Synthetic and Mechanistic Studies into Enzymatic Degradation of Waste Plastics

Plastics are a broad range of solid polymeric materials that have found widespread application as industrial components and consumer goods. However, there has been a steady accumulation of discarded plastics throughout the world, and there is now growing awareness that they present a significant hazard to the natural environment and human health. In relation to these concerns, there is increasing emphasis on the recovery (and subsequent reuse) of plastic materials, or their conversion into other materials than can serve as feedstocks for new products.

Some enzymes that catalyse oxidations in the decomposition of biomass are known to convert compounds that are usually resistant to other types of chemical reactions; and have therefore been proposed to be able to decompose plastics. This project will aim to investigate the application of a range of oxidative enzymes for the degradation of plastics that contain chemically unreactive C-C, C-H and C-O chemical bonds, for which there are currently no viable reprocessing methods.

Thus, the research will involve the chemical synthesis of small molecule models of the plastics, heterologous production of the enzymes, testing of the enzymes with the model molecules and mechanistic studies of the enzymatic reactions by a range of analytical methods (spectroscopic, electrochemical and chromatographic). By using small model molecules, it is intended that detailed chemical reactivity information can be gathered, which will enable a more rational approach to the subsequent reengineering of any promising enzyme candidates for this application. Subsidiary research objectives include investigations of the physicochemical properties of candidate enzymes that are relevant for the processing of plastic materials, such as identifying the tolerance of enzymes towards organic solvents, and their thermostability.

The application of oxidative enzymes for this purpose is currently poorly explored and has largely been conducted in a piecemeal manner, resulting in empirical observations that are difficult to rationalize (and therefore to further exploit). This research will aim to fill this knowledge gap. From a strategic perspective, the EPSRC's most recent International Review of Chemistry (IRC) highlighted the UK's chemical biology as world-leading, and it is classified as a "grow" area of the EPSRC portfolio. This research will consolidate the UK's position in this area. Furthermore, the developments here will underpin activities in synthetic biology, which is amongst the UK Government's "Eight Great Technologies". Indeed, this work is particularly timely since synthetic biology is now at the cusp of transitioning from fundamental research to tangible applications with
wider impact.