L. A. Kochergina

Thermodynamic characteristics of protolytic equilibria of L-serine in aqueous solutions

The heat effects of the reaction of aqueous solution of L-serine with aqueous solutions of HNO3 and KOH were determined by calorimetry at temperatures of 288.15, 298.15, and 308.15 K, and ionic strength values of 0.2, 0.5, and 1.0 (background electrolyte, KNO3). Standard thermodynamic characteristics (ΔrHo, ΔrGo, ΔrSo, ΔCpo) of the acid-base reactions in aqueous solutions of L-serine were calculated. The effect of the concentration of background electrolyte and temperature on the heats of dissociation of amino acid was considered. The combustion energy of L-serine by bomb calorimetry in the medium of oxygen was determined. The standard combustion and formation enthalpies of crystalline L-serine were calculated. The heats of dissolution of crystalline L-serine in water and solutions of potassium hydroxide at 298.15 K were measured by direct calorimetry. The standard enthalpies of formation of L-serine and products of its dissociation in aqueous solution were calculated.

Thermochemistry of complex formation of Ni2+ with glycyl-L-asparagine in aqueous solutions

The heats of formation of complexes in the glycyl-L-asparagine—Ni2+ system were determined by calorimetry in an aqueous solution at ionic strengths of 0.5, 1.0, and 1.5 (KNO3) and a temperature of 298.15 K. The thermodynamic characteristics of the formation of nickel complexes with dipeptide were determined. The influence of the ligand structure on the complexation thermodynamics in solutions was discussed.

Thermodynamics of Ni(II) Complexation with L-Asparagine in Aqueous Solution

Complexation of the Ni2+ ion with L-asparagine (HAsn±) is studied by potentiometric titration at 298.15 K and at the 0.3, 0.5 and 1.0 ionic strength of the solution (KNO3). The formation of the NiAsn+ and NiAsn2 complexes was established and their stability constants were determined. The thermodynamic stability constants of the mono- and bis(L-asparagine)nickel(II) complexes were obtained by extrapolation to zero ionic strength. The direct calorimetry method was used to measure the heat effect of the L-asparagine reaction with the Ni(II) nitrate solution in different pH intervals at 298.15 K and at the 0.5, 1.0, and 1.5 ionic strength (KNO3). The standard enthalpies of the NiAsn+ and NiAsn2 formation were found using extrapolation and the equation with one individual parameter. The enthalpies of the formation of the Ni(II) complexes with L-asparagine in aqueous solution were calculated in the standard hypothetically undissociated state.