The protonated ions of fucose-containing oligosaccharides are prone to undergo internal glycan rearrangement which results in chimeric fragments that obfuscate mass-spectrometry analysis. Lack of systematic analysis of glycans in the gas phase limits understanding of the factors that influence the thermodynamics and kinetics of the process. In this work, we use density functional theory modeling to reinterpret the cryogenic IR spectrum of lewis a and blood group type H1 trisaccharides and answer whether the fucose migration in these glycans occurs. The structurally-unconstrained search reveals that none of the parent ion constitutes a thermodynamic global minimum. Comparison of their predicted collision cross-sections and anharmonic IR spectra confirms that lewis a and blood group type H1 undergo the rearrangement to yield a fucose connected to O6 at either galactose of N-acetylglucosoamine. The proximity of the mobile proton, and the large free-energy gap between the parent ions and the products are attributed to be key-contributor to this phenomenon.

中文翻译：

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Lewis a 和 H1 型血型表位的内部聚糖重排的重新研究

含岩藻糖寡糖的质子化离子容易发​​生内部聚糖重排，从而产生嵌合片段，从而混淆质谱分析。缺乏对气相聚糖的系统分析限制了对影响该过程的热力学和动力学因素的理解。在这项工作中，我们使用密度泛函理论模型重新解释了路易斯a和血型H1三糖的低温红外光谱，并回答了这些聚糖中是否发生岩藻糖迁移。结构不受约束的搜索表明，没有一个母离子构成热力学全局最小值。比较预测的碰撞截面和非谐红外光谱证实，路易斯 a 和 H1 型血型经历重排，产生在 N-乙酰氨基葡萄糖的任一半乳糖处与 O6 连接的岩藻糖。移动质子的接近以及母离子和产物之间较大的自由能间隙被认为是造成这种现象的关键因素。