The Gibbs Energies, Enthalpies, and Entropies of the Dilution of Aqueous Sodium Chondroitin-4-sulfate and -6-sulfate

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Abstract
The osmotic coefficients of a solvent, φ, in aqueous solutions of sodium chondroitin-4-sulfate (NaChS-A) with a relatively low molecular weight and -6-sulfate (NaChS-C) with various molecular weight were measured by means of vapor-pressure osmometry. The molar Gibbs energes of dilution, ΔdilG were determined from the thermodynamic analysis of the φ values. The molar entropies of dilution, ΔdilS were calculated through the substitution of the molar dilution enthalpies, ΔdilH which had been measured previously, into ΔdilG. These thermodynamic quantities of dilution were discussed by taking Manning’s limiting law into consideration. The concentration and temperature dependencies of the observed ΔdilH agreed well quantitatively with those of the electrostatic ΔdilH calculated by Manning’s limiting law, when the distance between the neighboring charges of the polyion, b, was assumed to be 4.8 Å, whereas the observed ΔdilG and ΔdilS values did not agree quantitatively with the theoretical ones based on electrostatic interactions. From a comparison of the experimental ΔdilS values with the theoretical ones, the non-electrostatic dilution entropy was evaluated and discussed.