Solvation Structure in Trifluoroethanol/Water Solvent Mixtures

Trifluoroethanol (TFE) is a frequently used solvent in experimental studies of proteins and peptides. The TFE/water solvent mixtures induce various secondary structures, especially alpha helices in proteins and peptides [1]. However, the exact mechanism of this process is not completely known. One of the interesting properties of TFE indicated by NMR and X-ray studies is the presence of a microheterogeneity in TFE/water mixtures [2]. The cluste formation reaches a maximum at around 30% (v/v) of TFE and disappears at higher concentrations. There is a correlation between the extent of this cluster formation and conformational transitions of proteins induced by TFE. In this study, the microheterogeneity in TFE/water mixtures is characterized using radial and spatial distribution functions. The radial distribution function (RDF) is a useful tool for solvation structure analysis, but in the case of complex or nonspherical solute molecules, the angular averaging in the RDF causes the loss of some structural information. Spatial distribution functions (SDF) that are the three-dimensional atomic density maps are used to provide complete information about solvation structure.