Potentiometric and spectroscopic study of ternary complexes of copper(II), substituted 1,10-phenanthrolines and oxidised glutathione

A series of ternary systems consisting of copper(II), oxidised glutathione (a S–S′ bonded hexapeptide) and five differently substituted 1,10-phenanthrolines has been studied in aqueous solvent in the range pH 3–8. The stability constants of the complexes formed, together with the relevant distributions as a function of pH, have been evaluated by elaboration of data from acid–base potentiometric titrations. Electron paramagnetic resonance and electronic spectroscopy have been used to identify the chromophore in the 1 : 1 : 1 complexes, i.e. the ternary species are in all cases the predominant ones at pH close to the physiological values. The data from the spectroscopic measurements, when considered together with the trend in stability constant values, allowed reasonable hypotheses about the effect of the substituents on the phenanthroline ring on the stability and configuration of the complexes.