An Artificial Molecular Shuttle Operates in Lipid Bilayers for Ion Transport

Inspired by natural biomolecular machines, synthetic molecular-level machines have been proven to perform well-defined mechanical tasks and measurable work. To mimic the function of channel proteins, we herein report the development of a synthetic molecular shuttle, <b>[2]­rotaxane 3</b>, as a unimolecular vehicle that can be inserted into lipid bilayers to perform passive ion transport through its stochastic shuttling motion. The [2]­rotaxane molecular shuttle is composed of an amphiphilic molecular thread with three binding stations, which is interlocked in a macrocycle wheel component that tethers a K<sup>+</sup> carrier. The structural characteristics enable the rotaxane to transport ions across the lipid bilayers, similar to a cable car, transporting K<sup>+</sup> with an EC<sub>50</sub> value of 1.0 μM (3.0 mol % relative to lipid). We expect that this simple molecular machine will provide new opportunities for developing more effective and selective ion transporters.