Vacuum-ultraviolet circular dichroism study of oligosaccharides using a synchrotron-radiation spectrophotometer

Abstract

Vacuum-ultraviolet circular dichroism (VUVCD) spectra of malto-, laminari-, isomalto-, and cello-oligosaccharide series and their corresponding polysaccharides (laminarin and dextran) were measured from 200 to 168 nm in aqueous solution at 25°C using a synchrotron-radiation VUVCD spectrophotometer. Disaccharides exhibited markedly different CD spectra depending on the types of glycosidic linkages, and the CD spectra of each oligosaccharide series (with the exception of the isomalto-oligosaccharide series) varied with the chain length below 190 nm while retaining the spectral shape of the constituent disaccharide. These results indicate that the basic structures of oligosaccharides were greatly affected by the configurations of their constituent disaccharides, which had unique torsion angles restricted by the intramolecular hydrogen bonds between glucose units. Based on comparisons between the experimental and theoretical data, we suggest that the chain-length dependence of CD above 180 nm reflects the backbone structure of oligosaccharides (e.g., helical structures), while those below 180 nm are influenced by other factors associated with higher-energy chromophores such as the hydroxyl groups. The reported comprehensive VUVCD spectra provide basic information for understanding the complicated structures of oligosaccharides in aqueous solution that can be used in their theoretical assignments.