Hydrophobic Hydration and Assembly of Nanoscopic Solutes

The free energetic cost of hydrating hydrophobic solutes undergoes a crossover at roughly 1 nm, from being entropic for smaller solutes to being enthalpic for larger solutes. The crossover has important implications on hydrophobically driven assembly, including the fact that the driving force for hydrophobically-driven molecular assembly increases with increasing temperature. Previous simulation studies have demonstrated the existence of the crossover and explored how it is manifest in model spherical solutes. Here we examine the crossover in hydrophobic hydration in the presence of 2 kinds of anisotropies: (1) anisotopy in solute shape, with a particular focus on cylindrical solutes, and (2) anisotopy in the hydration environment, with a focus on hydration in interfacial environments. The hydration free energies and entropies of anisotropic solutes, estimated using molecular dynamics simulations with enhanced sampling techniques, will be presented. The implications of our results on the thermodynamics driving force and the kinetics of assembly will also be discussed.