Enthalpy characteristics of solution of L-cysteine and L-asparagine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-cysteine and L-asparagine in mixtures of water with ethanol, n-propanol, and isopropanol at a mole fraction of alcohol of up to 0.32 were determined by calorimetry of solution. The standard enthalpies of solution (Δ_sol H ⁰) of L-serine and of its transfer (Δ_tr H ⁰) from water to a mixed solvent were calculated. The dependences of Δ_sol H ⁰ and Δ_tr H ⁰ on the composition of water-alcohol mixtures pass through a maximum. The calculated enthalpy coefficients of pair interaction of amino acids with alcohol molecules are positive and increase in the order ethanol, n-propanol, isopropanol. The data obtained were interpreted from the viewpoint of various types of interaction in solution and effect of the amino acid residue on the thermochemical characteristics of solution.