Nanomachines in the macrocycle lane

A molecular motor has first to generate movements that are not swamped by Brownian motion, a dominant force at that scale, and cannot exploit angular momentum as a means of directional control. Despite these constraints, David Leigh and colleagues have developed a system that consumes a single chemical fuel to power a molecular machine that achieves continuous rotary motion as long as the fuel is present, and does not require any further chemical input or external stimulus. The motor consists of two interlocked molecular rings, the smaller of which (the macrocycle) is continuously transported directionally around the larger (the cyclic molecular track) when powered by irreversible reactions of a chemical fuel. Directionality is achieved via asymmetry in reaction rates of the chemical fuel added to the track, forcing the macrocycle to continue travelling in the same direction, rather than reversing towards the previous reactive point.