A Catalysis-Driven Dual Molecular Motor

Abstract

We report on a head-to-tail dual molecular motor consisting of two (identical) motor units whose pyrrole-2-carboxylic rings are turned in contra-rotary (i.e., disrotatory) fashion about a common phenyl-2,5-dicarboxylic acid stator. The motors directionally rotate via information ratchet mechanisms, in which the hydration of a carbodiimide (fuel) to form urea (waste) is catalyzed through the chemomechanical cycle of a motor unit, resulting in directional rotation about a biaryl C–N bond. The head-to-tail arrangement of the motor units produces coaxial contra-rotation of the end groups while the central phenyl ring of the axis remains dynamically unbiased. The electron-rich nature of the phenyl stator contributes to rotary catalysis by the dual-motor (and therefore motor rotation itself) being ∼7× faster than the parent 1-phenylpyrrole-2,2-dicarboxylic acid single-motor when operated under identical conditions, and 90× faster than the single-motor operated using the originally reported reaction conditions. Under batch-fueled operation (i.e., all of the fuel present at the start of motor operation), the dual-motor rotates at an initial rate of 0.43 rotations per minute (rpm). Chemostating the fuel concentration by syringe pump addition produced sustained repetitive contra-rotation at a rate of 0.24 rpm for a period of 100 min. The demonstration of chemically fueled continuous contra-rotation on a time scale of 2–4 min per rotation significantly advances the chemistry and mechanics of artificial catalysis-driven molecular machinery.