The thermodynamic characteristics of complex formation between Ni2+ ions and dl-leucine

The heat effects of the interaction of nickel(II) ions with dl-leucine in aqueous solutions at ionic strengths of 0.5, 1.0, and 1.5 with sodium nitrate as a background electrolyte and the necessary heats of dilution were determined by direct calorimetric measurements at 288, 298, and 308 K. The heats of formation of NiL+ and NiL2 were calculated by the RRSU universal program taking into account protolytic equilibria. Temperature and background electrolyte concentration effects on the heat of complex formation between the amino acid and nickel ions were considered. Solution ionic strength growth increased exothermic complex formation effects, whereas an increase in temperature had the opposite action. The standard enthalpies of complex formation were found by extrapolation to a zero ionic strength. The Gurney scheme was used to calculate the temperature-dependent and temperature-independent components of the standard thermodynamic characteristics of complex formation.