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Zheng M, Zhang X, Cheng Y, Sun L, Zhang X. Hydroxyl transfer versus cyclization reaction in the gas phase: Sequential loss of NH 3 and CH 2CO from protonated phenylalanine derivatives. Front Chem 2023; 10:1094329. [PMID: 36700082 PMCID: PMC9868239 DOI: 10.3389/fchem.2022.1094329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Accepted: 12/23/2022] [Indexed: 01/10/2023] Open
Abstract
Collisional activation of protonated phenylalanine derivatives deamination products leads to hydroxyl skeletal rearrangement versus cyclization reaction, and to form hydroxylbenzyl cation via elimination of CH2CO. To better clarify this unusual fragmentation reaction, accurate mass measurements experiments, native isotope experiments, multiple-stage mass spectrometry experiments, different substituents experiments, and density functional theory (DFT) calculations were carried out to investigate the dissociation mechanistic pathways of protonated phenylalanine derivatives deamination products. In route 1, a three-membered ring-opening reaction and a 1,3-hydroxyl transfer (from the carbonyl carbon atom to the interposition carbon atom of carbonyl) occurs to form 3-hydroxy-1-oxo-3-phenylpropan-1-ylium, followed by dissociation to lose CH2CO to give hydroxy (phenyl)methylium. In route 2, a successive cyclization rearrangement reaction and proton transfer occur to form a 2-hydroxylphenylpropionyl cation or protonated 2-hydroxy-4H-benzopyran, followed by dissociation to lose CH2CO or CH≡COH to give 2-hydroxylbenzyl cation. In route 3, a successive hydroxyl transfer (from the carbonyl carbon atom to the ortho carbon atom on benzene) and two stepwise proton transfer (1,2-proton transfer to the ipso-carbon atom of the phenyl ring followed by 1,3-proton transfer to the ortho carbon atom of carbonyl) occurs to form a 2-hydroxylphenylpropionyl cation, which subsequently dissociates to form 2-hydroxylbenzyl cation by elimination of CH2CO. DFT calculations suggested that route 1 was more favorable than route 2 and route 3 from a thermodynamic point of view.
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Li J, Pan Y, Chen B. The ion-neutral complex-mediated fragmentation reaction in electrospray ionization tandem mass spectrometric analysis of N-phenyl-3-(phenylthio)propanamides. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2022; 36:e9333. [PMID: 35705519 DOI: 10.1002/rcm.9333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 06/07/2022] [Accepted: 06/13/2022] [Indexed: 06/15/2023]
Abstract
RATIONALE Amides are the fundamental units of both peptides and proteins, and also important functional groups of medical chemicals. Investigation of the fragmentation mechanism of amides in the gas phase is scientifically important for structural analysis. However, understanding of this problem is still elusive. METHODS Protonated N-phenyl-3-(phenylthio)propanamide and its derivatives were investigated using positive ion tandem mass spectrometry (ESI-MS/MS) with an LCQ mass spectrometer. Accurate mass analysis was conducted with a micrOTOF-QII mass spectrometer. Density functional theory (DFT) calculations using the Gaussian 03 program and deuterium-labelling (D-labelling) experiments were performed to verify the proposed fragmentation mechanism. RESULTS Interpretation of the fragment ions in the collision-induced dissociation mass spectra showed that the ionizing proton in the protonated ion transferred from the most thermodynamically favorable carbonyl oxygen to the dissociative protonation site at amide nitrogen or sulfur atom upon collisional activation. The dissociation of the amide or the C-S bond was induced by such proton transfer. An ion-neutral complex (INC) was generated via the dissociation of the amide bond. In the INC, it was observed that the carbocation of the ionic part attacked the ortho phenyl carbon atom adjacent to the sulfur atom, and proton transfer from the carbon atom to the nitrogen atom led to the formation of protonated aniline. CONCLUSIONS The fragmentation mechanism of protonated N-phenyl-3-(phenylthio)propanamide and its derivatives was proposed and elucidated. All the compounds studied showed similar fragmentation pathways, and the competitive formation of two ions, RC9 H9 OS+ and C6 H8 N+ , was observed. The generation of protonated aniline is mediated by INC in ESI-MS/MS.
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Affiliation(s)
- Jing Li
- Key Laboratory of Biomass Chemical Engineering of Ministry of Education, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, Zhejiang, China
- Institute of Zhejiang University-Quzhou, Quzhou, Zhejiang, China
| | - Yuanjiang Pan
- Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China
| | - Bajin Chen
- Zhejiang Transfar Functional New Materials Co. Ltd, Hangzhou, Zhejiang, China
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Saeidian H, Malekian H, Vessally E. Density functional estimation of hydride and proton affinities of substituted allenes and heteroallenes. J PHYS ORG CHEM 2021. [DOI: 10.1002/poc.4251] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Hamid Saeidian
- Department of Science Payame Noor University (PNU) Tehran Iran
| | - Hadi Malekian
- Department of Science Payame Noor University (PNU) Tehran Iran
| | - Esmail Vessally
- Department of Science Payame Noor University (PNU) Tehran Iran
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Yin Q, Guo N, Yin X, Ma G, Huang Y, Pan Y. Intramolecular benzyl cation transfer in the gas-phase fragmentation of protonated benzyl phenyl sulfones. JOURNAL OF MASS SPECTROMETRY : JMS 2021; 56:e4691. [PMID: 33295108 DOI: 10.1002/jms.4691] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 11/16/2020] [Accepted: 11/18/2020] [Indexed: 06/12/2023]
Abstract
In this study, the gas-phase fragmentations of protonated benzyl phenyl sulfones were investigated by electrospray ionization tandem mass spectrometry (ESI-MSn ). Upon collisional activation, several characteristic fragment ions were observed, and the similar results occurred with different substituted benzyl phenyl sulfones. A mechanism involving an intramolecular benzyl cation transfer and the formation of intermediate ion was proposed and further identified by density functional theory (DFT) calculations. In addition, a reference compound, benzenesulfinic acid benzyl ester, has been synthesized, and its protonated ion has the same gas-phase behavior as compared to the protonated benzyl phenyl sulfone. This work provides access to some insight into the intramolecular benzyl-transfer reactions of benzyl phenyl sulfones in the gas phase and orients the characteristic peaks in collision-induced dissociation spectrometry (CID-MS).
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Affiliation(s)
- Qi Yin
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Nian Guo
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Xinchi Yin
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Ge Ma
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yu Huang
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yuanjiang Pan
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
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Chai Y, Chen H, Lu C. An intriguing "reversible reaction" in the fragmentation of deprotonated dicamba and benzoic acid in a Q-orbitrap mass spectrometer: Loss and addition of carbon dioxide. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2020; 34:e8893. [PMID: 32666557 DOI: 10.1002/rcm.8893] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Revised: 07/10/2020] [Accepted: 07/10/2020] [Indexed: 06/11/2023]
Abstract
RATIONALE Loss of carbon dioxide is an important characteristic fragmentation reaction of deprotonated benzoic acid and its derivatives in electrospray ionization mass spectrometry. However, researchers have rarely noticed or believed that the loss of carbon dioxide in multistage mass spectrometry is a "reversible reaction," that is, the fragment anion generated by carbon dioxide loss can capture another carbon dioxide to regenerate its precursor ion. METHODS The fragmentation of the [M - H]- ions of dicamba (3,6-dichloro-2-methoxybenzoic acid) and benzoic acid was performed with an electrospray ionization hybrid quadrupole-orbitrap mass spectrometer. The structural confirmation of the precursor ions and their product ions was supported by accurate mass (elemental composition) analysis. Pseudo-MS3 experiments (in-source collision-induced dissociation as MS2 ) and isotope labelling experiments were used to confirm the addition of carbon dioxide to the product ions in MS2 . RESULTS In the fragmentation of deprotonated dicamba (m/z 219), the relative abundance of the precursor ion does not decrease significantly or even increases as the collision energy increases. When the m/z 145 and 175 product ions were isolated in the mass analyzer, the ions 44 m/z units larger (m/z 189 and 219) were generated spontaneously, indicating the formation of carbon dioxide adduct ions. In the fragmentation of deprotonated [carboxyl-13 C]-benzoic acid (m/z 122), a deprotonated [carboxyl-12 C]-benzoic acid ion (m/z 121) was generated which was derived from 13 CO2 loss and 12 CO2 addition. The isotope labelling experiment further supports the formation of CO2 -attached ions in the fragmentation of deprotonated benzoic acids. CONCLUSIONS Under collisional activation, deprotonated dicamba and benzoic acids easily undergo carbon dioxide loss, but the decarboxylated product anions have an appropriate nucleophilicity to carbon dioxide and they can capture a background carbon dioxide molecule remaining in the vacuum system to regenerate the precursor ions. This study provides a new and deeper understanding of the gas-phase chemistry of deprotonated benzoic acid derivatives in mass spectrometry.
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Affiliation(s)
- Yunfeng Chai
- Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, China
- Key Laboratory of Tea Quality and Safety Control, Ministry of Agriculture and Rural Affairs, 9 South Meiling Road, Hangzhou, 310008, China
- Laboratory of Quality and Safety Risk Assessment for Tea Products (Hangzhou), Ministry of Agriculture and Rural Affairs, 9 South Meiling Road, Hangzhou, 310008, China
| | - Hongping Chen
- Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, China
- Key Laboratory of Tea Quality and Safety Control, Ministry of Agriculture and Rural Affairs, 9 South Meiling Road, Hangzhou, 310008, China
- Laboratory of Quality and Safety Risk Assessment for Tea Products (Hangzhou), Ministry of Agriculture and Rural Affairs, 9 South Meiling Road, Hangzhou, 310008, China
| | - Chengyin Lu
- Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, China
- Key Laboratory of Tea Quality and Safety Control, Ministry of Agriculture and Rural Affairs, 9 South Meiling Road, Hangzhou, 310008, China
- Laboratory of Quality and Safety Risk Assessment for Tea Products (Hangzhou), Ministry of Agriculture and Rural Affairs, 9 South Meiling Road, Hangzhou, 310008, China
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Britt HM, Prakash AS, Appleby S, Mosely JA, Sanderson JM. Lysis of membrane lipids promoted by small organic molecules: Reactivity depends on structure but not lipophilicity. SCIENCE ADVANCES 2020; 6:eaaz8598. [PMID: 32426467 PMCID: PMC7176411 DOI: 10.1126/sciadv.aaz8598] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 01/30/2020] [Indexed: 06/11/2023]
Abstract
Several organic molecules of low molecular weight (<150 Da) are demonstrated to have substantial membrane-lytic potential despite having a low predicted lipophilicity (logD < 1 at neutral pH). In aqueous liposome dispersions, 38 aromatic compounds were tested for their ability to either promote lipid hydrolysis or directly participate in chemical reactions with lipid molecules. Behaviors observed included acyl transfer from the lipid to form a lipidated compound, both with and without concomitant lysolipid formation; increases in the rate of lipid hydrolysis without lipidation; and no reactivity. The variation in activity, including a notably higher activity for heterocycles such as amino-substituted benzimidazoles and indazoles, demonstrates the potential to predict or "design-in" lytic activity once the rules that govern reactivity are better understood. The nature of this chemical instability has significant ramifications for the use or presence of lipids in diverse fields such as materials chemistry, food chemistry, and cell physiology.
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Xu J, Zhu G, Zhang H, Liu J, Jiang K. Differentiation of isomeric cresols by silylation in combination with gas chromatography/mass spectrometry analysis. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2020; 34:e8576. [PMID: 31498942 DOI: 10.1002/rcm.8576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 08/26/2019] [Accepted: 08/30/2019] [Indexed: 06/10/2023]
Abstract
RATIONALE m-Cresol is listed as a priority controlled contaminant in many countries, but it is very difficult to accurately determine isomeric cresols due to their incomplete chromatographic separation on commercially available chromatographic columns and their nearly identical mass spectra. METHODS Silylation of isomeric cresols was carried out by treatment with N-methyl-N-(trimethylsilyl)trifluoroacetamide. The formed trimethyl(tolyloxy)silanes were analyzed by gas chromatography/mass spectrometry (GC/MS). Theoretical calculations were carried out with the Gaussian 03 program using the density functional theory (DFT) method at the B3LYP/6-311 + G(2d,p) level. RESULTS The derivatives of three isomeric cresols and six isomeric xylenols have been completely separated on an HP-5MS capillary column within a GC run of only 10 minutes. In addition, the derivative o-cresol can be very easily differentiated from its isomers due to its characteristic base peak ion at m/z 91 in electron ionization (EI)-MS. DFT calculation results indicated that the formation of the abundant fragment ion at m/z 91 is attributed to a facile dissociation pathway involving the shift of a neighboring phenylmethyl hydrogen atom in EI-MS of trimethyl(o-tolyloxy)silane. CONCLUSIONS Silylation provides a promising solution for simultaneous determination of isomeric cresols and isomeric xylenols.
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Affiliation(s)
- Jiaxiang Xu
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China
| | - Guohua Zhu
- Zhejiang Province Environmental Monitoring Center, Hangzhou, 310015, China
| | - Huarong Zhang
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China
| | - Jinsong Liu
- Zhejiang Province Environmental Monitoring Center, Hangzhou, 310015, China
| | - Kezhi Jiang
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China
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Lee JH, Park HN, Kim NS, Park S, Lee YM, Kang H. Development of a specific fragmentation pattern-based quadrupole-Orbitrap™ mass spectrometry method to screen drugs in illicit products. Sci Justice 2020; 60:86-94. [DOI: 10.1016/j.scijus.2019.08.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2019] [Revised: 07/23/2019] [Accepted: 08/11/2019] [Indexed: 12/29/2022]
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9
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Baira SM, Ragampeta S, Talluri MVNK. A comprehensive study on rearrangement reactions in collision-induced dissociation mass spectrometric fragmentation of protonated diphenyl and phenyl pyridyl ethers. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2019; 33:1440-1448. [PMID: 31115092 DOI: 10.1002/rcm.8488] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 05/01/2019] [Accepted: 05/13/2019] [Indexed: 06/09/2023]
Abstract
RATIONALE Recently, we have reported a forced degradation study of a pharmaceutical drug regorafenib which contains a phenyl pyridyl ether derivative as building block. We observed interesting rearrangements in two of its degradation products in tandem mass spectrometry (MS/MS) experiments. As diphenyl ether derivatives are also molecular building blocks of biological importance and used as herbicides and flame retardants, we decided to investigate specifically the fragmentation behavior of these compounds along with phenyl pyridyl derivatives in detail using high-resolution electrospray ionization (ESI) MS/MS. METHODS To understand the fragmentation reactions of protonated substituted diphenyl ethers and phenyl pyridyl ethers, ESI-MS/MS experiments were performed using a quadrupole time-of-flight (QTOF) mass spectrometer. RESULTS In contrast to radical cations of diphenyl ether derivatives which do not eliminate CO, the [M + H]+ ions of substituted diphenyl ethers undergo rearrangement reactions after loss of neutral molecules (H2 O, HCl, etc.) to form a bicyclic structure containing a keto group and do eliminate CO. Similar rearrangement followed by fragmentation was observed for protonated phenyl pyridyl ethers and the degradation products formed from regorafenib and sorafenib. CONCLUSIONS The protonated ions of substituted diphenyl ethers and phenyl pyridyl ethers on collision-induced dissociation have exhibited interesting rearrangement reactions, despite the nature of the substituent on both the aryl moieties. The proposed fragmentation patterns of these compounds give an insight into the understanding of gas-phase reactions in mass spectrometric studies of diphenyl ether and phenyl pyridyl ether derivatives.
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Affiliation(s)
- Shandilya Mahamuni Baira
- Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education & Research, Balanagar, Hyderabad, Telangana, India
| | - Srinivas Ragampeta
- Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education & Research, Balanagar, Hyderabad, Telangana, India
- Analytical Department, CSIR - Indian Institute of Chemical Technology, Hyderabad, Telangana, India
| | - M V N Kumar Talluri
- Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education & Research, Balanagar, Hyderabad, Telangana, India
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10
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Setner B, Stefanowicz P, Szewczuk Z. Quaternary ammonium isobaric tag for a relative and absolute quantification of peptides. JOURNAL OF MASS SPECTROMETRY : JMS 2018; 53:115-123. [PMID: 29087004 DOI: 10.1002/jms.4040] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Revised: 10/11/2017] [Accepted: 10/17/2017] [Indexed: 06/07/2023]
Abstract
Isobaric labeling quantification of peptides has become a method of choice for mass spectrometry-based proteomics studies. However, despite of wide variety of commercially available isobaric tags, none of the currently available methods offers significant improvement of sensitivity of detection during MS experiment. Recently, many strategies were applied to increase the ionization efficiency of peptides involving chemical modifications introducing quaternary ammonium fixed charge. Here, we present a novel quaternary ammonium-based isobaric tag for relative and absolute quantification of peptides (QAS-iTRAQ 2-plex). Upon collisional activation, the new stable benzylic-type cationic reporter ion is liberated from the tag. Deuterium atoms were used to offset the differential masses of a reporter group. We tested the applicability of QAS-iTRAQ 2-plex reagent on a series of model peptides as well as bovine serum albumin tryptic digest. Obtained results suggest usefulness of this isobaric ionization tag for relative and absolute quantification of peptides.
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Affiliation(s)
- Bartosz Setner
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, Wrocław, 50-383, Poland
| | - Piotr Stefanowicz
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, Wrocław, 50-383, Poland
| | - Zbigniew Szewczuk
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, Wrocław, 50-383, Poland
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Chai Y, Shao Y, Wang L, Wang L. Loss of benzaldehyde in the fragmentation of protonated benzoylamines: Benzoyl cation as a hydride acceptor in the gas phase. JOURNAL OF MASS SPECTROMETRY : JMS 2017; 52:664-671. [PMID: 28708326 DOI: 10.1002/jms.3969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 07/04/2017] [Accepted: 07/12/2017] [Indexed: 06/07/2023]
Abstract
In electrospray ionization tandem mass spectrometry of protonated 1-benzoylamines (1-benzoylpiperadine, 1-benzoylmorpholine, and 1-benzoyl-4-methylpiperazine), the dominant fragmentation pathway was amide bond cleavage to form benzoyl cation and neutral amine. Meanwhile, in their fragmentations, an interesting loss of benzaldehyde (106 Da) was observed and identified to derive from hydride transfer reaction between the benzoyl cation and amine. A stepwise mechanism for loss of 106 Da (benzene and CO) could be excluded with the aid of deuterium labeling experiment. Theoretical calculations indicated that hydride transfers from amines (piperadine, morpholine, and 1-methylpiperazine) to benzoyl cation were thermodynamically permitted, and 1-methylpiperazine was the best hydride donor among the 3 amines. The mass spectrometric experimental results were consistent with the computational results. The relative abundance of the iminium cation (relative to the benzoyl cation) in the fragmentation of protonated 1-benzoyl-4-methylpiperazine was higher than that in the fragmentation of the other 2 protonated 1-benzoylamines. By comparing the fragmentations of protonated 1-benzyl-4-methylpiperazine and protonated 1-benzoyl-4-methylpiperazine and the energetics of their hydride transfer reactions, this study revealed that benzoyl cation was a hydride acceptor in the gas phase, but which was weaker than benzyl cation.
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Affiliation(s)
- Yunfeng Chai
- Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, China
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yunlong Shao
- Department of Chemistry and Chemical Engineering, Beijing University of Technology, Beijing, 100124, China
| | - Lu Wang
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China
| | - Lin Wang
- Department of Chemistry and Chemical Engineering, Beijing University of Technology, Beijing, 100124, China
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Sugimura N, Igarashi Y, Aoyama R, Shibue T. Energy-decomposition analysis of ion-neutral complexes along reaction coordinates of unimolecular proton-transfer reaction in gas phase: Comparison between 2-butanol radical ion and protonated 2-ethoxypropane ion. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.08.048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Ma G, Liu G, Shen S, Chai Y, Yue L, Zhao S, Pan Y. Competitive benzyl cation transfer and proton transfer: collision-induced mass spectrometric fragmentation of protonated N,N-dibenzylaniline. JOURNAL OF MASS SPECTROMETRY : JMS 2017; 52:197-203. [PMID: 28109035 DOI: 10.1002/jms.3914] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 01/14/2017] [Accepted: 01/17/2017] [Indexed: 06/06/2023]
Abstract
Collision-induced dissociation of protonated N,N-dibenzylaniline was investigated by electrospray tandem mass spectrometry. Various fragmentation pathways were dominated by benzyl cation and proton transfer. Benzyl cation transfers from the initial site (nitrogen) to benzylic phenyl or aniline phenyl ring. The benzyl cations transfer to the two different sites, and both result in the benzene loss combined with 1,3-H shift. In addition, after the benzyl cation transfers to the benzylic phenyl ring, 1,2-H shift and 1,4-H shift proceed competitively to trigger the diphenylmethane loss and aniline loss, respectively. Deuterium labeling experiments, substituent labeling experiments and density functional theory calculations were performed to support the proposed benzyl cation and proton transfer mechanism. Overall, this study enriches the knowledge of fragmentation mechanisms of protonated N-benzyl compounds. Copyright © 2017 John Wiley & Sons, Ltd.
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Affiliation(s)
- G Ma
- Deparment of Chemistry, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, Zhejiang, China
| | - G Liu
- Radiation Monitoring Technical Center, Ministry of Environmental Protection of China, 306 Wen Yi Road, Hangzhou, 310012, China
| | - S Shen
- Deparment of Chemistry, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, Zhejiang, China
| | - Y Chai
- College of Pharmaceutical Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China
| | - L Yue
- Deparment of Chemistry, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, Zhejiang, China
| | - S Zhao
- Radiation Monitoring Technical Center, Ministry of Environmental Protection of China, 306 Wen Yi Road, Hangzhou, 310012, China
| | - Y Pan
- Deparment of Chemistry, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, Zhejiang, China
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Chai Y, Wang L, Wang L. How does a CC double bond cleave in the gas phase? Fragmentation of protonated ketotifen in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2016; 51:1105-1110. [PMID: 27591732 DOI: 10.1002/jms.3843] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 08/28/2016] [Accepted: 08/30/2016] [Indexed: 06/06/2023]
Abstract
In the literature, it is reported that the protonated ketotifen mainly undergoes CC double bond cleavage in electrospray ionization tandem mass spectrometry (ESI-MS/MS); however, there is no explanation on the mechanism of this fragmentation reaction. Therefore, we carried out a combined experimental and theoretical study on this interesting fragmentation reaction. The fragmentation of protonated ketotifen (m/z 310) always generated a dominant fragment ion at m/z 96 in different electrospray ionization mass spectrometers (ion trap, triple quadrupole and linear trap quadrupole (LTQ)-orbitrap). The mechanism of the generation of this product ion (m/z 96) through the CC double bond cleavage was proposed to be a sequential hydrogen migration process (including proton transfer, continuous two-step 1,2-hydride transfer and ion-neutral complex-mediated hydride transfer). This mechanism was supported by density functional theory (DFT) calculations and a deuterium labeling experiment. DFT calculations also showed that the formation of the product ion m/z 96 was most favorable in terms of energy. This study provides a reasonable explanation for the fragmentation of protonated ketotifen in ESI-MS/MS, and the fragmentation mechanism is suitable to explain other CC double bond cleavage reactions in mass spectrometry. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Yunfeng Chai
- Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, PR China
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, PR China
| | - Lu Wang
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, PR China
| | - Lin Wang
- Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, Beijing University of Technology, Beijing, 100124, PR China
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Cao X, Wang Y, Mo Y, Wu L, Mo W. Friedel-Crafts dealkylation reaction mediated by a stereoselective proton transfer in the fragmentation of protonated cyclic indolyl α-amino esters. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:1454-1460. [PMID: 27321832 DOI: 10.1002/rcm.7579] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Revised: 03/01/2016] [Accepted: 04/02/2016] [Indexed: 06/06/2023]
Abstract
RATIONALE Chiral cyclic indolyl α-amino esters are valuable substructures of peptides and peptidomimetics. Systematically exploring the fragmentation behavior of the protonated cyclic indolyl α-amino esters by a combination of high-resolution high-energy collisional dissociation mass spectrometry, hydrogen-deuterium exchange experiments and density functional theory (DFT) calculations is useful for further understanding their intrinsic properties and the fragmentation mechanisms of peptidomimetics constructed with them. METHODS All high-resolution high-energy collisional dissociation tandem mass spectrometry experiments were carried out using electrospray ionization hybrid Quadrupole-Orbitrap mass spectrometry in positive ion mode. Only the labile hydrogens were exchanged with deuterium in hydrogen-deuterium exchange experiments. 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 cyclic indolyl α-amino esters, when the two labile hydrogens on the N(8) position are successively transferred to the C(3) and C(4) positions, a Friedel-Crafts dealkylation reaction takes place spontaneously, with concomitant formation of an ion-neutral complex of [cyclic N-sulfonyl ketimino esters/protonated indoles]. Direct separation of this complex formed the protonated indoles, while a stereoselective proton transfer between the two components in the complex gave rise to protonated cyclic N-sulfonyl ketimino esters, which coincided with the hydrogen-deuterium experiments. CONCLUSIONS Using H/D exchange experiments combined with theoretical calculations, a Friedel-Crafts dealkylation reaction mediated by a stereoselective proton transfer in the [cyclic N-sulfonyl ketimino esters/protonated indoles] complex was proposed for the fragmentation of protonated cyclic indolyl α-amino esters in high-energy collisional dissociation tandem mass spectrometry for the first time. Copyright © 2016 John Wiley & Sons, Ltd.
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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
| | - Ye Wang
- College of Chemical Engineering, Zhejiang University of Technologys, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R., China
| | - Yawen Mo
- College of Chemical Engineering, Zhejiang University of Technologys, 18 Chaowang Rd, Hangzhou, Zhejiang, 310014, P.R., China
| | - Liang Wu
- College of Chemical Engineering, Zhejiang University of Technologys, 18 Chaowang Rd, 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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Yue L, Li J, Xie X, Guo C, Yin X, Yin Q, Chen Y, Pan Y, Ding C. Ortho-hydroxyl effect and proton transfer via ion-neutral complex: the fragmentation study of protonated imine resveratrol analogues in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2016; 51:518-523. [PMID: 27434810 DOI: 10.1002/jms.3778] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 03/30/2016] [Accepted: 04/20/2016] [Indexed: 06/06/2023]
Abstract
The fragmentation pathways of protonated imine resveratrol analogues in the gas-phase were investigated by electrospray ionization-tandem mass spectrometry. Benzyl cations were formed in the imine resveratrol analogues that had an ortho-hydroxyl group on the benzene ring A. The specific elimination of the quinomethane neutral, CH2 = C6 H4 = O, from the two isomeric ions [M1 + H](+) and [M3 + H](+) via the corresponding ion-neutral complexes was observed. The fragmentation pathway for the related meta-isomer, ion [M2 + H](+) and the other congeners was not observed. Accurate mass measurements and additional experiments carried out with a chlorinated analogue and the trideuterated isotopolog of M1 supported the overall interpretation of the fragmentation phenomena observed. It is very helpful for understanding the intriguing roles of ortho-hydroxyl effect and ion-neutral complexes in fragmentation reactions and enriching the knowledge of the gas-phase chemistry of the benzyl cation. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Lei Yue
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Jing Li
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
- Institute of Biological Engineering, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, Zhejiang, China
| | - Xiaodong Xie
- Department of Chemistry, Fudan University, 220 Handan Road, Shanghai, 200433, China
| | - Cheng Guo
- Cancer Institute, The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310009, China
| | - Xinchi Yin
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Qi Yin
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yinjuan Chen
- Department of Chemistry, Fudan University, 220 Handan Road, Shanghai, 200433, China
| | - Yuanjiang Pan
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Chuanfan Ding
- Department of Chemistry, Fudan University, 220 Handan Road, Shanghai, 200433, China
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Zhang X, Bai X, Fang L, Jiang K, Li Z. Decarboxylative Coupling Reaction in ESI(-)-MS/MS of 4-Nitrobenzyl 4-Hydroxybenzoates: Triplet Ion-Neutral Complex-Mediated 4-Nitrobenzyl Transfer. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:940-943. [PMID: 26926444 DOI: 10.1007/s13361-016-1339-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Revised: 01/09/2016] [Accepted: 01/10/2016] [Indexed: 06/05/2023]
Abstract
In negative electrospray ionization mass spectrometry of 4-nitrobenzyl 4-hydroxybenzoates, a decarboxylation reaction, which was significantly promoted by the presence of a nitro group on the benzyl group, competed with radical elimination reactions. Density functional theory calculations indicated that decarboxylation of deprotonated 4-nitrobenzyl vanillate occurred via a radical route involving homolytic cleavage of the Cbenzyl-O bond to give a triplet ion-neutral complex, followed by decarboxylative coupling.
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Affiliation(s)
- Xiaoping Zhang
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, China
| | - Xingfeng Bai
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China
| | - Liwen Fang
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China
| | - Kezhi Jiang
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 311121, China.
| | - Zuguang Li
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, China.
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Yan X, Bain RM, Li Y, Qiu R, Flick TG, Cooks RG. Online Inductive Electrospray Ionization Mass Spectrometry as a Process Analytical Technology Tool To Monitor the Synthetic Route to Anagliptin. Org Process Res Dev 2016. [DOI: 10.1021/acs.oprd.6b00039] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Xin Yan
- Department
of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Ryan M. Bain
- Department
of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Yafeng Li
- Department
of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Ran Qiu
- Department
of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Tawnya G. Flick
- Department of Analytical Research & Development, Amgen Inc., 1 Amgen Center Drive, Thousand Oaks, California 91320, United States
| | - R. Graham Cooks
- Department
of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
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19
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Paulose J, Achuthan RP, Linsha MPL, Mathai G, Prasanth B, Kumar Talluri MVN, Srinivas R. Protonated N-benzyl- and N-(1-phenylethyl)tyrosine amides dissociate via ion/neutral complexes. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:1577-1584. [PMID: 28339153 DOI: 10.1002/rcm.7256] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Revised: 06/08/2015] [Accepted: 06/15/2015] [Indexed: 06/06/2023]
Abstract
RATIONALE The collisional-induced dissociations (CID) of the [M+H]+ ions of molecules having benzyl groups attached to N-atoms have been proposed to involve migration of the benzyl group through the intermediacy of ion/neutral complexes (INCs). We report the investigation of the mechanism of dissociation of protonated N-benzyl- and N-(1-phenylethyl)tyrosine amides by electrospray ionization (ESI) tandem mass spectrometry (MS/MS) and density functional theory (DFT) calculations. METHODS The amides were synthesized from the corresponding amino acids and amines. The ESI-MS/MS spectra were recorded using an Agilent QTOF 6540 mass spectrometer. The DFT calculations were performed by using Gaussian 09 software. The structures of the [M+H]+ ions, intermediates, products and transition states (TS) were optimized at the B3LYP/6-31G(d,p) level of theory. RESULTS CID of the [M+H]+ ions of N-benzyltyrosine amide yields two product ions due to rearrangements: (i) the [M+H-74]+ ion (m/z 197) due to benzyl migration to the hydroxyphenyl ring and (ii) the [M+H-45]+ ion (m/z 226) due to benzyl migration to the NH2 group. DFT calculations suggest that the rearrangements occur through an INC in which the benzyl cation is the cation partner. The [M+H]+ ion of N-(1-phenylethyl)tyrosine amide rearranges to an INC of the 1-phenylethyl cation. Subsequent elimination of styrene occurs by transfer of a proton from the 1-phenylethyl cation to the neutral partner. CONCLUSIONS The [M+H]+ ions of both N-benzyl (1) and N-(1-phenylethyl) (2) tyrosine amide rearrange into INCs. The dissociation of [M+H]+ ion of 1 yields the benzyl cation and [M+H-74]+ and [M+H-45]+ due to benzyl migration to the hydroxyphenyl ring and NH2 group, respectively. However, the formation of the [M+H-74]+ ion is not observed when the aromatic ring is deactivated. The [M+H]+ ion of 2 either dissociates to form the 1-phenylethyl cation or [M+H-styrene]+ . Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Justin Paulose
- Department of Chemistry, Sacred Heart College, Thevara, Kochi, India
- Bharathiyar University, Coimbatore, Tamilnadu, India
| | - Revi P Achuthan
- Department of Chemistry, Sacred Heart College, Thevara, Kochi, India
- Bharathiyar University, Coimbatore, Tamilnadu, India
| | - Maria P L Linsha
- Department of Chemistry, Sacred Heart College, Thevara, Kochi, India
- Bharathiyar University, Coimbatore, Tamilnadu, India
| | - George Mathai
- Department of Chemistry, Sacred Heart College, Thevara, Kochi, India
- Bharathiyar University, Coimbatore, Tamilnadu, India
| | - B Prasanth
- National Institute of Pharmaceutical Education and Research, Hyderabad, India
| | - M V N Kumar Talluri
- National Institute of Pharmaceutical Education and Research, Hyderabad, India
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20
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Chendo C, Moreira G, Tintaru A, Posocco P, Laurini E, Lefay C, Gigmes D, Viel S, Pricl S, Charles L. Anomerization of Acrylated Glucose During Traveling Wave Ion Mobility Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1483-1493. [PMID: 26041082 DOI: 10.1007/s13361-015-1170-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 04/16/2015] [Accepted: 04/18/2015] [Indexed: 06/04/2023]
Abstract
Anomerization of simple sugars in the liquid phase is known as an acid- and base-catalyzed process, which highly depends on solvent polarity. This reaction is reported here to occur in the gas phase, during traveling wave ion mobility spectrometry (TWIMS) experiments aimed at separating α- and β-anomers of penta-acrylated glucose generated as ammonium adducts in electrospray ionization. This compound was available in two samples prepared from glucose dissolved in solvents of different polarity, namely tetrahydrofuran (THF) and N,N-dimethylacetamide (DMAC), and analyzed by electrospray tandem mass spectrometry (ESI-MS/MS) as well as traveling wave ion mobility (ESI-TWIMS-MS). In MS/MS, an anchimerically-assisted process was found to be unique to the electrosprayed α-anomer, and was only observed for the THF sample. In ESI-TWIMS-MS, a signal was measured at the drift time expected for the α-anomer for both the THF and DMAC samples, in apparent contradiction to the MS/MS results, which indicated that the α-anomer was not present in the DMAC sample. However, MS/MS experiments performed after TWIMS separation revealed that ammonium adducts of the α-anomer produced from each sample, although exhibiting the same collision cross section, were clearly different. Indeed, while the α-anomer actually present in the THF sample was electrosprayed with the ammonium adducted at the C2 acrylate, its homologue only observed when the DMAC sample was subjected to TWIMS hold the adducted ammonium at the C1 acrylate. These findings were explained by a β/α inter-conversion upon injection in the TWIMS cell, as supported by theoretical calculation and dynamic molecular modeling.
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Affiliation(s)
- Christophe Chendo
- Aix-Marseille Université - CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France
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21
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Li Y, Chai Y, Wang L, Pan Y, Zeng S, Sun C. Gas-phase Smiles rearrangement reactions of deprotonated N-phenylbenzamides studied by electrospray ionization tandem mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:864-870. [PMID: 26377014 DOI: 10.1002/rcm.7172] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 02/11/2015] [Accepted: 02/15/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE Electrospray ionization tandem mass spectrometry (ESI-MS(n)) is an invaluable tool for the study of gas-phase reactions. When N-phenylbenzamide is analyzed in negative ion mode, the nucleophilic deprotonated site of nitrogen or oxygen, together with the adjacent electrophilic phenyl carbon in the same molecule, provides a useful opportunity to study the intramolecular nucleophilic reaction in the gas phase. METHODS All MS(n) experiments of deprotonated N-phenylbenzamides were conducted on an ion trap mass spectrometer using ESI in negative ion mode. The accurate masses of fragments were measured on an ESI quadrupole time-of-flight mass spectrometer in negative ion mode. Theoretical calculations were conducted at the B3LYP/6-31++G(d,p) level of density functional theory using the Gaussian 03 program. RESULTS When the polarity of the substituent on the aniline ring was changed, gas-phase Smiles rearrangement reactions could be initiated by different atoms in the anionic center. Upon collisional activation, loss of CO from deprotonated N-phenylbenzamides could be observed, which can be interpreted as a nitrogen anion triggering the Smiles rearrangement reaction through a three-membered ring transition state. As the aniline ring was substituted by a strong electron-withdrawing group (e.g., NO(2), COCH(3), or CF(3)) at the para position, a characteristic phenolate anion was obtained, which was derived from the Smiles rearrangement reaction initiated by the oxygen anion through a four-membered ring transition state. CONCLUSIONS In the fragmentation of deprotonated N-phenylbenzamides, the gas-phase Smiles rearrangement reaction initiated by either the nitrogen or the oxygen atom can proceed. The findings in this study have not only enriched knowledge on the gas-phase Smiles rearrangement reactions, but also provided valuable information for understanding the rearrangements of deprotonated aromatic amides in gas phase.
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Affiliation(s)
- Yikun Li
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yunfeng Chai
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Lin Wang
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Yuanjiang Pan
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
| | - Su Zeng
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China
| | - Cuirong Sun
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China
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22
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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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Yao L, Chai Y, Sun C, Pan Y. Competitive proton and hydride transfer reactions via ion-neutral complexes: fragmentation of deprotonated benzyl N-phenylcarbamates in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2015; 50:364-370. [PMID: 25800018 DOI: 10.1002/jms.3537] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Revised: 10/28/2014] [Accepted: 10/31/2014] [Indexed: 06/04/2023]
Abstract
The gas-phase chemistry of deprotonated benzyl N-phenylcarbamates was investigated by electrospray ionization tandem mass spectrometry. Characteristic losses of a substituted phenylcarbinol and a benzaldehyde from the precursor ion were proposed to be derived from an ion-neutral complex (INC)-mediated competitive proton and hydride transfer reactions. The intermediacy of the INC consisting of a substituted benzyloxy anion and a phenyl isocyanate was supported by both ortho-site-blocking experiments and density functional theory calculations. Within the INC, the benzyloxy anion played the role of either a proton abstractor or a hydride donor toward its neutral counterpart. Relative abundances of the product ions were influenced by the nature of the substituents. Electron-withdrawing groups at the N-phenyl ring favored the hydrogen transfer process (including proton and hydride transfer), whereas electron-donating groups favored direct decomposition to generate the benzyloxy anion (or substituted benzyloxy anion). By contrast, electron-withdrawing and electron-donating substitutions at the O-benzyl ring exhibited opposite effects.
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Affiliation(s)
- Liqing Yao
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, Zhejiang, China
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Yue L, Guo C, Chai Y, Yin X, Pan Y. Gas-phase reaction: alkyl cation transfer in the dissociation of protonated pyridyl carbamates in mass spectrometry. Tetrahedron 2014. [DOI: 10.1016/j.tet.2014.10.067] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Shen S, Chai Y, Weng G, Pan Y. Intramolecular electrophilic aromatic substitution in gas-phase fragmentation of protonated N-benzylbenzaldimines. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1662-1669. [PMID: 24957300 DOI: 10.1007/s13361-014-0935-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 05/21/2014] [Indexed: 06/03/2023]
Abstract
In this study, the gas-phase fragmentations of protonated N-benzylbenzaldimines were investigated by electrospray ionization tandem mass spectrometry (ESI-MS(n)). Upon collisional activation, several characteristic fragment ions are produced and their fragmentation mechanisms are rationalized by electrophilic aromatic substitution accompanied by benzyl cation transfer. (1) For N-(p-methoxybenzylidene)-1-phenylmethanimine, concomitant with a loss of HCN, a product ion at m/z 121 was observed. It is proposed to be generated from electrophilic substitution at the ipso-position by transferring benzyl cation rather than cleavage of the C-N double bond. (2) For N-(m-methoxybenzylidene)-1-phenylmethanimine, a product ion at m/z 209 was obtained, corresponding to the elimination of NH(3) carrying two hydrogens from the two aromatic rings respectively. This process can be rationalized by two sequential electrophilic substitutions and cyclodeamination reaction based on the benzyl cation transfer. Deuterium-labeled experiments, density functional theory (DFT) calculation and substituent effect results also corroborate the proposed mechanism.
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Affiliation(s)
- Shanshan Shen
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
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Grossert JS, Cubero Herrera L, Ramaley L, Melanson JE. Studying the chemistry of cationized triacylglycerols using electrospray ionization mass spectrometry and density functional theory computations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1421-1440. [PMID: 24867430 DOI: 10.1007/s13361-014-0917-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 04/01/2014] [Accepted: 04/02/2014] [Indexed: 06/03/2023]
Abstract
Analysis of triacylglycerols (TAGs), found as complex mixtures in living organisms, is typically accomplished using liquid chromatography, often coupled to mass spectrometry. TAGs, weak bases not protonated using electrospray ionization, are usually ionized by adduct formation with a cation, including those present in the solvent (e.g., Na(+)). There are relatively few reports on the binding of TAGs with cations or on the mechanisms by which cationized TAGs fragment. This work examines binding efficiencies, determined by mass spectrometry and computations, for the complexation of TAGs to a range of cations (Na(+), Li(+), K(+), Ag(+), NH4(+)). While most cations bind to oxygen, Ag(+) binding to unsaturation in the acid side chains is significant. The importance of dimer formation, [2TAG + M](+) was demonstrated using several different types of mass spectrometers. From breakdown curves, it became apparent that two or three acid side chains must be attached to glycerol for strong cationization. Possible mechanisms for fragmentation of lithiated TAGs were modeled by computations on tripropionylglycerol. Viable pathways were found for losses of neutral acids and lithium salts of acids from different positions on the glycerol moiety. Novel lactone structures were proposed for the loss of a neutral acid from one position of the glycerol moiety. These were studied further using triple-stage mass spectrometry (MS(3)). These lactones can account for all the major product ions in the MS(3) spectra in both this work and the literature, which should allow for new insights into the challenging analytical methods needed for naturally occurring TAGs.
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Affiliation(s)
- J Stuart Grossert
- National Research Council Canada, Halifax, Nova Scotia, B3H 3Z1, Canada,
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Gillis EAL, Grossert JS, White RL. Rearrangements leading to fragmentations of hydrocinnamate and analogous nitrogen-containing anions upon collision-induced dissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:388-397. [PMID: 24408178 DOI: 10.1007/s13361-013-0788-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 11/14/2013] [Accepted: 11/18/2013] [Indexed: 06/03/2023]
Abstract
Tandem mass spectrometry (MS/MS) confirmed decarboxylation as the major collision-induced dissociation (CID) pathway of deprotonated hydrocinnamic acid (C6H5CH2CH2CO2H), N-phenylglycine (C6H5NHCH2CO2H) and 3-pyridin-2-ylpropanoic acid (C5H4NCH2CH2CO2H). The structure and stability of isomeric precursor and product anions were examined using density functional theory and ab initio methods. Geometry optimizations and frequency calculations were performed using the B3LYP/6-31++G(2d,p) level of theory and basis set with additional single point energies calculated at the MP2/6-311++G(2d,p) level. The formation of a delocalized product anion by carboxyl group-mediated migration of a benzylic proton to the ortho position of the ring and subsequent Cα-CO2(-) bond cleavage was energetically more favorable than direct decarboxylation and rearrangements of anions within ion-neutral complexes with carbon dioxide. The energy barrier for rearrangement of the delocalized product anion to the more stable benzylic anion was lowest in the fragmentation pathway of 3-pyridin-2-ylpropanoate. More energetically demanding fragmentation processes were indicated by the formation of other product anions at higher collision energy. Computations supported the feasibility of the formation of hydroxycarbonyl, styrene, and phenide ions from the benzylic anion of hydrocinnamate and the corresponding product anions from the nitrogen-containing analogues. The loss of dihydrogen from decarboxylated 3-pyridin-2-ylpropanoate was characterized computationally as hydride abstraction of an aryl proton. Overall, the results highlight the importance of exploring rearrangements in the fragmentation pathways of ions formed by electrospray ionization (ESI).
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Affiliation(s)
- Elizabeth A L Gillis
- Department of Chemistry, Dalhousie University, 6274 Coburg Road, PO Box 15000, Halifax, Nova Scotia, B3H 4R2, Canada
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Sun H, Wang L, Pan Y. Gas-phase arylmethyl transfer and cyclodeamination of argentinated N-arylmethyl-pyridin-2-ylmethanimine. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:169-175. [PMID: 24356863 DOI: 10.1007/s13361-013-0778-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 10/16/2013] [Accepted: 10/23/2013] [Indexed: 06/03/2023]
Abstract
In collisional activation of argentinated N-arylmethyl-pyridin-2-ylmethanimine, a neutral molecule of AgNH2 is eliminated, carrying one hydrogen from the methylene and the other one from the ortho position (relative to the ipso carbon) of the aryl ring. Taking argentinated N-benzyl-pyridin-2-ylmethanimine for example, the proposition that the AgNH2 loss results from intramolecular arylmethyl transfer combined with cyclodeamination is rationalized by deuterium labeling experiments, blocking experiments, and theoretical calculations. The structure of the final product ion from loss of AgNH2 was confirmed further by multistage mass spectrometry.
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Affiliation(s)
- Hezhi Sun
- Department of Chemistry, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, China
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Li F, Zhang X, Zhang H, Jiang K. Gas-phase fragmentation of the protonated benzyl ester of proline: intramolecular electrophilic substitution versus hydride transfer. JOURNAL OF MASS SPECTROMETRY : JMS 2013; 48:423-429. [PMID: 23584935 DOI: 10.1002/jms.3162] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 12/11/2012] [Accepted: 12/19/2012] [Indexed: 06/02/2023]
Abstract
In this study, the gas phase chemistry of the protonated benzyl esters of proline has been investigated by electrospray ionization mass spectrometry and theoretical calculation. Upon collisional activation, the protonated molecules undergo fragmentation reactions via three primary channels: (1) direct decomposition to the benzyl cation (m/z 91), (2) formation of an ion-neutral complex of [benzyl cation + proline](+), followed by a hydride transfer to generate the protonated 4,5-dihydro-3H-pyrrole-2-carboxylic acid (m/z 114), and (3) electrophilic attack at the amino by the transferring benzyl cation, and the subsequent migration of the activated amino proton leading to the simultaneous loss of (H2O + CO). Interestingly, no hydrogen/deuterium exchange for the fragment ion m/z 114 occurs in the d-labeling experiments, indicating that the transferring hydride in path-b comes from the methenyl hydrogen rather than the amino hydrogen. For para-substituted benzyl esters, the presence of electron-donating substituents significantly promotes the direct decomposition (path-a), whereas the presence of electron-withdrawing ones distinctively inhibits that channel. For the competing channels of path-b and path-c, the presence of electron-donating substituents favors path-b rather than path-c, whereas the presence of electron-withdrawing ones favors path-c rather than path-b.
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Affiliation(s)
- Fei Li
- Key Laboratory of Organosilicon Chemistry and Material Technology, Hangzhou Normal University, Hangzhou, 310012, China
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Guo C, Yue L, Guo M, Jiang K, Pan Y. Elimination of benzene from protonated N-benzylindoline: benzyl cation/proton transfer or direct proton transfer? JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:381-387. [PMID: 23361371 DOI: 10.1007/s13361-012-0561-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Revised: 12/06/2012] [Accepted: 12/07/2012] [Indexed: 06/01/2023]
Abstract
Collision-induced dissociation (CID) of protonated N-benzylindoline and its derivatives was investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Elimination of benzene was observed besides hydride transfer and electron transfer reactions. D-labeling experiments and accurate mass determinations of the product ions confirm that the external proton is retained in the fragment ion, and the elimination reaction was proposed to be initiated by benzyl cation transfer rather than proton transfer. Benzyl cation transfer from the nitrogen atom to one of the sp(2)-hybridized carbon atoms in the indoline core is the key step, and subsequent proton transfer reaction leads to the elimination of benzene. Density functional theory (DFT)-based calculations were performed and the computational results also support the benzyl cation/proton transfer mechanism. Figure ᅟ
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Affiliation(s)
- Cheng Guo
- Department of Chemistry, Zhejiang University, Hangzhou, China
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You Z, Guo C, Pan Y. An experimental and theoretical study on fragmentation of protonated N-(2-pyridinylmethyl)indole in electrospray ionization mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2012; 26:2509-2516. [PMID: 23008068 DOI: 10.1002/rcm.6371] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
RATIONALE The dissociation reactions of protonated molecules are the base of structural analysis in electrospray ionization tandem mass spectrometry (ESI-MS(n)). However, general rules for elucidating the numerous fragmentation reactions in ESI-MS(n) are still rather lacking. Therefore, it is very important at all times to carry out mechanistic investigations for fragmentation reactions in the gas phase. METHODS The fragmentation reactions of protonated N-(2-pyridinylmethyl)indoles were studied by both of ESI ion trap tandem mass spectrometry and ESI Fourier transform ion cyclotron resonance tandem mass spectrometry in positive-ion mode. RESULTS In ESI-MS/MS, the ionizing proton is first bound to the most thermodynamically favored site, the pyridine nitrogen; then it transfers to the dissociative protonation sites and triggers the fragmentation. In the fragmentation of the target compounds, some interesting reactions, such as rearrangement, proton transfer and electron transfer reactions, take place via ion/neutral complexes. The proposed mechanisms are supported by both theoretical calculations and isotopic labeling experiments. CONCLUSIONS This study is a case for better understanding the dissociative protonation sites and enriching the knowledge about the role of ion/neutral complexes in ESI-MS. It also provides useful information for the structural analysis of organic compounds, especially drug analysis in pharmaceutical chemistry.
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Affiliation(s)
- Zhushuang You
- Department of Chemistry, Zhejiang University, Hangzhou, China
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Zhang J, Chai Y, Jiang K, Yang H, Pan Y, Sun C. Gas phase retro-Michael reaction resulting from dissociative protonation: fragmentation of protonated warfarin in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:1059-1064. [PMID: 22899515 DOI: 10.1002/jms.3055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A mass spectrometric study of protonated warfarin and its derivatives (compounds 1 to 5) has been performed. Losses of a substituted benzylideneacetone and a 4-hydroxycoumarin have been observed as a result of retro-Michael reaction. The added proton is initially localized between the two carbonyl oxygens through hydrogen bonding in the most thermodynamically favorable tautomer. Upon collisional activation, the added proton migrates to the C-3 of 4-hydroxycoumarin, which is called the dissociative protonation site, leading to the formation of the intermediate ion-neutral complex (INC). Within the INC, further proton transfer gives rise to a proton-bound complex. The cleavage of one hydrogen bond of the proton-bound complex produces the protonated 4-hydroxycoumarin, while the separation of the other hydrogen bond gives rise to the protonated benzylideneacetone. Theoretical calculations indicate that the 1, 5-proton transfer pathway is most thermodynamically favorable and support the existence of the INC. Both substituent effect and the kinetic method were utilized for explaining the relative abundances of protonated 4-hydroxycoumarin and protonated benzylideneacetone derivative. For monosubstituted warfarins, the electron-donating substituents favor the generation of protonated substituted benzylideneacetone, whereas the electron-withdrawing groups favor the formation of protonated 4-hydroxycoumarin.
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Affiliation(s)
- Jia Zhang
- Department of Chemistry, Zhejiang University, Hangzhou, 310027, China
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Sun H, Chai Y, Pan Y. Dissociative Benzyl Cation Transfer versus Proton Transfer: Loss of Benzene from Protonated N-Benzylaniline. J Org Chem 2012; 77:7098-102. [DOI: 10.1021/jo301011e] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Hezhi Sun
- Department
of Chemistry, Zhejiang University, Hangzhou
310027, China
| | - Yunfeng Chai
- Department
of Chemistry, Zhejiang University, Hangzhou
310027, China
| | - Yuanjiang Pan
- Department
of Chemistry, Zhejiang University, Hangzhou
310027, China
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Ramesh M, Raju B, George M, Srinivas K, Jayathirtha Rao V, Bhanuprakash K, Srinivas R. The ESI CAD fragmentations of protonated 2,4,6-tris(benzylamino)- and tris(benzyloxy)-1,3,5-triazines involve benzyl-benzyl interactions: a DFT study. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:860-868. [PMID: 22791253 DOI: 10.1002/jms.3037] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6-tris(benzylamino)-1,3,5-triazine (1) and 2,4,6-tris(benzyloxy)-1,3,5-triazine (6) show abundant product ion of m/z 181 (C(14) H(13)(+)). The likely structure for C(14) H(13)(+) is α-[2-methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the 'N' analog (1) but low for the 'O' analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H-toluene](+) and [M + H-benzene](+) for compounds 1 and 6, respectively. The protonated 2,4,6-tris(4-methylbenzylamino)-1,3,5-triazine (4) exhibits competitive eliminations of p-xylene and 3,6-dimethylenecyclohexa-1,4-diene. Moreover, protonated 2,4,6-tris(1-phenylethylamino)-1,3,5-triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring 'N'. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H-shift from ring carbon to 'O' generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium-labeling and CAD experiments combined with DFT calculations.
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Affiliation(s)
- M Ramesh
- National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500607, India
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You Z, Wen Y, Jiang K, Pan Y. Fragmentation mechanism of product ions from protonated proline-containing tripeptides in electrospray ionization mass spectrometry. CHINESE SCIENCE BULLETIN-CHINESE 2012. [DOI: 10.1007/s11434-012-5117-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Chai Y, Wang L, Sun H, Guo C, Pan Y. Gas-phase chemistry of benzyl cations in dissociation of N-benzylammonium and N-benzyliminium ions studied by mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:823-833. [PMID: 22367690 DOI: 10.1007/s13361-012-0344-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 01/16/2012] [Accepted: 01/20/2012] [Indexed: 05/31/2023]
Abstract
In this study, the fragmentation reactions of various N-benzylammonium and N-benzyliminium ions were investigated by electrospray ionization mass spectrometry. In general, the dissociation of N-benzylated cations generates benzyl cations easily. Formation of ion/neutral complex intermediates consisting of the benzyl cations and the neutral fragments was observed. The intra-complex reactions included electrophilic aromatic substitution, hydride transfer, electron transfer, proton transfer, and nucleophilic aromatic substitution. These five types of reactions almost covered all the potential reactivities of benzyl cations in chemical reactions. Benzyl cations are well-known as Lewis acid and electrophile in reactions, but the present study showed that the gas-phase reactivities of some suitably ring-substituted benzyl cations were far richer. The 4-methylbenzyl cation was found to react as a Brønsted acid, benzyl cations bearing a strong electron-withdrawing group were found to react as electron acceptors, and para-halogen-substituted benzyl cations could react as substrates for nucleophilic attack at the phenyl ring. The reactions of benzyl cations were also related to the neutral counterparts. For example, in electron transfer reaction, the neutral counterpart should have low ionization energy and in nucleophilic aromatic substitution reaction, the neutral counterpart should be piperazine or analogues. This study provided a panoramic view of the reactions of benzyl cations with neutral N-containing species in the gas phase.
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Affiliation(s)
- Yunfeng Chai
- Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, 310027, China
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Kuck D. Concomitant hydride and proton transfer: an essay on competing and consecutive key reactions occurring in gaseousion/neutral complexes. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2012; 18:161-181. [PMID: 22641718 DOI: 10.1255/ejms.1171] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The interplay of proton transfer and hydride transfer reactions in alkylbenzenium ions and related protonated di- and oligophenylalkanes is presented and discussed. While intra- and interannular proton exchange has been recognised to be an ubiquitous feature in protonated arenes, hydride abstraction is much less obvious but can become a dominating fragmentation channel in metastable ions of tert-butyl-substituted alkylbenzenium ions and related carbocations. In such cases, proton-induced release of the tert-butyl cation gives rise to ion/neutral complexes as reactive intermediates, for example, [(CH(3))(3)C(+)...arylCH(2)(α)(CH(2))(n)CH(2)(ω)aryl '] with n ≥ 0, and highly regioselective intra-complex hydride transfer occurs from all of the benzylic methylene hydride ion donor groups (α-CH(2) and ω-CH(2)) to the tert-butyl cation acting as a Lewis acid. Substituent effects on the individual contributions to the overall hydride transfer from different donor sites, including ortho-methyl groups, in particular, and the concomitant intra- complex proton transfer from the tert-butyl cation to the neutral diarylalkane constituent corroborate the view of "bisolvated" complexes as the central intermediates, in which the carbenium ion is coordinated to both of the aromatic π-electron systems. The role of cyclisation processes converting the benzylic, [M - H](+) type, ions into the isomeric benzenium, [M + H](+)-type, ions prior to fragmentation is demonstrated for several cases. This overall scenario, consisting of consecutive and/or competing intra-complex hydride abstraction and proton transfer, intraannular proton shifts (H+ ring walk) and interannular proton transfer, hydrogen exchange ("scrambling") processes, and cyclisation and other electrophilic substitution reactions, is of general importance in this field of gas-phase ion chemistry, and more recent examples concerning protonated ethers, benzylpyridinium and benzylammmonium ions are discussed in which these recurring features play central and concerted mechanistic roles as well.
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Affiliation(s)
- Dietmar Kuck
- Department of Chemistry, Bielefeld University, Universitätsstrasse 25, 33615 Bielefeld, Germany.
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Chai Y, Guo C, Jiang K, Pan Y, Sun C. Cα–Cβand Cα–N bond cleavage in the dissociation of protonated N–benzyllactams: dissociative proton transfer and intramolecular proton-transport catalysis. Org Biomol Chem 2012; 10:791-7. [DOI: 10.1039/c1ob06020a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Chai Y, Sun H, Pan Y, Sun C. N-centered odd-electron ions formation from collision-induced dissociation of electrospray ionization generated even-electron ions: single electron transfer via ion/neutral complex in the fragmentation of protonated N,N'-dibenzylpiperazines and protonated N-benzylpiperazines. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:1526-1533. [PMID: 21953256 DOI: 10.1007/s13361-011-0176-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2011] [Revised: 05/19/2011] [Accepted: 05/19/2011] [Indexed: 05/31/2023]
Abstract
Single electron transfer (SET) via ion/neutral complex (INC) was proposed and confirmed to be the key step in the formation of N-centered odd-electron ions from fragmentation of protonated even-electron ions in the present study. Upon collisional activation, the model compounds, protonated N,N'-dibenzylpiperazine and protonated N-benzylpiperazines initially dissociated to form intermediate INCs consisting of N-benzylpiperazine (or piperazine) and benzyl cation. In these ion/neutral complexes, SET reaction and direct separation as well as other reactions were observed and characterized experimentally and theoretically. Density functional theory calculations demonstrated that the energy requirement for homolysis of the precursor ion was so large that it could not be achieved, whereas the heterolytic dissociation followed by electron transfer via INC was energetically preferred. The SET process occurred only when the radical products were more stable than the separation products. The energy barrier for SET in the compounds studied was roughly estimated by comparison with other competing reactions. When the INC contained electron donor with lower ionization energy and electron acceptor with higher electron affinity, the SET reaction was more efficient.
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Affiliation(s)
- Yunfeng Chai
- Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, 310027, China
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Chai Y, Jiang K, Sun C, Pan Y. Gas-Phase Nucleophilic Aromatic Substitution between Piperazine and Halobenzyl Cations: Reactivity of the Methylene Arenium Form of Benzyl Cations. Chemistry 2011; 17:10820-4. [DOI: 10.1002/chem.201101790] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2011] [Indexed: 11/10/2022]
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