Interaction of 2,2,2-trifluoroethanol with proteins: calorimetric, densimetric and surface tension approach

The thermal denaturation of hen egg-white lysozyme was studied in the presence of 2,2,2-trifluoroethanol (TFE) at various pH values using micro differential scanning calorimetry. Quantitative thermodynamic parameters accompanying the thermal transitions were evaluated. It is observed that thermal unfolding of lysozyme in the presence of TFE upto a concentration of 4.0 mol dm(-3) follows a two-state denaturation mechanism as indicated by the equality of van't Hoff and calorimetric enthalpies. The finer details of interaction were studied by measuring the partial molar volume of some constituent amino acids and glycine peptides from water to aqueous TFE at 298.15 K. The physico-chemical properties of aqueous TFE: apparent molar heat capacities, apparent molar volumes and surface tension were measured to understand the intrinsic properties of the cosolvent as well. From the correlation among the thermal unfolding data on lysozyme in aqueous TFE, calculated preferential interaction parameters, physico chemical properties of aqueous TFE and partial molar volumes of transfer, it is concluded that both solvent mediated effect and direct interaction constitute the mechanism of TFE-protein interactions.