Thermodynamics of the Formation of a Nickel(II) and Glycylglycine Complex in an Aqueous Solution

Direct calorimetry is used to determine the enthalpies of formation of complexes of Ni(II) and diglycine in aqueous solutions with ionic strengths of 0.2, 0.5, and 1.0 (KNO3) at a temperature of 298.15 K. Standard thermodynamic values Delta H-r degrees, Delta(r)G degrees, and Delta S-r degrees of complex formation in the considered system are calculated. A comparative analysis is performed of the obtained data and known thermodynamic values of complex formation in Ni2+-glycine and Ni2+-triglycine systems. Possible structures are proposed for diglycinate complexes with formulas NiL+, NiH-1L, NiL2, NiH-2L22-, NiL3-, and NiH-3L34-.