The dependence of hydrophobic interactions on solute size

The dependence of hydrophobic interactions as a function of solute size has been investigated as an extension to our recent study detailing the physical origin of hydrophobic interactions. By determining the hydration free energy of two identical hydrophobic solutes dissolved in water, the critical radius (Rc) was calculated to be 3.25 a, at ambient conditions. With reference to Rc, an initial process and a hydrophobic solvation process have been shown to govern the behavior of the dissolved solutes. These processes can be demonstrated by molecular dynamic simulations on C-60-C-60 fullerenes in water, and CH4 dimers in water. In the case of the former, by decreasing the distance between the C-60 fullerene molecules, the hydrophobic interactions switch between H1w- and H2s type hydrophobic processes. Additionally, maximizing hydrogen bonding was found to be the driving force that influenced the behavior of the hydrophobic solutes.