Selective aerobic oxidation reactions using a combination of photocatalytic water oxidation and enzymatic oxyfunctionalisations

The effect of UV365/Fenton process on the removal of gaseous ethylbenzene in a bubble column reactor

As volatile organic compounds (VOCs), gaseous ethylbenzene has adverse effects on human health and ecology. Therefore, an effective degradation process is highly desirable. The Fenton process under UV 365 nm was selected as the first option to remove gaseous ethylbenzene in a bubble column reactor. The main parameters for the batch experiments were systematically studied, including H2O2 concentration, [H2O2]/[Fe2+], pH, UV wavelength, UV intensity, gaseous ethylbenzene concentration, gas flow rate, and process stability towards removal efficiency. The optimum conditions were found to be H2O2 concentration of 100 mmol·L-1, [H2O2]/[Fe2+] of 4, pH of 3.0, UV wavelength of 365 nm, UV power of 5 W, gas flow rate of 900 mL·min-1, and gaseous ethylbenzene concentration of 30 ppm, resulting in a removal efficiency of 76.3%. The study found that the Fenton process, when coupled with UV 365 nm, was highly effective in removing gaseous ethylbenzene. The degradation mechanism of gaseous ethylbenzene was proposed in the UV365/Fenton process based on EPR, radical quenching experiments, iron analysis, carbon balance, and GC-MS analysis. The results indicated that •OH played a crucial role in the process.

Enhanced Photobiocatalytic Cascades at Pickering Droplet Interfaces

Developing new methods to engineer photobiocatalytic reactions is of utmost significance for artificial photosynthesis, but it remains a grand challenge due to the intrinsic incompatibility of biocatalysts with photocatalysts. In this work, photocatalysts and enzymes were spatially colocalized at Pickering droplet interfaces, where the reaction microenvironment and the spatial distance between two distinct catalysts were exquisitely regulated to achieve unprecedented photobiocatalytic cascade reactions. As proof of the concept, ultrathin graphitic carbon nitride nanosheets loaded with Au nanoparticles were precisely positioned in the outer interfacial layer of Pickering oil droplets to produce H2O2 under light irradiation, while enzymes were exactly placed in the inner interfacial layer to catalyze the subsequent biocatalytic oxidation reactions using in situ formed H2O2 as an oxidant. In the alkene epoxidation and thioether oxidation, our interfacial photobiocatalytic cascades showed a 2.0-5.8-fold higher overall reaction efficiency than the photobiocatalytic cascades in the bulk water phase. It was demonstrated that spatial localization of the photocatalyst and the enzyme at Pickering oil droplet interfaces not only provided their respective preferable reaction environments and intimate proximity for rapid H2O2 transport but also protected the enzyme from oxidative inactivation caused by the photogenerated species. These remarkable interfacial effects contributed to the significantly enhanced photobiocatalytic cascading efficiency. Our work presents an innovative photobiocatalytic reaction system with manifold benefits, providing a cutting-edge platform for solar-driven chemical transformations via photobiocatalysis.

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.

Engineering carboxylic acid reductases and unspecific peroxygenases for flavor and fragrance biosynthesis

Emerging consumer demand for safer, more sustainable flavors and fragrances has created new challenges for the industry. Enzymatic syntheses represent a promising green production route, but the broad application requires engineering advancements for expanded diversity, improved selectivity, and enhanced stability to be cost-competitive with current methods. This review discusses recent advances and future outlooks for enzyme engineering in this field. We focus on carboxylic acid reductases (CARs) and unspecific peroxygenases (UPOs) that enable selective productions of complex flavor and fragrance molecules. Both enzyme types consist of natural variants with attractive characteristics for biocatalytic applications. Applying protein engineering methods, including rational design and directed evolution in concert with computational modeling, present excellent examples for property improvements to unleash the full potential of enzymes in the biosynthesis of value-added chemicals.

Reaction engineering blocks ether cleavage for synthesizing chiral cyclic hemiacetals catalyzed by unspecific peroxygenase

Hemiacetal compounds are valuable building blocks in synthetic chemistry, but their enzymatic synthesis is limited and often hindered by the instability of hemiacetals in aqueous environments. Here, we show that this challenge can be addressed through reaction engineering by using immobilized peroxygenase from Agrocybe aegerita (AaeUPO) under neat reaction conditions, which allows for the selective C-H bond oxyfunctionalization of environmentally significant cyclic ethers to cyclic hemiacetals. A wide range of chiral cyclic hemiacetal products are prepared in >99% enantiomeric excess and 95170 turnover numbers of AaeUPO. Furthermore, by changing the reaction medium from pure organic solvent to alkaline aqueous conditions, cyclic hemiacetals are in situ transformed into lactones. Lactams are obtained under the applied conditions, albeit with low enzyme activity. These findings showcase the synthetic potential of AaeUPO and offer a practical enzymatic approach to produce chiral cyclic hemiacetals through C-H oxyfunctionalization under mild conditions.

In Situ Generation of H2O2 over MoOx Decorated on Cu2O@CuO Core-Shell Particle Nanoarchitectonics for Boosting Photocatalytic Oxidative Desulfurization

Photocatalytic oxidation desulfurization (PODS) has emerged as a promising, ecofriendly alternative to traditional, energy-intensive fuel desulfurization methods. Nevertheless, its progress is still hindered due to the slow sulfide oxidation kinetics in the current catalytic systems. Herein, we present a MoOx decorated on a Cu2O@CuO core-shell catalyst, which enables a new, efficient PODS pathway by in situ generation of hydrogen peroxide (H2O2) with saturated moist air as the oxidant source. The photocatalyst delivers remarkable specific activity in oxidizing dibenzothiophene (DBT), achieving a superior rate of 7.8 mmol g-1 h-1, while maintaining a consistent performance across consecutive reuses. Experimental investigations reveal that H2O2 is produced through the two-electron oxygen reduction reaction (ORR), and both H2O2 and the hydroxyl radicals (•OH) generated from it act as the primary reactive species responsible for sulfide oxidation. Importantly, our catalyst accomplishes complete PODS of real diesel fuel, underscoring an appealing industrial prospect for our photocatalyst.

Photocatalytic aerobic oxidation of C(sp3)-H bonds

In modern industries, the aerobic oxidation of C(sp3)-H bonds to achieve the value-added conversion of hydrocarbons requires high temperatures and pressures, which significantly increases energy consumption and capital investment. The development of a light-driven strategy, even under natural sunlight and ambient air, is therefore of great significance. Here we develop a series of hetero-motif molecular junction photocatalysts containing two bifunctional motifs. With these materials, the reduction of O2 and oxidation of C(sp3)-H bonds can be effectively accomplished, thus realizing efficient aerobic oxidation of C(sp3)-H bonds in e.g., toluene and ethylbenzene. Especially for ethylbenzene oxidation reactions, excellent catalytic capacity (861 mmol g cat-1) is observed. In addition to the direct oxidation of C(sp3)-H bonds, CeBTTD-A can also be applied to other types of aerobic oxidation reactions highlighting their potential for industrial applications.

Anchoring a Structurally Editable Proximal Cofactor-like Module to Construct an Artificial Dual-center Peroxygenase

A recent novel strategy for constructing artificial metalloenzymes (ArMs) that target new-to-nature functions uses dual-functional small molecules (DFSMs) with catalytic and anchoring groups for converting P450BM3 monooxygenase into a peroxygenase. However, this process requires excess DFSMs (1000 equivalent of P450) owing to their low binding affinity for P450, thus severely limiting its practical application. Herein, structural optimization of the DFSM-anchoring group considerably enhanced their binding affinity by three orders of magnitude (Kd ≈10-8  M), thus approximating native cofactors, such as FMN or FAD in flavoenzymes. An artificial cofactor-driven peroxygenase was thus constructed. The co-crystal structure of P450BM3 bound to a DFSM clearly revealed a precatalytic state in which the DFSM participates in H2 O2 activation, thus facilitating peroxygenase activity. Moreover, the increased binding affinity substantially decreases the DFSM load to as low as 2 equivalents of P450, while maintaining increased activity. Furthermore, replacement of catalytic groups showed disparate selectivity and activity for various substrates. This study provides an unprecedented approach for assembling ArMs by binding editable organic cofactors as a co-catalytic center, thereby increasing the catalytic promiscuity of P450 enzymes.

A Simple Access to γ- and ε-Keto Arenes via Enzymatic Divergent C─H Bond Oxyfunctionalization

Performing divergent C─H bond functionalization on molecules with multiple reaction sites is a significant challenge in organic chemistry. Biocatalytic oxyfunctionalization reactions of these compounds to the corresponding ketones/aldehydes are typically hindered by selectivity issues. To address these challenges, the catalytic performance of oxidoreductases is explored. The results show that combining the peroxygenase-catalyzed propargylic C─H bond oxidation with the Old Yellow Enzyme-catalyzed reduction of conjugated C─C triple bonds in one-pot enables the regio- and chemoselective oxyfunctionalization of sp3 C─H bonds that are distant from benzylic sites. This enzymatic approach yielded a variety of γ-keto arenes with diverse structural and electronic properties in yields of up to 99% and regioselectivity of 100%, which are difficult to achieve using other chemocatalysis and enzymes. By adjusting the C─C triple bond, the carbonyl group's position can be further tuned to yield ε-keto arenes. This enzymatic approach can be combined with other biocatalysts to establish new synthetic pathways for accessing various challenging divergent C─H bond functionalization reactions.

Photoredox/Enzymatic Catalysis Enabling Redox-Neutral Decarboxylative Asymmetric C-C Coupling for Asymmetric Synthesis of Chiral 1,2-Amino Alcohols

Photocatalysis offers tremendous opportunities for enzymes to access new functions. Herein, we described a redox-neutral photocatalysis/enzymatic catalysis system for the asymmetric synthesis of chiral 1,2-amino alcohols via decarboxylative radical C-C coupling of N-arylglycines and aldehydes by combining an organic photocatalyst, eosin Y, and carbonyl reductase RasADH. Notably, this protocol avoids using any sacrificial reductants. A possible reaction mechanism proposed is that the transformation proceeds through sequential photoinduced decarboxylative radical addition to an aldehyde and a photoenzymatic deracemization pathway. This redox-neutral photoredox/enzymatic strategy is promising not only for effective synthesis of a series of chiral amino alcohols in a green and sustainable manner but also for the design of other novel C-C radical coupling transformations for the synthesis of bioactive molecules.

Nanofibrous Dressing with Nanocomposite Monoporous Microspheres for Chemodynamic Antibacterial Therapy and Wound Healing

The excessive use of antibiotics and consequent bacterial resistance have emerged as crucial public safety challenges for humanity. As a promising antibacterial treatment, using reactive oxygen species (ROS) can effectively address this problem and has the advantages of being highly efficient and having low toxicity. Herein, electrospinning and electrospraying were employed to fabricate magnesium oxide (MgO)-based nanoparticle composited polycaprolactone (PCL) nanofibrous dressings for the chemodynamic treatment of bacteria-infected wounds. By utilizing electrospraying, erythrocyte-like monoporous PCL microspheres incorporating silver (Ag)- and copper (Cu)-doped MgO nanoparticles were generated, and the unique microsphere-filament structure enabled efficient anchoring on nanofibers. The composite dressings produced high levels of ROS, as confirmed by the 2,7-dichloriflurescin fluorescent probe. The sustained generation of ROS resulted in efficient glutathione oxidation and a remarkable bacterial killing rate of approximately 99% against Staphylococcus aureus (S. aureus). These dressings were found to be effective at treating externally infected wounds. The unique properties of these composite nanofibrous dressings suggest great potential for their use in the medical treatment of bacteria-infected injuries.

Light-Controlled Biocatalysis by Unspecific Peroxygenases with Genetically Encoded Photosensitizers

Fungal unspecific peroxygenases (UPOs) have gained substantial attention for their versatile oxyfunctionalization chemistry paired with impressive catalytic capabilities. A major drawback, however, remains their sensitivity towards their co-substrate hydrogen peroxide, necessitating the use of smart in situ hydrogen peroxide generation methods to enable efficient catalysis setups. Herein, we introduce flavin-containing protein photosensitizers as a new general tool for light-controlled in situ hydrogen peroxide production. By genetically fusing flavin binding fluorescent proteins and UPOs, we have created two virtually self-sufficient photo-enzymes (PhotUPO). Subsequent testing of a versatile substrate panel with the two divergent PhotUPOs revealed two stereoselective conversions. The catalytic performance of the fusion protein was optimized through enzyme and substrate loading variation, enabling up to 24300 turnover numbers (TONs) for the sulfoxidation of methyl phenyl sulfide. The PhotUPO concept was upscaled to a 100 mg substrate preparative scale, enabling the extraction of enantiomerically pure alcohol products.

Versatile synthesis of nano-icosapods via cation exchange for effective photocatalytic conversion of biomass-relevant alcohols

Branched metal chalcogenide nanostructures with well-defined composition and configuration are appealing photocatalysts for solar-driven organic transformations. However, precise design and controlled synthesis of such nanostructures still remain a great challenge. Herein, we report the construction of a variety of highly symmetrical metal sulfides and heterostructured icosapods based on them, in which twenty branches were radially grown in spatially ordered arrangement, with a high degree of structure homogeneity. Impressively, the as-obtained CdS-PdxS icosapods manifest a significantly improved photocatalytic activity for the selective oxidation of biomass-relevant alcohols into corresponding aldehydes coupled with H2 evolution under visible-light irradiation (>420 nm), and the apparent quantum yield of the benzyl alcohol reforming can be achieved as high as 31.4% at 420 nm. The photoreforming process over the CdS-PdxS icosapods is found to be directly triggered by the photogenerated electrons and holes without participation of radicals. The enhanced photocatalytic performance is attributed to the fast charge separation and abundant active sites originating from the well-defined configuration and spatial organization of the components in the branched heterostructures.

An Atomically Dispersed Mn-Photocatalyst for Generating Hydrogen Peroxide from Seawater via the Water Oxidation Reaction (WOR)

In this work, we have fabricated an aryl amino-substituted graphitic carbon nitride (g-C₃N₄) catalyst with atomically dispersed Mn capable of generating hydrogen peroxide (H₂O₂) directly from seawater. This new catalyst exhibited excellent reactivity, obtaining up to 2230 μM H₂O₂ in 7 h from alkaline water and up to 1800 μM from seawater under identical conditions. More importantly, the catalyst was quickly recovered for subsequent reuse without appreciable loss in performance. Interestingly, unlike the usual two-electron oxygen reduction reaction pathway, the generation of H₂O₂ was through a less common two-electron water oxidation reaction (WOR) process in which both the direct and indirect WOR processes occurred; namely, photoinduced h⁺ directly oxidized H₂O to H₂O₂ via a one-step 2e^- WOR, and photoinduced h⁺ first oxidized a hydroxide (OH^-) ion to generate a hydroxy radical (^•OH), and H₂O₂ was formed indirectly by the combination of two ^•OH. We have characterized the material, at the catalytic sites, at the atomic level using electron paramagnetic resonance, X-ray absorption near edge structure, extended X-ray absorption fine structure, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, magic-angle spinning solid-state NMR spectroscopy, and multiscale molecular modeling, combining classical reactive molecular dynamics simulations and quantum chemistry calculations.

Optimization of the tandem enzyme activity of V-MOF and its derivatives for highly sensitive nonenzymatic detection of cholesterol in living cells

It remains a great challenge to properly design and synthesize single-component artificial tandem enzymes for specific substrates with high selectivity. Herein, V-MOF is synthesized by solvothermal method and its derivatives are constructed via pyrolyzing V-MOF in nitrogen atmosphere at different temperatures, which are denoted as V-MOF-y (y = 300, 400, 500, 700 and 800). V-MOF and V-MOF-y possess tandem enzyme-like activity, i.e. cholesterol oxidase-like and peroxidase-like activity. Among them, V-MOF-700 shows the strongest tandem enzyme activity for V-N bonds. Based on the cascade enzyme activity of V-MOF-700, the nonenzymatic detection platform for cholesterol by fluorescent assay can be established in the presence of o-phenylenediamine (OPD) for the first time. The detection mechanism is that V-MOF-700 catalyzes cholesterol to generate hydrogen peroxide and further form hydroxyl radical (•OH), which can oxidize OPD to obtain oxidized OPD (oxOPD) with yellow fluorescence. The linear detection of cholesterol ranges of 2-70 μM and 70-160 μM with a lower detection limit of 0.38 μM (S/N = 3) are obtained. This method is used to detect cholesterol in human serum successfully. Especially, it can be applied to the rough quantification of membrane cholesterol in living tumor cells, indicating that it has the potential for clinical application.

Photobiocatalytic Strategies for Organic Synthesis

Biocatalysis has revolutionized chemical synthesis, providing sustainable methods for preparing various organic molecules. In enzyme-mediated organic synthesis, most reactions involve molecules operating from their ground states. Over the past 25 years, there has been an increased interest in enzymatic processes that utilize electronically excited states accessed through photoexcitation. These photobiocatalytic processes involve a diverse array of reaction mechanisms that are complementary to one another. This comprehensive review will describe the state-of-the-art strategies in photobiocatalysis for organic synthesis until December 2022. Apart from reviewing the relevant literature, a central goal of this review is to delineate the mechanistic differences between the general strategies employed in the field. We will organize this review based on the relationship between the photochemical step and the enzymatic transformations. The review will include mechanistic studies, substrate scopes, and protein optimization strategies. By clearly defining mechanistically-distinct strategies in photobiocatalytic chemistry, we hope to illuminate future synthetic opportunities in the area.

Coalescence of As(II) with •OH: The pivot for co-processing of As(III) and butyl xanthate

Although water metalloid pollution is widely studied, the effect of the combined pollution of organic matter and metalloids in mining water and, especially, the possible interaction mechanisms between metalloids and flotation reagents, are both poorly understood. Existence of mixed pollution of metalloids and organic compounds tends to cause more serious harm to natural organisms. In this study, a synergistic removal of arsenite (As(III)) and butyl xanthate (Bx) in an advanced oxidation system was reported using biochar-based catalyst loaded with nano-zero-valent iron from an inexpensive iron source (iron slag) to activate peroxodisulfate. The removal efficiencies were improved by 30 % in the co-existence of As(III) and Bx compared to those of the single pollutant. The theoretical calculations, especially frontier molecular orbital theory, revealed the generation of [AsO₂-OH]^•- by the combination of As(II) with •OH. This [AsO₂-OH]^•- participated in the oxidative degradation of Bx with high activity and combined with the sulfur falling off Bx after the reaction to form a novel Fe-As-S complex as indicated by X-ray absorption +fine structure analysis. Overall, this study reports the generation of low-valent arsenic active substances of [AsO₂-OH]^•- and their effect on the removal of organic pollution containing S atoms in advanced oxidation systems under typical mining water conditions with the coexistence of As(III) and expands the understanding and application of traditional free radicals.

Horseradish Peroxidase-Coupled Ag3 PO4 /BiVO4 Photoanode for Biophotoelectrocatalytic Degradation of Organic Contaminants

Photoelectrocatalysis (PEC) is regarded as a promising and sustainable process for removal of organic contaminants from wastewater. Meanwhile, enzymatic catalysis also provides an effective way to carry out polluted environment remediation under mild conditions. In this study, a biophotoelectrocatalytic (BPEC) system is designed to remove 4-nitrophenol (4-NP) based on a combination of PEC and enzymatic catalysis. The developed BPEC system is constructed with a Ag₃ PO₄ /BiVO₄ photoanode and a horseradish peroxidase (HRP)-loaded carbon cloth (CC) cathode. On the photoanode, the construction of a direct Z-scheme Ag₃ PO₄ /BiVO₄ heterojunction enhanced the separation efficiency of photogenerated carriers, which promoted the PEC degradation of 4-NP under visible light irradiation. After HRP was immobilized on the cathode, the degradation efficiency of 4-NP reached 97.1 % after 60 min PEC treatment. The result could be ascribed to the HRP-catalyzed oxidation reaction via in situ-generated H₂ O₂ from the CC cathode during the PEC process. Moreover, the possible degradation pathways of 4-NP in such a BPEC system are also discussed.

Lignocellulosic biomass valorization via bio-photo/electro hybrid catalytic systems

Lignocellulosic biomass valorization is regarded as a promising approach to alleviate energy crisis and achieve carbon neutrality. Bioactive enzymes have attracted great attention and been commonly applied for biomass valorization owing to their high selectivity and catalytic efficiency under environmentally benign reaction conditions. Same as biocatalysis, photo-/electro-catalysis also happens at mild conditions (i.e., near ambient temperature and pressure). Therefore, the combination of these different catalytic approaches to benefit from their resulting synergy is appealing. In such hybrid systems, harness of renewable energy from the photo-/electro-catalytic compartment can be combined with the unique selectivity of biocatalysts, therefore providing a more sustainable and greener approach to obtain fuels and value-added chemicals from biomass. In this review, we firstly introduce the pros/cons, classifications, and the applications of photo-/electro-enzyme coupled systems. Then we focus on the fundamentals and comprehensive applications of the most representative biomass-active enzymes including lytic polysaccharide monooxygenases (LPMOs), glucose oxidase (GOD)/dehydrogenase (GDH) and lignin peroxidase (LiP), together with other biomass-active enzymes in the photo-/electro- enzyme coupled systems. Finally, we propose current deficiencies and future perspectives of biomass-active enzymes to be applied in the hybrid catalytic systems for global biomass valorization.

Coupling anodic and cathodic reactions using an electrocatalytic dual-membrane system actuates ultra-efficient degradation with regulable mechanisms

The versatile reaction possibilities arising from the interaction between the anodic and cathodic reactions naturally contained in electrocatalytic membrane filtration (EMF) systems are of great valuable in meeting the current complex water treatment requirements. But currently, most studies only focus on half-cell reactions with a single electrocatalytic membrane, which limits the research progress of the EMF technology. Here we report a coupling strategy that utilizes the interaction between the anodic and cathodic reactions to actuate ultra-efficient degradation performance with regulable reaction mechanisms. An electrocatalytic dual-membrane filtration (EDMF) system was established. Six typical configurations of the EDMF system were set up and systematically investigated by adjusting the electrode distance and filtration sequence. Based on the obtained results of degradation performance and mechanisms, a regulation strategy which enabled flexible tuning of direct nonradical oxidation (e.g., h⁺) and indirect oxidation (e.g., ¹O₂, ·OH, HO₂·, O₂·^-, etc.) was proposed. In particular, cathodic reactions were found to adversely affect the anodic reactions at the relatively short electrode distance of 0.9 mm. Anodic reactions could inhibit the generation of ¹O₂ at short distance of 0.9 mm but promote its generation at long distances of 9 and 17 mm. The A-C_0.9 configuration achieved the highest degradation performance, while the C-A_9 configuration was revealed to be much more conducive to ¹O₂ production. Overall, our findings demonstrate the versatility and tunability of the reaction mechanism and performance of the EDMF system due to the flexible coupling of the anodic and cathodic reactions, which potentially lays a foundation for future development of ultra-efficient mechanism-adjustable electrocatalysis technologies.

Ni(NH3)62+ more efficient than Ni(H2O)62+ and Ni(OH)2 for catalyzing water and phenol oxidation on illuminated Bi2MoO6 with visible light

Nickel (hydr)oxide (NiOH) is known to be good co-catalyst for the photoelectrochemical oxidation of water, and for the photocatalytic oxidation of organics on different semiconductors. Herein we report a greatly improved activity of Bi₂MoO₆ (BMO) by nickel hexammine perchlorate (NiNH). Under visible light, phenol oxidation on BMO was slow. After NiNH, NiOH, and Ni²⁺ loading, a maximum rate of phenol oxidation increased by factors of approximately 16, 8.8, and 4.7, respectively. With a BMO electrode, all catalysts inhibited O₂ reduction, enhanced water (photo-)oxidation, and facilitated the charge transfer at solid-liquid interface, respectively, the degree of which was always NiNH > NiOH > Ni²⁺. Solid emission spectra indicated that all catalysts improved the charge separation of BMO, the degree of which also varied as NiNH > NiOH > Ni²⁺. Furthermore, after a phenol-free aqueous suspension of NiNH/BMO was irradiated, there was a considerable Ni(III) species, but a negligible NH₂ radical. Accordingly, a plausible mechanism is proposed, involving the hole oxidation of Ni(II) into Ni(IV), which is reactive to phenol oxidation, and hence promotes O₂ reduction. Because NH₃ is a stronger ligand than H₂O, the Ni(II) oxidation is easier for Ni(NH₃)⁶⁺ than for Ni(H₂O)⁶⁺. This work shows a simple route how to improve BMO photocatalysis through a co-catalyst.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

Efficient Doping Induced by Charge Transfer at the Hetero-Interface to Enhance Photocatalytic Performance

The construction of heterojunction photocatalysts is an effective method to improve photocatalytic efficiency since the potential gradient and built-in electron field established at the junction could enhance the efficiency of charge separation and interfacial charge transfer. Nevertheless, heterojunction photocatalysts with strong built-in electron fields remain difficult to build since the two adjacent constitutes must be satisfied with an appropriate band alignment, redox potential, and carrier concentration gradient. Here, an efficient charge transfer-induced doping strategy is proposed to enhance the heterojunction built-in electron field for stable and efficient photocatalytic performance. Carrier transfer tests show that the rectification ratio of the n-TiO_2-X/n-BiOI heterojunction is significantly enhanced after being coated with graphene oxide (GO). Consequently, both the hydrogen production and photodegradation performance of the GO composite heterojunction are considerably enhanced compared with pure TiO_2-X, BiOI, and n-TiO_2-X/n-BiOI. This work provides a facile method to prepare heterojunction photocatalysts with a high catalytic activity.

An economic, self-supporting, robust and durable LiFe5O8 anode for sulfamethoxazole degradation

Electrochemically activating peroxydisulfate (PDS) to degrade organic pollutants is one of the most attractive advanced oxidation processes (AOPs) to address environmental issues, but the high cost, poor stability, and low degradation efficiency of the anode materials hinder their application. Herein, an economic, self-supporting, robust, and durable LiFe₅O₈ on Fe substrate (Fe@LFO) anode is reported to degrade sulfamethoxazole (SMX). When PDS is electrochemically activated by the Fe@LFO anode, the degradation rate of SMX is significantly improved. It is found that hydroxyl radicals (•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), Fe(Ⅳ), activated PDS (PDS*), and direct electron transfer (DET) reactions synergistically contribute to the degradation of SMX, which can realize the degradation of SMX in four possible routes: cleavage of the isoxazole ring, hydroxylation of the benzene ring, oxidation of the aniline group, and cleavage of the S-N bond, as evidenced by a series of tests of radicals quenching, electron paramagnetic resonance (EPR), linear sweep voltammetry (LSV) and liquid chromatograph mass spectrometer (LC-MS). Furthermore, Fe@LFO has good structural stability, excellent cyclability and low degradation cost, demonstrating its great potential for practical applications. This work contributes to a stable and effective anode material in the field of AOPs.

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.

Carbonized polyaniline-activated peracetic acid advanced oxidation process for organic removal: Efficiency and mechanisms

Recently, advanced oxidation processes (AOPs) based upon peracetic acid (PAA) with high efficiency for degrading aqueous organic contaminants have attracted extensive attention. Herein, a novel metal-free N-doped carbonaceous catalyst, namely, carbonized polyaniline (CPANI), was applied to activate PAA to degrade phenolic and pharmaceutical pollutants. The results showed that the CPANI/PAA system could effectively degrade 10 μM phenol in 60 min with low concentrations of PAA (0.1 mM) and catalyst (25 mg L^-1). This system also performed well within a wide pH range of 5-9 and displayed high tolerance to Cl^-, HCO₃^- and humic acid. The nonradical pathway [singlet oxygen (¹O₂)] was found to be the dominant pathway for degrading organic contaminants in the CPNAI/PAA system. Systematic characterization revealed that the graphitic N, pyridinic N, carbonyl groups (CO) and defects played the role of active sites on CPANI during the activation of PAA. The catalytic capacity of spent CPANI could be conveniently recovered by thermal treatment. The findings will be helpful for the application of metal-free carbonaceous catalyst/PAA processes in decontaminating water.

Single Copper Atom Photocatalyst Powers an Integrated Catalytic Cascade for Drug-Resistant Bacteria Elimination

To address the issue posed by drug-resistant bacteria and inspired by natural antimicrobial enzymes, we report the atomically doped copper on guanine-derived nanosheets (G-Cu) that possess the integrated catalytic cascade property of glucose oxidase and peroxidase, yielding free radicals to eliminate drug-resistant bacteria upon light irradiation. Density functional theory calculations demonstrate that copper could notably promote oxygen activation and H₂O₂ splitting on the G-Cu complexes. Further all-atom simulation and experimental data indicate that the lysis of bacteria is mainly induced by cell membrane damage and the elevation of intracellular reactive oxygen species. Lastly, the G-Cu complexes efficiently eliminate the staphylococci in the infected wounds and accelerate their closure in a murine model, with negligible side effects on the normal tissues. Therefore, our G-Cu complexes may provide an efficient nonantibiotic alternative to the current treatments for bacterial infections.

A Photoenzymatic Strategy for Radical-Mediated Stereoselective Hydroalkylation with Diazo Compounds

Carbene insertion reactions initiated with diazo compounds have been widely used to develop unnatural enzymatic reactions. However, alternative functionalization of diazo compounds in enzymatic processes has been unexploited. Herein, we describe a photoenzymatic strategy for radical-mediated stereoselective hydroalkylation with diazo compounds. This method generates carbon-centered radicals through an ene reductase catalyzed photoinduced electron transfer process from diazo compounds, enabling the synthesis of γ-stereogenic carbonyl compounds in good yields and stereoselectivities. This study further expands the possible reaction patterns in photo-biocatalysis and offers a new approach to solving the selectivity challenges of radical-mediated reactions.

Regiodivergent and Enantioselective Hydroxylation of C-H bonds by Synergistic Use of Protein Engineering and Exogenous Dual-Functional Small Molecules

It is a great challenge to optionally access diverse hydroxylation products from a given substrate bearing multiple reaction sites of sp³ and sp² C-H bonds. Herein, we report the highly selective divergent hydroxylation of alkylbenzenes by an engineered P450 peroxygenase driven by a dual-functional small molecule (DFSM). Using combinations of various P450BM3 variants with DFSMs enabled access to more than half of all possible hydroxylated products from each substrate with excellent regioselectivity (up to >99 %), enantioselectivity (up to >99 % ee), and high total turnover numbers (up to 80963). Crystal structure analysis, molecular dynamic simulations, and theoretical calculations revealed that synergistic effects between exogenous DFSMs and the protein environment controlled regio- and enantioselectivity. This work has implications for exogenous-molecule-modulated enzymatic regiodivergent and enantioselective hydroxylation with potential applications in synthetic chemistry.

Cost-Effective H2 O2 -Regeneration of Powdered Activated Carbon by Isolated Fe Sites

The reuse of powdered activated carbon (PAC) vitally determines the economics and security of the PAC-based adsorption process, while state-of-the-art PAC regeneration technologies are usually unsatisfactory. Here, it is demonstrated that isolated Fe sites anchored on commercial PAC enable fast H₂ O₂ activation to produce Fe-based reactive oxygen species for highly efficient PAC regeneration at room temperature. Taking rhodamine B as a representative pollutant, PAC decorated with isolated Fe sites realize H₂ O₂ based regeneration with negligible adsorption capacity degradation for 10 cycles. Moreover, in terms of the PAC loss rate, this technology is greatly superior to traditional Fenton-based regeneration technology. Further operando experiments and theoretical calculations reveal that the high regeneration performance can be attributed to the isolated HOFeO motifs, which activate H₂ O₂ via a nonradical reaction pathway. These findings provide a very promising strategy toward reducing the cost of H₂ O₂ -based PAC regeneration technology.

Introduction to Cyanobacteria

Cyanobacteria are highly interesting microbes with the capacity for oxygenic photosynthesis. They fulfill an important purpose in nature but are also potent biocatalysts. This chapter gives a brief overview of this diverse phylum and shortly addresses the functions these organisms have in the natural ecosystems. Further, it introduces the main topics covered in this volume, which is dealing with the development and application of cyanobacteria as solar cell factories for the production of chemicals including potential fuels. We discuss cyanobacteria as industrial workhorses, present established chassis strains, and give an overview of the current target products. Genetic engineering strategies aiming at the photosynthetic efficiency as well as approaches to optimize carbon fluxes are summarized. Finally, main cultivation strategies are sketched.

A Horseradish Peroxidase-Mediator System for Benzylic C-H Activation

Enzyme-mediator systems generate radical intermediates that abstract hydrogen atoms under mild conditions. These systems have been employed extensively for alcohol oxidation, primarily in biomass degradation, but they are underexplored for direct activation of C(sp3)-H bonds in alkyl groups. Here, we combine horseradish peroxidase (HRP), H2O2, and redox mediator N-hydroxyphthalimide (NHPI) for C(sp3)-H functionalization of alkylbenzene-type substrates. The HRP-NHPI system is >10-fold more active than existing enzyme-mediator systems in converting alkylbenzenes to ketones and aldehydes under air, and it operates from 0-50 °C and in numerous aqueous-organic solvent mixtures. The benzylic substrate radical can be trapped through a reaction with NHPI, demonstrating the formation of benzylic products beyond ketones. Furthermore, we demonstrate a one-pot, two-step enzymatic cascade for converting alkylbenzenes to benzylic amines. Overall, the HRP-NHPI system enables the selective benzylic C-H functionalization of diverse substrates under mild conditions using a straightforward procedure.

Deracemization of racemic alcohols combining photooxidation and biocatalytic reduction

We described a cascade reaction for deracemization of racemic alcohols combining photooxidation and enzymatic reduction under mild conditions without the isolation of intermediate ketones. Using different ketoreductases, a variety of racemic alcohols can be successfully converted into (R)- or (S)-enantiomers in high yields (up to 95%) and stereoselectivity (up to 99%).

Modulating the Electronic Coordination Configuration and d-Band Center in Homo-Diatomic Fe2N6 Catalysts for Enhanced Peroxymonosulfate Activation

The electronic coordination configuration of metal active sites and the reaction mechanism were investigated by constructing homo-diatomic Fe sites for visible-light-assisted heterogeneous peroxymonosulfate (PMS) activation. A novel Fe₂N₆ catalyst was synthesized by selecting uniform pyridinic-N of graphitic carbon nitride (g-C₃N₄) as anchoring sites. The results demonstrated that homo-diatomic Fe sites modulated the d-band center and electron delocalization and thus enhanced the PMS activation kinetics (3.58 times vs single-atom Fe catalyst) with k_obs of 0.111 min^-1 owing to the synergistic effect between adjacent Fe atoms. New Fe-Fe coordination significantly decreased the contribution of the antibonding state in the Fe-O bond due to the coupling of the Fe-3d orbitals, which facilitated the O-O bond cleavage of the Fe₂-HOO-SO₃ complex with a reduced thermodynamic energy barrier of only -0.29 eV. This work provided comprehensive mechanistic insights into developing homo-diatomic catalysts governed by the coordination configuration and radical pathway for efficient heterogeneous PMS catalysis.

Insights into the removal of organic contaminants by calcium sulfite activation with Fe(III): Performance, kinetics, and mechanisms

S(IV)-based advanced oxidation process has been applied for contaminants remediation. However, as a traditional source of sulfite (SO₃^2-), Na₂SO₃ is extremely soluble in water, resulting in a high concentration of SO₃^2- to quench the generated reactive oxygen species (ROS). In this work, CaSO₃ was introduced instead of Na₂SO₃ for its slow-released SO₃^2- ability and Fe(III)/CaSO₃ system was established for the removal of trichloroethylene (TCE) and other organic contaminants. The degradation efficiency of TCE reached 94.0% and TCE could be completely dechlorinated and mineralized, while the removal of other contaminants was all over 85.0% at the optimal tested conditions. Through EPR detection, ROS scavenging and probe tests, and quantification of ROS amounts, it was concluded that the dominant ROS in Fe(III)/CaSO₃ system were SO₄^-· and ¹O₂, of which the transformation mechanism of SO₄^-· to ¹O₂ was revealed and demonstrated comprehensively. The synergistic contaminants degradation performance in different sulfur-iron-containing systems and in the presence of oxidants was evaluated. The effects of various solution conditions were assessed and Fe(III)/CaSO₃ system was of higher resistance on complex solution matrixes, suggesting the broad-spectrum and application perspective for the remediation of complex contaminants in actual water.

Visible-light-driven 3D Bi5O7I/BiOCl microsphere with enhanced photocatalytic capability: Performance, degradation pathway, antibacterium and mechanism

It is well known that both of the separation efficiency of photogenerated carriers and the response capability to visible light remarkably affect the photocatalytic performance. In the present work, a 3D microsphere of Bi₅O₇I/BiOCl heterojunction catalyst was synthetised. The synergy of Bi₅O₇I and BiOCl not only significantly enhances the transfer rate and separation efficiency of carriers, but also heightens light absorption capacity. As-prepared Bi₅O₇I/BiOCl (40 wt% BiOCl) has a higher degradation efficiency on doxycycline hydrochloride (DC) (90 min, 83.0%) and super high inhibition rate (90 min, 99.92%) on Escherichia coli under visible light, compared to the two monomers. Pollutants DC is finally decomposed into CO₂, H₂O and small molecule intermediates by generated h⁺, •OH and •O₂^-. The effects of reactive radicals follow the order of •OH radicals > h⁺ radicals ≫ •O₂^- and e^- radicals. The possible structures of intermediates and four possible degradation pathways involved were also discussed. In addition, As-synthetised Bi₅O₇I/BiOCl has preferable reusability and excellent chemical stability. Biological toxicity experiments also verify that Bi₅O₇I/BiOCl is a green and environmentally friendly composite material. This strategy provides a green, low-toxic way for the application of traditional type II heterojunction in the fields of environmental remediation and photocatalysis.

Heat-fueled enzymatic cascade for selective oxyfunctionalization of hydrocarbons

Heat is a fundamental feedstock, where more than 80% of global energy comes from fossil-based heating process. However, it is mostly wasted due to a lack of proper techniques of utilizing the low-quality waste heat (<100 °C). Here we report thermoelectrobiocatalytic chemical conversion systems for heat-fueled, enzyme-catalyzed oxyfunctionalization reactions. Thermoelectric bismuth telluride (Bi₂Te₃) directly converts low-temperature waste heat into chemical energy in the form of H₂O₂ near room temperature. The streamlined reaction scheme (e.g., water, heat, enzyme, and thermoelectric material) promotes enantio- and chemo-selective hydroxylation and epoxidation of representative substrates (e.g., ethylbenzene, propylbenzene, tetralin, cyclohexane, cis-β-methylstyrene), achieving a maximum total turnover number of rAaeUPO (TTN_rAaeUPO) over 32000. Direct conversion of vehicle exhaust heat into the enantiopure enzymatic product with a rate of 231.4 μM h⁻¹ during urban driving envisions the practical feasibility of thermoelectrobiocatalysis.

Thermoelectric materials enable us to convert heat into electricity, but their application has been limited to high-temperature heat sources. Here, the authors show the direct conversion of low-grade waste heat into chemical energy via combining thermoelectric materials with biocatalysts below 100 °C.

Peroxygenase-Catalyzed Selective Synthesis of Calcitriol Starting from Alfacalcidol

Calcitriol is an active analog of vitamin D3 and has excellent physiological activities in regulating healthy immune function. To synthesize the calcitriol compound, the concept of total synthesis is often adopted, which typically involves multiple steps and results in an overall low yield. Herein, we envisioned an enzymatic approach for the synthesis of calcitriol. Peroxygenase from Agrocybe aegerita (AaeUPO) was used as a catalyst to hydroxylate the C-H bond at the C-25 position of alfacalcidol and yielded the calcitriol in a single step. The enzymatic reaction yielded 80.3% product formation in excellent selectivity, with a turnover number up to 4000. In a semi-preparative scale synthesis, 72% isolated yield was obtained. It was also found that AaeUPO is capable of hydroxylating the C-H bond at the C-1 position of vitamin D3, thereby enabling the calcitriol synthesis directly from vitamin D3.

Preparation of Two-Dimensional Pd@Ir Nanosheets and Application in Bacterial Infection Treatment by the Generation of Reactive Oxygen Species

Noble metal nanozymes have shown great promise in biomedicine; however, developing novel and high-performance noble metal nanozymes is still highly pressing and challenging. Herein, we, for the first time, prepared two-dimensional (2D) Pd@Ir bimetal nanosheets (NSs) with well-defined size and composition by a facile seed-mediated growth strategy. Enzyme-mimicked investigations find that the Pd@Ir NSs possess oxidase (OXD)-, peroxidase (POD)-, and catalase (CAT)-like multienzyme-mimetic activities. Especially, they exhibited much higher OXD- and POD-like activities than individual Pd NSs and Ir nanoparticles (NPs). The density functional theory (DFT) calculations reveal that the adsorption energy of O2 on Pd@Ir NSs is lower than that on the pure Pd NSs, which is more favorable for the conversion of O2 molecules from the triplet state (3O2) into the singlet state (1O2). Finally, based on the outstanding nanozyme activities to yield highly active singlet oxygen (1O2) and hydroxyl radicals (•OH) as well as excellent biosafety, the as-prepared Pd@Ir NSs were applied to treat bacteria-infected wounds, and satisfactory therapeutic outcomes were achieved. We believe that the highly efficient 2D Pd@Ir nanozyme will be an effective therapeutic reagent for various biomedical applications.

Protein Engineering of an Artificial P450BM3 Peroxygenase System Enables Highly Selective O-Demethylation of Lignin Monomers

The O-demethylation of lignin monomers, which has drawn substantial attention recently, is critical for the formation of phenols from aromatic ethers. The P450BM3 peroxygenase system was recently found to enable the O-demethylation of different aromatic ethers with the assistance of dual-functional small molecules (DFSM), but these prepared mutants only have either moderate O-demethylation activity or moderate selectivity, which hinders their further application. In this study, we improve the system by introducing different amino acids into the active site of P450BM3, and these amino acids with different side chains impacted the catalytic ability of enzymes due to their differences in size, polarity, and hydrophobicity. Among the prepared mutants, the combination of V78A/F87A/T268I/A264G and Im-C6-Phe efficiently catalyzed the O-demethylation of guaiacol (TON = 839) with 100% selectivity. Compared with NADPH-dependent systems, we offer an economical and practical bioconversion avenue.

Valorization of Small Alkanes by Biocatalytic Oxyfunctionalization

The oxidation of alkanes into valuable chemical products is a vital reaction in organic synthesis. This reaction, however, is challenging, owing to the inertness of C-H bonds. Transition metal catalysts for C-H functionalization are frequently explored. Despite chemical alternatives, nature has also evolved powerful oxidative enzymes (e. g., methane monooxygenases, cytochrome P450 oxygenases, peroxygenases) that are capable of transforming C-H bonds under very mild conditions, with only the use of molecular oxygen or hydrogen peroxide as electron acceptors. Although progress in alkane oxidation has been reviewed extensively, little attention has been paid to small alkane oxidation. The latter holds great potential for the manufacture of chemicals. This Minireview provides a concise overview of the most relevant enzyme classes capable of small alkanes (C_<6 ) oxyfunctionalization, describes the essentials of the catalytic mechanisms, and critically outlines the current state-of-the-art in preparative applications.

Aerobic Photobiocatalysis Enabled by Combining Core-Shell Nanophotoreactors and Native Enzymes

Biocatalysis has become a powerful tool in synthetic chemistry, where enzymes are used to produce highly selective products under mild conditions. Using photocatalytically regenerated cofactors in synergistic combination with enzymes in a cascade fashion offers an efficient synthetic route to produce specific compounds. However, the combination of enzymes and photocatalysts has been limited due to the rapid degradation of the biomaterials by photogenerated reactive oxygen species, which denature and deactivate the enzymatic material. Here, we design core-shell structured porous nano-photoreactors for highly stable and recyclable photobiocatalysis under aerobic conditions. The enzymatic cofactor NAD⁺ from NADH can be efficiently regenerated by the photoactive organosilica core, while photogenerated active oxygen species are trapped and deactivated through the non-photoactive shell, protecting the enzymatic material. The versatility of these photocatalytic core-shell nanoreactors was demonstrated in tandem with two different enzymatic systems, glycerol dehydrogenase and glucose 1-dehydrogenase, where long-term enzyme stability was observed for the core-shell photocatalytic system.

An osmium-peroxo complex for photoactive therapy of hypoxic tumors

The limited therapeutic effect on hypoxic and refractory solid tumors has hindered the practical application of photodynamic therapy. Herein, we report our investigation of an osmium-peroxo complex (Os2), which is inactive in the dark, but can release a peroxo ligand O₂^•− upon light irradiation even in the absence of oxygen, and is transformed into a cytotoxic osmium complex (Os1). Os1 is cytotoxic in the presence or absence of irradiation in hypoxic tumors, behaving as a chemotherapeutic drug. At the same time, the light-activated Os2 induces photocatalytic oxidation of endogenous 1,4-dihydronicotinamide adenine dinucleotide in living cancer cells, leading to ferroptosis, which is mediated by glutathione degradation, lipid peroxide accumulation and down-regulation of glutathione peroxidase 4. In vivo studies have confirmed that the Os2 can effectively inhibit the growth of solid hypoxic tumors in mice. A promising strategy is proposed for the treatment of hypoxic tumors with metal-based drugs.

Photodynamic therapy has been a promising technique for the treatment of tumours. In this manuscript, the authors report on the photoactivation of the osmium peroxo complex and its potential use for chemotherapy and photodynamic therapy under blue light irradiation against tumours in their hypoxic environment.