Water structuring above solutes with planar hydrophobic surfaces

Area of Science:

• Physical Chemistry
• Computational Biophysics
• Chemical Physics

Background:

• Biological solutes often have both polar and hydrophobic surfaces.
• Solute size influences hydration, transitioning from wetting to dewetting around 1 nm.
• This transition involves shifts from entropy to enthalpy dominance in non-polar aggregations.

Purpose of the Study:

• To investigate the hydration behavior transition of hydrophobic surfaces with increasing size.
• To explore the relationship between solute geometry and water molecule arrangement.
• To simulate aqueous solutions of planar organic molecules from cyclopropane to circumcircumcoronene.

Main Methods:

• Molecular dynamics simulations of organic molecules in aqueous solution.
• Systematic variation of planar hydrophobic surface size.
• Analysis of solute-water interactions, including dewetting and hydrogen bonding.

Main Results:

• A gradual dewetting transition was observed, stabilizing at a ~3.3 Å separation for first-layer water.
• Hydrogen bonding orientational structure changes occurred between cyclopropane and cyclopentadene.
• Water near large hydrophobic surfaces adopted structures similar to the basal planes of ice.

Conclusions:

• Solute size is a critical factor in determining hydration regimes (wetting vs. dewetting).
• The study provides insights into water's structural response to hydrophobic surfaces of varying scales.
• Observed water ordering near large hydrophobic surfaces has implications for understanding biomolecular interactions.