Extraction of Thermodynamic Data from Ternary Diffusion Coefficients of Lysozyme Chloride in Water and Aqueous Na2SO4

This paper presents, for ternary lysozyme-Na2SO4-water system, the thermodynamic data extracted from the measured values of four ternary diffusion coefficients and the Onsager reciprocal relations. The calculation for derivatives of solute chemical potentials with respect to solute molar concentrations was made using the method presented in [1]. This method is applicable to systems in which the molar concentration of one solute is very small compared to that of the other, like in our case. The approach is illustrated for the lysozyme chlorideNa2SO4-water system at 25 o C, pH 4.5 and at 0.6 mM (8.6 mg/mL) lysozyme chloride and 0.1, 0.25, 0.5, 0.65, and 0.8 M Na2SO4 concentrations. The calculated solute chemical potential derivatives were used to compute the protein cation charge approximately. We also compute the diffusion Onsager coefficients (Lij)o for each composition at pH 4.5. Physics Department, Politehnica University, Bucharest, 77206, Romania. Department of Theoretical Physics, National Institute for Physics and Nuclear Engineering, Bucharest-Măgurele, 76900, Romania. Department of Chemistry, Texas Christian University, USA