Vacuum Uv Circular Dichroism of Polysaccharides

Polysaccharides are of great commercial and biological importance. At the molecular level they display a richness in structural and conformational variability, and helical structures are commonplace. Of the various experimental techniques applicable to the study of polysaccharide conformation, optical spectroscopy has been limited by the relatively high energy of the electronic excitations, the first excitation in unsubstituted saccharides being in the vacuum ultraviolet region. In the past decade, the development of VUV CD spectrometers, including the use of synchrotron radiation, has allowed the chiroptical properties of polysaccharides to be observed directly. In this brief review the major CD features of polysaccharides are summarized, and several applications are described illustrating the usefulness of VUV CD spectroscopy in the study of the polysaccharide conformation. Examples include the glucans, dextran and acetylated cellulose; the glycosaminoglycan, heparin; and the microbial polysaccharides, gellan and xanthan. A recently proposed quadrant rule which describes the sign of the 175 nm n‐σ* polysaccharide CD band also is discussed. This rule is the first attempt to place the descriptionof polysaccharide VUV CD on a theoretical foundation.