Autonomous fuelled directional rotation about a covalent single bond
Biology operates through autonomous chemically fuelled molecular machinery1, including rotary motors such as adenosine triphosphate synthase2 and the bacterial flagellar motor3. Chemists have long sought to create analogous molecular structures with chemically powered, directionally rotating, components4–17. However, synthetic motor molecules capable of autonomous 360° directional rotation about a single bond have proved elusive, with previous designs lacking either autonomous fuelling7,10,12 or directionality6. Here we show that 1-phenylpyrrole 2,2′-dicarboxylic acid18,19 (1a) is a catalysis-driven20,21 motor that can continuously transduce energy from a chemical fuel9,20–27 to induce repetitive 360° directional rotation of the two aromatic rings around the covalent N–C bond that connects them. On treatment of 1a with a carbodiimide21,25–27, intramolecular anhydride formation between the rings and the anhydride’s hydrolysis both occur incessantly. Both reactions are kinetically gated28–30 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 additive31. More than 97% of fuel molecules are consumed through the chemical engine cycle24 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 tasks32–36. The molecular chemical ‘fuelling’ of the catalysis-driven motor 1-phenylpyrrole 2,2′-dicarboxylic acid, which operates by a Brownian information ratchet mechanism, facilitates dynamics that are otherwise kinetically inaccessible.