Surface morphology and dispersion interaction induced anomalous dynamics of solvation water of a hydrophobic fullerene molecule

Abstract

Knowledge of accurate structural and dynamical features of the surrounding water of a C60 molecule is essential for the proposed uses of C60 in a wide variety of applications viz., in inhibiting HIV protease, DNA cleaving, macromolecular binding and drug delivery. Using molecular dynamics simulations, the present study demonstrates that the solute-water dispersion interaction induces anomalous bulk density dependence of dynamics of solvation water of the C60. In order to elucidate the origin of such behaviour, the analyses of the simulation trajectories are performed and it reveals the presence of two dynamically different types of water molecules: one (designated as Type 1 here), which has no radially outward movements (with respect to C60) throughout the simulation time and performs “bouncing ball” movements on the C60 surface by hopping from one face to another and the other one (Type 2) is fast and goes in and out of the solvation shell frequently. The anomalous dynamics is a consequence of the variable presence of such dynamically heterogeneous water molecules as a function of bulk density, and it, in turn, arises due to the interplay between two opposing effects emanating from the free volume (which depends on bulk density) and the inhomogeneous energy surface of the C60 arising due to icosahedral arrangement of carbon atoms on the surface and attractive solute-water dispersion interaction. It is to emphasize that model C60 with no attractive dispersion interaction does not show any anomalous dynamics.