Configurational statistics of polysaccharides. VI. Linear (1→4)-linked galactan

Abstract

The conformational energies for (1→4)-linked α -D- and β -D-galactans have been computed by considering nonbonded, torsional, and electrostatic interactions. The electrostatic interactions are estimated by assigning the charges to various atoms in the molecule by the method of Del Re. The characteristic ratios C_N = 〈r²〉₀/Nl_v² are computed for α -D- and β -D-galactans as a function of the degree of polymerization N and the angle Τ at the bridge oxygen atom. These values of characteristic ratios obtained for α -D-galactan are very much higher than for β -D-galactan, indicating that the former assumes a highly extended conformation compared to the latter. The values of characteristic ratios of both these polysaccharides show a decrease with increase in Τ similar to that observed for other (1→4)-linked polysaccharides. The calculated values of C_∞ of (1→4)-linked polysaccharides show no correlation with the number of allowed conformations but are affected both by the orientation of the interunit glycosidic bonds and the hindered potential associated with chain units. It has also been shown that the magnitude of the steric factor σ may not be used as an index of flexibility for polysaccharides which differ in type of linkage.