Copper(II) mixed ligands complexes of hydroxamic acids with glycine, histamine and histidine

A potentiometric and spectrophotometric study of physiologically interesting Cu-II mixed ligand complexes has been performed involving hydroxamic acids as primary ligands (A) and secondary ligands (B) represented either by histamine or the aminoacids glycine and histidine. All are potentially able to form chelate complexes with either five or six membered rings. The formation constant and the visible absorption spectrum were calculated for each one of the identified species, both binary and mixed ones. The most probable structures of the mixed species are discussed based upon their formation constants, their stabilization with regard to the two binary species as well as their visible absorption. It was evidenced that Cu-hydroxamate complexes do not favour significantly mixed ligand complex formation with aminoacids having only the carboxylate and amino groups; however, these complexes are strongly formed with histidine, due to the presence of the imidazol group.