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Theoretical study of the main fragmentation pathways for protonated glycylglycine
Author(s) -
Paizs Béla,
Suhai Sándor
Publication year - 2001
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.273
Subject(s) - chemistry , glycylglycine , fragmentation (computing) , protonation , ion , computational chemistry , kinetics , dipeptide , chemical physics , organic chemistry , quantum mechanics , glycine , biochemistry , physics , amino acid , computer science , operating system
Quantum chemical and RRKM calculations were carried out on protonated glycylglycine in order to determine the atomic details of the main fragmentation pathways leading to formation of a 1 and y 1 ions. Two possible mechanisms were considered. The first path results in elimination of aziridinone as a neutral counterpart of the y 1 ion formed. Our calculations show that this pathway has a relatively high threshold energy (48.6 kcal/mol) and the corresponding unimolecular rate constants are quite small even at large internal energy. An alternative pathway (a 1 ‐y 1 ) proposed in the present paper seems, however, to be favored against the above ‘aziridinone’ one from the points of view of both energetics and kinetics. The ‘a 1 ‐y 1 ’ pathway leads to simultaneous formation of a 1 and y 1 ions, the ratio of which depends on the energy distribution of the fragmenting species for a particular dipeptide. However, even if y 1 ions are formed via the ‘a 1 ‐y 1 ’ pathway, the corresponding neutrals eliminated do not have a strained cyclic aziridinone structure. Instead, in a two‐step process, CO and NHCH 2 are formed leading to neutral products energetically more favored than aziridinone. The available experimental data reevaluated in the present paper lend support to the ‘a 1 ‐y 1 ’ pathway. Copyright © 2001 John Wiley & Sons, Ltd.