Spatially resolved structure and dynamics of the hydration shell of pyridine in sub- and supercritical water

Abstract

Molecular dynamics simulations of a pyridine solute in sub- and supercritical water are performed to investigate the organization and dynamics of water molecules at different parts of the solute solvation shell. The radial/angular and spatial orientational functions provide information on the spatially resolved angular preferences of water molecules around the pyridine solute. The pyridine ring is found to interact with water rather strongly and induce different orientational behavior for water at the CH periphery and around nitrogen of the pyridine ring. The higher thermal energy at sub- and supercritical conditions tends to randomize the orientational distributions of water molecules. However, the average preferential orientations in different regions remain similar to that at ambient conditions. The dynamics of water molecules around the pyridine ring is found to be faster in the small axial regions than that in the equatorial region around the pyridine solute.