Molecule makes electric motor
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
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).
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
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