A computational study of anion-modulated cation-π interactions

Area of Science:

• Computational Chemistry
• Supramolecular Chemistry
• Biophysical Chemistry

Background:

• Cation-π interactions are crucial in biological systems, involving positively charged amino acid residues and aromatic systems.
• Understanding how other species, like anions, modulate these interactions is vital for comprehending molecular recognition and function.
• Guanidinium is a biologically relevant cation, and benzene serves as a model π system.

Purpose of the Study:

• To computationally investigate the influence of anions on cation-π complexes formed between guanidinium and benzene.
• To analyze the energetic contributions and structural factors governing these ternary interactions.
• To elucidate the role of polarization and three-body effects in anion-modulated cation-π interactions.

Main Methods:

• Potential energy surface scans to map interaction landscapes.
• Supermolecule calculations to determine interaction energies of ternary complexes (guanidinium-benzene-anion).
• Local molecular orbital energy decomposition analysis (LMO-EDA) to dissect interaction energies into components (electrostatic, polarization, dispersion, etc.).

Main Results:

• Anion interaction with the guanidinium-benzene complex is significantly influenced by polarization effects.
• The relative positioning of the cation, anion, and π system dictates the nature of three-body interactions (cooperative or anticooperative).
• Anticooperative three-body effects occur when the cation and anion are on the same side of the π system; cooperative effects occur when they are on opposite sides.

Conclusions:

• Anions modulate cation-π interactions primarily through polarization, altering the binding energy and geometry.
• The spatial arrangement of interacting species is critical for determining the overall binding stability and mechanism.
• This study provides novel insights into anion-guanidinium-π system interactions, relevant to biological contexts.