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

The ternary system consisting of oxidised glutathione (a S–S′ bonded dimeric hexapeptide), 1,10-phenanthroline (phen) and copper(II) has been studied in aqueous solution in the range pH 3–8 by potentiometry, electronic spectroscopy and electron paramagnetic resonance. Potentiometric titrations have allowed the evaluation of stoichiometry and formation constants of the complexes in the system; EPR and electronic spectroscopy were used to define the chromophore of one particularly important adduct predominant at physiological pH, [Cu(HL)(phen)]–(H6L2+= completely protonated oxidised glutathione). The results obtained suggest that in the stable conformation of this complex only one glutamyl moiety is involved, the other two positions in the plane being occupied by two nitrogen atoms from phenanthroline.