Electrostatic Contributions to Chain Stiffness and Excluded-Volume Effects in Sodium Hyaluronate Solutions

Abstract

Intrinsic viscosities [η] for sodium hyaluronate in aqueous sodium chloride at 25°C were determined for 12 samples ranging in weight-average molecular weight Mw from 3.8×103 to 3.5×105 at NaCl concentrations Cs between 0.005 and 2.5 M. They were analyzed on the basis of the Yamakawa-Fujii-Yoshizaki theory for [η] of an unperturbed wormlike chain combined with the Yamakawa-Stockmayer-Shimada theory for excluded-volume effects to estimate the total persistence length q and the excluded-volume strength B as functions of Cs. At any Cs studied, excluded-volume effects on [η] became appreciable when Mw exceeded 1×104–2×104. The Cs dependence of q yielded 4.0 nm for q0 (the intrinsic persistence length) of the polysaccharide chain at infinite ionic strength. It was found that the values of q−q0 (i.e., the electrostatic contribution to q) at Cs<0.02 M were roughly 70% larger than predlcted by the Le Bret theory and the Odijk-Skolnick-Fixman theory. On the other hand, the estimated B values agreed fairly well with Fixman and Skolnick’s theory for the excluded-volume interaction between a pair of charged rodlike segments unless Cs was lower than 0.05 M.