Autonomous fuelled directional rotation about a covalent single bond

Biology operates through autonomous chemically fuelled molecular machinery(1), including rotary motors such as adenosine triphosphate synthase(2) and the bacterial flagellar motor(3). Chemists have long sought to create analogous molecular structures with chemically powered, directionally rotating, components(4-17). However, synthetic motor molecules capable of autonomous 360 degrees directional rotation about a single bond have proved elusive, with previous designs lacking either autonomous fuelling(7,10,12) or directionality(6). Here we show that 1-phenylpyrrole 2,2'-dicarboxylic acid(18,19) (1a) is a catalysis-driven(20,21) motor that can continuously transduce energy from a chemical fuel(9,20-27) to induce repetitive 360 degrees directional rotation of the two aromatic rings around the covalent N-C bond that connects them. On treatment of 1a with a carbodiimide(21,25-27), intramolecular anhydride formation between the rings and the anhydride's hydrolysis both occur incessantly. Both reactions are kinetically gated(28-30) causing directional bias. Accordingly, catalysis of carbodiimide hydration by the motor molecule continuously drives net directional rotation around the N-C bond. The directionality is determined by the handedness of both an additive that accelerates anhydride hydrolysis and that of the fuel, and is easily reversed additive(31). More than 97% of fuel molecules are consumed through the chemical engine cycle(24) with a directional bias of up to 71:29 with a chirality-matched fuel and additive. In other words, the motor makes a 'mistake' in direction every three to four turns. The 26-atom motor molecule's simplicity augurs well for its structural optimization and the development of derivatives that can be interfaced with other components for the performance of work and tasks(32-36).