Rotaxanes and catenanes in motion: towards molecular machines and motors

Molecular systems whose motions can be triggered by applying an external si gnal are of special current interest, both as mimics of biological systems (redox proteins) and as potential bistable molecular devices. Transition me tal-based catenanes and rotaxanes are particularly well suited in this cont ext since reversible molecular motions using interlocked or threaded rings can be easily performed. In fact, these elements may constitute the working parts of future molecular machines and engines, such as ball and socket jo ints, universal joints, wheels and axles, etc. We have recently proposed mo lecular systems which can be set in motion under the action of an electroch emical signal.