Amino acid behavior in aqueous amide solutions: Temperature dependence of the l-phenylalanine–N,N-dimethylformamide interaction

• Thermodynamics of amino acid solvation in aqueous DMF solutions was studied at 288–318 K.
• The pair interaction parameters were compared with those for urea solutions.
• For hydrophobic solutes enthalpies and entropies of interaction reveal strong temperature changes.
• The relationship between the temperature dependence of solvation and solute–solute interactions was found.

We have studied thermodynamics of the l-phenylalanine (Phe) pair interaction with denaturing agents – urea (U) and dimethylformamide (DMF) at 288–318 K. Our study does indicate that enthalpies and entropies of the Phe–U interaction reveal the anomalous temperature dependence which does not occur for DMF solutions. The anomalous Phe behavior in U solutions appears to be closely related to peculiarities of U hydration. One more result is in the fact that for hydrophobic solutes such as l-phenylalanine and substituted amides it is not justified to use the results obtained at 298 K for predicting the solute behavior at physiological temperatures.