Studies on Nickel(II)-Pyridoxamine-Imidazole Containing Mixed Ligand Complex Systems

Abstract

<em>The stability constants of species present in the systems Ni(II)-pyridoxamine(pym)(A) and Ni(II)-pyridoxamine(pym)(A)-imidazole containing ligands(B) [B = imidazole(him), benzimidazole(bim), histamine(hist) and L-histidine(his)] have been determined pH-metrically using the MINIQUAD computer program. The existence of the species NiAH, NiA and NiA₂ was proven for the Ni(II)-pym(A) system, whereas for the Ni(II)-pym(A)-B systems NiABH₂, NiABH, NiAB and NiAB₂ species were identified. The pym ligand(A) binds the metal ion via its phenolic oxygen and amino methyl nitrogen atoms in the NiAB and NiAB₂ species, and the binding of ligand B in these complexes is similar to their binding in the respective binary species. The site of protonation in NiABH and NiABH₂ species is explained. A more positive D log K values for NiAB compared to NiAB₂species is discussed. The computer simulated distribution of the complexes in solution has been evaluated. The mixed ligand pyridoxamine complex of Ni(II) with L-histidine was prepared and characterized by conventional methods.</em>