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.

Comparison and Characterization of Compounds with Antioxidant Activity in Lycium barbarum Using High‐Performance Thin Layer Chromatography Coupled with DPPH Bioautography and Tandem Mass Spectrometry

“…Moreover, the MS/MS spectrum showed that with the collision energy of 35.0 eV, the precursor anion [M‐H] − ( m / z 337.0724) was collided to 2 fragment ions, including the parent anion m / z 337.0712 and another fragment ion m / z 277.0517 (Figure B). It was considered consistent with the loss of C‐5 and C‐6 from the ascorbic acid portion of the molecule (Figure C), by which could be tentatively identified as 2‐ O ‐β‐ d ‐glucopyranosyl‐ l ‐ascorbic acid (AA‐2βG) according to the literatures (Toyoda‐Ono and others ; Tai and Gohda ; Kanawati and others ). Furthermore, Hancock and others () revealed that the maximum wavelengths of targeted compound identified by ESI‐Q‐TOF‐MS/MS were 235 and 259 nm, which was homologous to HPTLC‐UV results (Figure A) and could further verify the identified compound.…”

Exploring the Arabidopsis sulfur metabolome

“…The 146.058 [M‐H] − cleaved‐off fragment has the predicted elemental composition of C 6 H 10 O 4 (0.7 ppm) and was not detected in the analysis. The fragmentation of this group probably occurred as a neutral loss accompanied by a proton shift from the conjugated group to the glutathione moiety, which induces an intramolecular rearrangement of the group (Kanawati et al ., ). Thus, the original conjugated group in the neutral GS conjugate has a sum formula of C 6 H 11 O 4 .…”

The Intracellular Bacteria Chlamydia Hijack Peroxisomes and Utilize Their Enzymatic Capacity to Produce Bacteria-Specific Phospholipids

“…HILIC and RP LC-MS were performed on the crude lipid extracts with an ACQUITY UPLC® (Waters, Milford, USA) connected to an UHR QqToF mass spectrometer (maXis™, Bruker, Bremen, Germany). Molecules of interest were further analyzed at ultra-high resolution (<300,000 at m/z 300) and fragmented in negative electrospray ionization mode to identify the fatty acid side chains with an Ion Cyclotron Resonance Fourier Transform Mass Spectrometer (ICR-FT/MS, solariX™, Bruker Daltonics GmbH, Bremen, Germany) [45]. See Figure S1 and Movie S1 for further details and controls.…”