Conformational studies of β-glucans

Abstract

Steric and energy contour diagrams have been plotted for disaccharide-like and for helical structures of linear β-D-glucans having (1 → 2), (1 → 3) and (1 → 4) linkages. The allowed conformations constitute only about. 4% of the total conformations, indicating that the freedom of rotation of glucose residues is highly restricted in all the three polysaccharides. The additional restrictions of the monomer unit, as one passes from disaccharide to polysaccaride structures, are severe in the case of (1 → 2) and (1 → 3) linked polysaccharides but not in (1 → 4) linked polysaccharide. The difference in the nature of linkages also has shown to affect the energetically preferred conformations: (1 → 2) linkages lead only to left handed helical conformations; (1 → 3) linkages lead to both right and left handed wide and extended helical conformations, (1 → 4) linkages lead to both right and left handed extended helical conformations. The possible hydrogen bonds between adjacent residues are also dependent on the nature of linkage.