Silicon and carbon are both abundant elements on Earth, but the existence of silicon-carbon bonds has never been found in nature. For the first time, scientists at the California Institute of Technology have designed an enzyme that can break the strong artificial bond between silicon and carbon. This bond is found in widely used siloxane or silicone chemicals that may remain in the environment. The results are expected to enable the biodegradation of chemicals such as siloxanes, and the related paper is published in the journal Science.

Directed evolution is a method of modifying enzymes and other proteins using the principle of artificial selection. In the new study, the research team used directed evolution to culture a bacterial enzyme called cytochrome P450. The researchers mutated the DNA of cytochrome P450 and tested the new variant enzyme. The best-performing enzyme then mutates again, and the test is repeated until the enzyme is active enough for the researchers to identify the reaction product and study the enzyme's mechanism of action. The resulting improved enzyme does not directly crack the silicon-carbon bond, but instead oxidizes the methyl group in the siloxane in two successive steps. This means that two carbon-hydrogen bonds are replaced by carbon-oxygen bonds, a change that makes the silicon-carbon bond more likely to break.

Siloxane chemicals are found in a variety of products, including those used in home cleaning, personal care, and automotive, construction, electronics, and aerospace products. Of all the bonds in siloxanes, the decomposition of the silicon-carbon bond is the slowest. While it may be a decade or more before the engineered enzyme reaches real-world applications, its development opens up the possibility that siloxanes could be biodegraded, the researchers said.