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Guy Bouchoux - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of the protonation thermochemistry obtained by the extended Kinetic Method.
Journal of Mass Spectrometry, 2006Co-Authors: Guy BouchouxAbstract:An evaluation of the results obtained by the extended Kinetic Method for a series of representative bases is presented here. Analysis of the original experimental data is conducted using the orthogonal distance regression (ODR) statistical treatment. A comparison with the proton affinities and protonation entropies obtained from variable temperature equilibrium constant measurements demonstrate deviations, which may be ascribed to random and systematic errors. Considerable random errors are associated with the extended Kinetic Method if the number of reference bases and the range of effective temperatures are too low. It is also confirmed that large systematic errors on proton affinities and protonation entropies are obtained when large protonation entropy is associated with the considered system. It is, however, encouraging to note that the gas phase basicities obtained by the extended Kinetic Method are generally comparable to that obtained by other Methods within a few kJ/mol. Copyright 2006 John Wiley & Sons, Ltd.
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Evaluation of the protonation thermochemistry obtained by the extended Kinetic Method.
Journal of mass spectrometry : JMS, 2006Co-Authors: Guy BouchouxAbstract:An evaluation of the results obtained by the extended Kinetic Method for a series of representative bases is presented here. Analysis of the original experimental data is conducted using the orthogonal distance regression (ODR) statistical treatment. A comparison with the proton affinities and protonation entropies obtained from variable temperature equilibrium constant measurements demonstrate deviations, which may be ascribed to random and systematic errors. Considerable random errors are associated with the extended Kinetic Method if the number of reference bases and the range of effective temperatures are too low. It is also confirmed that large systematic errors on proton affinities and protonation entropies are obtained when large protonation entropy is associated with the considered system. It is, however, encouraging to note that the gas phase basicities obtained by the extended Kinetic Method are generally comparable to that obtained by other Methods within a few kJ/mol.
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Obtaining thermochemical data by the extended Kinetic Method.
Journal of Mass Spectrometry, 2004Co-Authors: Guy Bouchoux, F. Berruyer-penaud, Michel SablierAbstract:A microcanonical analysis of the extended Kinetic Method is performed using statistical rate calculations based on orbiting transition state theory. The model systems simulate polydentate bases M which exhibit losses of entropy upon protonation of up to 35 kJ mol(-1) K(-1). It is shown that the correlations using the natural logarithm of the ratio of rate constants vs the proton affinity of the reference bases, at several effective temperatures, lead to correct proton affinity and protonation entropy of the base M of interest. A systematic underestimate of the latter quantity (by 5-15%), mainly due to the use of a linear rather than a polynomial curve fitting procedure, is noted, however. When considering experimental data, more severe underestimates are observed for the protonation entropies of polydentate bases (by 50-90%). The origins of these considerable discrepancies are beyond the limits of the present modeling and remain to be determined.
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Application of the Kinetic Method to bifunctional bases
International Journal of Mass Spectrometry, 2003Co-Authors: Guy Bouchoux, Fayçal Djazi, Fanny Gaillard, Delphine VierezetAbstract:Abstract An assessment of the Kinetic Method and its applicability to the determination of the basicity of bidentate molecules is done by considering several examples previously studied by equilibrium Methods. Selected examples are: 1,2-ethanediol, 1,3-propanediol, glycerol, 1,4-butanediol, 1,2-dimethoxyethane, 2-methoxyethanol methoxyacetone, 1,2-diamino ethane, 1,3-diamino propane and 1,4-diaminobutane. It is generally observed that the orthodox use of the Method leads to GB(M), PA(M) and protonation entropy values different from that obtained by the equilibrium Method.
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Application of the Kinetic Method to bifunctional bases MIKE and CID-MIKE test cases
International Journal of Mass Spectrometry, 2003Co-Authors: Guy Bouchoux, Fayçal Djazi, Fanny Gaillard, Delphine VierezetAbstract:An assessment of the Kinetic Method and its applicability to the determination of the basicity of bidentate molecules is done by considering several examples previously studied by equilibrium Methods. Selected examples are: 1,2-ethanediol, 1,3-propanediol, glycerol, 1,4-butanediol, 1,2-dimethoxyethane, 2-methoxyethanol methoxyacetone, 1,2-diamino ethane, 1,3-diamino propane and 1,4-diaminobutane. It is generally observed that the orthodox use of the Method leads to GB(M), PA(M) and protonation entropy values different from that obtained by the equilibrium Method. (C) 2003 Published by Elsevier Science B.V.
R G Cooks - One of the best experts on this subject based on the ideXlab platform.
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Mass spectrometric quantitation of chiral drugs by the Kinetic Method.
Analytical chemistry, 2001Co-Authors: W. A. Tao, Fabio C. Gozzo, R G CooksAbstract:A novel mass spectrometric Method for rapid, accurate (2-4% ee) quantitation of chiral drugs is described. Copper(II)-bound complexes of seven model drugs (atenolol, DOPA, ephedrine, pseudoephedrine, isoproterenol, norepinephrine, propranolol) with chiral reference compounds (L-amino acids) are generated by electrospray ionization mass spectrometry. The trimeric complex ions (three chiral ligands--one of the analyte and two of the reference compound) are collisionally activated, and they undergo dissociation by competitive loss of either the neutral reference or the neutral drug molecule. The ratio of the two competitive dissociation rates, viz. the product ion branching ratio, is related via the Kinetic Method to the enantiomeric composition of the drug mixture. A two-point calibration curve, derived from the Kinetic Method, allows rapid quantitation of enantiomeric excess of drug mixtures. The chiral sensitivity of the Method is such as to allow determination of mixtures with a few percent enantiomeric contamination.
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The Kinetic Method of making thermochemical determinations
Journal of Mass Spectrometry, 1999Co-Authors: R G Cooks, Jere T. Koskinen, P. D. ThomasAbstract:This critical examination of the Kinetic Method is carried out as part of a dialog-in-print with Peter Armentrout and Laszlo Drahos and Karoly Vekey. We summarise the characteristics of the Kinetic Method and try to place it in the context of other thermoKinetic Methods of making thermochemical determinations, especially the threshold collision-induced dissociation Method. We cover the approximations made in deriving the Method and tabulate five forms of the Method which have been used over the past 21 years. We show that many criticisms of the Method apply to the simplest forms and, conversely, that a great deal of information can be obtained from those forms which do not assume that entropy effects cancel. A number of cases of apparent failure of the Method are examined, including the alcohol/Li+ case described by Armentrout. We encourage continued use of each of the thermochemical Methods but recommend that these uses be informed by knowledge of the subtleties of deriving thermochemical information from relative rate measurements. Copyright © 1999 John Wiley & Sons, Ltd.
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Estimation of Free Radical Ionization Energies by the Kinetic Method and the Relationship between the Kinetic Method and the Hammett Equation.
Analytical chemistry, 1997Co-Authors: Chen G, Wong P, R G CooksAbstract:Substituted 1,2-diphenylethanes undergo competitive dissociations upon electron ionization (EI) to generate substituted benzyl cation and benzyl radical pairs. Application of the Kinetic Method to the previous reported EI mass spectra of these covalently bound precursor ions (data are taken from McLafferty et al. J. Am. Chem. Soc. 1970, 92, 6867)) is used to estimate the ionization energies of substituted benzyl free radicals. A correlation is observed between the Hammett σ constant of the substituents and the Kinetic Method parameter, ln(kx/kH), where kx is the rate of fragmentation to give the substituted product ion and kH is the rate to give the benzyl ion itself. Systems involving weakly bound cluster ions, including proton-bound dimers of meta- and para-substituted pyridines and meta- and para-substituted anilines, and electron-bound dimers of meta- and para-substituted nitrobenzenes, also show good correlations between the Kinetic Method parameter and the Hammett σ constant.
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Steroisomeric Distinction By the Kinetic Method: 2,3-Butanediol
Rapid Communications in Mass Spectrometry, 1997Co-Authors: Wenyue Shen, Philip S. H. Wong, R G CooksAbstract:The Kinetic Method is used to differentiate the diastereomers and enantiomers of 2,3-butanediol. By using a number of reference compounds of known gas phase basicity (GB), the GBs of (2R,3R- and meso-butanediol are determined as 191.5 and 191.2 kcal/mol, respectively, with an estimated uncertainty of ±0.4 kcal/mol and an uncertainty in the 0.3 kcal/mol difference of 0.12 kcal/mol. This result is consistent with a literature GB value for a mixture of isomers of 192.3 kcal/mol (C. Gruenat et al, Helv. Chim, Acta, 68, 1647 (1985). The smaller GB of the meso form is ascribed to destabilization associated with the two eclipsed methyl groups in the eclipsed conformation which is energetically favored by simultaneous bonding (chelation) of the two oxygen atoms to the proton. Differentiation between the enantiomers is achieved by collision-induced dissociation of the diasteromeric proton-bound dimers formed from each isomer with a chiral reference compound; this experiment is successful for both positively- and negatively-charged cluster ions. The observed small difference in fragment ion abundance ratios in the dissociation of these two dimers is ascribed to a difference in free energy barriers to enantiomeric product formation from the two diastereomeric intermediates. The present study demonstrates that the Kinetic Method can reveal small differences in free energies resulting from differences in chirality and, in this case at least, it provides a simple Method to differentiate steroisomers. © 1997 John Wiley & Sons, Ltd.
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Ionization energy determination by the Kinetic Method
Analytical chemistry, 1996Co-Authors: Philip S. H. Wong, R G CooksAbstract:Ionization energies of organic compounds can be determined by the Kinetic Method by dissociation of radical cations of van der Waals complexes. The ionized dimeric complexes of benzene and substituted benzenes, generated in the ion source of a multiquadrupole instrument by gentle charge exchange chemical ionization using carbon disulfide as reagent gas, when mass-selected and allowed to undergo collision-induced dissociation with argon, yield only the two individual radical cations as products. The logarithm of the ratio of their ion abundances correlates linearly with their ionization energies. Using this linear relationship, the ionization energy of 3-iodobenzonitrile was determined to be 9.39 ± 0.05 eV, and this case serves to illustrate the application of the Kinetic Method in the determination of an unknown ionization energy. From the slope of the Kinetic Method plot, it is evident that the clusters are weakly bound (effective temperature, 1670 K). Strengths of this Method are the simplicity of the p...
P. B. Armentrout - One of the best experts on this subject based on the ideXlab platform.
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Critical Evaluation of Kinetic Method Measurements: Possible Origins of Nonlinear Effects
Journal of the American Society for Mass Spectrometry, 2013Co-Authors: Sandrine Bourgoin-voillard, Carlos Afonso, Denis Lesage, Emilie Laure Zins, Jean-claude Tabet, P. B. ArmentroutAbstract:The Kinetic Method is a widely used approach for the determination of thermochemical data such as proton affinities (PA) and gas-phase acidities (ΔH° acid ). These data are easily obtained from decompositions of noncovalent heterodimers if care is taken in the choice of the Method, references used, and experimental conditions. Previously, several papers have focused on theoretical considerations concerning the nature of the references. Few investigations have been devoted to conditions required to validate the quality of the experimental results. In the present work, we are interested in rationalizing the origin of nonlinear effects that can be obtained with the Kinetic Method. It is shown that such deviations result from intrinsic properties of the systems investigated but can also be enhanced by artifacts resulting from experimental issues. Overall, it is shown that orthogonal distance regression (ODR) analysis of Kinetic Method data provides the optimum way of acquiring accurate thermodynamic information.
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Systematic and random errors in ion affinities and activation entropies from the extended Kinetic Method.
Journal of mass spectrometry : JMS, 2004Co-Authors: Kent M. Ervin, P. B. ArmentroutAbstract:An evaluation of the extended Kinetic Method with full entropy analysis was conducted using RRKM theory to simulate data for collision-induced dissociation under single-collision conditions. A rigorous Method for analyzing Kinetic Method data, orthogonal distance regression, is introduced and compared with previous Methods in the literature. The results demonstrate that the use of the extended Kinetic Method is definitely superior to the standard Kinetic Method, but final ion affinities and activation entropies differ intrinsically from the correct values. Considering the effects of both systematic and random error in Monte Carlo simulations of the full entropy analysis, error distributions of ±4 to ±12 kJ mol−1 for ion affinities and of ±9 to ±30 J mol−1 K−1 for activation entropy differences are found (±2 standard deviations of the sample populations). The systematic errors in ion affinities are larger for systems with large activation entropy differences. These uncertainties do not include any error in the absolute calibration of the reference ion affinity scale. We argue that application of an empirical correction factor is inadvisable. Copyright © 2004 John Wiley & Sons, Ltd.
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Entropy measurements and the Kinetic Method: A statistically meaningful approach
Journal of the American Society for Mass Spectrometry, 2000Co-Authors: P. B. ArmentroutAbstract:In the literature, data obtained using the Kinetic Method have been analyzed to provide both ion affinities and relative entropies for the competitive dissociations involved. In this work, the procedure used to extract this information is shown to be statistically flawed. Using more rigorous statistical procedures, we outline alternative Methods of acquiring the same information, including straightforward means of analyzing the uncertainties in the thermodynamic quantities obtained. Fortunately, it is expected that the central values reported in previous work need not be changed, but the uncertainties are much larger than has been previously detailed. The validity of the assumptions involved in the extraction of entropy effects is discussed in some detail.
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Is the Kinetic Method a thermodynamic Method
Journal of Mass Spectrometry, 1999Co-Authors: P. B. ArmentroutAbstract:The Kinetic Method is examined from the point of view of a proponent of a complementary and sometimes competitive technique, threshold collision-induced dissociation. Limitations in the Kinetic Method and assumptions that have not been thoroughly examined in the literature are pointed out. A case study involving recent experiments in the author's laboratory is used to illlustrate the importance of including entropic effects in the data analysis, even for systems where the ligands are fairly similar. The author concludes by encouraging the use of the advanced Kinetic Methods outlined by Cooks et al. in the accompanying Commentary. Copyright © 1999 by John Wiley & Sons, Ltd.
John C. Poutsma - One of the best experts on this subject based on the ideXlab platform.
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Proton Affinity of Lysine Homologues from the Extended Kinetic Method
The Journal of Physical Chemistry A, 2004Co-Authors: Olivia E. Schroeder, Kathryn E. Colyer, Erica J. Andriole, Krista L. Carver, John C. PoutsmaAbstract:The proton affinities of lysine (1) and its three homologues ornithine (2), 2,4-diaminobutanoic acid (3), and 2,3-diaminopropanoic acid (4) have been determined using two different variants of the extended Kinetic Method in an electrospray ionization−quadrupole ion trap instrument. A value of 1004.2 ± 8.0 kJ/mol is recommended for the proton affinity for lysine on the basis of this work and previous experimental measurements and theoretical predictions. Values of 1001.1 ± 6.6, 975.8 ± 7.3, and 950.2 ± 7.1 kJ/mol have been determined for the proton affinities of 2−4. These experimental results are supported by hybrid density functional theory calculations at B3LYP/6-311++G**//B3LYP/6-31+G*. An analysis of the derived entropy terms lends support to the notion that these values can be used as a quantitative prediction for the thermodynamic entropy of protonation provided that appropriate error bars are assigned. Finally, for systems in which this entropy term is large, it is essential that the extended kinet...
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The proton affinity of proline analogs using the Kinetic Method with full entropy analysis.
Journal of the American Society for Mass Spectrometry, 2002Co-Authors: Andrew F. Kuntz, Andrew W. Boynton, Geoffrey A. David, Kathryn E. Colyer, John C. PoutsmaAbstract:The proton affinity of proline analogs, L-azetidine-2-carboxylic acid (Aze), L-proline (Pro), and L-pipecolic acid (Pip), have been measured using the Armentrout modification of the extended Kinetic Method in a quadrupole ion trap instrument. Experimental values of 223.0 ± 1.5, 224.9 ± 1.6, and 225.6 ± 1.6 kcal/mol have been determined for the 298K proton affinities of Aze, Pro, and Pip respectively. High level theoretical calculations using both MP2 and B3LYP Methods at a variety of basis sets were carried out in order to give theoretical predictions for the 298 K proton affinity and gas phase basicity of all three analogs. Recommended values for the gas phase basicity and proton affinity for proline based on our work and other recent determinations are 216 ± 2 and 224 ± 2 kcal/mol.
Paul M. Mayer - One of the best experts on this subject based on the ideXlab platform.
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The applicability of the Kinetic Method for measuring relative affinities of macromolecules for polyatomic substrates.
European journal of mass spectrometry (Chichester England), 2012Co-Authors: Justin B. Renaud, Paul M. MayerAbstract:This paper is a review of the Kinetic Method for the determination of thermochemical values for gas-phase molecules. In addition, we have explored the utility of the Kinetic Method to obtain meaningful relative binding energies of macromolecules for polyatomic substrates using a system comprising poly(methylmethacrylate) (PMMA) oligomers and doubly protonated diaminoalkanes. The major factors which determined the suitability of the Kinetic Method for this system were identified as (i) the structural arrangement of the parent ion complex, (ii) possible reverse activation barriers, and (iii) the evaluations of Δ(ΔS‡). Molecular mechanics/molecular dynamics (MM/MD) simulations, together with ion mobility spectrometry, suggests the parent ion complexes represent a relatively equal sharing of the substrate between two the PMMA oligomers within the complex and that the two PMMA oligomers interact almost exclusively with the substrate, and not with each other. MS/MS of the trimeric parent complexes resulted in one PMMA unit leaving as a neutral which suggests very limited coulombic repulsion (that would contribute to a reverse activation barrier). The drift times of PMMA-diaminoalkane complexes that were generated directly by ESI-MS or by dissociation of a trimeric PMMA-diaminoalkane-PMMA complex were found to be identical, and when combined with MM/MD simulations suggested that the product PMMA-diaminoalkane dication has the same conformation as it does when part of a trimeric complex. This is evidence for Δ(ΔS‡) ≃ Δ(ΔS) and using a statistical mechanics approach, Δ(ΔS) ≃ 0. The effective temperature variable in the Kinetic Method expression was found to decrease as a function of the size of the trimeric complex, suggesting that the population distribution of the dissociating ensemble of complexes narrows as size increases.
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Proton Affinities of Primary Alkanols: An Appraisal of the Kinetic Method
The Journal of Physical Chemistry A, 1999Co-Authors: John L. Holmes, Christiane Aubry, Paul M. MayerAbstract:The Kinetic Method is a now well-established technique for determining thermochemical properties such as acidities and proton affinities. We present here a study of the application of the Kinetic m...
