Thermodynamics and structure of aqueous electrolyte solutions of glycine at different temperatures

The enthalpies of dissolution of glycine in aqueous electrolyte solutions are measured by calorimetry at temperatures of 288 K, 298 K, and 313 K in the molality range from 0.25 mol/kg to 6 mol/kg NaCl and to 4.5 mol/kg KCl. The enthalpy and heat capacity parameters are determined for the pair and triple interactions of glycine with electrolyte in water. Special (singular) points are discovered on the concentration dependences of the heats of dissolution of glycine in aqueous electrolyte solutions and in urea solutions at different temperatures. At these points, such a structurally sensitive property as the entropy of dissolution is temperature independent and the partial heat capacity of glycine is equal to that of the crystalline amino acid. The position of the singular point on the concentration axis is identical for NaCl and KCl solutions; in the case of urea solutions, the singular point is achieved at a much higher concentration of urea.