"We have a proof of principle of a rotary motor driven by chemical energy," researcher Ben Feringa told nanotechweb.org, "i.e. a sequence of chemical reactions induces a 360° unidirectional rotation for the first time, as far as we know, in a fully artificial system. Despite the fact that it is an extremely primitive system and far from any biological motor, these findings tell us that ultimately we will be able to build a useful chemically powered rotary motor."

The motor basically consists of a phenyl rotor that rotates about a single carbon-carbon bond axle relative to a naphthyl stator. The researchers say the rotation is driven by a combination of chemical reactions and random thermal motion.

The molecular rotor turns through four structurally distinct stations, driven by a different chemical reaction each time. The first and third steps of the rotation involve bond-breaking, while the second and fourth steps involve bond creation. The chemical events are highly selective for a specific direction; each step drives rotation by about 90°.

While the molecule is in the configuration of the first and third station, additional chemical bonds restrict the rotor's position. This prevents random thermal motion from causing the rotor to move back the way it came. In the second and fourth station, nonbonding interactions mean that the rotor and stator cannot pass each other.

"A very delicate balance of chemical and stereochemical events is required," said Feringa. "Some elegant stereochemical studies by the Brinkmann group on biaryl ring opening were very important. In combination with a so-called Corey asymmetric reduction and careful functional group manipulation we were able to demonstrate the principle."

The team says the combination of reactions, purifications and the timescale involved make the motor less practical than light-driven synthetic motors. The reaction time for one complete rotation of the motor was roughly 128 hours. But the research does establish that the technique is possible.

"We will have to redesign the motor and the chemistry," said Feringa. "It is currently way too complex to be used for any application. But with the principles in hand and a few years of effort we might get somewhere. Ultimately we will be able to power, move or transport something."

According to Feringa, the next step is to reduce the number of chemical conversions needed and speed up the whole process. "That might need new chemistry and molecular architectures to be developed," he said. "I am sure others will be stimulated to come up with completely different and elegant designs."

The researchers reported their work in Science.