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YOU won’t find it powering a Formula 1 racing car, but it’s still a world
first: a motor consisting of a single molecule that’s been designed from
scratch. Almost all life depends on nature’s molecular motors—components
in cells that turn chemical energy into physical movement to help transport
substances around the cell. But Ross Kelly and his colleagues at the Eugene F.
Merkert Chemistry Center at Boston College, Massachusetts, have invented an
artificial molecular motor.

Their invention is a rotor that turns on a stator—the static part of
the device—just like an electric motor. These two components are linked by
a chemical bond between two carbon atoms. While the stator, called a helicene,
stays still, the rotor spins for one-third of a revolution about its “axle”.

Kelly’s rotor is a three-bladed paddle, with each hexagon-shaped blade
separated from the next by one-third of a revolution. Energy from phosgene,
better known as a chemical warfare gas, drives the rotor. To do this, a tiny
amount of phosgene alters a chemical group
(marked A on the diagram) on the
rotor. The altered grouping reacts with a second group (B) on the stator,
turning the rotor clockwise through about 60°. Heat absorbed from the
environment takes the rotor a further 60°. There it stops, although adding a
reagent restores A and B to their original form.

Kelly admits that the motor is unlikely to find a use. “It’s so much smaller
than anything you might want to move,” he says. “But figuring out how a
molecular motor works, from scratch, may help biologists work out how nature’s
motors work,” he adds.