A combined molecular dynamics simulation, atoms in molecule analysis and IR study on the biologically important bulk fluorinated ethanols to understand the role of weak interactions in their cluster formation and hydrogen bond network

Abstract

The unique physicochemical nature of the fluorocarbon group makes fluorinated alcohols an interesting class of molecules which have diverse applications from the field of biology to chemical industries. In this paper, we have performed molecular dynamics (MD) simulation, atoms in molecule analysis (AIM) as well as IR study on the two biologically important fluorinated alcohols, trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) as well as compared them with ethanol (ETH) in order to understand the cluster formation as well as hydrogen bond network in their respective bulk media. The cluster size calculation shows that HFIP prefer to form smaller clusters than TFE and ETH. We have found the evidence of weak fluorous (F⋯F) interaction in TFE and HFIP by the radial distribution function (rdf) calculations and the extent of interaction is more significant in the case of HFIP which has also been confirmed by the AIM analysis. Significant amount of weak CH⋯F as well as CH⋯O interactions have been found to contribute in the cluster formation of the bulk HFIP, whereas, only CH⋯F interaction was evident in the case of bulk TFE. The rdf data shows that OH⋯O and OH⋯F hydrogen bonds are the main contributors in the hydrogen bond network of TFE and HFIP. However, the number as well as the strength of OH⋯O hydrogen bond is significantly less for HFIP compared to TFE and the strength of OH⋯F hydrogen bond is more for HFIP. Due to the presence of less as well as weak OH⋯O hydrogen bond in HFIP, its average hydrogen bond strength is less as compared to TFE and ETH which is also reflected by the experimental IR data of HFIP which is significantly blue shifted as compared to TFE. The MD simulation, AIM analysis and IR data clearly indicate that the organic fluorine plays significant role in the cluster formation and hydrogen bond network of TFE and HFIP through the formation of weak OH⋯F hydrogen bond along with the fluorous interaction.