Molecular Machines and Motors Based on Transition Metal-Containing Catenanes and Rotaxanes

Abstract

Molecular motors of various kind (linear, rotary) are very common in biology where they play an essential role. However, the number of synthetic molecular ensembles whose dynamic behavior is reminiscent of biological motors is presently very limited. In order for an object to be regarded as a motor, several basic requirements have to be fulfilled. Even without trying to apply a strict thermodynamic definition, the system will have to convert a certain type of energy into another form of energy, while undergoing some kind of continuous motion. Threaded or interlocked rings are ideally suited to the construction of fully artificial molecular motors. If a ring is threaded onto a rod, it can either rotate around the axle or undergo a translation movement. Similarly, in catenanes, a ring can glide at will within another ring. Several examples of such compounds have been elaborated and studied in recent years, using threaded and interlocked molecules either based on acceptor-donor and hydrogen-bonded complexes or on transition metal complexes.