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.

Immobilization of Enzymes on Cyclodextrin-Anchored Dehiscent Mesoporous TiO2 for Efficient Photoenzymatic Hydroxylation

A three-in-one heterogeneous catalyst (UPO@dTiO₂-CD) was fabricated by grafting cyclodextrins (CDs) on the dehiscent TiO₂ (dTiO₂) surface and subsequently immobilizing unspecific peroxygenase (rAaeUPO), which exhibited double enhanced electron/mass transfer in photo-enzymatic enantioselective hydroxylation of the C-H bond. The tunable anatase/rutile phase ratio and dehiscent mesoporous architectures of dTiO₂ and the electron donor feature and hydrophobic inner cavity of the CDs are independently responsible for accelerating both electron and mass transfer. The coordination of the photocatalytic and enzymatic steps was achieved by structural and compositional regulation. The optimized UPO@dTiO₂-CD not only displayed high catalytic efficiency (turnover number and turnover frequency of rAaeUPO up to >65,000 and 91 min^-1, respectively) but also exhibited high stability and reusability.

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.

Carrier-Free Cross-linked Laccase Crystals for Biocatalytic Degradation of Textile Industrial Effluents

Herein, laccase from Trametes versicolor was used to fabricate carrier-free cross-linked laccase crystals (CLLCs) and deployed as a robust catalyst for waste effluent treatment. The surface morphology and involvement of functional group attributes of CLLCs were scrutinized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). As fabricated CLLCs were subjected to kinetic characterization by assessing the effects of pH environment, thermal profile, and substrate (determination of K_m and V_max) on the activity. A fully characterized CLLCs fraction was used to treat synthetic dyes containing waste effluents taken from various industries, i.e., Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills. Degradation profile revealed 36.8%, 27.6%, 39.9%, and 26.4% degradation of Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills, respectively, by the free form of laccase, whereas the biocatalytic activity of CCLCs led to 78.6%, 75.6%, 85.5%, and 63.3% degradation of those effluents. The decrease in peak and mass region alongside the presence of new peaks in GC-MS affirms the effective decolorization of contaminated waste effluents. CLLCs retained over 70% and 50% of their degradation activity after 3 and 5 cycles, respectively. In conclusion, CLLCs might represent a robust bioprocess to improve the usability of laccase for various synthetic dyes containing waste effluents to diminish environmental pollution from the dye-based industries.

Recent advanced development of metal-loaded mesoporous organosilicas as catalytic nanoreactors

Ordered periodic mesoporous organosilicas have been widely applied in adsorption/separation/sensor technologies and the fields of biomedicine/biotechnology as well as catalysis. Crucially, surface modification with functional groups and metal complexes or nanoparticle loading has ensured high efficacy and efficiency. This review will highlight the current state of design and catalytic application of transition metal-loaded mesoporous organosilica nanoreactors. It will outline prominent synthesis approaches for the grafting of metal complexes, metal salt adsorption and in situ preparation of metal nanoparticles, and summarize the catalytic performance of the resulting mesoporous organosilica hybrid materials. Finally, the potential prospects and challenges of metal-loaded mesoporous organosilica nanoreactors are addressed.

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.