Reis Ana, Pinto Paula, Coimbra M A, Evtuguin Dmitry V, Neto Carlos P, Ferrer Correia A J, Domingues M Rosário M
Department of Chemistry, University of Aveiro, Aveiro, Portugal.
J Am Soc Mass Spectrom. 2004 Jan;15(1):43-7. doi: 10.1016/j.jasms.2003.09.007.
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.
通过电喷雾串联质谱法（ESI-MS/MS）区分了两种分子量相同（634 Da）的酸性木寡糖（XOS）低聚物Xyl(2)MeGlcAHex和Xyl(2)GlcA(2)的结构。这些低聚物存在于通过酸水解从蓝桉木材（Xyl(2)MeGlcAHex）和油橄榄果实（Xyl(2)GlcA(2)）中提取的杂木聚糖获得的XOS混合物中。在XOS的ESI-MS谱图中，观察到m/z 657和652处的离子，分别归属于M + Na和M + NH(4)。Xyl(2)MeGlcAHex的M + Na离子的ESI-MS/MS谱图显示，还原端的己糖残基丢失，随后是甲基葡萄糖醛酸部分的丢失。同时，检测到还原端或非还原端的一个木糖残基的丢失。另一方面，由于两个木糖残基之间的糖苷键断裂，Xyl(2)GlcA(2)的碎片化主要是通过一个和两个葡萄糖醛酸残基的丢失或通过葡萄糖醛酸-木糖部分的丢失。仅在该低聚物中观察到一个和两个CO(2)分子的丢失，其中葡萄糖醛酸位于相邻的木糖残基中。两种低聚物的M + NH(4)的ESI-MS/MS谱图显示NH(3)的丢失，产生质子化分子，其中归属于醛糖二糖酸残基质子化分子的离子MeGlcA - Xyl + H和GlcA - Xyl + H的存在是XOS中甲基葡萄糖醛酸和葡萄糖醛酸部分存在的诊断离子。由于这些结构在复杂的酸性XOS混合物中含量很少，并且如果可能的话很难分离，串联质谱法被证明是表征杂木聚糖中存在的这些类型取代模式的有力工具。
