Making silicon naturally: Chemists glimpse organic substance in plankton

9:54am, January 23, 2002
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For the first time, signs of a compound composed of both carbon and silicon have been found within a living organism. Besides its biological novelty, the find could open new routes for making silicon-based materials, according to researchers who report discovering the substance in diatoms, a type of plankton.

The diatoms' ability to pull silicon-containing chemicals from water and use them to build microscopic shells of pure silica has long tantalized researchers.

Some scientists have suspected that to pull off this feat of ceramic engineering, diatoms must make a carbon-silicon compound during the process.

In an upcoming issue of the British journal Dalton Transactions, Christopher T.G. Knight of the University of Illinois at Urbana–Champaign

and his colleagues at Lakehead University in Thunder Bay, Ontario, report what they say is the first solid indication of a so-called organosilicon compound in an organism.

To capture a glimpse of the short-lived compound, which survives for no more than a few hours, the researchers first deprived Navicula pelliculosa diatoms of silicon. Without the element, the diatoms can't make their shells.

Next, the researchers fed the diatoms an isotope of silicon that a nuclear magnetic resonance (NMR) instrument can detect. Then, they placed the live diatoms within the instrument to determine what compounds the diatoms produced while making their shells.

About 6 hours after receiving the silicon, the diatoms produced a silicon-carbon compound that the researchers detected as a characteristic peak in the NMR spectrum. The scientists identified the small but telling signal because it matched one produced by synthetic organosilicon compounds they had made previously.

In laboratories, researchers need extreme conditions such as high temperatures and pressures to extract silicon compounds from water and transform those into solid silica. Understanding how diatoms do it could lead to less expensive routes for making silicon-based materials, says Knight.

Silicon is an important nutrient for many plants, so the new research might also eventually help researchers combat silicon depletion in crops, a problem in some parts of the world, says Knight. Silicon can also stimulate bone growth, so the work could lead to new treatments for osteoporosis, he adds.

"The potential . . . is profound," comments Daniel Morse of the University of California, Santa Barbara. However, Knight and his coworkers haven't yet determined the compound's exact structure, Morse notes. Moreover, the NMR signal indicating an organosilicon compound is weak, he says.

Despite these caveats, Morse adds, the work "is suggestive" that organosilicon compounds are made by organisms.

Although Knight concedes that the NMR signal for the new compound isn't strong, "we have no doubt about it," he says. One reason for his confidence is that the characteristic signal always appeared 6 hours after the researchers gave silicon to starved diatoms. Further, Knight notes, his team has reproduced the experiment on multiple NMR instruments and with several diatom colonies.

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