Statistical thermodynamics of aromatic-aromatic interactions in aqueous solution

Area of Science:

• Biophysics
• Physical Chemistry
• Computational Chemistry

Background:

• Aromatic ring interactions are crucial in biological systems, influencing protein folding and DNA structure.
• The role of water in mediating these interactions, particularly in aqueous environments, requires detailed investigation.

Purpose of the Study:

• To analyze water-mediated interactions between toluene molecules in face-to-face (FF) stacked and T-shaped (TS) configurations.
• To decompose interaction energies and elucidate the contributions of hydration effects, including entropy.

Main Methods:

• Application of a statistical-mechanical theory of liquids.
• Integration with a molecular model for water.
• Decomposition of interaction energies into physically meaningful components.

Main Results:

• In vacuum, FF stacking and TS contact exhibit similar stability.
• In water, FF stacking gains stability while TS contact loses stability.
• Hydration effects significantly alter interactions: FF stacking sees reduced dispersion and screened electrostatics with significant water entropy gain; TS contact experiences near-complete dispersion cancellation and repulsive electrostatics, also with entropy gain.

Conclusions:

• Water-mediated interactions, particularly the entropic effects, are critical for aromatic ring arrangements in biological contexts.
• The term "π-π stacking" is misleading for interactions in aqueous solutions, as it overlooks the dominant role of water and other forces.
• Understanding these hydration effects is essential for comprehending the assembly of biomolecules.