Ohio University physicists have used a simple molecule of chlorophyll taken from spinach to develop a complex nanobiological switch. They used a scanning tunneling microscope (STM) to image chlorophyll-a and then injected it with a single electron to manipulate the molecule into four positions. The researchers say this biological switch might be used in future applications for green energy, technology and medicine. But read more...
Let's start with some images obtained by Saw-Wai Hla, an associate professor of physics at Ohio University, and his research group.
 On the right you can see images taken with a scanning tunneling microscope showing the four-step molecular conformation switching of chlorophyll-a (Credit: Ohio University). From top to bottom, you can see: (1) a straight-tail conformation; (2) a bent-tail conformation obtained by changing the tail angle at A; (3) another conformation obtained by a 60° bending at B; (4) and a new conformation obtained by a further 60° bent at A.
Here are some brief explanations provided by Ohio University.
The scientists used a scanning tunneling microscope to image chlorophyll-a and then injected it with a single electron to manipulate the molecule into four positions, ranging from straight to curved, at varying speeds.
Though the Ohio University team and others have created two-step molecule switches using scanning tunneling microscope manipulation in the past, the new experiment yields a more complex multi-step switch on the largest organic molecule to date.
This research work has been published by the Proceedings of the National Academy of Sciences under the title "Realization of a four-step molecular switch in scanning tunneling microscope manipulation of single chlorophyll-a molecules" (Volume 103, Pages 13718-13721, September 5, 2006). Here is an excerpt from the abstract -- for those of you who are familiar with this branch of science.
By injecting tunneling electrons from the scanning tunneling microscope tip, we are able to bend the phytyl-chain, which enables the switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunneling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.
Here are two links to the abstract and to the full paper (PDF format, 4 pages, 1.13 MB) from which the above image has been extracted.
In this paper, the researchers add that "because of their nontoxic nature and their abundance in the natural world, plant molecules like chlorophyll-a are given special interest in the quest for green energy resources and for the development of environment-friendly nanoscale devices.
So they think their spinach-based biological switch might have important applications in solar cells and medical devices.
Sources: Andrea Gibson, Ohio University news release, via EurekAlert!, September 5, 2006; and various web sites
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