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Furthering the Diverse Hydrogen Atom Transfer and Carbon Bond Dissociation of Amino Acids under Vacuum Ultraviolet
Author(s) -
Guo Mengdi,
Wu Haiming,
Zhang Hanyu,
Luo Zhixun
Publication year - 2019
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201803564
Subject(s) - chemistry , dissociation (chemistry) , hydrogen bond , bond cleavage , mass spectrometry , hydrogen atom , ionization , photochemistry , molecule , crystallography , stereochemistry , organic chemistry , ion , catalysis , alkyl , chromatography
Hydrogen atom transfer (HAT) and bond dissociation of amino acids are studied utilizing a customized vacuum ultraviolet laser ionization mass spectrometer (VUV‐LIMS). Three typical molecules (glycine, threonine and cysteine) which have similar structures but a minor difference by having one or two bonds associated with C α or having a sulfhydryl were select in this study. As results, glycine finds a simplex dissociation pathway by producing CNH 4 + (m/z 30) indicative of direct bond cleavage of C α ‐C 1 (C 1 stands for the carbon atom of the carboxyl group here). Threonine bears two bonds associated with C α and they both dissociate under VUV excitation, giving rise to three major mass peaks at m/z 30 (CNH 4 + ), 44 and 75 respectively along with selective HAT process. Interestingly, cysteine also bears two dissociative bonds associated with C α , however, the dominant HAT for producing NH 3 , CNH 4 + or CO 2 was found to be dramatically restrained by the production of H 2 S which is known as an important gasotransmitter in biological nervous system. Based on density functional theory (DFT) calculations, an in‐depth analysis is conducted to show the thermodynamics and reaction kinetics in forming these fragments with or without a HAT process. It is demonstrated that the HAT‐accommodated structure relaxation and incidental elongation of the bonds associated with C α , depending on the residual energies after ionization, bring forth competitive and cooperative effect in determining the selectivity of alpha‐beta carbon chemistry.