GAS-PHASE STRUCTURES OF SODIATED OLIGOSACCHARIDES BY ION MOBILITY IONCHROMATOGRAPHY METHODS

Matrix assisted laser desorption ionization (MALDI) was used to genera te sodiated parent ions of a number of oligosaccharides, including thr ee tetraoses and two hexaoses. No fragmentation was observed in any of the systems. Ion mobility studies yielded gas phase cross sections wh ich could be compared with predictions made by molecular mechanics/mol ecular dynamics calculations. In all three tetraoses (cellotetraose, m altotetraose and isomaltotetraose) the Na+ ion coordinated with all fo ur sugar moities forming very similar structures even though the neutr al structures are very different. In the two hexaose systems (alpha-cy clodextrin and maltohexaose) again the Na+ ion coordinated with four s ugars. Molecular dynamics studies indicated that at temperatures above 300 K the Na+ ion was mobile and sampled all six sugars of the hexaos es. This work is compared to other work in the literature, and differe nces are discussed. (C) 1997 Elsevier Science B.V.