Anion-Binding Macrocycles Operate Beyond the Electrostatic Regime: Interaction Distances Matter.

Area of Science:

• Supramolecular Chemistry
• Anion Recognition
• Computational Chemistry

Background:

• Anion recognition is crucial in various chemical applications.
• Small molecule studies suggest electrostatics dominate anion binding.
• This principle's applicability to macrocyclic receptors remains unevaluated.

Purpose of the Study:

• To assess the contribution of electrostatics to gas-phase binding energies in macrocyclic-anion complexes.
• To compare binding energy correlations in macrocyclic versus small-molecule systems.
• To identify the role of non-electrostatic forces in macrocyclic anion recognition.

Main Methods:

• Computational evaluation of electrostatic contributions to binding energy.
• Analysis of gas-phase binding energies for diverse macrocyclic receptors.
• Comparison of interaction energies across different receptor architectures.

Main Results:

• Electrostatic interactions alone inaccurately predict binding energies for many macrocycles (calix[4]pyrroles, triazolophanes, etc.).
• Multiple contact points in macrocycles lead to larger interaction distances.
• Induction and dispersion forces contribute significantly (up to 32%) to binding energy.

Conclusions:

• Simple electrostatic models are insufficient for understanding anion binding in macrocyclic systems.
• Induction and dispersion forces play a critical role in macrocyclic anion recognition.
• Findings align with and extend previous observations on non-electrostatic contributions.