Critical surface phase behavior governs hydrophobic attraction between extended solutes

Area of Science:

• Thermodynamics and Statistical Mechanics
• Soft Matter Physics
• Computational Biophysics

Background:

• Hydrophobic interactions are fundamental to biological self-assembly and the organization of soft matter.
• The strengthening of hydrophobic attraction with increasing temperature is a key characteristic, often explained by entropy changes related to water's hydrogen bonding network.
• The microscopic origins of hydrophobic interactions remain a subject of debate.

Purpose of the Study:

• To present an alternative framework for understanding hydrophobic interactions based on surface phase behavior.
• To investigate the solvent-mediated effective potential between hydrophobic solutes using molecular dynamics simulations.
• To develop a morphometric model linking hydrophobic attraction to interfacial thermodynamics and critical drying phenomena.

Main Methods:

• Extensive molecular dynamics simulations were performed.
• Metadynamics was employed to quantify the effective potential between nanometer-scale hydrophobic solutes.
• Simulations utilized the monatomic water (mW) model, the Simple Point Charge Extended (SPC/E) water model, and a Lennard-Jones solvent.

Main Results:

• A morphometric model was developed, incorporating scaling theory of critical drying.
• The model successfully reproduced the effective potential across various solute sizes, hydrophobicity levels, and thermodynamic states.
• Simulations confirmed the inverse temperature dependence of hydrophobicity, attributing it to the thermal expansion of the solvation shell.

Conclusions:

• Hydrophobic attraction arises generically from the rapid thermal expansion of the solvation shell.
• Surface phase behavior and proximity to vapor-liquid coexistence are key determinants of hydrophobic interaction strength and range.
• The findings offer a new perspective on the microscopic origins of hydrophobic interactions in diverse systems.