Thermodynamic study of the parent and mixed complexes of aspartic acid, glutamic acid and glycine with copper(II)

Abstract

Abstract The equilibrium constants and in part the ΔH and ΔS data for the parent and mixed complexes copper(II)-aspartic acid, copper(II)-glutamic acid, copper(II)-aspartic acid-glycine, copper(II)-glutamic acid-glycine and copper(II)-aspartic acid-glutamic acid were determined pH-metrically and calorimetrically. Protonated complexes are formed in significant concentration in the copper(II)-aspartic acid and copper(II)-glutamic acid systems. The thermodynamic data led to the assumption that in the CuA complex of aspartic acid the β-carboxyl group of the ligand also forms a bond with the metal. The glutamic acid is bound “glycine-like” to the copper(II). There is an appreciable stabilization in the copper(II)-aspartic acid-glycine mixed complex, while in the copper(II)-glutamic acid-glycine system the stability of the mixed complex agrees with the statistical value. The above statements are supported by the dependence of the stability constants on the ionic strength.