Transducing chemical energy through catalysis by an artificial molecular motor

Abstract

Cells display a range of mechanical activities enabled by the cytoskeleton, a viscoelastic hydrogel manipulated by motor proteins powered through catalysis. This raises the question of how the acceleration of a chemical reaction can enable the energy released from that reaction to be transduced, and thereby work to be done, by a molecular catalyst. Here we demonstrate the molecular-level transduction of chemical energy to mechanical force in the form of the powered contraction and powered re-expansion of a crosslinked polymer gel driven by the directional rotation of embedded artificial catalysis-driven molecular motors. Continuous 360° rotation of the rotor about the stator of motor-molecules incorporated within the polymeric framework of the gel, twists the polymer chains of the crosslinked network around one another (either clockwise or anti-clockwise, depending on the chirality of the fuelling system). This progressively increases writhe and tightens entanglements, causing macroscopic contraction of the gel to ~70% of its original volume. The limit of contraction corresponds to the stall force of the motor; the point at which, despite catalysis continuing, the untwisting force exerted by the entwined strands balances conformation selection in the motor’s catalytic cycle. Subsequent addition of the opposite enantiomeric fuelling system powers rotation of the motor-molecules of the contracted gel in the reverse direction, unwinding the entanglements and causing the gel to re-expand. Continued powered twisting of the strands in the new direction causes the gel to contract once again. The experimental demonstration of work against a load by a synthetic catalyst, and the mechanism of the transduction of energy by a catalyst through kinetic asymmetry in its acceleration of a fuel-to-waste reaction, informs both the debate surrounding the mechanism of force generation by biological motors and the design principles for artificial molecular nanotechnology.