Molecular dynamics and NMR study of methane-water systems

Abstract

Molecular dynamics of methane-water systems have been studied through computer simulations (MD), nuclear spin relaxation and self diffusion methods (NMR). MD simulation results give support to the concept of hydrophobic hydration by enhancing the water structure around the methane to create a clathrate. Spontaneous contacts between methanes is observed only at high densities, while so-called solvent-separated configurations are present in all simulations. The dynamics of the solvent water molecules is slowed down. In particular, the reorientational motion is sensitive to the presence of methane in solution. The simulated translational diffusion of methanes as solutes is also slowed down, but is higher than observed experimentally. The rotational motion of methanes is very sensitive to variation of the density while, the translational motion of methane is more constant and follows that of water. Methane acts nearly as a free rotor. The simulated reorientational correlation times for methane in water solution are in good agreement with experiment.