Excluded-Volume Effects in Sodium Hyaluronate Solutions Revisited

Abstract

Five sodium salt samples of hyaluronic acid ranging in weight-average molecular weight Mw from 1.9×105 to 1.5×106 have been studied by light scattering and viscometry in aqueous sodium chloride at 25°C. The intrinsic viscosity ([η]) data obtained at 10 different NaCl concentrations Cs covering a range from 0.005 to 2.5 M are analyzed along with previous data for lower Mw on the basis of the Yamakawa-Fujii-Yoshizaki theory for unperturbed wormlike chains combined with the quasi-two-parameter (QTP) theory for excluded-volume effects. Fairly satisfactory agreement is observed between theory and experiment at Cs higher than 0.01 M over the range of molecular weight from 3.8×103 to 1.5×106, though the degree of agreement tends to lower with decreasing Cs. When the wormlike chain parameters and the excluded-volume strength estimated from [η] are used, the QTP theory with the known expression for 〈S2〉 (the mean-square radius of gyration) of the unperturbed wormlike chain is found to describe almost quantitatively the measured 〈S2〉 for Na hyaluronate at Cs=0.02, 0.1, and 0.5 M. Thus, it is concluded that this theory for nonionic chains is applicable, in a fairly good approximation, to 〈S2〉 and [η] of the charged polysaccharide in aqueous NaCl unless Cs is lower than 0.02 M.