Thermodynamic parameters and stability constants of lanthanide(III) complexes of biologically active glutathione (GSH) and their chemical speciation

79-83The stability constants of lanthanide(III) complexes of reduced glutathione (GSH) have been determined by potentiometric estimation of [H+], in aqueous medium at different ionic strengths and at various temperatures. The effect of dielectric constant on stability has been studied at different percentage of solvent variations and at different solvent systems. The and pL values have been calculated by the method of Irving and Rossotti. Computation of stability constants are carried out on an IBM compatible PC computer using the weighted least squares method. The values of Smin are also evaluated. To visualise the nature of the equilibria involving lanthanide(III) with glutathione, species distribution curves of complexes have been plotted as a function of pH using the program SPE. The order of stability constants is found to be La(III) The thermodynamic parameters ΔG, ΔH and ΔS have been calculated at a fixed temperature of 25±0.5°C