Solvent Effect on Cation⊗3π Interactions: A First-Principles Study.

Cation⊗3π interactions play a special role in the behaviors of biological molecules and carbon-based materials in aqueous solutions, yet the effects of solvation on these interactions remain poorly understood. This study examines the sequential attachment of water molecules to cation⊗3π systems (cation = Li⁺, Na⁺, K⁺), revealing that solvation influences interaction strengths in opposing ways: solvation of the metal cation decreases the strengths of cation⊗3π interactions, while the solvation of the benzene molecule increases the strengths of cation⊗3π interactions, compared with the strengths of cation⊗3π interactions in the gas phase. The mechanism analyses revealed that in the presence of surrounding water molecules, the stability of cation⊗3π systems is generally enhanced by cation-π, π-π, water-π, and water-ion interactions, while water-water interactions typically have a destabilizing effect. In addition, the primary effect of water molecules at different adsorption sites is to modulate the Coulombic multipole-multipole interactions and the overlap between monomeric charge distributions, thereby influencing the changes in strengths of cation⊗3π interactions. Moreover, AIMD simulations further underscore the practical significance of cation⊗3π interactions. These findings provide valuable insights into the structures and the strengths of cation⊗3π interactions with the effect of solvation.