Conformational energy calculations on alginic acid I. Helix parameters and flexibility of the homopolymers

Conformational energy maps have been calculated for the 1-4-linked dimers of β-D -mannuronic acid and α-L -guluronic acid. Helix parameters have been calculated for poly(mannuronic acid) and for poly(guluronic acid), which are in reasonable agreement with data from x-ray fiber diffraction studies of these polysaccharides. The flexibility of the homopolymers was investigated by calculating the characteristic ratios, i.e., the ratio of the mean-square end-to-end lengths of the unperturbed chains to the product of the number of residues in the chains and the virtual bond lengths. The general conclusions are that both polymers are very stiff and extended, but that poly(mannuronic acid) is less extended than poly(guluronic acid).