MULTIPLE NEUTRAL ALKALI-HALIDE ATTACHMENTS ONTO OLIGOSACCHARIDES IN ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Oligosaccharides perform essential functions in a variety of biologica l and agricultural processes. Recent approaches to characterization of these molecules by mass spectrometry have utilized mainly soft-ioniza tion methods such as electrospray ionization (ESI) and thermospray (TS ), as well as fast atom bombardment (FAB). The behavior of a series of maltooligosaccharides with alpha-(1-->4) linkages, maltose (G(2)) thr ough maltoheptaose (G(7)), under ESI conditions, has been investigated here, The oligosaccharides were dissolved in N,N-dimethylacetamide co ntaining lithium chloride (DMAc/LiCl) prior to analysis by ESI-MS, A h ighly unusual feature, evident in all mass spectra obtained using this solvent system, was the presence of multiple 'neutral' salt attachmen ts onto lithium adducts of the sugars. Resultant ions took the form of [G(x) + Li + nLiCl](+), where n may reach a value as high as eight. C ompared to LiCl, the propensity for alkali halide attachment using oth er alkali chlorides or lithium halides was greatly reduced. An investi gation of this phenomenon is presented in which the organic and inorga nic portions of the employed solvent were systematically varied, and s emi-empirical computer modeling was performed to better understand lit hium coordination by the sugars. (C) 1997 Elsevier Science B.V.