Configuration and hydrodynamic properties of fully acetylated salep glucomannan

Abstract

AbstractThe polysaccharide of salep orchid tuber was shown to be a glucomannan with a glucose/mannose ratio of 2.6 and an acetyl content of 2.1%. After extraction from the powdered root with water, the triacetate derivative was prepared and its configurational and hydrodynamic properties examined. The polymer yielded a series of fractions from 615 to 4170 in weight‐average degree of polymerization. Light‐scattering, viscosity, and osmometry experiments were conducted. Intrinsic viscosity results were interpreted according to the hydrodynamic theory of Eizner and Ptitsyn resulting in a value of ζ/η0 = 20 ± 6 A. for the ratio of monomeric friction coefficient to solvent viscosity and a corresponding value of a = 55 ± 4 A. for the persistence length, closely similar to those reported for other β‐1,4‐linked polysaccharides. The theoretical Flory coefficient increased with increasing molecular weight but was less than the limiting value of Φ0 = 2.86 × 1023 mole−1. The dependence of the light‐scattering radius of gyration of the glucomannan polymer on the contour length showed that the configuration of the heteropolymer was similar to that of other β‐1,4‐linked polysaccharides which have only glucose or mannose in the main chain. Calculated radii of gyration based on the Porod‐Kratky persistence length were found to be smaller than radii found by light scattering on the fractions.