Precise synthesis of non-equilibrium rotaxanes via pumping in water

Abstract

Water is the matrix of life in which biomolecular machines carry out vital functions through ordered mechanical movements. The controlled active transport in artificial systems within aqueous environments, however, remains challenging at the molecular level, resulting from the inherent difficulties in manipulating molecular motions accurately in water. Herein, we present artificial molecular pumps (AMPs) capable of forming and maintaining non-equilibrium concentration differences of cucurbit[7]uril rings (up to 350 times) in aqueous media. Acid-base neutralization energy is exploited to add efficiently and precisely one ring per cycle to the dumbbells of both a solo and a duet pump by a rationally optimized pumping cassette. Operation is achieved under ambient conditions through simple pH modulation (2–7). A combination of kinetic investigations, computational modeling, and theoretical analysis provides a mechanistic understanding of how the aqueous AMPs harness chemical energy to produce and sustain high-energy oligorotaxanes in a non-equilibrium steady state.