title: Mass spectrometric stereoisomeric differentiation between α- and β-ascorbic acid 2-O-glucosides. Experimental and density functional theory study.
abstract: 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.
authors.affiliation: Institute of Ecological Chemistry, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany. Basem.Kanawati@helmholtz-muenchen.de
authors.forename: Basem
authors.initials: B
authors.lastname: Kanawati
authors.forename: Veronica
authors.initials: V
authors.lastname: von Saint Paul
authors.forename: Constanze
authors.initials: C
authors.lastname: Herrmann
authors.forename: Anton R
authors.initials: AR
authors.lastname: Schäffner
authors.forename: Philippe
authors.initials: P
authors.lastname: Schmitt-Kopplin
mesh_terms: D000838:Anions / Q000737:chemistry; D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D005960:Glucosides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D053719:Tandem Mass Spectrometry
chemical_list: D000838:Anions; D005960:Glucosides; C065378:ascorbic acid 2-O-glucoside; D001205:Ascorbic Acid