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Isomer differentiation via collision‐induced dissociation: The case of protonated α‐, β 2 ‐ and β 3 ‐phenylalanines and their derivatives
Author(s) -
Lam Adrian K. Y.,
O'Hair Richard A. J.
Publication year - 2010
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.4576
Subject(s) - chemistry , phenylalanine , protonation , fragmentation (computing) , dissociation (chemistry) , stereochemistry , medicinal chemistry , amino acid , organic chemistry , ion , biochemistry , computer science , operating system
A combination of electrospray ionisation (ESI), multistage and high‐resolution mass spectrometry experiments is used to examine the gas‐phase fragmentation reactions of the three isomeric phenylalanine derivatives, α‐phenylalanine, β 2 ‐phenylalanine and β 3 ‐phenylalanine. Under collision‐induced dissociation (CID) conditions, each of the protonated phenylalanine isomers fragmented differently, allowing for differentiation. For example, protonated β 3 ‐phenylalanine fragments almost exclusively via the loss of NH 3 , only β 2 ‐phenylalanine via the loss of H 2 O, while α‐ and β 2 ‐phenylalanine fragment mainly via the combined losses of H 2 O + CO. Density functional theory (DFT) calculations were performed to examine the competition between NH 3 loss and the combined losses of H 2 O and CO for each of the protonated phenylalanine isomers. Three potential NH 3 loss pathways were studied: (i) an aryl‐assisted neighbouring group; (ii) 1,2 hydride migration; and (iii) neighbouring group participation by the carboxyl group. Finally, we have shown that isomer differentiation is also possible when CID is performed on the protonated methyl ester and methyl amide derivatives of α‐, β 2 ‐ and β 3 ‐phenylalanines. Copyright © 2010 John Wiley & Sons, Ltd.