Enthalpy characteristics of dissolution of l-cysteine and l-asparagine in aqueous solutions of acetonitrile and dimethyl sulfoxide at 298.15 K

The integral enthalpies of dissolution Delta(sol) H (m) of l-cysteine and l-asparagine in mixtures of water with acetonitrile and dimethyl sulfoxide at the concentration of organic solvent up to 0.32 molar fractions were measured by means of dissolution calorimetry. The standard enthalpies of dissolution (Delta(sol) HA degrees) and transfer (Delta(trans) HA degrees) of the amino acids from water to a mixed solvent were calculated. The enthalpy coefficients of pair interactions for L-cysteine and L-asparagine with cosolvent molecules are positive, except for the L-asparagine-water-acetonitrile system. The concepts on the prevailing effect of specific interactions in solutions and the influence of the nature of the cosolvents and lateral substituents of the amino acids on the thermochemical characteristics of dissolution were used to explain the data obtained.