Hydrophobic Guests Influencing Assembling of Six Water Molecules

Abstract

Assemblies of six water molecules serve as a pivotal hydrogen-bonded unit for understanding the bulk properties of water and have been extensively studied. The energetics of various forms of different geometries have been investigated earlier. However, the influence of stimuli and hydrophobic molecules on the assemblies of six water molecules has not been understood yet. In this study, the role of different hydrophobic molecules in stabilizing different geometries of assemblies of six water molecules was determined from geometrical optimization using DFT calculations with the method ωB97X using def2-TZV basis set. Different geometries such as open-book, closed-bag, prism, and double-envelope were stabilized by one or more hydrophobic molecules in assemblies with six water molecules. There are infinite possibilities among the open-book geometries, where incremental differences in bond parameters or hydrophobic effects cause disturbances to the geometries of hydrogen bonds. The changes in the scheme of interactions in the assembly of six water molecules guided by O–H···O hydrogen bonds largely influenced the geometries. Weak interactions such as C–H···O, O–H···π, and O–H···F–C interactions contributed to such subtle changes and influenced the geometries. Energies of optimized geometries have suggested a net gain in each assembly, and the Gibbs free energies of formation were less than 1 kJ/mol. Aliphatic and aromatic hydrocarbons, fluoro-hydrocarbons, phenols, pyridine analogues, etc., influenced the geometry of their assemblies with six molecules of water.