Switching on Supramolecular Catalysis via Cavity Mediation and Electrostatic Regulation.

Synthetic supercontainers constructed from divalent metal ions, carboxylate linkers, and sulfonylcalix[4]arene-based container precursors exhibit great promise as enzyme mimics that function in organic solvents. The capacity of these artificial hosts to catalyze Knoevenagel condensation can be switched on when the aldehyde substrate possesses a molecular size and shape matching the nanocavity of the supercontainers. In contrast, little reactivity is observed for other aldehydes that do not match the binding pocket. This substrate-dependent catalytic selectivity is attributed to the Brønsted acidity of the metal-bound water molecules located inside the nanocavity, which is amplified when the size/shape of the aldehyde substrate fits the binding cavity. The electrostatic environment of the binding cavity and the Brønsted acidity of the supercontainer can be further modulated using tetraalkylammonium-based regulators, leading to higher reactivity for the otherwise unreactive aldehydes.