Enthalpy characteristics of dissolution of L-tryptophan in water + formamides binary solvents at 298.15 K

Enthalpies of dissolution of L-tryptophan in aqueous solutions of formamide (FA), N-methylformamide (MFA), and N,N-dimethylformamide (DMF) are measured according to calorimetry at the concentration of amides x2 = 0−0.4 mole fraction. Standard values of enthalpies of dissolution and transfer ΔtrHo of L-tryptophan from water to binary solvent, as well as enthalpy coefficients of pair-wise interactions hxy of L-tryptophan with formamide molecules are calculated. The effect the composition of a waterorganic mixture has on the enthalpy characteristics of L-tryptophan is considered. The relation of ΔtrHo of L-tryptophan with the structure of amides is shown. A quantitative estimation of the contributions to the energy of L-tryptophan-formamide pair-wise interactions determined by polarity/polarizability, acidity, and basicity of organic solvent is performed using the four-parameter Kamlet-Taft correlation equation.