FORMATION OF COBALT(III) COMPOUNDS WITH SOME PEPTIDES

The complexes formed from cobalt(III) and dipeptides such as glycylglycine, glycylaspartic acid, glycylthreonine, glycyltyrosine and glycylproline were studied. The formation process of cobalt(III)-dipeptide species was investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The formation of the cobalt(III) complexes occurs through an oxointermediate, as shown by the spectral behaviour, and depends on the pH of the solutions. Complex stoichiometries, molar absorptivities and concentration ratios at the equilibrium of the cobalt(III)- dipeptide complexes were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes.