Artificial molecular pumps (AMPs) are a class of synthetic molecules designed to mimic the away-from-equilibrium chemistries found in nature. AMPs utilize redox energy to take macrocyclic rings from relatively dilute solutions and accumulate them on collecting chains to form rotaxanes, incrementally building local concentration gradients. Pumping is achieved through a flashing energy ratchet mechanism, harnessing the redox-switchable radical-complexation behavior of bipyridinium recognition sites on the pump and ring units. Previously AMPs have been restricted to operation with a single type of macrocycle, typically the venerable cyclobis(paraquat-p-phenylene) (CBPQT4+). This contrasts with their biological cousins, where pumps are known that transport a variety of substrates from ions to carbohydrates and lipids. Herein we report a new artificial molecular pump that is capable of selective rotaxane formation. We demonstrate the selective pumping of CBPQT4+ in preference to an alternative macrocycle, resulting in controlled formation of a [2]rotaxane. These results open the door to the use of a broad family of CBPQT4+ derived macrocycles and enable the construction of more complex mechanically interlocked architectures than previously possible.

Selective rotaxane formation using artificial molecular pumps

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