -pyrido[3,4- b]indole (HN) in the presence of the proton donor hexafluoroisopropanol (HFIP) in cyclohexane,toluene mixtures (CY,TL; 10% vol/vol of TL) have been studied. Three excited state species have been identified: a 1:2 hydrogen-bonded proton transfer complex (PTC), between the pyridinic nitrogen of the substrate and the proton donor, a hydrogen-bonded cationlike exciplex (CL*) with a stoichiometry of at least 1:3 and a zwitterionic exciplex (Z*). Time-resolved fluorescence measurements evidence that upon excitation of ground state PTC, an excited state equilibrium is established between PTC* and the cationlike exciplex, CL*, ,em, 390 nm. This excited state reaction is assisted by another proton donor molecule. Further reaction of CL* with an additional HFIP molecule produces the zwitterionic species, Z*, ,em, 500 nm. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the mechanism of these excited state reactions has been established. Thus, three rate constants and three reciprocal lifetimes have been determined. The simultaneous study of 1,9-dimethyl-9H -pyrido[3,4- b]indole (MHN) under the same experimental conditions has helped to understand the excited state kinetics of these processes. [source]