Chloride capture using a C–H hydrogen-bonding cage

Abstract

Tight binding and high selectivity are hallmarks of biomolecular recognition. Achieving these behaviors with synthetic receptors has usually been associated with OH and NH hydrogen bonding. Contrary to this conventional wisdom, we designed a chloride-selective receptor in the form of a cryptand-like cage using only CH hydrogen bonding. Crystallography showed chloride stabilized by six short 2.7-angstrom hydrogen bonds originating from the cage's six 1,2,3-triazoles. Attomolar affinity (10¹⁷ M^-1) was determined using liquid-liquid extractions of chloride from water into nonpolar dichloromethane solvents. Controls verified the additional role of triazoles in rigidifying the three-dimensional structure to effect recognition affinity and selectivity: Cl^- > Br^- > NO₃ ^- > I^- This cage shows anti-Hofmeister salt extraction and corrosion inhibition.