Viscosity and sedimentation studies on amylose in aqueous solution—further evidence for non-helical character

Abstract

Viscosity and sedimentation measurements have been carried out on subfractions of native amylose dissolved in a thermodynamically ideal solvent (0·33 M KCl) and a good solvent (0·2 M KOH). The relations: [ƞ] KC1 = 1·12 x 10 -1 M W 0.50; [ƞ] KOH = 6·92 x 10 -3 M W 0.78; ( S 0) KC1 = 1·11 x 10 -15 M W 0.50; ( S 0) SOH = 2·73 x 10 -15 M W 0.41; were obtained. The divergence of the exponents from a value of 0·50 for the measurements in KOH is shown to be due to expansion of the molecule through solvent-polymer interaction rather than to partial free-draining character. The unperturbed dimensions of amylose were found to be the same in both solvents, on the basis of the Burchard-Stockmayer-Fixman and the Cowie-Bywater treatments. Measures of ‘molecular stiffness’ were obtained (Kuhn-Kuhn and Hearst-Stockmayer theories) on the basis of different molecular models including that of the ‘interrupted helix’. The latter model appears to be incorrect: analysis of the hydrodynamic data shows that the amylose molecule in aqueous solution is best regarded as a fairly flexible coil.