Complexes of thallium(I) and cadmium(II) with dipeptides of L-phenylalanylglycine and glycyl-L-phenylalanine

Abstract

The stability constants of the complexes of thallium(I) and cadmium(II) ions with dipeptides of glycyl-L-phenylalanine and L-phenylalanylglycine were determined in aqueous solution at 25 °C and 0.1 mol dm-3 ionic medium using a combination of potentiometric and spectrophotometric techniques. Sodium perchlorate was used to maintain the ionic strength. The composition of the formed complexes was determined and it was shown that thallium(I) and cadmium(II) forms two mononuclear 1:1 species with the ligands, of the type [Tl(HL)]+, TlL, [Cd(HL)]2+ and [CdL]+ in the pH range of study (1.5-10.5), where L represents a fully dissociated ligand. The logarithms of the cumulative stability constants, βxyz, of the complexes, [(Metal ion)x(H+)y(ligand) z], are log β111 and log β101: 12.15, 3.39 (for Tl+ with L-phenylalanylglycine), 11.36, 2.13 (for Tl + with glycyl-L-phenylalanine), 12.06, 2.82 (for Cd2+ with L-phenylalanylglycine), 10.70 and 1.70 (for Cd2+ with glycyl-L-phenylalanine), respectively. ©2007 Sociedade Brasileira de Química.