Aqueous solvation of methane from first principles

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding solvation dynamics around hydrophobic solutes is crucial in various chemical and biological processes.
• Previous studies on water around hydrophobic groups yielded controversial conclusions regarding water molecule immobilization.

Purpose of the Study:

• To investigate the structural, dynamical, bonding, and electronic properties of water around a methane solute using first-principles calculations.
• To clarify the behavior of water molecules in the vicinity of hydrophobic solutes.

Main Methods:

• First-principles calculations to simulate water-methane systems.
• Analysis of molecular dynamics, bonding, and electronic properties.
• Generation of maximally localized Wannier functions for polarization analysis.

Main Results:

• Hydrophobic methane slightly reduces the mobility of surrounding water molecules (less than a 2-fold decrease).
• Water molecule immobilization is not limited to the closest neighbors but affects a broader hydration shell.
• Rotational slowing down correlates with excluded volume fraction, impacting hydrogen bond exchange rates.

Conclusions:

• The study supports findings of reduced, not immobilized, water mobility around hydrophobic groups.
• Careful selection of simulation temperatures is necessary to avoid artificial slowing-down effects.
• Detailed polarization analysis enhances the characterization of the solvation process.