Activity Coefficients in Aqueous Solutions of Sodium Glucuronate and Glucosamine Hydrochloride

Abstract

Isopiestic vapor pressure measurements were carried out on binary solutions of sodium glucuronate (NaGlcA) and glucosamine hydrochloride (GlcNH₃Cl) and on ternary solutions of NaG1cA and urea at 25° C. The activity coefficient of GlcNH₃Cl showed minimum at 1.3 mol/l, while that of NaGlcA decreased monotonously in all the concentration range studied. The activity coefficient of NaGlcA was decreased by the addition of urea. The lowering effect of urea largely depended on the concentration of NaGlcA.
The free energies of the transfer, ziGt, of NaGlcA from water to urea solutions with various concentration have been calculated. The values of ΔG, of NaGlcA from water to 5 m urea solution are 60 (J/mol) at infinite dilution of NaGlcA and 140 (J/mol) at 1 m NaG1cA. Partial molar volumes at infinite dilution, calculated from the density measurements, are 94.4 (ml/mol) for NaGlcA and 131 (ml/mol) for GlcNH₃Cl.
No difference was found in the hydration of GlcA- ion and GlcNF13+ ion at infinite dilution. The concentration dependence of the activity coefficients and that of apparent molar volumes of these salts, however, were dissimilar owing to the contribution of counter ions and non ionic parts of the sugar ions.
Two effects act on the activity coefficients of the solutes in the system NaG1cA-urea-water. One lowers the activity coefficients of the solutes and the other increases them. The lowering effect which includes the interaction of glucose part in GlcAT, is predominant at low concentrations.