Molecular motors spin slowly but surely

Science News,  Sept 11, 1999  by C. Wu

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Two groups of scientists have built from scratch the first working single-molecule motors: one powered by light and heat and the other by chemical reactions. The synthesized molecules both incorporate ratcheting mechanisms, which allow them to spin--albeit very slowly--in a single direction.

The organic molecule designed by researchers at the University of Groningen in the Netherlands and Tohoku University in Sendai, Japan, rotates via a four-step process. "We irradiate it with ultraviolet light, and one half rotates [180 [degrees]] with respect to the other half," explains Groningen's Ben L. Feringa.

Next, the molecule relaxes into a lower-energy conformation. Feringa and his colleagues then shine UV light on the molecule again, spinning it another 180 [degrees]. Finally, heating it to 60 [degrees] C enables the molecule to readjust and assume its original shape, so the researchers can begin the process again.

The molecule's corkscrew shape allows it to spin in only one direction. To get a motor that rotates in the other direction, Feringa says, the researchers simply constructed its mirror image.

To make their motor, T. Ross Kelly and his colleagues at Boston College in Chestnut Hill, Mass., have taken a different approach. They attached a triptycene molecule, which looks like a three-bladed fan, to a helicene molecule, which acts as a ratcheting mechanism.

By performing a series of chemical reactions, the researchers can cause one of the blades to brush past the ratchet, turning the fan 120 [degrees] . By modifying the chemical structure of all three blades, they hope to create a fan that will spin continuously, Kelly says.

Their molecule may lead to greater understanding of the biological motors that exist in living organisms, such as the ones that power flagella (SN: 2/7/98, p. 86) and cilia, says Kelly. "There's probably a parallel between the way ours works and the way nature's works," he suggests.

The two groups report their findings in the Sept. 9 NATURE.

Will such motors find their way into tiny machines? "The science that has been conceived and carried out by Kelly and Feringa is science at its very best," says J. Fraser Stoddart of the University of California, Los Angeles. "What will become of it? No one knows. That mystery is part and parcel of the excitement of it all."

COPYRIGHT 1999 Science Service, Inc.
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