A MOLECULE that can be made to twist from one shape to another could become a powerful motor for use in future nanomachines. Unlike previous molecular motors based on biomolecules, which needed the biochemical fuel adenosine triphosphate (ATP) to function (快猫短视频, 12 August 2000, p 14), the new molecular motor can be driven by light or electricity, potentially leading to much simpler nanomachines.
The new molecule is of a type known as a metallacarborane. It consists of a nickel atom attached to carborane structures, each consisting of a pair of carbon atoms and several hydrogen and boron atoms, which sit either side of the nickel atom like two birdcages.
The molecule begins in an untwisted state, with an overall neutral charge. In this state, the molecule is most stable in what is called a cis arrangement, in which the pairs of carbon atoms in the two cages are on the same side of the molecule.
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When the nickel atom accepts an electron from a reducing agent, the molecule is most stable in a 鈥渢rans鈥� state, in which the pairs of carbon atoms are on almost opposite sides of the molecule. To reach this state the molecule twists by 140掳. When an electron is removed, the molecule untwists.
Something similar happens when light of a particular wavelength strikes the nickel atom. The result is that an electron is kicked into a higher energy state, causing the molecule to twist to the trans state.
Applications could range from simple on/off switches and valves to molecular memory chips in which motor positions represent digital 0s and 1s, says Frederick Hawthorne at the University of California at Los Angeles, whose group synthesised the new molecule (Science, vol 303, p 1849). The researchers suggest that anchoring a large hydrocarbon molecule to the carborane would turn the molecule into a nanoscale shutter that could be used to give access to a small area covered with a chemical catalyst. This could give precise control of a chemical reaction, they say.
