The connection between monosaccharides influences the structure, solubility, and biological function of carbohydrates. Although tandem mass spectrometry (MS/MS) often enables the compositional identification of carbohydrates, traditional MS/MS fragmentation methods fail to generate abundant cross-ring fragments of intrachain monosaccharides that could reveal carbohydrate connectivity. We examined the potential of helium-charge transfer dissociation (He-CTD) as a method of MS/MS to decipher the connectivity of β-1,4- and β-1,3-linked oligosaccharides. In contrast to collision-induced dissociation (CID), He-CTD of isolated oligosaccharide precursors produced both glycosidic and cross-ring cleavages of each monosaccharide. The radical-driven dissociation in He-CTD induced single cleavage events, without consecutive fragmentations, which facilitated structural interpretation. He-CTD of various standards up to a degree of polymerization of 7 showed that β-1,4- and β-1,3-linked carbohydrates can be distinguished based on diagnostic 3,5A fragment ions that are characteristic for β-1,4-linkages. Overall, fragment ion spectra from He-CTD contained sufficient information to infer the connectivity specifically for each glycosidic bond. When testing He-CTD to resolve the order of β-1,4- and β-1,3-linkages in mixed-linked oligosaccharide standards, He-CTD spectra sometimes provided less confident assignment of connectivity. Ion mobility spectrometry-mass spectrometry (IMS-MS) of the standards indicated that ambiguity in the He-CTD spectra was caused by isobaric impurities in the mixed-linked oligosaccharides. Radical-driven dissociation induced by He-CTD can thus expand MS/MS to carbohydrate linkage analysis, as demonstrated by the comprehensive fragment ion spectra on native oligosaccharides. The determination of connectivity in true unknowns would benefit from the separation of isobaric precursors, through UPLC or IMS, before linkage determination via He-CTD.

中文翻译：

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通过电荷转移解离质谱法鉴别天然寡糖中的β-1,4-和β-1,3-键。

单糖之间的连接会影响碳水化合物的结构，溶解度和生物学功能。尽管串联质谱（MS / MS）通常可以对碳水化合物进行成分鉴定，但传统的MS / MS裂解方法无法生成可揭示碳水化合物连通性的链内单糖丰富的交叉环片段。我们检查了氦电荷转移解离（He-CTD）作为MS / MS破译β-1,4-和β-1,3-连接的寡糖的连通性的潜力。与碰撞诱导解离（CID）相反，分离的寡糖前体的He-CTD产生了每个单糖的糖苷和交叉环裂解。He-CTD中由自由基驱动的解离诱导了单个裂解事件，没有连续的断裂，这有助于结构解释。聚合度最高为7的各种标准的He-CTD表明，可以基于诊断性3,5A碎片离子来区分与β-1,4-和β-1,3-连接的碳水化合物，这些离子具有β-1的特征， 4个链接。总体而言，来自He-CTD的碎片离子谱图包含足够的信息，可以推断每个糖苷键的连接性。当测试He-CTD来解析混合连接的寡糖标准品中β-1,4-和β-1,3-键的顺序时，He-CTD谱图有时对连接的确定性较差。该标准的离子淌度质谱-质谱（IMS-MS）表明，He-CTD光谱中的歧义是由混合连接的寡糖中的同量异位杂质引起的。由He-CTD诱导的自由基驱动的解离可将MS / MS扩展到碳水化合物连锁分析，如天然寡糖上完整的碎片离子光谱所证明的。在通过He-CTD进行连锁测定之前，通过UPLC或IMS分离等压的前体，可以确定真实未知物中的连通性。