Bioinspired Approach to Multienzyme Cascade System Construction for Efficient Carbon Dioxide Reduction

Modularization of Immobilized Multienzyme Cascades for Continuous-Flow Enantioselective C-H Amination

Multienzyme cascades (MECs) have gained much attention in synthetic chemistry but remain far from being a reliable synthetic tool. Here we report a four-enzyme cascade comprising a cofactor-independent and a cofactor self-sustaining bienzymatic modules for the enantioselective benzylic C-H amination of arylalkanes, a challenging transformation from bulk chemicals to high value-added chiral amines. The two modules were subsequently optimized by enzyme co-immobilization with microenvironmental tuning, and finally integrated in a gas-liquid segmented flow system, resulting in simultaneous improvements in enzyme performance, mass transfer, system compatibility, and productivity. The flow system enabled continuous C-H amination of arylalkanes (up to 100 mM) utilizing the sole cofactor NADH (0.5 mM) in >90 % conversion, achieving a high space-time yield (STY) of 3.6 g ⋅ L-1 ⋅ h-1, which is a 90-fold increase over the highest value previously reported.

Glycine modified copper promotes CO2 electroreduction to multi-carbon products: a computational study

Molecular modification strategy exhibits great potential for electrocatalytic CO2 reduction. Here, DFT calculations were applied to study the mechanism of CO2 electroreduction on glycine modified copper. The results indicate that the interaction between the modified molecule and the intermediate could change the reaction energy of CO2 electroreduction.

Light-Driven CO2 Reduction with a Surface-Displayed Enzyme Cascade-C3N4 Hybrid

Efficient and cost-effective conversion of CO2 to biomass holds the potential to address the climate crisis. Light-driven CO2 conversion can be realized by combining inorganic semiconductors with enzymes or cells. However, designing enzyme cascades for converting CO2 to multicarbon compounds is challenging, and inorganic semiconductors often possess cytotoxicity. Therefore, there is a critical need for a straightforward semiconductor biohybrid system for CO2 conversion. Here, we used a visible-light-responsive and biocompatible C3N4 porous nanosheet, decorated with formate dehydrogenase, formaldehyde dehydrogenase, and alcohol dehydrogenase to establish an enzyme-photocoupled catalytic system, which showed a remarkable CO2-to-methanol conversion efficiency with an apparent quantum efficiency of 2.48% in the absence of externally added electron mediator. To further enable the in situ transformation of methanol into biomass, the enzymes were displayed on the surface of Komagataella phaffii, which was further coupled with C3N4 to create an organic semiconductor-enzyme-cell hybrid system. Methanol was produced through enzyme-photocoupled CO2 reduction, achieving a rate of 4.07 mg/(L·h), comparable with reported rates from photocatalytic systems employing mediators or photoelectrochemical cells. The produced methanol can subsequently be transported into the cell and converted into biomass. This work presents a sustainable, environmentally friendly, and cost-effective enzyme-photocoupled biocatalytic system for efficient solar-driven conversion of CO2 within a microbial cell.

Construction of co-immobilized multienzyme systems using DNA-directed immobilization technology and multifunctionalized nanoparticles

The multienzyme co-immobilization systems with high cascade catalytic efficiency and selectivity have attracted considerable attention. In this study, through DNA-directed immobilization (DDI) technology, two model enzymes, glucose oxidase (GOD) and horseradish peroxide (HRP) were co-immobilized on the multifunctional silica nanoparticles (DDI enzyme). In addition to the directional distribution promoted by DNA complementary chains, the multienzyme system allowed the control of the stoichiometric ratio of the enzymes by adjusting the ratio of amino/carboxyl groups. The optimal mole ratio of GOD/HRP was 1:2, while the protein loading amount could reach 8.06 mg·g-1. Compared with the conventional direct adsorption, the catalytic activity of the DDI enzyme was 2.49 times higher. Moreover, with the enhancement of thermal and mechanical stability, the DDI enzyme could still retain at least 50% of its initial activity after 12 cycles. Accompanied by an excellent response and good selectivity, the constructed multienzyme systems simultaneously showed the potential as a glucose detector. Therefore, based on the DDI technology, the highly efficient multienzyme co-immobilization system could be further extended for a wider range of research fields.

Construction of a biomimetic core-shell PDA@Lac bioreactor from intracellular laccase as a nano-confined biocatalyst for decolorization

Enzymes immobilized on the surface of the carriers are difficult to maintain their conformation and high activity due to the influence of the external harsh environments. A biomimetic core-shell PDA@Lac bioreactor was constructed by depositing polydopamine (PDA) on the surface of the recombinant Escherichia coli with CotA laccase gene, and releasing intracellular laccase into the PDA shell using ultrasound to break the cell wall of the bacteria. The bioreactor provided a nano-confined environment for the laccase and accelerated the mass and electron transfer in the volume-confined space, with a 2.77-fold increase in Km compared with the free laccase. Since there was no barrier of the cell wall, the crystal violet dye can enter the bioreactor to participate in the enzymatic reaction. As a result, PDA@Lac achieved excellent decolorization performance even without ABTS as an electron mediator. Moreover, the cytoplasmic solution retained in the PDA shell promoted the enzyme's tolerance to pH, temperature and harsh environments. In addition to PDA encapsulation, carbonyl and -NH₂ groups of PDA were bound covalently with -NH₂ and -COOH on the laccase in the PDA@Lac, resulting in an extremely high laccase loading of 817.59 mg/g. Also, the relative activity of the bioreactor maintained approximately 75% after 10 cycles of reuse. In addition, the protection of the PDA shell increased the resistance of laccase to UV irradiation. This work provides a novel method of laccase immobilization for application in wastewater treatment.

Artificial Photoenzymatic Reduction of Carbon Dioxide to Methanol by Using Electron Mediator and Co-factorAssembled ZnIn2 S4 Nanoflowers

Increased absorption of visible light, low electron-hole recombination, and fast electron transfer are the major objectives for highly effective photocatalysts in biocatalytic artificial photosynthetic systems. In this study, a polydopamine (PDA) layer containing electron mediator, [M], and NAD⁺ cofactor was assembled on the outer surface of ZnIn₂ S₄ nanoflower, and the as-prepared nanoparticle, ZnIn₂ S₄ /PDA@poly/[M]/NAD⁺ , was used for photoenzymatic methanol production from CO₂ . Because of effective capturing of visible light, reduced distance of electron transfer, and elimination of electron-holes recombination, a high NADH regeneration of 80.7±1.43 % could be obtained using the novel ZnIn₂ S₄ /PDA@poly/[M]/NAD⁺ . In the artificial photosynthesis system, a maximum methanol production of 116.7±11.8 μm was obtained. The enzymes and nanoparticles in the hybrid bio-photocatalysis system could be easily recovered using the ultrafiltration membrane at the bottom of the photoreactor. This is due to the successful immobilization of the small blocks including the electron mediator and cofactor on the surface of the photocatalyst. The ZnIn₂ S₄ /PDA@poly/[M]/NAD⁺ photocatalyst exhibited good stability and recyclability for methanol production. The novel concept presented in this study shows great promise for other sustainable chemical productions through artificial photoenzymatic catalysis.

Enzymatic Conversion of CO2: From Natural to Artificial Utilization

Enzymatic carbon dioxide fixation is one of the most important metabolic reactions as it allows the capture of inorganic carbon from the atmosphere and its conversion into organic biomass. However, due to the often unfavorable thermodynamics and the difficulties associated with the utilization of CO₂, a gaseous substrate that is found in comparatively low concentrations in the atmosphere, such reactions remain challenging for biotechnological applications. Nature has tackled these problems by evolution of dedicated CO₂-fixing enzymes, i.e., carboxylases, and embedding them in complex metabolic pathways. Biotechnology employs such carboxylating and decarboxylating enzymes for the carboxylation of aromatic and aliphatic substrates either by embedding them into more complex reaction cascades or by shifting the reaction equilibrium via reaction engineering. This review aims to provide an overview of natural CO₂-fixing enzymes and their mechanistic similarities. We also discuss biocatalytic applications of carboxylases and decarboxylases for the synthesis of valuable products and provide a separate summary of strategies to improve the efficiency of such processes. We briefly summarize natural CO₂ fixation pathways, provide a roadmap for the design and implementation of artificial carbon fixation pathways, and highlight examples of biocatalytic cascades involving carboxylases. Additionally, we suggest that biochemical utilization of reduced CO₂ derivates, such as formate or methanol, represents a suitable alternative to direct use of CO₂ and provide several examples. Our discussion closes with a techno-economic perspective on enzymatic CO₂ fixation and its potential to reduce CO₂ emissions.

Coimmobilized enzymes as versatile biocatalytic tools for biomass valorization and remediation of environmental contaminants - A review

Due to stringent regulatory norms, waste processing faces confrontations and challenges in adapting technology for effective management through a convenient and economical system. At the global level, attempts are underway to achieve a green and sustainable treatment for the valorization of lignocellulosic biomass as well as organic contaminants in wastewater. Enzymatic treatment in the environmental aspect thrived on being the promising rapid strategy that appeased the aforementioned predicament. On that account, coimmobilization of various enzymes on single support enhances the catalytic activity ensuing operational stability with industrial applications. This review pivoted towards the coimmobilization of enzymes on diverse supports and their applications in biomass conversion to industrial value-added products and removal of contaminants in wastewater. The limelight of this study chronicles the unique breakthroughs in biotechnology for the production of reusable biocatalysts, which inculcating various enzymes towards the scope of environment application.

Improving the Enzymatic Cascade of Reactions for the Reduction of CO2 to CH3OH in Water: From Enzymes Immobilization Strategies to Cofactor Regeneration and Cofactor Suppression

The need to decrease the concentration of CO2 in the atmosphere has led to the search for strategies to reuse such molecule as a building block for chemicals and materials or a source of carbon for fuels. The enzymatic cascade of reactions that produce the reduction of CO2 to methanol seems to be a very attractive way of reusing CO2; however, it is still far away from a potential industrial application. In this review, a summary was made of all the advances that have been made in research on such a process, particularly on two salient points: enzyme immobilization and cofactor regeneration. A brief overview of the process is initially given, with a focus on the enzymes and the cofactor, followed by a discussion of all the advances that have been made in research, on the two salient points reported above. In particular, the enzymatic regeneration of NADH is compared to the chemical, electrochemical, and photochemical conversion of NAD+ into NADH. The enzymatic regeneration, while being the most used, has several drawbacks in the cost and life of enzymes that suggest attempting alternative solutions. The reduction in the amount of NADH used (by converting CO2 electrochemically into formate) or even the substitution of NADH with less expensive mimetic molecules is discussed in the text. Such an approach is part of the attempt made to take stock of the situation and identify the points on which work still needs to be conducted to reach an exploitation level of the entire process.

Strategies for overcoming the limitations of enzymatic carbon dioxide reduction

The overexploitation of fossil fuels has led to a significant increase in atmospheric carbon dioxide (CO₂) concentrations, thereby causing problems, such as the greenhouse effect. Rapid global climate change has caused researchers to focus on utilizing CO₂ in a green and efficient manner. One of the ways to achieve this is by converting CO₂ into valuable chemicals via chemical, photochemical, electrochemical, or enzymatic methods. Among these, the enzymatic method is advantageous because of its high specificity and selectivity as well as the mild reaction conditions required. The reduction of CO₂ to formate, formaldehyde, and methanol using formate dehydrogenase (FDH), formaldehyde dehydrogenase (F_aldDH), and alcohol dehydrogenase (ADH) are attractive routes, respectively. In this review, strategies for overcoming the common limitations of enzymatic CO₂ reduction are discussed. First, we present a brief background on the importance of minimizing of CO₂ emissions and introduce the three bottlenecks limiting enzymatic CO₂ reduction. Thereafter, we explore the different strategies for enzyme immobilization on various support materials. To solve the problem of cofactor consumption, different state-of-the-art cofactor regeneration strategies as well as research on the development of cofactor substitutes and cofactor-free systems are extensively discussed. Moreover, aiming at improving CO₂ solubility, biological, physical, and engineering measures are reviewed. Finally, conclusions and future perspectives are presented.

Natural Deep Eutectic Solvents Enhanced Electro-Enzymatic Conversion of CO2 to Methanol

Electro-enzymatic conversion of CO₂ offers a promising solution for CO₂ utilization, while the conversion rate and efficiency were disappointing. To address the challenge, four kinds of natural deep eutectic solvents (NADES) with desirable biocompatibility were developed for the first time and used as the co-electrolyte in the electro-enzymatic conversion of CO₂. As a result, the SerGly-based solution presents high CO₂ solubility and high electrocatalytic activity, compared to the conventional buffer. By applying SerGly in the electro-enzymatic conversion of CO₂, the yield of the product (methanol) is two times higher than that in the Tris-HCl buffer (0.22 mM) and 16 times higher than the control reaction.

Developing and Regenerating Cofactors for Sustainable Enzymatic CO2 Conversion

Enzymatic CO2 conversion offers a promising strategy for alleviating global warming and promoting renewable energy exploitation, while the high cost of cofactors is a bottleneck for large-scale applications. To address the challenge, cofactor regeneration is usually coupled with the enzymatic reaction. Meanwhile, artificial cofactors have been developed to further improve conversion efficiency and decrease cost. In this review, the methods, such as enzymatic, chemical, electrochemical, and photochemical catalysis, developed for cofactor regeneration, together with those developed artificial cofactors, were summarized and compared to offer a solution for large-scale enzymatic CO2 conversion in a sustainable way.

CO2 to Methanol: A Highly Efficient Enzyme Cascade

Carbon dioxide (CO₂) has been increasingly regarded not only as a greenhouse gas but also as a valuable feedstock for carbon-based chemicals. In particular, biological approaches have drawn attention as models for the production of value-added products, as CO₂ conversion serves many natural processes. Enzymatic CO₂ reduction in vitro is a very promising route to produce fossil free and bio-based fuel alternatives, such as methanol. In this chapter, the advances in constructing competitive multi-enzymatic systems for the reduction of CO₂ to methanol are discussed. Different integrated methods are presented, aiming to address technological challenges, such as the cost effectiveness, need for material regeneration and reuse and improving product yields of the process.

A Review on the Design and Performance of Enzyme-Aided Catalysis of Carbon Dioxide in Membrane, Electrochemical Cell and Photocatalytic Reactors

Multi-enzyme cascade catalysis involved three types of dehydrogenase enzymes, namely, formate dehydrogenase (FDH), formaldehyde dehydrogenase (FaldDH), alcohol dehydrogenase (ADH), and an equimolar electron donor, nicotinamide adenine dinucleotide (NADH), assisting the reaction is an interesting pathway to reduce thermodynamically stable molecules of CO₂ from the atmosphere. The biocatalytic sequence is interesting because it operates under mild reaction conditions (low temperature and pressure) and all the enzymes are highly selective, which allows the reaction to produce three basic chemicals (formic acid, formaldehyde, and methanol) in just one pot. There are various challenges, however, in applying the enzymatic conversion of CO₂, namely, to obtain high productivity, increase reusability of the enzymes and cofactors, and to design a simple, facile, and efficient reactor setup that will sustain the multi-enzymatic cascade catalysis. This review reports on enzyme-aided reactor systems that support the reduction of CO₂ to methanol. Such systems include enzyme membrane reactors, electrochemical cells, and photocatalytic reactor systems. Existing reactor setups are described, product yields and biocatalytic productivities are evaluated, and effective enzyme immobilization methods are discussed.

Enzyme-catalyzed cascade reactions on multienzyme proteinosomes

In this research, to mimic the structures and the functionalities of the organelles in living cells multienzyme proteinosomes with β-galactosidase (β-gal), glucose oxidase (GOx) and horseradish peroxidase (HRP) on the surfaces are fabricated by hydrophobic-interaction induced self-assembly approach. To investigate the mechanism of the formation of proteinosomes, poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) and bovine serum albumin are employed in a model system and the study demonstrates that the hydrophobic interaction between the dehydrated polymer chains and the hydrophobic patches on the proteins plays a key role in the fabrication of the proteinosomes. Based on the model system, multienzyme proteinosomes with β-gal, GOx and HRP on the surfaces are fabricated through hydrophobic interaction between PDEGMA and enzyme molecules. Enzyme-catalyzed cascade reactions are performed on the surfaces of the proteinosomes, and the immobilized enzymes show higher bioactivities than the "free" enzymes, due to the direct transfer of the product as a substrate from one enzyme molecule to another. This research provides a unique method for the synthesis of multienzyme proteinosomes with improved bioactivities, and the biofunctional structures will find promising applications in medical and biological science.

Multi-enzyme co-immobilized nano-assemblies: Bringing enzymes together for expanding bio-catalysis scope to meet biotechnological challenges

Co-immobilization of multi-enzymes has emerged as a promising concept to design and signify bio-catalysis engineering. Undoubtedly, the existence and importance of basic immobilization methods such as encapsulation, covalent binding, cross-linking, or even simple adsorption cannot be ignored as they are the core of advanced co-immobilization strategies. Different strategies have been developed and deployed to green the twenty-first century bio-catalysis. Moreover, co-immobilization of multi-enzymes has successfully resolved the limitations of individual enzyme loaded constructs. With an added value of this advanced bio-catalysis engineering platform, designing, and fabricating co-immobilized enzymes loaded nanostructure carriers to perform a particular set of reactions with high catalytic turnover is of supreme interest. Herein, we spotlight the emergence of co-immobilization strategies by bringing multi-enzymes together with various types of nanocarriers to expand the bio-catalysis scope. Following a brief introduction, the first part of the review focuses on multienzyme co-immobilization strategies, i.e., random co-immobilization, compartmentalization, and positional co-immobilization. The second part comprehensively covers four major categories of nanocarriers, i.e., carbon based nanocarriers, polymer based nanocarriers, silica-based nanocarriers, and metal-based nanocarriers along with their particular examples. In each section, several critical factors that can affect the performance and successful deployment of co-immobilization of enzymes are given in this work.

Construction of Multienzyme Co-immobilized Hybrid Nanoflowers for an Efficient Conversion of Cellulose into Glucose in a Cascade Reaction

Today, we are seeking an efficient biotransformation of cellulosic material into sustainable biochemical products to meet the increasing global energy demand. Herein, we report the fabrication of multienzyme hybrid nanoflowers (ECG-NFs) by co-immobilizing three recombinant enzymes (cellobiohydrolase (CBH), endo-glucanase (EG), and β-glucosidase (BG)) integrating a binary tag composed of elastin-like polypeptide (ELP) and His-tag to act as a tri-enzyme biocatalyst, which catalyzes the hydrolysis of cellulose into glucose. The prepared ECG-NFs exhibited excellent performance in terms of pH stability, thermal stability, storage stability, and catalytic efficiency compared to free multienzyme system. Notably, ECG-NFs could be recycled for up to eight consecutive runs. The K_m and k_cat/K_m values for ECG-NFs were 9.33 g L^-1 and 0.0051 L min^-1 g^-1, respectively, which were better than those of the free multienzyme system, indicating a better substrate affinity. Finally, the overall enzyme activity of ECG-NFs increased by 1.12 times and the degradation efficiency of ECG-NFs was superior to the free multienzyme system, which revealed that ECG-NFs could facilitate an effective one-pot hydrolysis of cellulose into glucose.

Integrated catalytic insights into methanol production: Sustainable framework for CO2 conversion

A continuous increase in the amount of greenhouse gases (GHGs) is causing serious threats to the environment and life on the earth, and CO₂ is one of the major candidates. Reducing the excess CO₂ by converting into industrial products could be beneficial for the environment and also boost up industrial growth. In particular, the conversion of CO₂ into methanol is very beneficial as it is cheaper to produce from biomass, less inflammable, and advantageous to many industries. Application of various plants, algae, and microbial enzymes to recycle the CO₂ and using these enzymes separately along with CO₂-phillic materials and chemicals can be a sustainable solution to reduce the global carbon footprint. Materials such as MOFs, porphyrins, and nanomaterials are also used widely for CO₂ absorption and conversion into methanol. Thus, a combination of enzymes and materials which convert the CO₂ into methanol could energize the CO₂ utilization. The CO₂ to methanol conversion utilizes carbon better than the conventional syngas and the reaction yields fewer by-products. The methanol produced can further be utilized as a clean-burning fuel, in pharmaceuticals, automobiles and as a general solvent in various industries etc. This makes methanol an ideal fuel in comparison to the conventional petroleum-based ones and it is advantageous for a safer and cleaner environment. In this review article, various aspects of the circular economy with the present scenario of environmental crisis will also be considered for large-scale sustainable biorefinery of methanol production from atmospheric CO₂.

Enzymes for Efficient CO2 Conversion

The accumulation of carbon dioxide in the atmosphere as a result of human activities has caused a number of adverse circumstances in the world. For this reason, the proposed solutions lie within the aim of reducing carbon dioxide emissions have been quite valuable. However, as the human activity continues to increase on this planet, the possibility of reducing carbon dioxide emissions decreases with the use of conventional methods. The emergence of compounds than can be used in different fields by converting the released carbon dioxide into different chemicals will construct a fundamental solution to the problem. Although electro-catalysis or photolithography methods have emerged for this purpose, they have not been able to achieve successful results. Alternatively, another proposed solution are enzyme based systems. Among the enzyme-based systems, pyruvate decarboxylase, carbonic anhydrase and dehydrogenases have been the most studied enzymes. Pyruvate dehydrogenase and carbonic anhydrase have either been an expensive method or were incapable of producing the desired result due to the reaction cascade they catalyze. However, the studies reporting the production of industrial chemicals from carbon dioxide using dehydrogenases and in particular, the formate dehydrogenase enzyme, have been remarkable. Moreover, reported studies have shown the existence of more active and stable enzymes, especially the dehydrogenase family that can be identified from the biome. In addition to this, their redesign through protein engineering can have an immense contribution to the increased use of enzyme-based methods in CO₂ reduction, resulting in an enormous expansion of the industrial capacity.

Synthesis and characterization of ordered mesoporous silicas for the immobilization of formate dehydrogenase (FDH)

This work studied the influence of the pore size and morphology of the mesoporous silica as support for formate dehydrogenase (FDH), the first enzyme of a multi-enzymatic cascade system to produce methanol, which catalyzes the reduction of carbon dioxide to formic acid. Specifically, a set of mesoporous silicas was modified with glyoxyl groups to immobilize covalently the FDH obtained from Candida boidinii. Three types of mesoporous silicas with different textural properties were synthesized and used as supports: i) SBA-15 (D_P = 4 nm); ii) MCF with 0.5 wt% mesitylene/pluronic ratio (D_P = 20 nm) and iii) MCF with 0.75 wt% mesitylene/pluronic ratio (D_P = 25 nm). As a whole, the immobilized FDH on MCF_0.75 exhibited higher thermal stability than the free enzyme, with 75% of residual activity after 24 h at 50 °C. FDH/MCF_0.5 exhibited the best immobilization yields: 69.4% of the enzyme supplied was covalently bound to the support. Interestingly, the specific activity increased as a function of the pore size of support and then the FDH/MCF_0.75 exhibited the highest specific activity (namely, 1.05 IU/g_MCF0.75) with an immobilization yield of 52.1%. Furthermore, it was noted that the immobilization yield and the specific activity of the FDH/MCF_0.75 varied as a function of the supported enzyme: as the enzyme loading increased the immobilization yield decreased while the specific activity increased. Finally, the reuse test has been carried out, and a residual activity greater than 70% was found after 5 cycles of reaction.

Nature Inspired Multienzyme Immobilization: Strategies and Concepts

In a biological system, the spatiotemporal arrangement of enzymes in a dense cellular milieu, subcellular compartments, membrane-associated enzyme complexes on cell surfaces, scaffold-organized proteins, protein clusters, and modular enzymes have presented many paradigms for possible multienzyme immobilization designs that were adapted artificially. In metabolic channeling, the catalytic sites of participating enzymes are close enough to channelize the transient compound, creating a high local concentration of the metabolite and minimizing the interference of a competing pathway for the same precursor. Over the years, these phenomena had motivated researchers to make their immobilization approach naturally realistic by generating multienzyme fusion, cluster formation via affinity domain-ligand binding, cross-linking, conjugation on/in the biomolecular scaffold of the protein and nucleic acids, and self-assembly of amphiphilic molecules. This review begins with the discussion of substrate channeling strategies and recent empirical efforts to build it synthetically. After that, an elaborate discussion covering prevalent concepts related to the enhancement of immobilized enzymes' catalytic performance is presented. Further, the central part of the review summarizes the progress in nature motivated multienzyme assembly over the past decade. In this section, special attention has been rendered by classifying the nature-inspired strategies into three main categories: (i) multienzyme/domain complex mimic (scaffold-free), (ii) immobilization on the biomolecular scaffold, and (iii) compartmentalization. In particular, a detailed overview is correlated to the natural counterpart with advances made in the field. We have then discussed the beneficial account of coassembly of multienzymes and provided a synopsis of the essential parameters in the rational coimmobilization design.

Improved biocatalytic cascade conversion of CO2 to methanol by enzymes Co-immobilized in tailored siliceous mesostructured cellular foams

CO2 can be enzymatically reduced to methanol in a cascade reaction involving three enzymes: formate-, formaldehyde- and alcohol dehydrogenase (FateDH, FaldDH, ADH).

Immobilization of Multi-Enzymes on Support Materials for Efficient Biocatalysis

Multi-enzyme biocatalysis is an important technology to produce many valuable chemicals in the industry. Different strategies for the construction of multi-enzyme systems have been reported. In particular, immobilization of multi-enzymes on the support materials has been proved to be one of the most efficient approaches, which can increase the enzymatic activity via substrate channeling and improve the stability and reusability of enzymes. A general overview of the characteristics of support materials and their corresponding attachment techniques used for multi-enzyme immobilization will be provided here. This review will focus on the materials-based techniques for multi-enzyme immobilization, which aims to present the recent advances and future prospects in the area of multi-enzyme biocatalysis based on support immobilization.

Construction of a Multienzymatic Cascade Reaction System of Coimmobilized Hybrid Nanoflowers for Efficient Conversion of Starch into Gluconic Acid

Introducing an efficient method for the rapid conversion of starch into gluconic acid is desirable to solve the current problems existing in traditional gluconic acid preparation processes. In this study, a robust and easy-to-use multienzymatic cascade reaction system of coimmobilized GA@GOx hybrid nanoflowers with a specific spatial distribution of enzymes by compartmentalization was constructed and applied to catalyze starch to gluconic acid in one pot. In the preparation processes, the glucose oxidase (GOx) hybrid nanoflowers were first synthesized via a self-assembly mechanism, and then, glucoamylase (GA) was adsorbed on the surface of GOx hybrid nanoflowers through the interaction of Cu²⁺ and amino acids of GA. The optimum preparation conditions and reaction parameters of the GA@GOx hybrid nanoflowers had been investigated. In addition, the morphology, composition, and crystallization of the GA@GOx hybrid nanoflowers had been fully studied. Based on the lower K_m, the GA@GOx hybrid nanoflowers with compartmentalization had a better effect of the substrate channeling on the catalytic efficiency. The final results indicated that the overall enzyme activity of the GA@GOx hybrid nanoflowers increased by 1.5 times, and the conversion efficiency was 92.12% within 80 min significantly superior to the free multienzyme system, which showed the outstanding conversion of starch into gluconic acid in one pot.

Sequential Co-immobilization of Enzymes in Metal-Organic Frameworks for Efficient Biocatalytic Conversion of Adsorbed CO2 to Formate

The main challenges in multienzymatic cascade reactions for CO₂ reduction are the low CO₂ solubility in water, the adjustment of substrate channeling, and the regeneration of co-factor. In this study, metal-organic frameworks (MOFs) were prepared as adsorbents for the storage of CO₂ and at the same time as solid supports for the sequential co-immobilization of multienzymes via a layer-by-layer self-assembly approach. Amine-functionalized MIL-101(Cr) was synthesized for the adsorption of CO₂. Using amine-MIL-101(Cr) as the core, two HKUST-1 layers were then fabricated for the immobilization of three enzymes chosen for the reduction of CO₂ to formate. Carbonic anhydrase was encapsulated in the inner HKUST-1 layer and hydrated the released CO₂ to HCO3-. Bicarbonate ions then migrated directly to the outer HKUST-1 shell containing formate dehydrogenase and were converted to formate. Glutamate dehydrogenase on the outer MOF layer achieved the regeneration of co-factor. Compared with free enzymes in solution using the bubbled CO₂ as substrate, the immobilized enzymes using stored CO₂ as substrate exhibited 13.1-times higher of formate production due to the enhanced substrate concentration. The sequential immobilization of enzymes also facilitated the channeling of substrate and eventually enabled higher catalytic efficiency with a co-factor-based formate yield of 179.8%. The immobilized enzymes showed good operational stability and reusability with a cofactor cumulative formate yield of 1077.7% after 10 cycles of reusing.

Confinement Catalysis with 2D Materials for Energy Conversion

The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of "confinement catalysis with 2D materials." Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high-performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy-related reaction processes, especially in the conversion of small energy-related molecules such as O₂ , CH₄ , CO, CO₂ , H₂ O, and CH₃ OH. Two representative strategies, i.e., 2D lattice-confined single atoms and 2D cover-confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure-performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.

Monodisperse Alginate Microcapsules with Spatially Confined Bioactive Molecules via Microfluid-Generated W/W/O Emulsions

A simple process is developed for the one-step preparation of dual-compartment alginate microcapsules with controlled size and structure from microfluid-generated water-in-water-in-oil (W/W/O) emulsion droplet. Unlike other methods that rely on transient W/W/O emulsion droplet, we introduce an aqueous two-phase system (ATPS) to form a stable W/W/O emulsion droplet as a template for preparing dual-compartment alginate microcapsules. Two different bioactive molecules are able to be spatially confined encapsulated in the shell and core of alginate microcapsules due to the partitioning effect of ATPS and the high viscosity of alginate solution. Moreover, an enzyme cascade reaction with a spatial confined glucose oxidase and horseradish peroxidase in the shell and core of alginate microcapsules confirms its excellent biocompatibility and high activity. This method provides a green platform for enzyme-catalyzed tandem reactions and controlled sequential release of multiple drugs based on alginate microcapsules.

Ordered Coimmobilization of a Multienzyme Cascade System with a Metal Organic Framework in a Membrane: Reduction of CO2 to Methanol

Enzymatic reduction of CO₂ is of great significant, which involves an efficient multienzyme cascade system (MECS). In this work, formate dehydrogenase (FDH), glutamate dehydrogenase (GDH), and reduced pyridine nucleotide (NADH) (FDH&GDH&NADH), formaldehyde dehydrogenase (FalDH), GDH, and NADH (FalDH&GDH&NADH), and alcohol dehydrogenase (ADH), GDH, and NADH (ADH&GDH&NADH) were embedded in ZIF-8 (one kind of metal organic framework) to prepare three kinds of enzymes and coenzymes/ZIF-8 nanocomposites. Then by dead-end filtration these nanocomposites were sequentially located in a microporous membrane, which was combined with a pervaporation membrane to timely achieve the separation of product methanol. Incorporation of the pervaporation membrane was helpful to control reaction direction, and the methanol amount increased from 5.8 ± 0.5 to 6.7 ± 0.8 μmol. The reaction efficiency of an immobilized enzymes-ordered distribution in a membrane was higher than that disordered distribution in the membrane, and the methanol amount increased from 6.7 ± 0.8 to 12.6 ± 0.6 μmol. Moreover, it appeared that introduction of NADH into ZIF-8 enhanced the transformation of CO₂ to methanol from 12.6 ± 0.6 to 13.4 ± 0.9 μmol. Over 50% of their original productivity was retained after 12 h of use. This method has wide applicability and can be used in other kinds of multienzyme systems.

Unveiling Electrochemical Reaction Pathways of CO2 Reduction to CN Species at S-Vacancies of MoS2

Although C₁ species such as CO and CH₄ constitute the majority of CO₂ reduction (CO₂  R) products on known catalysts, recent experiments showed that 1-propanol with two C-C bonds is produced as the main CO₂  R product on MoS₂ single crystals in aqueous electrolytes. Herein, the CO₂  R mechanism on MoS₂ is investigated by using first-principle calculations. Focusing on S-vacancies (V_S ) as the catalytic site, potential free-energy pathways to various CO₂  R products are obtained by means of a computational hydrogen electrode model. The results underline the role of HCHO, which is one of the elemental C₁ products, in opening pathways to C_N species for N>1. Key steps to increase C-C bonds are the adsorption of HCHO at the V_S site and binding of another HCHO to the adsorbed one. The predicted products and theoretical working potentials to open their pathways are consistent with experiments, which indicates that V_S is an important active site for CO₂  R on the MoS₂ basal plane.

Multiple-Enzyme Graphene Microparticle Presenting Adaptive Chemical Network Capabilities

Interrelated reaction networks steered by multiple types of enzymes are among the most intriguing enzyme-based cellular features. These reaction networks display advanced features such as adaptation, stimuli-responsiveness, and decision-making in accordance with environmental cues. However, artificial enzyme particles are still deficient in network-level capabilities, mostly because delicate enzymes are difficult to immobilize and assemble. In this study, we propose a general strategy to prepare enzyme-based particles that demonstrate network reaction capability. We assembled multiple types of proteins with a nanoscopic binder prepared from polyelectrolyte and graphene. After assembly, the enzymes all preserved their catalytic capabilities. By incorporating multiple types of enzymes, the particles additionally displayed network-reaction capabilities. We were able to use NIR irradiations to quasi-reversibly adjust the catalytic abilities of these enzyme-based particles. In addition, after a biomimetic mineralization process was used to wrap the protein complexes in a MOF shell, the particles were more robust and catalytically active even after being immersed in acidic (pH 4) or basic (pH 10) solutions for 3 days. This study provides an insight into the study of network properties of functional enzyme particles experimentally and enriches scientific understanding of multifunctional or stimuli-responsive behaviors at the reaction network level. The building of artificial reaction networks possesses high potential in realizing intelligent microparticles that can perform complicated tasks.

Preserving the adhesion of catechol-conjugated hydrogels by thiourea-quinone coupling

Mussel adhesion has inspired the development of catechol-based adhesive polymers. However, conventional strategies require basic pH conditions and lead to the loss of adhesion. To solve the problem, we report the first attempt to use thiourea-functionalized polymers for preserving hydrogel adhesion. We believe that this simple thiourea-quinone coupling chemistry is instrumental to synthetic adhesive materials.

Ionic Liquids as Bifunctional Cosolvents Enhanced CO2 Conversion Catalysed by NADH-Dependent Formate Dehydrogenase

Efficient CO2 conversion by formate dehydrogenase is limited by the low CO2 concentrations that can be reached in traditional buffers. The use of ionic liquids was proposed as a manner to increase CO2 concentration in the reaction system. It has been found, however, that the required cofactor (NADH) heavily degraded during the enzymatic reaction and that acidity was the main reason. Acidity, indeed, resulted in reduction of the conversion of CO2 into formic acid and contributed to overestimate the amount of formic acid produced when the progression of the reaction was followed by a decrease in NADH absorbance (method N). Stability of NADH and the mechanism of NADH degradation was investigated by UV, NMR and by DFT calculations. It was found that by selecting neutral–basic ionic liquids and by adjusting the concentration of the ionic liquid in the buffer, the concentration of NADH can be maintained in the reaction system with little loss. Conversion of CO2 to methanol in BmimBF4 (67.1%) was more than twice as compared with the conversion attained by the enzymatic reaction in phosphate buffer (24.3%).

Bioinspired construction of multi-enzyme catalytic systems

Enzyme catalysis, as a green, efficient process, displays exceptional functionality, adaptivity and sustainability. Multi-enzyme catalysis, which can accomplish the tandem synthesis of valuable materials/chemicals from renewable feedstocks, establishes a bridge between single-enzyme catalysis and whole-cell catalysis. Multi-enzyme catalysis occupies a unique and indispensable position in the realm of biological reactions for energy and environmental applications. Two complementary strategies, i.e., compartmentalization and substrate channeling, have been evolved by living organisms for implementing the complex in vivo multi-enzyme reactions (MERs), which have been applied to construct multi-enzyme catalytic systems (MECSs) with superior catalytic activity and stabilities in practical biocatalysis. This tutorial review aims to present the recent advances and future prospects in this burgeoning research area, stressing the features and applications of the two strategies for constructing MECSs and implementing in vitro MERs. The concluding remarks are presented with a perspective on the construction of MECSs through rational combination of compartmentalization and substrate channeling.