A molecular twist on hydrophobicity.

Area of Science:

• Physical Chemistry
• Molecular Dynamics
• Computational Chemistry

Background:

• Hydrophobicity is traditionally explained by molecular repulsion between nonpolar substances and water.
• Understanding the molecular basis of hydrophobicity is crucial for various scientific fields.

Purpose of the Study:

• To explore the molecular basis of hydrophobicity using theoretical tools.
• To investigate the interactions between organic solvents (S) and water in binary systems.

Main Methods:

• Utilized a comprehensive set of theoretical tools.
• Analyzed extensive sets of organic solvent (S)/water binary systems.
• Employed quantum descriptors of bonding to analyze S⋯water interactions.

Main Results:

• Quantum descriptors consistently indicated stabilizing S⋯water interactions, with no evidence of repulsion.
• Molecular exclusion of S by water is driven by a complex interplay of entropic, enthalpic, and dynamic factors.
• Interfaces are non-isotropic regions with density gradients, stabilized by weak dihydrogen contacts.

Conclusions:

• The etymological definition of hydrophobicity is not supported at the molecular level.
• A new definition of an interface as a region with non-constant component density is proposed.
• This study provides fundamental molecular insights into hydrophobicity and phase separation.