CHAMPAIGN, Ill. Evidence of a carbon-silicon compound found in a living colony of diatoms could lead to a variety of beneficial applications, from low-cost synthesis of high-performance materials to therapeutic treatments for osteoporosis.
Silicon forms the backbone of the semiconductor industry and is essential for many plants and animals.
Silicon deprivation causes reduced yield in plants and abnormal bone growth in animals. But how carbon-based life forms interact with the inorganic world of silicon is largely unknown. Although silicon is the second most abundant element in Earths crust, not a single carbon-silicon compound has been identified in a living organism.
Now, however, the first evidence of such a compound has been reported. Christopher Knight, a research scientist at the University of Illinois; Stephen Kinrade, chair of the chemistry department at Lakehead University in Thunder Bay, Canada; and Ashley Gillson, an undergraduate student at Lakehead, observed a carbon-silicon compound in living freshwater diatoms. The scientists reported their findings in the Jan. 3 Advance Articles edition of Dalton Transactions, the journal of the Royal Society of Chemistry (www.rsc.org/dalton).
A form of algae, diatoms are single-celled aquatic plants found by the billions in lakes and oceans. “Each cell possesses a beautiful, delicate and precisely engineered shell of pure silica,” Knight said. “One of natures enduring mysteries is how diatoms and other plants actually build these unique silicate structures.”
Diatoms must isolate silicon from water, transport it across the cell membrane and then deposit it as a solid, Knight said. “To do this in the laboratory requires high temperatures, high pressures or extreme pH levels, but diatoms somehow manage under normal physiological conditions.”
The researchers used a technique called nuclear magnetic resonance spectroscopy to detect the compound in a colony of diatoms that were fed isotopically labeled silicon. “This signal is the first direct evidence of a carbon-silicon compound formed during the life cycle of an organism,” Kinrade said.
To metabolize silicon, plants and animals must draw the material into their cells through some kind of interaction with organic (carbon-based) chemicals. “Certain bio-sugars, for example, have a very high affinity for silicon,” Knight said. “These sugars can wrap themselves around the silicon and bump up the coordination number from four to five or even six.”
Although the full chemical structure of the observed compound remains unclear, it does not contain the normal four-coordinate silicon typically found in nature, Kinrade said. “Our results show that the silicon in the compound is six-coordinated, and possibly also bound to nitrogen.”
The observation of a carbon-silicon compound in a living system may open the door to understanding the molecular processes controlling biosilicification the way in which plants and animals build structures using silicon.
“This is important since it promises to provide low-temperature, low-cost synthetic routes for the production of high-performance materials based on silicon nanostructures,” Knight said. “Understanding biologically controlled assembly processes could allow us to design and build structures on a molecular scale.” Moreover, according to Kinrade, “Silicon has been shown to stimulate bone growth, so determining how it is metabolized may help in developing treatments for osteoporosis.”
The work was supported by the National Institutes of Health and the Natural Sciences and Engineering Research Council of Canada.
