[1,n]-Metal migrations for directional translational motion at the molecular level

Abstract

The controlled translational motion displayed by nature’s motor proteins underpins a wealth of processes integral to life, from organelle transport to muscle contraction. The motor proteins move along one dimensional cytoskeletal tracks, with their motion characterised by high association of the enzyme to the biopolymer combined with highly dynamic motion along the track. Efforts to mimic this dynamic association and control translational motion in fully synthetic systems have been dominated by rotaxane-based systems, where the properties of the mechanical bond ensure complete association between the moving component (the macrocycle) and the track it encircles, while allowing high rates of translation through shuttling of the moving component under Brownian motion. In addition to the dynamic association displayed by many rotaxane systems, by careful design of the track and macrocyclic component, elegant strategies have been employed to further control the motion in these mechanically interlocked systems, with both energy and information ratchet mechanisms allowing directional translational motion to be achieved. Other than mechanical bonds, alternative platforms for achieving controlled translational motion in fully synthetic systems have had more limited success, with bipedal walker systems that exhibit dynamic association lacking mechanisms to achieve inherent directionality, and bipedal systems that do display high levels of directionality requiring stepwise intervention of an experimentalist (i.e., they lack the dynamic autonomous behaviour that underpins nature’s walkers). Here we introduce carbon-to-carbon metal migration as a new platform for dynamic association and show how such migrations, in combination with the incorporation of a simple hydrocarbon fuel, can be harnessed to achieve autonomous directional translational motion of a metal centre along the length of a polyaromatic thread.