2020 Fiscal Year Annual Research Report
Energy-resolved tandem mass spectrometry for in-situ differentiation and identification of isomers
| Project/Area Number |
17K08262
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
中村 健道 国立研究開発法人理化学研究所, 環境資源科学研究センター, 特別嘱託研究員 (10360611)
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| Project Period (FY) |
2017-04-01 – 2021-03-31
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| Keywords | Energy-resolved MS/MS / Isomer Differentiation / CID / Breakdown Diagram / Protonated Amino Acid / Fragmentation Mechanism / Activation Barrier / Computational Chemistry |
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| Outline of Annual Research Achievements |
The study to fundamental side since originally planned experiments could not be carried out due to the reduced accessibility to biological samples in last year. Future direction of the study was shown by the insight into complex nature of the fragmentation process.
We've shown three C4 amino acid isomers, 2-aminobutylic acid (ABA), 2-methylalanine (MAL), N,N-dimethylglycine (DMG) cannot be identified based on their fragmentation patterns as they are essentially the same. Each isomer, however, can be clearly distinguishable based on the energy requirement to give m/z 58 fragment ions, which can be visualized by ER MS2 experiments. To understand the mechanism behind the difference in energy requirement, a computational study has been carried out.
The mechanism to give m/z 58 fragment ions was considered to be a consecutive loss of H2O and CO. The barrier for the H2O and CO loss in Gly was known to be at the transition state from protonated amino group to protonated hydroxyl group. We've modelled the similar transition states for the generation of m/z 58 and estimated the energy barriers. The theoretical energy barrier for DMG was substantially higher (ca. 10 kcal/mol) than those for the other isomers and Gly. The higher barrier for DMG was consistent to the highest energy requirement of DMG in ER MS2. On the other hand, the higher energy requirement for MAL compared to ABA cannot be explained by the calculated activation barriers. It turned out that we need to refine the model to fully understand the observed CID process.
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