STUDIES ON HELICAL CONFORMATIONAL OF AMYLOSE AND POSSIBLE INTERCONVERSIONS

The nonbonded energy (van der Waals) was computed for isolated helical amylose chains as a function of the dihedral angles (ϕ,ψ), i.e., the relative orientations of the glucose residues in the polysaccharide chain. In conformity with x‐ray data, different helical conformations have been proposed for different crystalline modifications of amylose. Right‐handed helical conformations were preferred for 71.13, 61.33, and 42.65‐type helices from minimum energy considerations. The hydrogen bond search reveals the possibility of formation of strong OH ⃛O type hydrogen bonds between contiguous residues in the polymer chain for 61.33 and 71.13 helices. Smooth transition from a 71.13 to a 61.13 helix is possible with small changes in the values of (ϕ,ψ) and without the loss of intramolecular hydrogen bonds, whereas all the intramolecular hydrogen bonds will be broken during the conversion from 61.33 to 42.65 helix. Copyright © 1969 John Wiley & Sons, Inc.