Local density profiles are coupled to solute size and attractive potential for nanoscopic hydrophobic solutes

We employ constant pressure molecular dynamics simulations to investigate the effects of solute size and solute-water dispersion interactions on the solvation behavior of nanoscopic hydrophobic model solutes in water at normal temperature and pressure. The hydration behavior around a single planar atomic model solute as well as a pair of such solutes have been considered. The hydration water structure of a model nanoscopic solute with standard Lennard-Jones interaction is shown to be significantly different from that of their purely repulsive analogues. The density of water in the first solvation shell of a Lennard-Jones solute is much higher than that of bulk water and it remains almost unchanged with the increase of the solute dimensions from one to a few nanometers. On the other hand, for a purely repulsive analogue of the above model, solute hydration behavior shows a marked solute size dependence. The contact density of water in this case decreases with the increasing dimension of the solute. We also demonstrate the effect of solute-solvent attraction on the cavity formation in the inter solute region between two solutes with an inter solute separation of 6.8 Å, corresponding to the first solvent separated minimum in the free energy profile as obtained in our earlier work.