Biocatalytic degradation of poly(lactic acid) to monomers using a chemically modified lipase in ionic liquids Susana M. Meza Huaman, Jake H. Nicholson, Alex P. S. Brogan King's College London, UK The demand for plastics has increased every year since they were first introduced, with global plastic production exceeding 300 metric tons in 2015, and is expected to double in 20 years.Unfortunately, and despite the clear hazard to living systems caused by accumulation in the environment, less than 50% of plastic waste is currently recycled in the UK, with the rest sent to landfills or incinerated.There is therefore a clear necessity to design new methods to recycle plastics to reduce their unfavourable environmental impact. An attractive solution to enable a circular economy of plastics is to degrade them to monomers either for further production of plastics or as a precursor for fine chemicals.One possible solution to generating a more sustainable circular economy is presented through the use of enzymes to break down plastics to monomers. However, employing enzymes for biocatalysis is currently limited by their low stability at the high temperatures and non-aqueous solvents required for efficient degradation of plastics. Ionic liquids are promising solvents for many industrial processes due to their ability to solubilise polymers such as cellulose and poly(lactic acid) (PLA), presenting an alternative option to organic solvents.Enzymes are not naturally stable in ionic liquids due to their tendency to denature in the absence of water. However, Brogan et al. (2018) showed that chemically modified glucosidase was soluble and stable in ionic liquids and was able to release sugars from cellulose at high temperatures. Here, we will present a study on the biocatalytic degradation of PLA by chemically modified lipase B from Candida antarctica (CalB) in ionic liquids. Using circular dichroism (CD) and Ultraviolet-visible spectroscopy (UV-Vis), we will present the biophysical characterisation of the chemically modified CalB to show the conservation of its secondary structure and activity, and the high thermostability acquired after said modifications. Additionally, synchrotron radiation circular dichroism (SRCD) will show enhanced thermostability of the modified enzyme in different ionic liquids. The half-denaturation temperature (T m ) of chemically modified CalB is 70 ºC in water and over 80 ºC in ionic liquids, higher than the T m of native CalB (60 ºC). Finally, the advantages of using the modified CalB in ionic liquids for the catalysis of PLA and the production of lactic acid will be presented. The results show that the modified CalB in ionic liqud improved the catalysis of both the degradation of PLA and the production of lactic acid by up to 20%.
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