A comparative investigation has been developed for the stability constants of several amino acid complexes with divalent metal ions, which have been determined by potentiometric pH titration. Depending on the metal ion–binding properties, vital differences in the building complexes were observed. The present study indicates that in some M(L) complexes, metal ions are arranged in carboxyl groups, but in other M(L)complexes, some metal ions are able to build chelate over amine groups. The results mentioned-above demonstrate that for some M(L) complexes, the stability constants are also largely determined by the affinity of metal ions for amine group. This leads to a kind of selectivity of metal ions, and transfers them through building complexes accompanied with some amino acids. For heavy metal ions, this building complex helps the absorption and filtration of blood plasma. This is an important method in micro-dialysis. In this study the different aspects of stabilization of metal ion complexes regarding the Irving-Williams sequence have been investigated.
Keywords: Acidity and stability constants, alanine, amino acids, aspartic acid, cystein, divalent metal ions, glycine, glutamic acid, leucine, methionine, potentiometric titration, tartaric acid, trypthophan, valine.