Light-scattering and specific refractive increment behavior of amylose and dextran in methyl sulfoxide-water

Abstract

Light-scattering measurements on polysaccharides in methyl sulfoxide or methyl sulfoxide-water are most reliable when made on a dialyzed solution-solvent system and when proper technique is used to remove the “micro gel” that seems unavoidably present when dried polysaccharide is dissolved in solvent. Discrepancies in published molecular weight-intrinsic viscosity relationships for amylose in methyl sulfoxide appear to be caused in part by differences the preparation and treatment of samples and possibly by differences in botanical source. The specific refractive increment of dextran is not a linear function of solvent composition in methyl sulfoxide-water. Measurements at osmotic equilibrium indicate that, over a moderate range of composition in methyl sulfoxide-water, dextran preferentially associates with about 2.5 molecules of water per glucopyranosyl residue of the polymer. Effects of long-term storage, sample treatment, and botanical source upon the specific rotation of amylose are examined.