Calorimetric studies of interactions of some peptides with electrolytes, urea and ethanol in water at 298.15 K

The standard molar enthalpies of solution at infinite dilution of glycylglycine, dl -alanyl- dl -alanine and glycylglycylglycine in aqueous solutions of potassium chloride and ethanol as well as of glycylglycine and glycylglycylglycine in the solutions containing urea and water have been determined by calorimetry at the temperature 298.15 K. Changes of solution enthalpy, expressed in a form so-called heterotactic interaction coefficients, were used for analysis of interactions occurring between the investigated solutes in water. The group contributions illustrating the interactions of KCl, urea and ethanol with selected functional groups in the peptide molecules, namely CH 2 , “pep,” and “ion” groups, were calculated and discussed.