Energy–Entropy Compensation in the Transfer of Nonpolar Solutes from Water to Cosolvent/Water Mixtures

Microscopic view on solvation: Preferential interactions between solutes and cosolvent molecules in binary solvents are determined by using molecular dynamics computer simulations. The picture shows the solvent molecules water (red) and urea (blue) in the first solvation shell of a propane molecule. Urea preferentially interacts with propane driven by the solute-solvent van der Waals energy. The interaction is entropically opposed because urea hydration water molecules impose an excluded volume restriction upon formation of urea-propane contacts.