Thermodynamics of mixed-ligand complex formation of zinc nitrilotriacetate with amino acids and dipeptides in solution

Highlights: • Stable mixed ligand complexes of ZnNta with amino acids and dipeptides. • Histamine-like coordination mode of His in the complex ZnNtaHis. • Glycine-like coordination of Lys and Orn in the complexes ZnNtaL and ZnNtaHL • NH₂, CO-coordination mode of GlyGly in the complex ZnNtaGG. • NH₂, N⁻ or NH2, N⁻, COO-coordination modes of GlyGly in the complex ZnNtaGGH₋₁. - Abstract: The isothermal calorimetry, pH-potentiometric titration and ¹H and ¹³C NMR methods has been used to study the mixed-ligand complex formation in the systems Zn²⁺–Nta^3––L⁻ (L = His, Orn, Lys, GlyGly, AlaAla) in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of the mixed complexes have been determined. The relationship between the probable coordination modes of the complexone and amino acid or dipeptide molecules in the mixed-ligand complex and the thermodynamic parameters has been discussed