Institute of Ecological Chemistry, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany.
Rapid Commun Mass Spectrom. 2011 Mar 30;25(6):806-14. doi: 10.1002/rcm.4908.
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.
抗坏血酸及其两种独特的差向异构体，即 α-D-吡喃葡萄糖基-和 β-D-吡喃葡萄糖基-(1→2)-L-抗坏血酸（立体异构体），在碰撞诱导解离（CID）实验范围内进行了研究，通过线性离子加速和在六极四极六极离子束导向器内与氩原子碰撞来进行实验，该导向器与具有 12 特斯拉磁场的离子回旋共振（ICR）细胞耦合，用于进行高分辨率测量。观察到 L-抗坏血酸的M-H阴离子失去 C(2)H(4)O(2)中性。在 6-311+G(2d,p)//6-31+G(d)理论水平上的密度泛函理论（DFT）计算揭示了一种新的分子内气相重排的协同机制，通过该机制可以发生观察到的被逐出的中性 C(2)H(4)O(2)。类似的重排也发生在 α-和 β-D-吡喃葡萄糖基-(1→2)-L-抗坏血酸的情况下。对于 α 异构体，仅观察到均裂糖苷键断裂。对于 β 异构体，均裂和异裂糖苷键断裂都是可能的。通过实施准确的 DFT 计算，完全理解了所有观察到的碎片途径背后的机制。通过串联质谱（MS/MS）实验和理论解释，可以揭示 L-抗坏血酸-2-O-葡萄糖苷的 α 和 β 异构体之间的立体异构区分。
