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Mass spectrometric stereoisomeric differentiation between α‐ and β‐ascorbic acid 2‐ O ‐glucosides. Experimental and density functional theory study
Author(s) -
Kanawati Basem,
von Saint Paul Veronica,
Herrmann Constanze,
Schäffner Anton R.,
SchmittKopplin Philippe
Publication year - 2011
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.4908
Subject(s) - chemistry , ascorbic acid , homolysis , heterolysis , density functional theory , fragmentation (computing) , tandem mass spectrometry , dissociation (chemistry) , intramolecular force , stereochemistry , computational chemistry , mass spectrometry , photochemistry , radical , organic chemistry , chromatography , food science , computer science , operating system , catalysis
L‐Ascorbic acid and two distinct anomers, namely the α‐D‐glucopyranosyl and β‐D‐glucopyranosyl‐(1→2)‐L‐ascorbic acid (stereoisomers), were studied within the scope of collision‐induced dissociation (CID) experiments, performed by linear ion acceleration and collision with argon atoms inside a hexapole quadrupole hexapole ion beam guide, which is coupled to an ion cyclotron resonance (ICR) cell with a 12 Tesla magnet for high‐resolution measurements. Loss of C 2 H 4 O 2 neutral from the [M–H] − anion of L‐ascorbic acid was observed. Density functional theory (DFT) calculations on the 6‐311+G(2d,p)//6‐31+G(d) level of theory reveal a new concerted mechanism for an intramolecular gas‐phase rearrangement, through which the observed ejected neutral C 2 H 4 O 2 can take place. A similar rearrangement also occurs in the case of α‐ and β‐D‐glucopyranosyl‐(1→2)‐L‐ascorbic acid. For the α isomer, only homolytic glycoside fragmentation was observed. For the β isomer, both homolytic and heterolytic glycoside cleavages were possible. The mechanisms behind all observed fragmentation pathways were fully understood by the implementation of accurate DFT calculations. Stereoisomeric differentiation between α and β isomers of the L‐ascorbic acid‐2‐ O ‐glucoside could be revealed by tandem mass spectrometry (MS/MS) experiments and were explained theoretically. Copyright © 2011 John Wiley & Sons, Ltd.