Spectrophotometric, potentiometric, and conductometric studies of binary complex formation between copper(II) and three forms of vitamin B6 in aqueous solutions

This article reports the detailed study concerning the mode of binding of three forms of vitamin B-6, pyridoxamine (pm), pyridoxine (pn), and pyridoxal (pl), with Cu(II) in aqueous solutions using three independent methods: potentiometry, conductometry, and UV-vis spectroscopy. The stability constants of complexes formed between copper(II) and vitamin B-6 were investigated by potentiometric titration in 0.1 M KNO3 ionic medium at 25 degrees C. While drawing the relations between molar conductance and the ratio of metal to ligand concentrations, different types of lines were obtained indicating the formation of 1 : 1 and 1 : 2 stoichiometric compounds. The stability constants have been determined using EQUID and CVEQUID computer programs and the obtained results were in agreement. The relatively high values of stability constants of Cu(II)-vitamin B-6 complexes obtained from three independent methods in comparison to those with other competing cations suggest that the complexes studied are relatively stable in aqueous solutions.