Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
J Am Soc Mass Spectrom. 2012 Nov;23(11):2031-42. doi: 10.1007/s13361-012-0459-y. Epub 2012 Aug 22.
Chloride anion attachment has previously been shown to aid determination of saccharide anomeric configuration and generation of linkage information in negative ion post-source decay MALDI tandem mass spectrometry. Here, we employ electron detachment dissociation (EDD) and collision activated dissociation (CAD) for the structural characterization of underivatized oligosaccharides bearing a chloride ion adduct. Both neutral and sialylated oligosaccharides are examined, including maltoheptaose, an asialo biantennary glycan (NA2), disialylacto-N-tetraose (DSLNT), and two LS tetrasaccharides (LSTa and LSTb). Gas-phase chloride-adducted species are generated by negative ion mode electrospray ionization. EDD and CAD spectra of chloride-adducted oligosaccharides are compared to the corresponding spectra for doubly deprotonated species not containing a chloride anion to assess the role of chloride adduction in the stimulation of alternative fragmentation pathways and altered charge locations allowing detection of additional product ions. In all cases, EDD of singly chloridated and singly deprotonated species resulted in an increase in observed cross-ring cleavages, which are essential to providing saccharide linkage information. Glycosidic cleavages also increased in EDD of chloride-adducted oligosaccharides to reveal complementary structural information compared to traditional (non-chloride-assisted) EDD and CAD. Results indicate that chloride adduction is of interest in alternative anion activation methods such as EDD for oligosaccharide structural characterization.
氯离子的附着以前被证明有助于确定糖的端基构型，并在负离子源后降解 MALDI 串联质谱中产生键合信息。在这里，我们采用电子脱附解离（EDD）和碰撞活化解离（CAD）来对带有氯离子加合物的未衍生寡糖进行结构表征。中性和唾液酸化的寡糖都进行了研究，包括麦芽七糖、无唾液酸双触角聚糖（NA2）、二唾液酰乳糖-N-四糖（DSLNT）和两种 LS 四糖（LSTa 和 LSTb）。通过负离子模式电喷雾电离生成气相氯离子加合物。将氯离子加合寡糖的 EDD 和 CAD 光谱与不含有氯离子的双去质子化物种的相应光谱进行比较，以评估氯离子加合在刺激替代碎裂途径和改变电荷位置中的作用，从而允许检测到额外的产物离子。在所有情况下，单氯化和单去质子化物种的 EDD 都会导致观察到的跨环裂解增加，这对于提供糖键合信息至关重要。糖苷键裂解也在氯离子加合寡糖的 EDD 中增加，与传统的（非氯离子辅助）EDD 和 CAD 相比，揭示了互补的结构信息。结果表明，氯离子加合对于替代阴离子激活方法（如 EDD）在寡糖结构表征中具有重要意义。
