Investigating the Structure of / Carbohydrate Linkage Isomers as a Function of Group I Metal Adduction and Degree of Polymerization as Revealed by Cyclic Ion Mobility Separations

In high-resolution ion mobility spectrometry-mass spectrometry ( IMS-MS)-based separations individual, pure, oligosaccharide species often produce multiple IMS peaks presumably from their alpha/beta anomers, cation attachment site conformations, and/or other energetically favorable structures. Herein, the use of high-resolution traveling wave-based cyclic IMS-MS to systematically investigate the origin of these multiple peaks by analyzing alpha 1,4- and beta 1,4-linked D-glucose homopolymers as a function of their group I metal adducts is presented. Across varying degrees of polymerization, and for certain metal adducts, at least two major IMS peaks with relative areas that matched the similar to 40:60 ratio for the alpha/beta anomers of a reducing-end D-glucose as previously calculated by NMR were observed. To further validate that these were indeed the alpha/beta anomers, rather than other substructures, the reduced versions of several maltooligosaccharides were analyzed and all produced a single IMS peak. This result enabled the discovery of a mobility fingerprint trend: the beta anomer was always higher mobility than the a anomer for the cellooligosaccharides, while the alpha anomer was always higher mobility than the beta anomer for the maltooligosaccharides. For maltohexaose, a spurious, high mobility, fourth peak was present. This was hypothesized to potentially be from a highly compacted conformation. To investigate this, alpha-cyclodextrin, a cyclic oligosaccharide, produced similar arrival times as the high mobility maltohexaose peak. It is anticipated that these findings will aid in the data deconvolution of IMS-MS-based glycomics workflows and enable the improved characterization of biologically relevant carbohydrates.