Thermal properties and interpartical interactions of l-proline, glycine, and l-alanine in aqueous urea solutions at 288–318 K

The enthalpies of solution of l-proline have been measured in aqueous urea solutions at 0–6 mol urea kg−1 water at 288.15, 298.15, 308.15, and 318.15 K by the calorimetric method. The two-parameter relation connecting the values of solution enthalpies of proline with urea concentration and temperature has been obtained. The enthalpy and heat capacity parameters of pair interaction of l-proline with urea in water have been computed. Using the thermodynamic relations, the temperature changes of reduced enthalpy, and also the change of entropy and reduced Gibbs energy of solution of l-proline in aqueous solutions of urea at the temperature rise from 288 to 318 K have been determined. Their comparison with the data for glycine and l-alanine has been carried out. It has been shown that the entropy–enthalpy compensation (Barclay–Butler rule) takes place for dissolution and transfer processes.