Synchrotron-Radiation Vacuum-Ultraviolet Circular-Dichroism Spectroscopy for Characterizing the Structure of Saccharides

Circular-dichroism (CD) spectroscopy is a powerful tool for analyzing the structures of chiral molecules and biomolecules. The development of CD instruments using synchrotron radiation has greatly expanded the utility of this method by extending the spectra to the vacuum-ultraviolet (VUV) region below 190 nm and thereby yielding information that is unobtainable by conventional CD instruments. This technique is especially advantageous for monitoring the structure of saccharides that contain hydroxy and acetal groups with high-energy transitions in the VUV region. Combining VUVCD spectra with theoretical calculations provides new insight into the contributions of anomeric hydroxy groups and rotational isomers of hydroxymethyl groups to the dynamics, intramolecular hydrogen bonds, and hydration of saccharides in aqueous solution.

Synchrotron-radiation vacuum-ultraviolet circular dichroism spectroscopy in structural biology: an overview

Circular dichroism spectroscopy is widely used for analyzing the structures of chiral molecules, including biomolecules. Vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy using synchrotron radiation can extend the short-wavelength limit into the vacuum-ultraviolet region (down to ~160 nm) to provide detailed and new information about the structures of biomolecules in combination with theoretical analysis and bioinformatics. The VUVCD spectra of saccharides can detect the high-energy transitions of chromophores such as hydroxy and acetal groups, disclosing the contributions of inter- or intramolecular hydrogen bonds to the equilibrium configuration of monosaccharides in aqueous solution. The roles of hydration in the fluctuation of the dihedral angles of carboxyl and amino groups of amino acids can be clarified by comparing the observed VUVCD spectra with those calculated theoretically. The VUVCD spectra of proteins markedly improves the accuracy of predicting the contents and number of segments of the secondary structures, and their amino acid sequences when combined with bioinformatics, for not only native but also nonnative and membrane-bound proteins. The VUVCD spectra of nucleic acids confirm the contributions of the base composition and sequence to the conformation in comparative analyses of synthetic poly-nucleotides composed of selected bases. This review surveys these recent applications of synchrotron-radiation VUVCD spectroscopy in structural biology, covering saccharides, amino acids, proteins, and nucleic acids.

Amphiphilic derivatives of dextran: Adsorption at air/water and oil/water interfaces

Ionic amphiphilic dextran derivatives were synthesized by the attachment of sodium sulfopropyl and phenoxy groups on the native polysaccharide. A family of dextran derivatives was thus obtained with varying hydrophobic content and charge density in the polymer chains. The surface-active properties of polymers were studied at the air-water and dodecane-water interfaces using dynamic surface/interfacial tension measurements. The adsorption was shown to begin in a diffusion-limited regime at low polymer concentrations, that is to say, with the diffusion of macromolecules in the bulk solution. In contrast, at long times the interfacial adsorption is limited by interfacial phenomena: adsorption kinetics or transfer into the adsorbed layer. A semiempirical equation developed by Filippov was shown to correctly fit the experimental curves over the whole time range. The presence of ionic groups in the chains strongly lowers the adsorption kinetics. This effect can be interpreted by electrostatic interactions between the free molecules and the already adsorbed ones. The adsorption kinetics at air-water and oil-water interfaces are compared.