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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. [ABSTRACT FROM AUTHOR]

Vacuum-ultraviolet (VUV) electronic circular-dichroism (ECD) spectra of methyl β-D-glucopyranoside (methyl β-D-Glc), methyl α- and β-D-galactopyranosides (methyl α- and β-D-Gal), and methyl α- and β-D-xylopyranosides (methyl α- and β-D-Xyl) were measured down to 163 nm in aqueous solution using a synchrotron-radiation VUV-ECD spectrophotometer. Five methyl aldopyranosides exhibited characteristic ECD spectra depending on the gauche (G) and trans (T) conformations of the hydroxymethyl group at C-5 and the α-/β-anomer configurations of the methoxy group at C-1. To elucidate the contributions of these structures to the spectrum, the ECD spectra of three rotamers (GT, GG and TG) of methyl β-D-Glc, methyl α-D-Gal and methyl β-D-Gal were calculated using a time-dependent density functional theory and molecular dynamics simulations. These theoretical spectra were very similar to those observed experimentally, indicating that the GT and GG rotamers show negative and positive ECD around 170 nm, respectively, and that the α- and β-anomers exhibit negative and positive ECD around 160 nm, respectively. These spectral differences between the two rotamers and between the two anomers were attributable to changes in steric configurations, including the intramolecular hydrogen bond around the ring oxygen and the methoxy oxygen, respectively. These relationships were supported by the ECD spectra experimentally observed for methyl α-D-Xyl and methyl β-D-Xyl, demonstrating that the VUV-ECD spectroscopy is a powerful technique for characterizing the structures of saccharides in aqueous solution. [ABSTRACT FROM AUTHOR]