Cation-π and π-π Interactions in Aqueous Solution Studied Using Polarizable Potential Models

Area of Science:

• Computational chemistry
• Physical chemistry
• Molecular modeling

Background:

• Cation-π interactions are crucial in various chemical and biological systems.
• Accurate modeling of these interactions requires sophisticated potential energy functions.
• Understanding ion solvation and interactions with aromatic systems is key.

Purpose of the Study:

• To develop and parametrize polarizable potential models for alkali metal cations (Li+, Na+, K+) and ammonium (NH4+) interacting with benzene.
• To validate these models against ab initio calculations for dimers and trimers.
• To investigate cation-π interactions in aqueous solution using molecular dynamics simulations.

Main Methods:

• Ab initio quantum mechanical calculations for parametrization.
• Development of polarizable potential models.
• Calculation of complexation energies and potential energy surfaces.
• Molecular dynamics simulations in aqueous solution.
• Potential of Mean Force (PMF) calculations.

Main Results:

• Models accurately reproduce ab initio energies and potential surfaces for cation-π dimers and trimers.
• NH4+ model correctly predicts hydration free energy and structure.
• Li+ and Na+ show preferential solvation by water, with minimal benzene association.
• K+ and NH4+ exhibit significant binding affinities towards benzene (1.2 and 1.4 kcal/mol, respectively).
• Simulations reveal enhanced cation-π and π-π interactions in aqueous solution, demonstrating cooperativity.

Conclusions:

• The developed polarizable potential models are reliable for studying cation-π interactions in solution.
• Ion-specific behaviors are observed, with K+ and NH4+ showing notable affinity for benzene.
• Cooperativity between cation-π and π-π interactions is confirmed in aqueous environments, impacting molecular organization.