Influence of the composition of aqueous-alcohol solvents on thermodynamic characteristics of dl-α-alanyl-dl-norleucine dissolution at 298.15 K

Dissolution enthalpies (ΔsolHm) of dl-α-alanyl-dl-norleucine in binary mixtures containing water + (EtOH, 1-PrOH and 2-PrOH at 0–0.4 mole fraction) at 298.15 K and atmospheric pressure have been determined as a function of the composition using an isothermic calorimeter. The results obtained have been used to calculate standard enthalpies of a solution (ΔsolH°) and transfer (ΔtrH) of dl-α-alanyl-dl-norleucine from water into the mixtures as well as enthalpy coefficients of pairwise interaction (hxy) of the solute with alcohols in aqueous media. The ΔtrH° values are positive for all mixtures over the whole composition range. The influence of the co-solvent structure and of the content of mixtures and of a side-chain of peptide on the change of ΔtrH° (hxy) is discussed.