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Miller ZM, Zhang JD, Donald WA, Prell JS. Gas-Phase Protonation Thermodynamics of Biological Lipids: Experiment, Theory, and Implications. Anal Chem 2020; 92:10365-10374. [PMID: 32628014 DOI: 10.1021/acs.analchem.0c00613] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Phospholipids are important to cellular function and are a vital structural component of plasma and organelle membranes. These membranes isolate the cell from its environment, allow regulation of the internal concentrations of ions and small molecules, and host diverse types of membrane proteins. It remains extremely challenging to identify specific membrane protein-lipid interactions and their relative strengths. Native mass spectrometry, an intrinsically gas-phase method, has recently been demonstrated as a promising tool for identifying endogenous protein-lipid interactions. However, to what extent the identified interactions reflect solution- versus gas-phase binding strengths is not known. Here, the "Extended" Kinetic Method and ab initio computations at three different levels of theory are used to experimentally and theoretically determine intrinsic gas-phase basicities (GB, ΔG for deprotonation of the protonated base) and proton affinities (PA, ΔH for deprotonation of the protonated base) of six lipids representing common phospholipid types. Gas-phase acidities (ΔG and ΔH for deprotonation) of neutral phospholipids are also evaluated computationally and ranked experimentally. Intriguingly, it is found that two of these phospholipids, sphingomyelin and phosphatidylcholine, have the highest GB of any small, monomeric biomolecules measured to date and are more basic than arginine. Phosphatidylethanolamine and phosphatidylserine are found to be similar in GB to basic amino acids lysine and histidine, and phosphatidic acid and phosphatidylglycerol are the least basic of the six lipid types studied, though still more basic than alanine. Kinetic Method experiments and theory show that the gas-phase acidities of these phospholipids are high but less extreme than their GB values, with phosphatidylserine and phosphatidylglycerol being the most acidic. These results indicate that sphingomyelin and phosphatidylcholine lipids can act as charge-reducing agents when dissociated from native membrane protein-lipid complexes in the gas phase and provide a straightforward model to explain the results of several recent native mass spectrometry studies of protein-lipid complexes.
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Affiliation(s)
- Zachary M Miller
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1253, United States
| | - J Diana Zhang
- School of Chemistry, University of New South Wales, Sydney, New South Wales, Australia, 2052
| | - W Alexander Donald
- School of Chemistry, University of New South Wales, Sydney, New South Wales, Australia, 2052
| | - James S Prell
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1253, United States.,Materials Science Institute, University of Oregon, Eugene, Oregon 97403-1252, United States
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Morrison KA, Bythell BJ, Clowers BH. Interrogating Proton Affinities of Organophosphonate Species Via Atmospheric Flow Tube Mass Spectrometry and Computational Methods. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:1308-1320. [PMID: 30993636 DOI: 10.1007/s13361-019-02202-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 03/19/2019] [Accepted: 03/19/2019] [Indexed: 06/09/2023]
Abstract
Within trace vapor analysis in environmental monitoring, defense, and industry, atmospheric flow tube mass spectrometry (AFT-MS) can fill a role that incorporates non-contact vapor analysis with the selectivity and low detection limits of mass spectrometry. AFT-MS has been applied to quantitating certain explosives by selective clustering with nitrate and more recently applied to detecting tributyl phosphate and dimethyl methylphosphonate as protonated species. Developing AFT-MS methods for organophosphorus species is appealing, given that this class of compounds includes a range of pollutants, chemical warfare agent (CWA) simulants, and CWA degradation products. A key aspect of targeting organophosphorus analytes has included the use of dopant ion chemistry to form adducts that impart additional analytical selectivity. The assessment of potential dopant molecules suited to enhance detection of these compounds is hindered by few published ion thermochemical properties for organophosphorus species, such as proton affinity, which can be used for approximating proton-bound dimer bond strength. As a preliminary investigation for the progression of sensing methods involving AFT-MS, we have applied both the extended kinetic method and computational approaches to eight organophosphorus CWA simulants to determine their respective gas-phase proton affinities. Notable observed trends, supported by computational efforts, include an increase in proton affinity as the alkyl chain lengths on the phosphonates increased. Graphical Abstract .
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Lesage D, Mezzache S, Gimbert Y, Dossmann H, Tabet JC. Extended kinetic method and RRKM modeling to reinvestigate proline's proton affinity and approach the meaning of effective temperature. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2019; 25:219-228. [PMID: 30630370 DOI: 10.1177/1469066718822054] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Proline proton affinity PA(Pro) was previously measured by extended kinetic methods with several amines as reference bases using a triple quadrupole mass spectrometer ( J Mass Spectrom 2005; 40: 1300). The measured value of 947.5 ± 5 kJ.mol-1 differs by more than 10 kJ.mol-1 from previous reported experimental or calculated values. This difference may be explained in part by the existence of relatively large entropy difference between the two dissociation channels (ΔΔS‡avg = 31 ± 10 J.mol-1.K-1) and by the inaccuracy of the amines proton affinity used as reference bases. In the present work, these experimental measurements were reinvestigated by RRKM modeling using MassKinetics software. From this modeling, a new PA value of 944.5 ± 5 kJ.mol-1 and a ΔΔS‡avg(600K) value of 33 ± 10 J.mol-1.K-1 are determined. However, the difference between experiment and recent theoretical calculations remains large (10 kJ.mol-1). These RRKM simulations allow also accessing to the effective temperature parameter (T eff) and to discuss the meaning of this term. As previously reported, T eff mainly depends on the internal energy and on the decomposition time as well. It also depends on the critical energies and on the transition state. Considering the entrance of the collision cell as a new ion source, T eff is finally shown to be close to a characteristic temperature (T char).
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Affiliation(s)
- Denis Lesage
- 1 CNRS, Institut Parisien de Chimie Moléculaire, Sorbonne Université, IPCM, Paris, France
| | - Sakina Mezzache
- 1 CNRS, Institut Parisien de Chimie Moléculaire, Sorbonne Université, IPCM, Paris, France
| | - Yves Gimbert
- 1 CNRS, Institut Parisien de Chimie Moléculaire, Sorbonne Université, IPCM, Paris, France
- 2 Université Grenoble Alpes and CNRS, DCM (UMR 5250) Grenoble Cedex 9, France
| | - Héloïse Dossmann
- 1 CNRS, Institut Parisien de Chimie Moléculaire, Sorbonne Université, IPCM, Paris, France
| | - Jean-Claude Tabet
- 1 CNRS, Institut Parisien de Chimie Moléculaire, Sorbonne Université, IPCM, Paris, France
- 3 Service de Pharmacologie et d'Immunoanalyse (SPI), Laboratoire d'Etude du Métabolisme des Médicaments, CEA, INRA, Université Paris Saclay, MetaboHUB, Gif-sur-Yvette, France
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Darii E, Alves S, Gimbert Y, Perret A, Tabet JC. Meaning and consequence of the coexistence of competitive hydrogen bond/salt forms on the dissociation orientation of non-covalent complexes. J Chromatogr B Analyt Technol Biomed Life Sci 2017; 1047:45-58. [DOI: 10.1016/j.jchromb.2016.09.038] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Revised: 07/23/2016] [Accepted: 09/25/2016] [Indexed: 10/20/2022]
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Bouchoux G. Gas-phase basicities of polyfunctional molecules. Part 4: Carbonyl groups as basic sites. MASS SPECTROMETRY REVIEWS 2015; 34:493-534. [PMID: 24399766 DOI: 10.1002/mas.21416] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 09/30/2013] [Accepted: 09/30/2013] [Indexed: 06/03/2023]
Abstract
This article constitutes the fourth part of a general review of the gas-phase protonation thermochemistry of polyfunctional molecules (Part 1: Theory and methods, Mass Spectrom Rev 2007, 26:775-835, Part 2: Saturated basic sites, Mass Spectrom Rev 2012, 31:353-390, Part 3: Amino acids, Mass Spectrom Rev 2012, 31:391-435). This fourth part is devoted to carbonyl containing polyfunctional molecules. After a short reminder of the methods of determination of gas-phase basicity and the underlying physicochemical concepts, specific examples are examined under two major chapters. In the first one, aliphatic and unsaturated (conjugated and cyclic) ketones, diketones, ketoalcohols, and ketoethers are considered. A second chapter describes the protonation energetic of gaseous acids and derivatives including diacids, diesters, diamides, anhydrides, imides, ureas, carbamates, amino acid derivatives, and peptides. Experimental data were re-evaluated according to the presently adopted basicity scale. Structural and energetic information given by G3 and G4 quantum chemistry computations on typical systems are presented.
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Affiliation(s)
- Guy Bouchoux
- Département de Chimie, Laboratoire des Mécanismes Réactionnels, Ecole Polytechnique, 91120, Palaiseau, France
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Abboud JLM, Koppel IA, Uggerud E, Leito I, Koppel I, Sekiguchi O, Kaupmees K, Saame J, Kütt K, Mishima M. Solution and gas-phase acidities of all-trans (all-E) retinoic acid: an experimental and computational study. Chemistry 2015; 21:11238-43. [PMID: 26186282 DOI: 10.1002/chem.201500717] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2015] [Revised: 04/21/2015] [Indexed: 11/08/2022]
Abstract
Retinoic acid is of fundamental biological importance. Its acidity was determined in the gas phase and in acetonitrile solution by means of mass spectrometry and UV/Vis spectrophotometry, respectively. The intrinsic acidity is slightly higher than that of benzoic acid. In solution, the situation is opposite. The experimental systems were described theoretically applying quantum chemical methods (wave function theory and density functional theory). This allowed the determination of the molecular structure of the acid and its conjugate base, both in vacuo and in solution, and for computational estimates of its acidity in both phases.
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Affiliation(s)
- José-Luis M Abboud
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan), Fax: (+81) 92-642-2715.
| | - Ilmar A Koppel
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia), Fax: (+372) 7-375264.
| | - Einar Uggerud
- Mass Spectrometric Laboratory and Center for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Oslo, P.O.B. 1033, Blindern, 0315 Oslo (Norway), Fax: (+47) 22855441.
| | - Ivo Leito
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia), Fax: (+372) 7-375264.
| | - Ivar Koppel
- Institute of Computer Sciences, University of Tartu, Liivi 2, 50409 Tartu (Estonia), Fax: (+372) 7-375468.
| | - Osamu Sekiguchi
- Mass Spectrometric Laboratory and Center for Theoretical and Computational Chemistry (CTCC), Department of Chemistry, University of Oslo, P.O.B. 1033, Blindern, 0315 Oslo (Norway), Fax: (+47) 22855441
| | - Karl Kaupmees
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia), Fax: (+372) 7-375264
| | - Jaan Saame
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia), Fax: (+372) 7-375264
| | - Karl Kütt
- University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia), Fax: (+372) 7-375264
| | - Masaaki Mishima
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan), Fax: (+81) 92-642-2715.
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Cao X, Zhu K, Song Q, Wang C, Wang Y, Cai R, Lin Y, Tang F, Zhang M, Mo W. Proton-bound complex mediating retro-Michael-type fragmentation of protonated 3-substituted oxindoles in the Orbitrap high-energy collisional dissociation cell. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:515-520. [PMID: 26160417 DOI: 10.1002/rcm.7128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2014] [Revised: 12/12/2014] [Accepted: 12/15/2014] [Indexed: 06/04/2023]
Abstract
RATIONALE Oxindole derivatives are valuable building blocks for indole chemistry. Systematically exploring the fragmentation behavior of the protonated 3-pyrazole-substituted oxindoles by kinetic methods combined with density functional theory (DFT) calculations is useful for further understanding their basic properties, and might provide some insights into their reactivity trends in synthesis and metabolism. METHODS All high-resolution high-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) experiments were carried out using electrospray ionization hybrid Quadrupole-Orbitrap mass spectrometry in positive ion mode. Theoretical calculations were carried out by the DFT method at the B3LYP level with the 6-311G (d, p) basis set in the Gaussian 03 package of programs. RESULTS In the fragmentation of protonated 3-pyrazole-substituted oxindoles, the characterized protonated 3-(3-methyl-5-oxo-1H-pyrazol-4(5H)-ylidene)indolin-2-one derivatives and the protonated 5-methylpyrazolone were observed, which were proposed from the cleavage of the C(β)-C(γ) bond in a retro-Michael reaction. With the kinetic plot, a linear correlation was established between the intensities of this two competitive product ions and the difference in proton affinities of the corresponding neutral molecules, which demonstrated that the retro-Michael reaction was mediated by a proton-bound complex. CONCLUSIONS Using the kinetic method combined with theoretical calculations, a proton-bound complex mediating retro-Michael reaction was proposed for the fragmentation of protonated 3-pyrazole-substituted oxindoles in the high-energy collisional dissociation tandem mass spectrometry for the first time, which provided potential evidence to further understand their intrinsic bioactivities.
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Affiliation(s)
- Xiaoji Cao
- Research Center of Analysis and Measurement, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Kundan Zhu
- College of Chemical Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Qingbao Song
- College of Chemical Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Chenlu Wang
- College of Chemical Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Ye Wang
- College of Chemical Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Ruonan Cai
- College of Chemical Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Yan Lin
- College of Chemical Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
| | - Fangliang Tang
- Hangzhou Environmental Monitoring Control Station, Hangzhou, Zhejiang, 310014, P.R. China
| | - Ming Zhang
- Hangzhou Environmental Monitoring Control Station, Hangzhou, Zhejiang, 310014, P.R. China
| | - Weimin Mo
- Research Center of Analysis and Measurement, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
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Pierson NA, Clemmer DE. An IMS-IMS threshold method for semi-quantitative determination of activation barriers: Interconversion of proline cis↔trans forms in triply protonated bradykinin. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2015; 377:646-654. [PMID: 25838788 PMCID: PMC4378547 DOI: 10.1016/j.ijms.2014.07.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Collisional activation of selected conformations by multidimensional ion mobility spectrometry (IMS-IMS), combined with mass spectrometry (MS), is described as a method to determine semi-quantitative activation energies for interconversion of different structures of the nonapeptide bradykinin (BK, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg). This analysis is based on a calibration involving collision-induced dissociation measurements of ions with known dissociation energies (i.e., "thermometer" ions) such as leucine enkephalin, BK, and amino acid-metal cation systems. The energetic barriers between six conformations of [BK+3H]3+ range from 0.23 ±0.01 to 0.55 ±0.03 eV. Prior results indicate that the major peaks in the IMS distributions correspond to specific combinations of cis and trans configurations of the three proline residues in the peptide sequence. The analysis allows us to directly assess pathways for specific transitions. The combination of structural assignments, experimentally determined barrier heights, onset of the quasi-equilibrium region, and dissociation threshold are used to derive a semi-quantitative potential energy surface for main features of [BK+3H]3+.
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Affiliation(s)
- Nicholas A. Pierson
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405 United States
| | - David E. Clemmer
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405 United States
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Nichols CM, Old WM, Lineberger WC, Bierbaum VM. Gas-phase acidities of nitrated azoles as determined by the extended kinetic method and computations. J Phys Chem A 2015; 119:395-402. [PMID: 25521708 DOI: 10.1021/jp5110533] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Making use of the extended kinetic method and the alternative method for data analysis, we have experimentally determined ΔH°acid (kcal/mol) for six mononitrated azole species (2-nitropyrrole = 337.0, 3-nitropyrrole = 335.8, 3-nitropyrazole = 330.5, 4-nitropyrazole = 329.5, 2-nitroimidazole = 327.4, and 4-nitroimidazole = 325.0). We report an absolute uncertainty of ±2.2 kcal/mol that arises from the uncertainties of the reference acids; the relative values are known within 0.4 kcal/mol. Combining these experimental ΔH°acid values with ΔS°acid values calculated at the B3LYP/aug-cc-pVTZ level of theory, we report ΔG°acid (kcal/mol) for the nitroazoles (2-nitropyrrole = 329.4, 3-nitropyrrole = 328.4, 3-nitropyrazole = 323.1, 4-nitropyrazole = 322.0, 2-nitroimidazole = 319.7, and 4-nitroimidazole = 317.6); the absolute uncertainties are ±2.4 kcal/mol. In addition to the experimental studies, we have computationally investigated the gas-phase acidities and electron affinities of the azoles in this work, as well as higher-order aza- and dinitro-substituted azoles. We discuss trends in the stabilities of the deprotonated azoles based on aza substitution and nitro group placement. 4-Nitroimidazole has already found use as the anionic component in ionic liquids, and we propose that the additional nitrated azolate ions are potential candidates for the anionic component of ionic liquids.
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Affiliation(s)
- Charles M Nichols
- Department of Chemistry and Biochemistry, JILA, University of Colorado , Boulder, Colorado 80309, United States
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Ervin KM, Nickel AA, Lanorio JG, Ghale SB. Anchoring the Gas-Phase Acidity Scale from Hydrogen Sulfide to Pyrrole. Experimental Bond Dissociation Energies of Nitromethane, Ethanethiol, and Cyclopentadiene. J Phys Chem A 2015; 119:7169-79. [DOI: 10.1021/jp510137g] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kent M. Ervin
- Department of Chemistry and
Chemical Physics Program, University of Nevada, Reno, 1664 North
Virginia Street MS 216, Reno, Nevada 89557-0216, United States
| | - Alex A. Nickel
- Department of Chemistry and
Chemical Physics Program, University of Nevada, Reno, 1664 North
Virginia Street MS 216, Reno, Nevada 89557-0216, United States
| | - Jerry G. Lanorio
- Department of Chemistry and
Chemical Physics Program, University of Nevada, Reno, 1664 North
Virginia Street MS 216, Reno, Nevada 89557-0216, United States
| | - Surja B. Ghale
- Department of Chemistry and
Chemical Physics Program, University of Nevada, Reno, 1664 North
Virginia Street MS 216, Reno, Nevada 89557-0216, United States
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Mayeux C, Burk P, Gal JF, Kaljurand I, Koppel I, Leito I, Sikk L. Gas-phase lithium cation basicity: revisiting the high basicity range by experiment and theory. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1962-1973. [PMID: 25190215 DOI: 10.1007/s13361-014-0970-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 07/14/2014] [Accepted: 07/14/2014] [Indexed: 06/03/2023]
Abstract
According to high level calculations, the upper part of the previously published FT-ICR lithium cation basicity (LiCB at 373 K) scale appeared to be biased by a systematic downward shift. The purpose of this work was to determine the source of this systematic difference. New experimental LiCB values at 373 K have been measured for 31 ligands by proton-transfer equilibrium techniques, ranging from tetrahydrofuran (137.2 kJ mol(-1)) to 1,2-dimethoxyethane (202.7 kJ mol(-1)). The relative basicities (ΔLiCB) were included in a single self-consistent ladder anchored to the absolute LiCB value of pyridine (146.7 kJ mol(-1)). This new LiCB scale exhibits a good agreement with theoretical values obtained at G2(MP2) level. By means of kinetic modeling, it was also shown that equilibrium measurements can be performed in spite of the formation of Li(+) bound dimers. The key feature for achieving accurate equilibrium measurements is the ion trapping time. The potential causes of discrepancies between the new data and previous experimental measurements were analyzed. It was concluded that the disagreement essentially finds its origin in the estimation of temperature and the calibration of Cook's kinetic method.
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Cao X, Zhang F, Zhu K, Ye X, Shen L, Chen J, Mo W. Identifying the proton transfer reaction mechanism via a proton-bound dimeric intermediate for esomeprazoles by a kinetic method combined with density functional theory calculations. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:1045-1050. [PMID: 24677526 DOI: 10.1002/rcm.6877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 01/13/2014] [Accepted: 02/19/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Esomeprazole analogs are a class of important proton pump inhibitors for the treatment of gastro-esophageal reflux diseases. Understanding the fragmentation reaction mechanism of the protonated esomeprazole analogs will facilitate the characterization of their complex metabolic fate in humans. In this paper, the kinetic method and theoretical calculations were applied to evaluate the fragmentation of protonated esomeprazole analogs. METHODS All collision-induced dissociation (CID) mass spectrometry experiments were carried out using electrospray ionization (ESI) ion trap mass spectrometry in positive ion mode. Also the accurate masses of fragments were measured on by ESI quadrupole time-of-flight (QTOF) MS in positive ion mode. Theoretical calculations were carried out by the density functional theory (DFT) method with the 6-31G(d) basis set in the Gaussian 03 program. RESULTS In the fragmentation of the protonated esomeprazole analogs, C-S bond breakage is observed, which gives rise to protonated 2-(sulfinylmethylene)pyridines and protonated benzimidazoles. DFT calculations demonstrate that the nitrogen atom of the pyridine part is the thermodynamically most favorable protonation site, and the C-S bond cleavage is triggered by the transfer of this ionizing proton from the nitrogen atom of the pyridine part to the carbon atom of the benzimidazole part to which the sulfinyl is attached. Moreover, with the kinetic plot, the intensity ratios of two protonated product ions yield a linear relationship with the differences in proton affinities of the corresponding neutral molecules, which provides strong experimental evidence that the reaction proceeds via proton-bound 2-(sulfinylmethylene)pyridine/benzimidazole complex intermediates. CONCLUSIONS The kinetic method combined with theoretical calculations was successfully applied to probe the proton transfer reaction by proton-bound 2-(sulfinylmethylene)pyridine/benzimidazole complexes in the fragmentation of protonated esomeprazole analogs by ESI CID MS, which is a strong evidence that the kinetic method can be applied in identifying a proton-bound dimeric intermediate in the fragmentation of protonated ions.
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Affiliation(s)
- Xiaoji Cao
- Research Center of Analysis and Measurement, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R. China
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Mayeux C, Tammiku-Taul J, Massi L, Gal JF, Burk P. Interaction between the Cesium Cation and Cesium Carboxylates: An Extended Cs+Basicity Scale. Chempluschem 2013; 78:1195-1204. [DOI: 10.1002/cplu.201300181] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 08/05/2013] [Indexed: 11/06/2022]
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Guerrero A, Baer T, Chana A, González J, Dávalos JZ. Gas Phase Acidity Measurement of Local Acidic Groups in Multifunctional Species: Controlling the Binding Sites in Hydroxycinnamic Acids. J Am Chem Soc 2013; 135:9681-90. [DOI: 10.1021/ja400571r] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Andres Guerrero
- Instituto
de Química Física “Rocasolano”, CSIC, C Serrano 119, Madrid, E-28006, Spain
| | - Tomas Baer
- Instituto
de Química Física “Rocasolano”, CSIC, C Serrano 119, Madrid, E-28006, Spain
| | - Antonio Chana
- Instituto
de Química Física “Rocasolano”, CSIC, C Serrano 119, Madrid, E-28006, Spain
| | - Javier González
- Instituto
de Química Física “Rocasolano”, CSIC, C Serrano 119, Madrid, E-28006, Spain
| | - Juan Z. Dávalos
- Instituto
de Química Física “Rocasolano”, CSIC, C Serrano 119, Madrid, E-28006, Spain
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