The structures of two oligomers of acidic xylo-oligosaccharides (XOS) of the same molecular weight (634 Da), Xyl(2)MeGlcAHex and Xyl(2)GlcA(2) were differentiated by electrospray tandem mass spectrometry (ESI-MS/MS). These oligomers were present in a mixture of XOS obtained by acid hydrolysis of heteroxylans extracted from Eucalyptus globulus wood (Xyl(2)MeGlcAHex) and Olea europaea olive fruit (Xyl(2)GlcA(2)). In the ESI-MS spectra of the XOS, ions at m/z 657 and 652 were observed and assigned to [M + Na](+) and [M + NH(4)](+), respectively. The ESI-MS/MS spectrum of [M + Na](+) ion of Xyl(2)MeGlcAHex showed the loss of Hex residue from the reducing end followed by the loss of MeGlcA moiety. Simultaneously, the loss of a Xyl residue from either the reducing or the non-reducing ends was detected. On the other hand, the fragmentation of Xyl(2)GlcA(2) occurs mainly by the loss of one and two GlcA residues or by the loss of the GlcAXyl moiety, due to the glycosidic bond cleavage between the two Xyl residues. Loss of one and two CO(2) molecules was only observed for this oligomer, where the GlcA are in vicinal Xyl residues. The ESI-MS/MS spectra of [M + NH(4)](+) of both oligomers showed the loss of NH(3), resulting in the protonated molecule, where the presence of ions assigned as protonated molecules of aldobiuronic acid residues, [MeGlcA - Xyl + H](+) and [GlcA - Xyl + H](+), are diagnostic ions of the presence of MeGlcA and GlcA moieties in XOS. Since these structures occur in small amounts in complex acidic XOS mixtures and are very difficult, if possible, to isolate, tandem mass spectrometry revealed to be a powerful tool for the characterization of these types of substitution patterns present in heteroxylans.

中文翻译：

---

通过电喷雾串联质谱分析酸性杂木聚糖中的尿苷基取代模式的结构差异。

通过电喷雾串联质谱（ESI-MS / MS）来区分两个相同分子量（634 Da）的酸性木糖低聚糖（XOS），Xyl（2）MeGlcAHex和Xyl（2）GlcA（2）的低聚物结构）。这些低聚物存在于XOS的混合物中，该混合物通过酸水解从球墨桉木（Xyl（2）MeGlcAHex）和油橄榄橄榄果实（Xyl（2）GlcA（2））中提取的异木聚糖而获得。在XOS的ESI-MS光谱中，观察到m / z 657和652处的离子，分别分配给[M + Na]（+）和[M + NH（4）]（+）。Xyl（2）MeGlcAHex的[M + Na]（+）离子的ESI-MS / MS光谱显示，还原端Hex残基丢失，随后MeGlcA部分丢失。同时，从还原或非还原端检测到Xyl残基的丢失。另一方面，Xyl（2）GlcA（2）的片段化主要是由于两个Xyl残基之间的糖苷键断裂，导致一个和两个GlcA残基的丢失或GlcAXyl基团的丢失。仅对于该低聚物观察到一个和两个CO（2）分子的损失，其中GlcA在邻近的Xyl残基中。两种低聚物的[M + NH（4）]（+）的ESI-MS / MS谱图均显示NH（3）的损失，从而导致了质子化分子，其中存在的离子被指定为醛二糖醛酸残基的质子化分子[MeGlcA-Xyl + H]（+）和[GlcA-Xyl + H]（+）是XOS中存在MeGlcA和GlcA部分的诊断离子。由于这些结构少量出现在复杂的酸性XOS混合物中，并且如果可能的话很难分离，