Anion Exchange Renders Hydrophobic Capsules and Cargoes Water-Soluble

Abstract

Control over the solubility properties of container molecules is a central challenge in host-guest chemistry. Herein we present a simple anion-exchange protocol that allows the dissolution in water of various hydrophobic metal-organic container molecules prepared by iron(II)-templated subcomponent self-assembly. Our process involved the exchange of less hydrophilic trifluoromethanesulfonate anions for hydrophilic sulfate; the resulting water-soluble cages could be rendered water-insoluble through reverse anion exchange. Notably, this strategy allowed cargoes within capsules, including polycyclic aromatic compounds and complex organic drugs, to be brought into water. Hydrophobic effects appeared to enhance binding, as many of these cargoes were not bound in non-aqueous media. Studies of the scope of this method revealed that cages containing tetratopic and tritopic ligands were more stable in water, whereas cages with ditopic ligands disassembled.

Keywords: anion exchange; host-guest systems; self-assembly; supramolecular chemistry; water-soluble capsules.