Mixed Ligand Zinc Complexation with Ornithine and Histidine in Aqueous Solution

The formation of mixed-ligand complexes of various compositions in the Zn–L-histidine (His)–L-ornithine (Orn) system has been studied by pH-metry, calorimetry, and NMR spectroscopy. The thermodynamic parameters (log K , Δ r G 0 Δ r H , Δ r S ) of the reactions of their formation at 298.15 K and ionic strength I = 0.5 (KNO 3 ) have been calculated. Based on the comparative analysis of thermodynamic parameters, the most probable method for the coordination of amino acid residues in mixed complexes has been proposed.