Copper(II), nickel(II) and zinc(II) complexes of amino acids containing bis(imidazol-2-yl)methyl residues.

Copper(II), nickel(II) and zinc(II) complexes of Phe-BIMA and His-BIMA
were
studied by potentiometric, UV-Vis and EPR spectroscopic methods. The
nitrogen donor atoms of the bis(imidazol-2-yl)methyl residues were
described as the primary metal binding sites in all systems studied.
Deprotonation and coordination of the terminal amino and amide nitrogen
atoms took place in the copper(II) complexes of both ligands and resulted
in the formation of dinuclear complexes containing tridentate ligands and
imidazole bridging. The presence of the histidyl side chain provides a
great versatility in the complex formation reactions of His-BIMA. The
existence of a dinuclear species was detected in slightly acidic solution
and its structure was described as a mixture of three isomeric forms.
Deprotonation of the imidazole-N(1)H donor functions was detected under
slightly alkaline conditions with pK values of 8.13 and 8.93. An excess of
copper(II) ions shifted this reactions even into the slightly acidic pH
range and resulted in the formation of a trinuclear complex.