Thermodynamics of protolytic equilibria in aqueous solutions of biologically active ligands

The protolytic equilibria in aqueous solutions of different amino acids and dipeptides were studied by a direct calorimetric method at 288-328 K. The measurements were made with an isothermal-shell calorimeter with automatic temperature recording. The thermodynamic characteristics of the processes o f acid-base equilibria were found from the combined results of thermochemic al measurements and equilibrium constant data. Gurney concepts were used to analyse the thermodynamic characteristics of reactions. Comparisons of the temperature-dependent and temperature-independent contributions to the Gib bs energy and enthalpy change afford the criteria of the variability in sig n of the Delta H of the process, i.e. they allow prediction of the magnitud e of the temperature a at which Delta H = 0.