Chapter 24 Polysaccharides and biological systems

Abstract

The high-resolution solid-state nuclear magnetic resonance (NMR) approach provides a convenient means to distinguish a variety of crystalline polymorphs and to reveal the secondary structures of biological macromolecules, because the 13 C chemical shifts of backbone carbons are displaced depending on their respective conformations. The chapter emphasizes that this type of empirical approach can be used as a valuable constraint to construct the three-dimensional structures of biological molecules, such as peptides and proteins, based on a set of accurately determined interatomic distances measured by a partial dipolar recoupling method, such as rotational echo double resonance (REDOR). The secondary structure of an individual polysaccharide is defined by a set of torsion angles about the glycosidic linkages. On the basis of the conformation-dependent 13 C chemical shifts, it is expected that 13 C NMR spectra can be utilized to distinguish one of the crystalline polymorphs in these polysaccharides from anothers. It is also probable that the 13 C chemical shifts of carbons at the glycosidic linkages are displaced in line with their particular conformations. The chapter describes how 13 C NMR methods can be utilized to clarify the secondary structure of some gel-forming polysaccharides and to relate the resulting secondary structures with gelation mechanism as well as biological properties.