Molecular Engineering and Morphology Control of Covalent Organic Frameworks for Enhancing Activity of Metal-Enzyme Cascade Catalysis

Metal-enzyme integrated catalysts (MEICs) that combine metal and enzyme offer great potential for sustainable chemoenzymatic cascade catalysis. However, rational design and construction of optimal microenvironments and accessible active sites for metal and enzyme in individual nanostructures are necessary but still challenging. Herein, Pd nanoparticles (NPs) and Candida antarctica lipase B (CALB) are co-immobilized into the pores and surfaces of covalent organic frameworks (COFs) with tunable functional groups, affording Pd/COF-X/CALB (X = ONa, OH, OMe) MEICs. This strategy can regulate the microenvironment around Pd NPs and CALB, and their interactions with substrates. As a result, the activity of the COF-based MEICs in catalyzing dynamic kinetic resolution of primary amines is enhanced and followed COF-OMe > COF-OH > COF-ONa. The experimental and simulation results demonstrated that functional groups of COFs modulated the conformation of CALB, the electronic states of Pd NPs, and the affinity of the integrated catalysts to the substrate, which contributed to the improvement of the catalytic activity of MEICs. Further, the MEICs are prepared using COF with hollow structure as support material, which increased accessible active sites and mass transfer efficiency, thus improving catalytic performance. This work provides a blueprint for rational design and preparation of highly active MEICs.

Bottom-Up Synthesis of Multicompartmentalized Microreactors for Continuous Flow Catalysis

The bottom-up assembly of biomimetic multicompartmentalized microreactors for use in continuous flow catalysis remains a grand challenge because of the structural instability or the absence of liquid microenvironments to host biocatalysts in the existing systems. Here, we address this challenge using a strategy that combines stepwise Pickering emulsification with interface-confined cross-linking. Our strategy allows for the fabrication of robust multicompartmentalized liquid-containing microreactors (MLMs), whose interior architectures can be exquisitely tuned in a bottom-up fashion. With this strategy, enzymes and metal catalysts can be separately confined in distinct subcompartments of MLMs for processing biocatalysis or chemo-enzymatic cascade reactions. As exemplified by the enzyme-catalyzed kinetic resolution of racemic alcohols, our systems exhibit a durability of 2000 h with 99% enantioselectivity. Another Pd-enzyme-cocatalyzed dynamic kinetic resolution of amines further demonstrates the versatility and long-term operational stability of our MLMs in continuous flow cascade catalysis. This study opens up a new way to design efficient biomimetic multicompartmental microreactors for practical applications.

Integration of chemo- and bio-catalysis to intensify bioprocesses

Nature has evolved highly efficient and complex systems to perform cascade reactions by the elegant combination of desired enzymes, offering a strategy for achieving efficient bioprocess intensification. Chemoenzymatic cascade reactions (CECRs) merge the complementary strengths of chemo-catalysis and bio-catalysis, such as the wide reactivity of chemo-catalysts and the exquisite selective properties of biocatalysts, representing an important step toward emulating nature to construct artificial systems for achieving bioprocess intensification. However, the incompatibilities between the two catalytic disciplines make CECRs highly challenging. In recent years, great advances have been made to develop strategies for constructing CECRs. In this regard, this chapter introduces the general concepts and representative strategies, including temporal compartmentalization, spatial compartmentalization and chemo-bio nanoreactors. Particularly, we focus on what platform methods and technologies can be used, and how to implement these strategies. The future challenges and strategies in this burgeoning research area are also discussed.

Preparation of Coupling Catalyst HamZIF-90@Pd@CALB with Tunable Hollow Structure for Efficient Dynamic Kinetic Resolution of 1-Phenylethylamine

Chiral amines are essential components for many pharmaceuticals and agrochemicals. However, the difficulty in obtaining enantiomerically pure amines limits their application. In this study, hollow amorphous ZIF-90 (HamZIF-90) materials were prepared by template engraving, and chemical-enzyme coupling catalysts (HamZIF-90@Pd@CALB) were constructed for the chiral resolution of 1-phenylethylamine. Different from conventional materials, HamZIF-90 had tunable hollow structures by altering its central node zinc ion concentrations, and the embedded hydrogel template gave it more pore structures, which facilitated the loading of enzyme molecules and Pd nanoparticles (NPs). The establishment of the coupling catalysts shortened the mass transfer distance of the reactant molecules between the metal nanoparticles and the enzyme catalyst in the dynamic kinetic resolution (DKR) reaction, resulting in 98% conversion of 1-phenylethylamine and 93% selectivity of Sel.R-amide. The proposal of this idea provided a good idea for future tailor-made MOFs loaded with chemical and enzyme coupled catalyst.

Expanding the Synthetic Toolbox through Metal-Enzyme Cascade Reactions

The combination of metal-, photo-, enzyme-, and/or organocatalysis provides multiple synthetic solutions, especially when the creation of chiral centers is involved. Historically, enzymes and transition metal species have been exploited simultaneously through dynamic kinetic resolutions of racemates. However, more recently, linear cascades have appeared as elegant solutions for the preparation of valuable organic molecules combining multiple bioprocesses and metal-catalyzed transformations. Many advantages are derived from this symbiosis, although there are still bottlenecks to be addressed including the successful coexistence of both catalyst types, the need for compatible reaction media and mild conditions, or the minimization of cross-reactivities. Therefore, solutions are here also provided by means of catalyst coimmobilization, compartmentalization strategies, flow chemistry, etc. A comprehensive review is presented focusing on the period 2015 to early 2022, which has been divided into two main sections that comprise first the use of metals and enzymes as independent catalysts but working in an orchestral or sequential manner, and later their application as bionanohybrid materials through their coimmobilization in adequate supports. Each part has been classified into different subheadings, the first part based on the reaction catalyzed by the metal catalyst, while the development of nonasymmetric or stereoselective processes was considered for the bionanohybrid section.

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives

Pickering emulsions are particle-stabilized surfactant-free dispersions composed of two immiscible liquid phases, and emerge as attractive catalysis platform to surpass traditional technique barrier in some cases. In this review, we have comprehensively summarized the development and the catalysis applications of Pickering emulsions since the pioneering work in 2010. The explicit mechanism for Pickering emulsions will be initially discussed and clarified. Then, summarization is given to the design strategy of amphiphilic emulsion catalysts in two categories of intrinsic and extrinsic amphiphilicity. The progress of the unconventional catalytic reactions in Pickering emulsion is further described, especially for the polarity/solubility difference-driven phase segregation, "smart" emulsion reaction system, continuous flow catalysis, and Pickering interfacial biocatalysis. Challenges and future trends for the development of Pickering emulsion catalysis are finally outlined.

Atomically Dispersed Co Clusters Anchored on N-doped Carbon Nanotubes for Efficient Dehydrogenation of Alcohols and Subsequent Conversion to Carboxylic Acids

The catalytic dehydrogenation of readily available alcohols to high value-added carbonyl compounds is a research hotspot with scientific significance. Most of the current research about this reaction is performed with noble metal-based homogeneous catalysts of high price and poor reusability. Herein, highly dispersed Co-cluster-decorated N-doped carbon nanotubes (Co/N-CNTs) were fabricated via a facile strategy and used for the dehydrogenation of alcohols with high efficiency. Various characterization techniques confirmed the presence of metallic Co clusters with almost atomic dispersion, and the N-doped carbon supports also enhanced the catalytic activity of Co clusters in the dehydrogenation reaction. Aldehydes as dehydrogenation products were further transformed in situ to carboxylic acids through a Cannizzaro-type pathway under alkaline conditions. The reaction pathway of the dehydrogenation of alcohols was clearly confirmed by theoretical calculations. This work should provide an effective and simple approach for the accurate design and synthesis of small Co-clusters catalysts for the efficient dehydrogenation-based transformation of alcohols to carboxylic acids under mild reaction conditions.

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.

Multicatalytic Hybrid Materials for Biocatalytic and Chemoenzymatic Cascades—Strategies for Multicatalyst (Enzyme) Co-Immobilization

During recent decades, the use of enzymes or chemoenzymatic cascades for organic chemistry has gained much importance in fundamental and industrial research. Moreover, several enzymatic and chemoenzymatic reactions have also served in green and sustainable manufacturing processes especially in fine chemicals, pharmaceutical, and flavor/fragrance industries. Unfortunately, only a few processes have been applied at industrial scale because of the low stabilities of enzymes along with the problematic processes of their recovery and reuse. Immobilization and co-immobilization offer an ideal solution to these problems. This review gives an overview of all the pathways for enzyme immobilization and their use in integrated enzymatic and chemoenzymatic processes in cascade or in a one-pot concomitant execution. We place emphasis on the factors that must be considered to understand the process of immobilization. A better understanding of this fundamental process is an essential tool not only in the choice of the best route of immobilization but also in the understanding of their catalytic activity.

Hybrid chemoenzymatic heterogeneous catalyst prepared in one step from zeolite nanocrystals and enzyme-polyelectrolyte complexes

The combination of inorganic heterogeneous catalysts and enzymes, in so-called hybrid chemoenzymatic heterogeneous catalysts (HCEHCs), is an attractive strategy to effectively run chemoenzymatic reactions. Yet, the preparation of such bifunctional materials remains challenging because both the inorganic and the biological moieties must be integrated in the same solid, while preserving their intrinsic activity. Combining an enzyme and a zeolite, for example, is complicated because the pores of the zeolite are too small to accommodate the enzyme and a covalent anchorage on the surface is often ineffective. Herein, we developed a new pathway to prepare a nanostructured hybrid catalyst built from glucose oxidase and TS-1 zeolite. Such hybrid material can catalyse the in situ biocatalytic formation of H₂O₂, which is subsequently used by the zeolite to trigger the epoxidation of allylic alcohol. Starting from an enzymatic solution and a suspension of zeolite nanocrystals, the hybrid catalyst is obtained in one step, using a continuous spray drying method. While enzymes are expectedly unable to resist the conditions used in spray drying (temperature, shear stress, etc.), we leverage on the preparation of "enzyme-polyelectrolyte complexes" (EPCs) to increase the enzyme stability. Interestingly, the use of EPCs also prevents enzyme leaching and appears to stabilize the enzyme against pH changes. We show that the one-pot preparation by spray drying gives access to hybrid chemoenzymatic heterogeneous catalysts with unprecedented performance in the targeted chemoenzymatic reaction. The bifunctional catalyst performs much better than the two catalysts operating as separate entities. We anticipate that this strategy could be used as an adaptable method to prepare other types of multifunctional materials starting from a library of functional nanobuilding blocks and biomolecules.

Enzyme-Metal Hybrid Catalysts for Chemoenzymatic Reactions

Enzyme-metal hybrid catalysts (EMHCs), which combine enzymatic and metal catalysis, provide tremendous possibilities for new chemoenzymatic cascade reactions. Here, an overview of the representative achievements in the design of EMHCs and their applications in chemoenzymatic cascade reactions are presented. The preparation of hybrid catalysts is classified into two categories: coimmobilized enzyme-metal heterogeneous catalysts and carrier-free enzyme-metal bioconjugates. Examples of one-pot chemoenzymatic cascade processes catalyzed by the hybrid catalysts are then provided as potential applications. Finally, the limitations and future perspectives of EMHCs are discussed.

Physically mixed catalytic system of amino and sulfo-functional porous organic polymers as efficiently synergistic co-catalysts for one-pot cascade reactions

Acid/base bi-functional polymeric materials were prepared using physically mixed porous polymers P(DVB-VBS) with sulfonic acid and P(DVB-VBA) with amino groups for various cascade reactions.

Hollow zeolite microspheres as a nest for enzymes: a new route to hybrid heterogeneous catalysts

In the field of heterogeneous catalysis, the successful integration of enzymes and inorganic catalysts could pave the way to multifunctional materials which are able to perform advanced cascade reactions. However, such combination is not straightforward, for example in the case of zeolite catalysts for which enzyme immobilization is restricted to the external surface. Herein, this challenge is overcome by developing a new kind of hybrid catalyst based on hollow zeolite microspheres obtained by the aerosol-assisted assembly of zeolite nanocrystals. The latter spheres possess open entry-ways for enzymes, which are then loaded and cross-linked to form cross-linked enzyme aggregates (CLEAs), securing their entrapment. This controlled design allows the combination of all the decisive features of the zeolite with a high enzyme loading. A chemo-enzymatic reaction is demonstrated, where the structured zeolite material is used both as a nest for the enzyme and as an efficient inorganic catalyst. Glucose oxidase (GOx) ensures the in situ production of H2O2 subsequently utilized by the TS-1 zeolite to catalyze the epoxidation of allylic alcohol toward glycidol. The strategy can also be used to entrap other enzymes or combination of enzymes, as demonstrated here with combi-CLEAs of horseradish peroxidase (HRP) and glucose oxidase. We anticipate that this strategy will open up new perspectives, leveraging on the spray-drying (aerosol) technique to shape microparticles from various nano-building blocks and on the entrapment of biological macromolecules to obtain new multifunctional hybrid microstructures.

CALB Immobilized onto Magnetic Nanoparticles for Efficient Kinetic Resolution of Racemic Secondary Alcohols: Long-Term Stability and Reusability

In this study, an immobilization strategy for magnetic cross-linking enzyme aggregates of lipase B from Candida antarctica (CALB) was developed and investigated. Magnetic particles were prepared by conventional co-precipitation. The magnetic nanoparticles were modified with 3-aminopropyltriethoxysilane (APTES) to obtain surface amino-functionalized magnetic nanoparticles (APTES⁻Fe₃O₄) as immobilization materials. Glutaraldehyde was used as a crosslinker to covalently bind CALB to APTES⁻Fe₃O₄. The optimal conditions of immobilization of lipase and resolution of racemic 1-phenylethanol were investigated. Under optimal conditions, esters could be obtained with conversion of 50%, enantiomeric excess of product (ee_p) > 99%, enantiomeric excess of substrate (ee_s) > 99%, and enantiomeric ratio (E) > 1000. The magnetic CALB CLEAs were successfully used for enzymatic kinetic resolution of fifteen secondary alcohols. Compared with Novozym 435, the magnetic CALB CLEAs exhibited a better enantioselectivity for most substrates. The conversion was still greater than 49% after the magnetic CALB CLEAs had been reused 10 times in a 48 h reaction cycle; both ee_s and ee_p were close to 99%. Furthermore, there was little decrease in catalytic activity and enantioselectivity after being stored at -20 °C for 90 days.

Synthesis of core–shell-structured mesoporous silica nanospheres with dual-pores for biphasic catalysis

A combination of a sol–gel process and oil–water biphase stratification was developed to fabricate dual-pore structured MSN.

Expanding the boundary of biocatalysis: design and optimization of in vitro tandem catalytic reactions for biochemical production

Biocatalysts have been increasingly used in the synthesis of fine chemicals and medicinal compounds due to significant advances in enzyme discovery and engineering. To mimic the synergistic effects of cascade reactions catalyzed by multiple enzymes in nature, researchers have been developing artificial tandem enzymatic reactions in vivo by harnessing synthetic biology and metabolic engineering tools. There is also growing interest in the development of one-pot tandem enzymatic or chemo-enzymatic processes in vitro due to their neat and concise catalytic systems and product purification procedures. In this review, we will briefly summarize the strategies of designing and optimizing in vitro tandem catalytic reactions, highlight a few representative examples, and discuss the future trend in this field.

Cell Membrane-Based Nanoreactor To Mimic the Bio-Compartmentalization Strategy of a Cell

Organelles of eukaryotic cells are structures made up of membranes, which carry out a majority of functions necessary for the surviving of the cell itself. Organelles also differentiate the prokaryotic and eukaryotic cells, and are arranged to form different compartments guaranteeing the activities for which eukaryotic cells are programmed. Cell membranes, containing organelles, are isolated from cancer cells and erythrocytes and used to form biocompatible and long-circulating ghost nanoparticles delivering payloads or catalyzing enzymatic reactions as nanoreactors. In this attempt, red blood cell membranes were isolated from erythrocytes, and engineered to form nanoerythrosomes (NERs) of 150 nm. The horseradish peroxidase, used as an enzyme model, was loaded inside the aqueous compartment of NERs, and its catalytic reaction with Resorufin was monitored. The resulting nanoreactor protected the enzyme from proteolytic degradation, and potentiated the enzymatic reaction in situ as demonstrated by maximal velocity (V_max) and Michaelis constant (K_m), thus suggesting the high catalytic activity of nanoreactors compared to the pure enzymes.

Colorimetric and Electrochemiluminescence Dual-Mode Sensing of Lead Ion Based on Integrated Lab-on-Paper Device

A highly selective two-point separation strategy was designed based on a cross-like all-in-one lab-on-paper analytical device. The stable and cleavable enzyme-coated reduced graphene oxide (rGO)-PdAu probe was fabricated as the signal reporter to enable the visualization and electrochemiluminescence (ECL) dual-mode sensing of Pb²⁺. Concretely, the experimental workflow consists of the following process: (i) fabrication of the lab-on-paper device and growth of Au nanoparticles on ECL detection zone, (ii) immobilization of Pb²⁺-specific DNAzyme, and (iii) hybridization between DNAzyme and rGO-PdAu-glucose oxidase (GOx) labeled oligonucleotide to form the double-stranded DNA. Upon addition of Pb²⁺ into the prepared system, the double-helix structure of the DNA was destroyed, resulting in the release of cleaved rGO-PdAu-GOx probe to visualization bar to promote the effective oxidation and color change of 3,3',5,5'-tetramethylbenzidine. As a consequence, the color change can be recognized by naked eye, meanwhile GOx on an uncleaved signal probe can oxidize glucose along with the H₂O₂ production. As a co-reaction reagent for luminol ECL system, the concentration of H₂O₂ is proportional to the ECL intensity, which constitutes a new mechanism for colorimetric and ECL dual mode to detect Pb²⁺. With the method developed here, the concentration of Pb²⁺ could be easily determined by the naked eye within a linear range from 5 to 2000 nM, as well as by monitoring the decreased ECL intensity of luminol in a linear range of 0.5-2000 nM. This work not only constructs a simple and versatile platform for on-site visible monitoring of Pb²⁺ in tap water and river water but also furnishes a strategy for designing a dual-mode sensing toward different heavy metal ions based on specific DNAzyme in the fields of environmental monitoring-related technologies.

Tandem catalysis induced by hollow PdO: highly efficient H2 generation coupled with organic dye degradation via sodium formate reforming

A unique tandem catalytic system by coupling H₂ production with organic dye degradation is achieved by hollow PdO.

Post-synthetically modified SBA-15 with NH2-coordinately immobilized iron-oxine: SBA-15/NH2-FeQ3 as a Fenton-like hybrid catalyst for the selective oxidation of organic sulfides

We herein report the synthesis and catalysis of SBA-15 grafted iron-oxine. SBA-15/NH₂-FeQ₃ showed efficient catalytic activity in sulfide oxidation.

Plasmolysis-Inspired Nanoengineering of Functional Yolk-Shell Microspheres with Magnetic Core and Mesoporous Silica Shell

Yolk-shell nanomaterials with a rattle-like structure have been considered ideal carriers and nanoreactors. Traditional methods to constructing yolk-shell nanostructures mainly rely on multistep sacrificial template strategy. In this study, a facile and effective plasmolysis-inspired nanoengineering strategy is developed to controllably fabricate yolk-shell magnetic mesoporous silica microspheres via the swelling-shrinkage of resorcinol-formaldehyde (RF) upon soaking in or removal of n-hexane. Using Fe₃O₄@RF microspheres as seeds, surfactant-silica mesostructured composite is deposited on the swelled seeds through the multicomponent interface coassembly, followed by solvent extraction to remove surfactant and simultaneously induce shrinkage of RF shell. The obtained yolk-shell microspheres (Fe₃O₄@RF@void@mSiO₂) possess a high magnetization of 40.3 emu/g, high surface area (439 m²/g), radially aligned mesopores (5.4 nm) in the outer shell, tunable middle hollow space (472-638 nm in diameter), and a superparamagnetic core. This simple method allows a simultaneous encapsulation of Au nanoparticles into the hollow space during synthesis, and it leads to spherical Fe₃O₄@RF@void-Au@mSiO₂ magnetic nanocatalysts, which show excellent catalysis efficiency for hydrogenation of 4-nitrophenol by NaBH₄ with a high conversion rate (98%) and magnetic recycling stability.