Gas phase structures of sodiated oligosaccharides by ion mobility ion chromatography methods

Matrix assisted laser desorption ionization (MALDI) was used to generate sodiated parent ions of a number of oligosaccharides, including three tetraoses and two hexaoses. No fragmentation was observed in any of the systems. Ion mobility studies yielded gas phase cross sections which could be compared with predictions made by molecular mechanics/molecular dynamics calculations. In all three tetraoses (cellotetraose, maltotetraose and isomaltotetraose) the Na+ ion coordinated with all four sugar moities forming very similar structures even though the neutral structures are very different. In the two hexaose systems (alpha-cyclodextrin and maltohexaose) again the Na+ ion coordinated with four sugars. Molecular dynamics studies indicated that at temperatures above 300 K the Na+ ion was mobile and sampled all six sugars of the hexaoses. This work is compared to other work in the literature, and differences are discussed. (C) 1997 Elsevier Science B.V.