Biocatalytic Approaches to the Synthetic Manipulation of Silicones

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Living organisms construct a tremendous variety of structures across a wide range of sizes, from bones to cells. Yet, the assembly of such structures ultimately rely on the organisation and production of building blocks that are essentially on the molecular to nanoscopic scale (Angstroms to nanometres). These structures, which are composed from a variety of compounds (proteins, fats, DNA) are synthesised by enzymes. These enzymes, which are the molecular machinery of all living organisms, are particularly interesting since they are able to perform a variety of reactions with high efficiency, giving mainly the desired compound with few unwanted by-products. Furthermore, they function under ambient conditions and do not rely on rare or toxic materials. As a result, many types of enzymes are now utilised in the production of medicines and other high-value chemicals.One area in which enzymes have not been widely studied so far is in the chemistry of organic compounds containing silicon. Such "organosilicon" compounds are mainly used in the form of "silicone", a plastic-like material. These silicones are extremely widely used in all sectors of human activity, from industrial machine parts, lubricants and sealants; to consumer goods such as homeware, cosmetics and paints; as well as in electronic and surgical devices. Indeed, these materials are economically very important, with the global production and use of silicones giving rise to a multi-£billion turnover annually.Unfortunately, current methods of producing silicones rely on chlorine-containing raw materials that are ecologically unfriendly and energy demanding to produce. In contrast, some species of marine sponges use silicon (in the form of glass-like silica) as part of their skeleton. To form this skeleton, the sponges employ a family of enzymes called "silicateins", which are able to react with silica. Recent research by the lead investigator has shown that, remarkably, these enzymes are able to catalyse the formation, as well as degradation, of a range of organosilicon compounds under relatively mild conditions (less than 100 degrees C, using non-toxic starting materials). Thus, these enzymes could potentially offer a sustainable means of producing silicone compounds that would find use in many areas of the chemical industry. Furthermore, the silicateins could also be applied to decompose unwanted silicone waste into compounds that could be recycled, which cannot currently be achieved using conventional chemical methods.Accordingly, the goals of this research are to investigate the feasibility of using silicateins for the efficient and precise synthesis of silicone materials, and develop modified versions of the enzymes that will be able to perform the production of silicones with a variety of chemical structures. The types of silicones that will be targeted include both silicones that are applicable to industrial applications, but also novel types that are otherwise difficult to synthesise by other means. In parallel, the feasibility of using them in the reprocessing and recycling of silicones will also be researched. In all cases, a major part of this research will be to study the chemical mechanisms by which the silicateins are able to perform these reactions. Such an understanding of how these enzymes function will therefore allow us to make modifications to improve their capabilities.