Enthalpies of solution of L-phenylalanine in aqueous solution of amides at 298.15Â K

The enthalpies of solution ΔsolHm have been determined for L-phenylalanine in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA). The measurements have been made at 298.15 K and mole fraction of amide x2 = (0-0.4) on the precise isothermic calorimeter. The results obtained have been used to calculate the standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of L-phenylalanine from water into mixtures as well as the enthalpy coefficients of pairwise interaction (hxy) of the solute with amide in aqueous media. The interrelation between enthalpy characteristics of dissolution (transfer) of L-phenylalanine and the composition of (water + amide) binary mixtures has been established. Contributions of the amides properties (molar volume, dipolarity/polarizability, acidity and basicity) to the energy of pairwise interactions have been estimated quantitatively by means of a modified Kamlet-Taft equation.