In this report, we focus our attention on the characterization of 2,2,2-trifluoroethanol(TFE)/H 2 O 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 from 0 ± 100% (v/v) TFE. Variation of these parameters is not linear and has a singular and unpredictable behavior depending on the precise composition of the mixture. Based on these parameters, we describe the TFE-induced changes in some physical properties; i.e., viscosity (h), partial molar volume (V Å ), density (1), dielectric constant (e), vapor pressure (p v ), and spectroscopic properties; i.e., NMR chemical shifts (d( 1 H)) 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, q, of a polypeptide, poly(l-lysine), in several TFE/H 2 O mixtures is adequately described by these mixture parameters. SA, SB, and SPP of TFE/H 2 O mixtures provide an excellent tool for the interpretation of formation and stability of intramolecular H-bonds, and, thus, of secondary structures in polypeptides.