Potentiometric and proton NMR studies on ternary metal (II) complexes containing thiaminepyrophosphate and a series of secondary ligands

Ternary metal complexes of the type MLA, where M = Cu (II), Zn (II),Ni (II) and Co (II), L = thiaminepyrophosphate (TPP) and A = glycine, alanine, phe nylalanine, tryptophan, tyrosine, pyrocatechol, oxalic acid, malonic acid, imidazole, benzimidazole, and 5,6-dimethylbenzimidazole have been investiga ted potentiometrically at 35 degrees C and mu = 0.1M (KNO3). The stability constants have been determined using BEST Computer program. The stabilities of ternary complexes increase in the order O- - O- donors < N-donors. Cu ( II) ternary complexes are found to be less stable than the corresponding Co (II), Ni(II) and Zn(II) complexes. Interaction of these ligands, TPP and tr yptophan or TPP and imidazole with Zn (II) in deuterium oxide solution are also studied by H-1 NMR.