Studies with model membranes. IX. Evaluation of thermodynamic parameters from the transition state theory of rate processes for electrolyte diffusion through silver chloride parchment-supported membranes

Diffusion rate of biologically important electrolytes through parchment-supported silver chloride membrane have been determined by the use of Nernst-Planck equation at various temperatures taking into account membrane resistance R_m, membrane potential E_m, etc. The diffusion rates were found to be primarily dependent upon the difference in the hydration energies of the counterion in the external solution. On the basis of Eisenman-Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strengths of the fixed charge groups. The various thermodynamic parameters, namely, ΔH^?, ΔF^?, and ΔS^? were evaluated. The values of ΔS^? found to be negative, indicating that the diffusion is taking place with partial immobilization in the membrane phase. A formal relation between ΔH_hydration, ΔF_hydration, and ΔS_hydration of cations with the corresponding values of ΔH^?, ΔF^?, and ΔS^? for diffusion was also found to exist for the investigated system.