Potentiometric studies on the stability constants of some alpha-amino acid-copper(II) and nickel(II) systems in ethanol-water mixture

摘要

The stability constants for the nickel(II) and copper(II)-alpha-amino acid (glycine, L-alanine, L-valine, L-leucine, L-isoleucine, L-serine, L-phenylalanine and L-methionine) binary complex systems have been studied using pH-measurements in 40% ethanol-60% water mixture. The study shows that at 25 deg C and ionic strength at 0.10 M the following species are present in this solvent mixture: CuHL~(2+), CuL~+, CuL_2 for copper (II) complexes and NIl~+, NiL_2, NiL_3~- for nickel(II) complexes. The stability of the nickel(II) complexes is lower than that of the copper(II) complexes. The study shows that the tendency of alpha-amino acids to form complexes with metal(II) ions is greater in 40% ethanol-60% water mixture as compared to that in only water.