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

Abstract

The stability constants for the nickel(II) and copper(II)-α-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 <i>p</i>H-measurements in 40% ethanol-60% water mixture. The study shows that at 25°C and ionic strength at 0.10 <i>M </i>the following species are present in this solvent mixture: CuHL²⁺, CuL⁺, CUL₂ for copper(II) complexes and NiL⁺, NiL₂, NiL₃- 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 a-amino acids to form complexes with metal(II) ions is greater in 40% ethanol-60% water mixture as compared to that in only water.