| Abstract |
Combined pH-metric and spectrophotometric Investigations on the mixed-ligand complex formation of Cu-II with histidine [H3+N-CH(-CH2C3H3N2)-COO-, hereafter, hisH(+/-)] and guanylurea [(H2NC)-C-1(=O)(NHC)-H-2(=(NH)-H-3)(NH2)-H-4, here-after, GaH] in aqueous solution (ionic strength, 0.1 mol dm(-3)) at 25 degrees C indicated the complexes : [Cu(hism)(+)], [Cu(hism-H)], [Cu(hism)(Gu)], [Cu(hism-H)(Gu)(-)], and [Cu(hism-H)(Gu-H)(2-)]; where, hism(-) stands for -COOH deprotonated bidentate histamine-like (NH2, N-3-imidazole) chelating histidinate mono anion, his-H2- stands for both -COOH and imidazole (NH)-H-1 deprotonated histidinate dianion, Gu(-) stands for =(NH)-H-3 deprotonated guanylurea mono anion and Gu-H(2-)stands for both =(NH)-H-3 and H2N1/(NH)-H-4 deprotonated guanylurea dianion. Formation constants of the proton-ligand and metal-ligand complexes were evaluated by mathematical motleling of the complex formation equilibria using computer based method. Varied modes of coordination of histidine and guanylurea to Cu-II involving interesting structural equilibria were established from the shifts of the electronic spectral absorption maxima of copper-histidine-guanylurea mixtures with change of pH of the solution. |
