As constantes de estabilidade dos complexos de íons tálio(I) e cádmio(II) com dipeptídeos de glicil-L-fenilalanina e L-fenilalanilglicina foram determinadas em solução aquosa a 25 ºC e meio iônico 0,1 mol dm-3 usando uma combinação de técnicas potenciométricas e espectrofotométricas. Perclorato de sódio foi usado para manter a força iônica. A composição dos complexos formados foi determinada e observou-se que tálio(I) e cádmio(II) formam duas espécies mononucleares 1:1 com os ligantes, do tipo [Tl(HL)]+, TlL, [Cd(HL)]2+ e [CdL]+ no intervalo do pH de estudo (1,5-10,5), onde L representa um ligante completamente dissociado. Os logaritmos das contantes de estabilidade cumulativas, betaxyz, dos complexos, [(íon metálico)x(H+)y (ligante)z], são log beta111 e log beta101: 12,15 e 3,39 (para Tl+ com L-fenilalanilglicina), 11,36 e 2,13 (para Tl+ com glicil-L-fenilalanina), 12,06 e 2,82 (para Cd2+ com L-fenilalanilglicina) e 10,70 e 1,70 (para Cd2+ com glicil-L-fenilalanina), respectivamente.
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 ºC 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, betaxyz, of the complexes, [(Metal ion)x(H+)y(ligand) z], are log beta111 and log beta101: 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.