The enthalpy of solution of DL-α-alanyl-DL-α-valine depending on the composition of water-alcohol binary solvents at 298.15 K

The integral enthalpies of solution of DL-α-alanyl-DL-α-valine in water-ethanol, water-n-propanol, and water-isopropanol mixtures at alcohol concentrations x2 = 0–0.4 mole fractions were measured calorimetrically. The enthalpies of solution of the peptide ΔsolH° and transfer from water to a mixed solvent ΔtrH° were calculated. The effect of the structure and properties of the peptide and mixture composition on the enthalpy characteristics of the peptide are discussed. The enthalpy coefficients of pair interactions hxy of DL-α-alanyl-DL-α-valine with alcohol molecules were calculated. It was found that they were positive and increased in the series ethanol, n-propanol, isopropanol. An analysis of the results allows the general features of changes in the thermodynamic parameters of solution of peptides of the DL-α-alanine series with different amino acid residues in water-alcohol mixtures to be established.