Polyvinylpyrrolidone-assisted in situ enzymes encapsulation within ZIF-8 for enhanced glycerol conversion

The growth of biodiesel and oleochemical industries results in substantial surpluses of glycerol and consistently low prices. To absorb this surplus, we report a polymer-assisted in situ enzymes encapsulation strategy in which glycerol dehydrogenase (GDH) is encapsulated with polyvinylpyrrolidone (PVP) and cysteine (Cys) within ZIF-8 for glycerol conversion. The results showed that the encapsulated GDH/ZIF-8 composites presented stronger substrate affinities and higher catalytic efficiencies than free GDH as well as good stability. Among the free GDH and GDH/ZIF-8 composites, GDH/Cys/PVP@ZIF-8 presented the highest relative activity of 300.7 %. This could be attributed to the structural evolution of the encapsulated GDH and the formation of a more hydrophilic microenvironment around GDH during complexation with PVP. To increase cofactor utilization, a cofactor self-sufficient cascade system was constructed by encapsulating GDH and forming H₂O NADH oxidase (Nox) with PVP and Cys within ZIF-8 for the conversion of glycerol to 1,3-dihydroxyacetone (DHA). At the optimal GDH:Nox molar ratio (4:1) and a substrate concentration of 100 mM, the DHA yield reached approximately 4.2 mM in GDH-Nox/Cys/PVP@ZIF-8, and the total turnover number of GDH-Nox/Cys/PVP@ZIF-8 reached 2787 at 0.05 µM NAD⁺, indicating its feasibility for large-scale DHA production. This work has thus provided a promising procedure of co-immobilizing enzymes via Cys/PVP-assisted in situ encapsulation within ZIF-8 for the development of economically viable multienzyme biocatalysts for glycerol conversion.