Standard thermodynamic functions of Co2+ complexation with glycine and L-histidine in aqueous solution

Abstract

The enthalpies of the reactions between solutions of Co(NO₃)₂ and solutions of glycine (Gly) and L-histidine (His) are determined via direct calorimetry at different pH values and metal: ligand ratios using KNO₃ as a background electrolyte (T = 298.15 K, I = 0.2–1.0). The enthalpy changes upon the formation of cobalt glycinate complexes and Co²⁺ mixed-ligand complex, viz., glycine–L-histidine, were calculated. The standard thermodynamic parameters (Δ_rH°, Δ_rG°, Δ_rS°) of complexation are determined. The CoGlyHis complex is shown to be stable toward decomposition into homogeneous complexes.