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

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.