1971 Volume 44 Issue 10 Pages 2716-2721
The aqueous solution equilibria of the systems containing copper(II) ion and glycinamide, β-alaninamide, glycine-N,N-diethylamide, or β-alanine-N,N-diethylamide have been investigated by potentiometric titration at 25°C (μ=0.1 (KNO3)). The stability constants K1 and K2 and the constants of the deprotonation reactions K1H, Kc1, and Kc2, for the glycinamide-copper(II) systems, and K1 and K2 for the other ligand-copper(II) systerrs were calculated by the method of non-linear least-squares with the aid of a computer. The K1 values were found to be in the order, glycine-N,N-diethylamide (6.17)>β-alanine-N,N-diethylamide (5.5)>glycinamide (5.30)>β-alaninamide (5.1). The sequence reveals that the five-membered chelates are more stable than the six-membered ones. The K1 and Kc1 values for glycylglycine and β-alanylglycine have been determined anew, and the structures of the chelates formed in acid solution have been discussed from comparative studies of the equilibrium constants, which suggest a tridentate nature of the dipeptides in the chelates of the type Cu(HL)+ where HL denotes free dipeptide.
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