Scientists at the California Institute of Technology have for the first time been able to use living organisms to create silicon-carbon bonds, a finding that could impact a number of industries which use silicon in their products, from paints and pharmaceuticals to semiconductors and TV screens.
An abundant element in nature, silicon is the eighth most common element in the universe by mass and the second most common found in the Earth’s crust after oxygen. Silicon dioxide or silica is a major component to most sands, of course, and in its compound form is used to create ceramics, concretes and glasses.
Yet, for all its abundance, silicon does not naturally bond with carbon and thus has remained at a distance from organic life (on Earth, at least – many a sci-fi tale has been written about silicon-based life forms traipsing about the cosmos). And thus, up to this point, chemists have had to synthetically force silicon to bond with carbon in the lab in order to create “organosilicons”, used today in a wide variety of materials and products, including sealants, caulking, surfactants, paints, drugs, computers and TV screens.
Normally, the synthesizing of organosilicons requires the use of expensive trace metals and toxic processes. Thus, it’s big news when a new way to bond silicon and carbon is devised, especially when the new process doesn’t involve pricey catalysts yet is decidedly organic. “No living organism is known to put silicon-carbon bonds together, even though silicon is so abundant, all around us, in rocks and all over the beach,” says Jennifer Kan, a postdoctoral scholar at Cal Tech’s Division of Chemistry and Chemical Engineering and lead author of the new study. “This iron-based, genetically encoded catalyst is nontoxic, cheaper, and easier to modify compared to other catalysts used in chemical synthesis,” says Kan.
The organic catalyst used by the research team is an enzyme called cytochrome c, taken from a bacterium that can be found in the geothermal hot springs of Iceland. The research team was able to selectively mutate the gene coding for that protein allowing it to serve as the catalyst for the silicon-carbon bond. Remarkably, the refurbished enzyme works 15 times more efficiently than the artificial catalysts now in use.
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“We decided to get nature to do what only chemists could do, only better,’ said Frances Arnold, principal investigator on the study, which is published in the journal Science. “It’s remarkable that nature is poised to do all sorts of wild things in the presence of this new manmade food,” Arnold says.
Researchers are constantly on the lookout for new catalysts to support the chemical processes central to much of today’s industry, with current searches often directed at building cheaper catalysts out of more “Earth-abundant” elements like iron, nickel and copper. Work by chemist Audrey Moores at McGill University in Montreal, for example, focuses on replacing heavy metal ion catalysts used in the pharmaceutical, cosmetics and food industries with much safer iron-based catalysts. A 2014 study by Moores showed that magnetic iron oxide nanoparticles can be used to create benzaldehyde, a commonly used additive in artificial flavourings, through the reaction of styrene and oxygen