Chemically fuelled autonomous directional linear motion at the molecular level

Autonomous, chemically fuelled directional motion underpins the function of many of nature's magnificent biological motor proteins. Mimicking or replicating such behaviour in small molecule systems is a hugely exciting challenge. Rotaxanes, comprising a macrocycle encircling a molecular thread, have been used extensively to study the directional linear motion of one molecular component with respect to another. With some notable exceptions, motion in these systems is generally controlled through "intelligent input", where the experimentalist changes the relative binding affinities of the macrocycle towards specific sites on the molecular thread through the addition of additives such as acid or metal ions. Conversely, in this research programme, we will design and develop a rotaxane-based system which operates autonomously. The macrocycle is associated with a transition metal and catalyses the introduction of kinetic barriers (functionalisations) along the molecular thread, in a sequential fashion, inhibiting movement in the "backwards" direction. The directional motion occurs autonomously: provided the macrocycle catalyst turns over with each functionalisation, the system requires no external input other than a constant supply of chemical fuel.