Mixed-Metal Complexes in Solution. 3. Thermodynamic Study of Heterobinuclear Copper(II)-L-Histidine and -Histamine Complexes in Aqueous Solution.

Potentiometric measurements have been used to characterize the equilibrium system containing copper(II), L-histidine (his) or histamine (hm), and M (M = NiII, ZnII, or CdII). The results obtained provide evidence for heterobinuclear species containing CuII, M, and his or hm. The thermodynamic parameters of these complexes were determined by direct calorimetry. Some hypotheses for the structures of [CuM(his)2]2+ and [CuM(hm)2]4+ are discussed.