Molecule makes electric motor

By Eric Smalley, Technology Research News

One difficulty in making machines at the scale of molecules is finding motors small enough to power them. Several research teams have come up with molecules that spin on command, but the question is how to harness that motion.

Researchers from the University of California at Los Angeles and the Hebrew University of Jerusalem in Israel have brought molecular motors a significant step forward with a prototype that rotates nearly half way around and can be switched from one direction to the other.

The motor can be powered by electricity or light. It promises to enable molecular machines capable of modifying surfaces, controlling valves and switching mechanisms on and off.

The molecule contains a pair of rings made from carbon, boron and hydrogen atoms that rotate 144 degrees in opposite directions around a single nickel atom when the nickel atom absorbs light or electricity. "We have synthesized a rotary motor... activated by the reversible one-electron oxidation/reduction of a nickel atom, which serves as an axle," said M. Frederick Hawthorne, a professor of chemistry at the University of California at Los Angeles.

An oxidation/reduction, or redox, reaction changes the structure of the molecule by adding or removing an electron. Oxidation removes electrons and reduction adds electrons. The direction of the motor's rotation depends on the direction of the flow of electrons during the reaction, which, in turn, depends on the number of electrons associated with the nickel atom.

The redox reactions can be powered by chemical reactants that donate or accept electrons, by molecules that donate an electron to the motor when they absorb photons, or by electrical current, said Hawthorne.

The reaction causes the carbon-boron-hydrogen rings to rotate around the nickel atom relative to each other. By fixing one ring to a surface and the other to an object, the molecule could be used to rotate the object relative to the surface.

The researchers' motor has an advantage over existing designs that have components that spin around a metal axis, said Hawthorne. In those designs, the spin-rate is determined and controlled by changing the oxidation states of the metal center. But it's not clear how the spinning parts of the molecules can be attached to objects are surfaces in order to perform useful tasks, he said. In contrast, the researchers' prototype rotates only part of the way around, and this limited motion can accommodate nanostructures like valves.

The motor can be bonded to tiny structures to power nanodevices, said Hawthorne. "The rotary motor we described may, upon command, modify solid surfaces, open and close nanovalves and nanopores in porous solids, block and unblock the active site of a catalyst or biomolecule, [or] function as an electromechanical or photomechanical switch," he said.

The researchers are working on finding different ways to use motor molecules that are bonded to solid surfaces, Hawthorne said.

Hawthorne's research colleagues were Jeffrey I. Zinc, Johnny M. Skelton, Michael J. Beyer, Chris Liu, Esther Livshits, Roi Baer, and Daniel Neuhauser. The work appeared in the March 19, 2004 issue of Science. The research was funded by the National Science Foundation (NSF).

Timeline:   Unknown
Funding:   Government
TRN Categories:  Nanotechnology; Chemistry
Story Type:   News
Related Elements:  Technical paper, "Electrical or for Control of the Rotary Motion of a Metallacarborane," Science, March 19, 2004


April 21/28, 2004

Page One

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Molecule makes electric motor

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Tiny rotors spin into place
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