Mass spectrometric stereoisomeric differentiation between alpha- and beta-ascorbic acid 2-O-glucosides. Experimental and density functional theory study

作者：Kanawati Basem^*; von Saint Paul Veronica; Herrmann Constanze; Schaeffner Anton R; Schmitt Kopplin Philippe

来源：Rapid Communications in Mass Spectrometry, 2011, 25(6): 806-814.

DOI：10.1002/rcm.4908

L-Ascorbic acid and two distinct anomers, namely the alpha-D-glucopyranosyl and beta-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)//6-31RG(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 alpha- and beta-D-glucopyranosyl-(1 -> 2)-L-ascorbic acid. For the alpha isomer, only homolytic glycoside fragmentation was observed. For the beta 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 alpha and beta isomers of the L-ascorbic acid-2-O-glucoside could be revealed by tandem mass spectrometry (MS/MS) experiments and were explained theoretically.

• 出版日期2011-3-30