Electron-catalysed molecular recognition

Molecular recognition^1-4 and supramolecular assembly^5-8 cover a broad spectrum^9-11 of non-covalently orchestrated phenomena between molecules. Catalysis¹² of such processes, however, unlike that for the formation of covalent bonds, is limited to approaches^13-16 that rely on sophisticated catalyst design. Here we establish a simple and versatile strategy to facilitate molecular recognition by extending electron catalysis¹⁷, which is widely applied^18-21 in synthetic covalent chemistry, into the realm of supramolecular non-covalent chemistry. As a proof of principle, we show that the formation of a trisradical complex²² between a macrocyclic host and a dumbbell-shaped guest-a molecular recognition process that is kinetically forbidden under ambient conditions-can be accelerated substantially on the addition of catalytic amounts of a chemical electron source. It is, therefore, electrochemically possible to control²³ the molecular recognition temporally and produce a nearly arbitrary molar ratio between the substrates and complexes ranging between zero and the equilibrium value. Such kinetically stable supramolecular systems²⁴ are difficult to obtain precisely by other means. The use of the electron as a catalyst in molecular recognition will inspire chemists and biologists to explore strategies that can be used to fine-tune non-covalent events, control assembly at different length scales^25-27 and ultimately create new forms of complex matter^28-30.