(572b) Boosting the Multienzymatic Conversion of CO2 through Spatially Separated Immobilization Strategy

Multienzymatic catalysis is considered to be the next generation of biocatalysis. As a central part, rational design and construction of multeinzyme systems have attracted great attention and become a hot research topic nowadays. When designing an efficient multienzyme system, three crucial issues should be taken into consideration: 1) synergistic catalysis among multienzymes; 2) efficient mass transfer of substrates and products; and 3) easy recyclability of multienyzmes. Inspired by the existence form and synergistic catalytic behavior of multienzymes in organisms, we put forward to the strategy of constructing spatially isolated multienzyme systems. In our recent study, a series of spatially isolated multienzyme systems (containing formate dehydrogenase and formaldehyde dehydrogenase) enabled by nanospheres/microcapsules are constructed by combining biomimetic mineralization with other biomimetic platform techniques (e.g., biomimetic adhesion, Pickering emulsion, surface segregation and layer-by-layer (LbL) self-assembly). When utilized for the conversion of CO₂, these systems exhibit desirable catalytic performance and easy recyclability.

Firstly, a spatially isolated multienzyme system enabled by active nanospheres was successfully constructed through the synergy between biomimetic mineralization and biomimetic adhesion, achieving the efficient process intensification. The first enzyme (formate dehydrogenase) was entrapped accompanying the formation of nanospheres through biomimetic titanification. After in situ surface functionalization of nanospheres with oligodopa, the second enzyme (formaldehyde dehydrogenase) was immobilized on the surface of active nanospheres through amine-catechol adduct reaction. When utilized for the conversion of CO₂, the as-constructed multienzyme system exhibited a formaldehyde yield of higher than 60.0%. Besides, after evaluating the performance of different-sized multienzyme systems, it was found that smaller sized multienzyme system possessed higher enzymatic activity but lower recyclability.

Secondly, a spatially isolated multienzyme system enabled by nanosphere-stabilized capsules (NSSCs) was constructed through the synergy of biomimetic mineralization and Pickering emulsion, achieving the efficient process intensification. The first enzyme-containing nanospheres were monodispersely spread on the surface of oil droplets through Pickeirng emulsion, maintaining their structural characteristics and integrity. Then, the gel titania, that was produced through sol-gel process of tetrabutyl titanate, was in charge of crosslinking the nanospheres, forming a stable and continuous capsule wall. The second enzyme was immobilized on the surface of capsule wall through amine-catechol adduct reaction between oligodopa and enzyme. During the construction process, the released butanol as a result of the sol-gel process of butyl titanate could be adsorbed on the surface of nanospheres, further inducing the self-assembly of the nanospheres at the oil/water interface. This process played key role on the formation of Pickering emulsions. When utilized for the conversion of CO₂, the as-constructed multienzyme system acquired a formaldehyde yield of higher than 50.0%. Meanwhile, the lower density of the oil core than that of water endowed the multienzyme system with excellent recyclability, especially the formaldehyde yield kept almost unaltered after 10 times recycling.

Thirdly, a spatially isolated multienzyme system enabled by mesoporous hybrid microcapsules was constructed through the synergy of biomimetic mineralization and surface segregation, achieving the efficient process intensification. The first enzyme was entrapped accompanying the formation of the PAH-segregated CaCO₃ template. Then, the PAH polymeric network was formed through crosslinking between GA and PAH. Afterwards, this polymeric network was utilized for implementing biomimetic mineralization with in situ entrapping the second enzyme. After removing the template, a spatially isolated multienzyme system was acquired. During the construction process, the CaCO₃ microsphere served as the dual templates for formation of both capsule lumen and mesopores on the capsule wall, whereas PAH played the following two crucial roles: (1) forming the bulk polymer network to render confined space for biomimetic mineralization and (2) triggering the mineralization of Ti-BALDH to produce titania nanoparticles. When utilized for the conversion of CO₂, the as-constructed multienzyme system exhibited a formaldehyde yield of higher than 70.0%. Meanwhile, the reaction rate was nearly two times higher than the average level. And no catalytic activity was lost after 10 times recycling. Besides, the mesoporous hybrid microcapsules can be utilized in various other applications and exhibited desired performance.

Fourthly, a spatially isolated multienzyme system enabled by mitochondria-like microcapsules was constructed through the synergy of biomimetic mineralization and LbL self-assembly, achieving the efficient process intensification. Inspired by the double membrane structure of mitochondria, we proposed to utilize process and structure biomimicism strategy instead of just process biomimicism strategy for constructing multienzyme systems. The first enzyme was entrapped accompanying the formation of the PSS-doped CaCO₃ template. The organic inner membrane was acquired via LbL self-assembly of oppositely charged polymers/proteins on the template. The silica template layer was then formed onto the inner membrane through biomimetic silicification with in situ entrapping the second enzyme, while the organic-inorganic hybrid outer membrane was acquired via biomimetic titanification subsequently. After removing the CaCO₃ template and the silica template, a spatially isolated multienzyme system was established. When utilized for the conversion of CO₂, the as-constructed multienzyme system exhibited a formaldehyde yield of higher than 82.0%, with a formaldehyde selectivity of 90.0%. Meanwhile, 70.0% of the initial activity was retained after 10 times recycling.

By using of a series of cases as the evidences, it can be conjectured the spatially separated immobilization strategy can boost the multienzymatic conversion of CO2. This study will shed light on the new strategies for the design and preparation of multicomponent catalysts.