Silicon-carbon compounds are useful in the modern world. In fact, you are probably much closer to one than you think, as they can be found in TV and computer screens, are used in coating and paint manufacturing, as well as semi-conductors, and agricultural chemical products . Which is surprising, considering that nature does not naturally bond silicon and carbon together, it must be synthetically manufactured.
Or at least until now, for scientists at the California Institute of Technology in Pasadena have discovered a way to make organic silicon-carbon compounds that they claim are more environmentally friendly to produce, and have the potential to be a lot cheaper.
Jennifer Kan, a postdoctoral scholar in Arnold’s lab and lead author of the new study, explained, “Even though silicon is so abundant, all around us, in rocks and all over the beach, no living organism is known to put silicon-carbon bonds together.”
“So, we decided to get nature to do what only chemists could do — only better,” adds Frances Arnold, Caltech’s Dick and Barbara Dickinson Professor of Chemical Engineering, Bioengineering and Biochemistry, and principal investigator of the new research.
They did this by finding a suitable bacterium which they could modify into doing what nature has apparently not thought of doing.
The scientific journal Nature described the discovery as follows; “By scouring protein databases, Arnold and her colleagues found a few dozen promising enzymes. After some screening, they settled on one from an extremophile bacterium that lives in Icelandic underwater hot springs, called Rhodothermus marinus. They synthesized the gene for this protein and inserted it into E. coli bacteria.”
To their delight, they found that the enzyme could catalyse silicon-carbon bonding, if “fed the right silicon-containing precursors”. This happened even though in nature the enzyme would not normally do this, as bacteria don’t naturally produce silicon-containing compounds.
However, the newly formed enzyme was not very efficient at making the compounds, so, “the team introduced mutations into the active region of the enzyme and selected the bacteria that showed an improvement.” They then studied each new generation of the bacterium to fine tune the process, noting that each generation had improved silicon-carbon compound producing efficiency.
“It’s like breeding a racehorse,” says Arnold, “A good breeder recognizes the inherent ability of a horse to become a racer and has to bring that out in successive generations. We just do it with proteins.”
And, as the scientific journal ScienceDaily reports, “After only three rounds, they had created an enzyme that can selectively make silicon-carbon bonds 15 times more efficiently than the best catalyst invented by chemists. Furthermore, the enzyme is highly selective, which means that it makes fewer unwanted byproducts that have to be chemically separated out.”
The researchers have published their results in the journal Science, where they claim that, “This iron-based, genetically encoded catalyst is nontoxic, cheaper, and easier to modify compared to other catalysts used in chemical synthesis.” Better still, says Jennifer Kan, also part of the team at CalTech, “The new reaction can also be done at room temperature and in water.”
Whilst it is too early for coating manufacturers, and the agrichemical industry to apply this technology in chemical production, the possibility of a greener, cheaper and more efficient way of producing silicon-carbon compounds could have major repercussions in the future. In fact, maybe the chemical industry as a whole should start to think about what synthetically produced compounds could be made better or cheaper if the process was organic.
Is it time for the chemical industry to think less synthetic and more organic?