Motor proteins are essential for moving muscles in animals and transporting molecules across cell membranes. Researchers have now mimicked them by designing and creating the first synthetic motor that runs autonomously—without further intervention—on chemical fuel.
Mother Nature isn’t easy to emulate, so an artificial chemically powered motor that works like a motor protein “is a major advance,” says Jonathan Clayden of the University of Bristol, an expert on chemistry-based biological mimicry. It could power motion “on a nanometer scale if attached to a polymer or solid support,” he says, and “could lead to molecular solenoids, paddles, propellers, and valves.”
Earlier nonautonomous chemically powered motors required constant intervention—they had to be fed a sequence of compounds to complete each operating cycle. Researchers have designed autonomous molecular motors, but those required a continuous source of external light instead of a tank of chemical fuel, making them more like a plugged-in electric motor than a car.
Ben L. Feringa of the University of Groningen, whose group has developed both types of earlier systems, says motors like the new autonomous chemically driven one “might ultimately have far-reaching prospects for powering nanomachines and robotics.”
David A. Leigh and coworkers at the University of Manchester got the new motor running by synthesizing a catenane, a small organic ring that is threaded onto and can travel around a track-like large ring (Nature 2016, DOI: 10.1038/nature18013). The small ring moves along the track by diffusing between two fixed fumaramide binding sites. Removable blocking groups on the track keep the small ring from moving backward, enforcing its progress as it diffuses in a forward direction.
The chemical fuel is 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) mixed with triethylamine (Et3N). Fmoc-Cl reacts catalytically to form the Fmoc carbonate blocking groups, and Et3N cleaves them. These reactions produce dibenzofulvene, triethylamine hydrochloride, and carbon dioxide as waste materials.
The motor runs very slowly, about 12 hours per turn. “Light-powered synthetic molecular motors are much faster,” Clayden says, “so raising the rate of motion will be a key challenge to overcome.”
Leigh says that, like most first versions, the new molecular motor is hopelessly inefficient. However, “the first motor cars could only go 5 miles per hour,” Leigh says. So you have to start somewhere.”