A hybrid molecular machine

A versatile example of a molecular machine is described. The stationary part is an iron protoporphyrin complex, bearing two movable side chains with terminal donor groups. Changing the pH or the electrochemical potential, as well as the injection of CO, alters the affinity of the donor groups toward the metal ion, thus promoting intra-molecular motion of the pendant arms. The possibility of controlling the molecular motion through inputs of different nature, changeable at will, makes this system the first example of a hybrid molecular machine.