Supramolecularly engineered nanobiocatalysts application to cofactor independent oxidoreductase biocatalysis in organic solvents

For further advancements in industrial catalysis, enzymes play an important role. Currently, there are numerous examples of industrial biocatalysis. However, when it comes to biocatalysis in organic solvents, cofactor-dependent oxidoreductase enzymes experience implementation difficulties. These enzymes often display reduced stability in organic solvents and their cofactors that are needed in stoichiometric amounts are strictly water soluble. Therefore, the synthesis and application of a novel nanobiocatalyst system for cofactor-independent oxidoreductase catalysis in organic solvents was investigated.
The nanobiocatalyst utilised mesoporous silica nanoparticles as a carrier, of which the mesopores could be exploited as an aqueous reservoir for the cofactor of the enzymes. The mesoporous core particle possessed radial pore channels with large pore size, allowing for a greater volume in which the cofactor could be contained. The inner core was surrounded by a second layer with reduced porosity, serving as a support for the immobilisation of the enzymes while also restricting the immobilisation to the particle’s surface. However, still allowing the diffusion of cofactor from the reservoir to the enzyme. The immobilised enzymes were shielded in a protecting organosilica layer grown at the surface of the nanoparticles with a controlled thickness completely covering the enzymes. The produced nanobiocatalysts were characterised by the means of scanning electron and cryogenic transmission electron microscopy to visualise the structure of the obtained nanobiocatalyst. The catalytic properties of the produced nanobiocatalysts were explored by catalysing the reduction of several relevant substrates in different organic solvents (methyl tert-butyl ether, ethyl acetate, toluene and heptane) with increasing hydrophobicity, in the absence of additional cofactor. The preserved catalytic properties of the nanobiocatalyst provided evidence of effective cofactor recycling, despite the lack of external cofactor. This inspired further implementation of the produced nanobiocatalyst within a continuous flow reactor for the transformation of the hydrophobic ketone benzylacetone to 4-phenyl-2-butanol with self-sustained cofactor recycling.