Hydrophobic Hydration: A Theoretical Investigation of Structure and Dynamics

The presence of external solutes alters the local structures, and dynamics of water. The nature and extent of these structural modifications depend on several factors. Particularly, the chemical nature of the solute is very crucial. The alteration of water structure and dynamics in the presence of hydrophobic substances draws considerable attention in biological systems. The present work is focused on exploring the microscopic arrangement of solvation shells of tiny hydrophobic solute methane. We explore the tetrahedral order, local structural index, and van Hove self-correlation function to get a quantitative understanding. We observe a slight increase in the structural order of water molecules in methane’s first solvation shell, similar to that of the low-temperature water. We also find that water facing the methane have lower structural order than bulk water. Furthermore, the water molecules in the first solvation shell around methane show relatively slower orientational relaxation.

The hydrophobicity-induced alterations of water structural and dynamical properties are investigated using solvation shell decomposition. We observe the slower relaxation of selected water molecules staying longer time in methane first solvation shell. We find enhanced structural order in the methane first solvation shell and some dangling water molecules.