The basic technology underlying many current chemically fueled systems is straightforward: the decomposition of the fuel causes the formation of a bond between two species that subsequently breaks, returning the system to its resting state. This simple behavior can be coupled to surprisingly complex behavior. For example, acid-base chemistry can be used to drive autonomous unidirectional rotation in the artificial molecular motor catenane shown in Figure , developed by Leigh. This system consists of two large interlocked macrocycles and is operated by trichloroacetic acid (CCl 3 CO 2 H), which will temporarily protonate the ring before decomposing to CHCl 3 and CO 2 . Key to this design is the incorporation of acidand base-labile blocking groups to control the direction of rotation.