A biocatalyst with the potential to green up industrial nylon production has been created by scientists in Italy and the UK. 

The nylon monomer adipic acid not only has a precursor derived from carcinogenic benzene, but its formation also requires an oxidation step using nitric acid. This process increases atmospheric nitrous oxide levels, contributing to global warming and ozone depletion.

Now, Gianfranco Gilardi from the University of Turin and colleagues have produced an alternative precursor, cis-cis muconic acid, from catechol, which is greener and cheaper than benzene. The team used their biocatalyst to cleave catechol, giving the muconic acid, which can be simply hydrogenated to give adipic acid. Gilardi explains: 'The availability of a biocatalytic system able to produce [muconic acid] has an important environmental impact for the full process [of nylon production].' 

Gilardi made the biocatalyst by immobilising an enzyme called catechol 1,2-dioxygenase onto nanosponges, which strongly increased the enzyme's stability, a result beyond the team's expectations. Not only does the biocatalyst have increased thermostability and pH tolerance, but it is also more stable to storage than the free enzyme.

The nanosponges consist of cyclodextrins (cyclic cone-shaped oligosaccharides) linked by carbonate groups. 'Cyclodextrins make an interesting immobilisation medium,' says Dean Brady, an expert in biocatalysis and applied enzyme and process biotechnologies from The Council of Scientific and Industrial Research, Biosciences, Modderfontein, South Africa. 'Not only are they enantioselective so may be selective in their binding, allowing for specific orientation of the protein, they can also re-fold denatured protein, which would be an advantage for extended biocatalyst performance.'

Gilardi's team engineered a small scale bioreactor containing their catalyst and they were able to efficiently convert catechol into muconic acid for 70 days. 'The idea now,' says Gilardi, 'is to develop a continuous flow system for the development of an industrial bioreactor.' 

Frances Galvin

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