Conformational studies of dextran [alpha-(1----6)-D-glucan].

A theoretical conformational study of dextran, a (1----6)-linked alpha-D-glucan polysaccharide, has been made to allow n explicit comparison with earlier results on pustulan, the corresponding (1----6)-linked beta-D-glucan. The nonbonded, torsional and hydrogen bond contributions to potential energy were calculated as a function of rotational angles phi, psi, and omega. The (phi, psi, omega)-space of the disaccharide and of helices contain many local energy minima with very small energy differences. A comparison of (1----6)-alpha-D-glucans with (1----6)-beta-D-glucans indicates significantly differences in conformational behavior. Specifically, our results shed light on the fact that dextran does not gel, whereas pustulan does. The difference in tendency to gel may be related to the fact that dextran has no particularly favored conformations with structural regularity whereas pustulan does.