Vacuum-ultraviolet circular dichroism study of saccharides by synchrotron radiation spectrophotometry Original Research Article

Vacuum-ultraviolet circular dichroism (VUVCD) spectra of five monosaccharides (d-glucose, d-mannose, d-galactose, d-xylose, and d-lyxose) and five disaccharides (maltose, isomaltose, cellobiose, gentiobiose, and lactose) were measured to 160 nm using a synchrotron-radiation VUVCD spectrophotometer in aqueous solution under high vacuum at 25 °C. Most of the saccharides show a positive peak with some shoulders at around 170 nm, except for d-galactose and lactose, which show two distinct negative peaks at around 165 and 177 nm. These spectra are influenced by such structural factors as α and β anomers at C-1, axial and equatorial hydroxyl groups at C-2 and C-4, trans (T) and gauche (G) conformations of the hydroxymethyl group at C-5, and the type of glycosidic linkage. Deconvolution of the VUVCD spectra of d-glucose, d-mannose, and d-galactose into six independent Gaussian components for α-GG, α-GT, α-TG, β-GG, β-GT, and β-TG conformations suggests that the α anomer has red-shifted spectra relative to the β anomer, and that GG and GT conformations have positive and negative circular dichroism signs, respectively, while the sign for TG conformation is anomer dependent. These speculations from the deconvolution analyses are also supported by the VUVCD spectra of disaccharides. These results give new insight into the equilibrium conformations of saccharides, demonstrating the usefulness of synchrotron-radiation VUVCD spectroscopy.