Anion Binding in Solution: Beyond the Electrostatic Regime

Abstract

Summary A fundamental understanding of anion binding by receptors is essential for managing salts during energy, water, and food production. However, the limited understanding of solvent effects in ion recognition leads to a persistent blind spot that prevents effective receptor design. We experimentally discovered an underlying 1/ ɛ r dependence of anion affinity on solvent dielectric constant ( ɛ r ). We found this relationship by measuring how chloride binds to macrocyclic triazolophane receptors across a wide range of solvents: ɛ r = 4.7–56.2. Solvent weakens affinity by screening electrostatics; electrostatics dominates when ɛ r ɛ r – affinity in solvents used in liquid-liquid extractions in the nuclear fuel cycle. This model offers a general foundation for anion recognition and electrostatically driven complexation.