Properties of 2,2,2-trifluoroethano/water mixtures:: Acidity, basicity, and dipolarity

In this report. we focus our attention oil the characterization of 2,2,2-trifluoroethanol(TFE)/H2O mixtures and describe their intrinsic parameters: i.e., solvent acidity (SA). solvent basicity (SB), and solvent dipolarity/ polarizability (SPP), by the probe/homomorph-couple method for a range of mixtures front 0-100% (v/v) TFE. Variation of these parameters is not lincar and has a singular and unpredictable behavior depending on the precise composition of the mixture. Based oil these parameters, we describe the TFE-induced changes in some physical properties: i.e., viscosity (eta). partial molar volume (V). density (p), dielectric constant (epsilon). vapor pressure (p(v)), and spectroscopic properties: i.e.. NMR chemical shifts (delta(H-1)) of TFE Me group for all molar fractions studied. In addition. by means of CD studies, we report that formation of the secondary structure. as percentage of helical content, theta. of a polypeptide, poly(L-lysine), in several TFE/H2O mixtures is adequately described by these mixture parameters. SA, SB. and SPP of TFE/H2O mixtures provide an excellent tool for the interpretation of formation and stability of intramolccular H-bonds, and, thus. of secondary structures in polypeptides.