Mode-coupling study on the dynamics of hydrophobic hydration

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Molecular Dynamics

Background:

• Understanding molecular motion in solutions is crucial for chemical processes.
• Hydrophobic solutes significantly impact solvent behavior.

Purpose of the Study:

• To investigate the molecular motion of water in mixtures with hydrophobic solutes.
• To elucidate the mechanism behind the slowing down of water's molecular motion.

Main Methods:

• Utilizing mode-coupling theory for molecular liquids.
• Employing an interaction-site description for molecular models.
• Comparing results with experimental data and molecular dynamics simulations.

Main Results:

• Both translational and reorientational motions of water slow down in the presence of hydrophobic solutes.
• This slowing is attributed to density fluctuations and dielectric friction caused by solute-induced cavities.
• Solute-solvent interaction strength, modulated by partial charges, affects water mobility, showing reduction for hydrophobic/strongly hydrophilic and enhancement for intermediate cases.

Conclusions:

• The mechanism of slowed water mobility by hydrophobic solutes is similar to pressure-induced effects.
• The study provides insights into positive and negative hydration phenomena.