A comparative investigation of interaction between metal ions with L-methionene and related compounds such as alanine, leucine, valine, and glycine in aqueous solution

The acidity and stability constants of M-L (M: M2+; L: Met, L-methionine) complexes, determined by potentiometric pH titrations, were used to make a comparative investigation. The stability constants of the 1:1 complexes formed between M2+ and L–, were determined by potentiometric pH titration in aqueous solution (I = 0.1 M, NaNO3, 25°C). The order of the stability constants was reported. It is shown that regarding to M ion – binding properties, vital differences on complex bilding were considered. It is demonstrated that in M-L complexes, M ion is coordinated to the carboxyl group, is also able to bild macrochelate over amine group. The aforementioned results demonstrate that for M (Met) complex, the stability constants are also largely determined by the affinity of Cu ion for amino group. It is indicated that this additional interaction with amino groups can influence the character of some amino acid complexes in biological systems.