"Others have said it's the most sophisticated artificial molecular 'machine' to date," Dave Leigh of the University of Edinburgh told nanotechweb.org. "This is the first example of the control of directionality of motion in an interlocked molecule or any synthetic hydrogen-bonded structure."

The motor, which was activated by light, consisted of two small molecular rings moving round one larger ring. One problem with molecular machines is that at temperatures above -273°C the components are constantly moving: controlling this motion is a key part of getting the devices to work. Leigh and colleagues used hydrogen bonds to achieve this.

"We got into this area by chance when, in 1995, we stumbled on a very simple reaction to form catenanes - mechanically interlocked rings - using hydrogen bonds to direct the required molecular threading," said Leigh. "Upon discovering the reaction we looked for ways to exploit it. The possibility of controlling molecular motion using these architectures was very appealing."

The two small molecular rings were held in place in the large ring by hydrogen bonds. To enable the small rings to move, the scientists applied light of specific wavelengths to break each hydrogen bond in turn. The small molecular ring that was fixed in place then blocked the path of the small ring that was free to move, forcing it to travel in one direction round the large ring.

"Applications are probably a few years off yet, since we've yet to work out how to 'wire' the molecular machines to the outside world," added Leigh. "However, the first applications are likely to be to make switchable surfaces - materials that change their properties in response to specific signals - for example, light-switching between dirt-binding and dirt-releasing to make a paint that is cleaned with a flash of light."

Other applications of the motors could include molecular "winches" that wind up polymer chains on demand, causing length or shape-changes, and motors that power the movement of objects across surfaces, possibly along a path drawn with a laser pointer.

Now the researchers, who reported their work in Nature, are trying to assemble more sophisticated and functional molecular machines.