Photobiocatalysis: Activating Redox Enzymes by Direct or Indirect Transfer of Photoinduced Electrons

Combining photo-redox and enzyme catalysis for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives in one pot

A novel strategy combining visible-light and enzyme catalysis in one pot for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives from alcohols is described for the first time. Fourteen 4H-pyrimido[2,1-b] benzothiazole derivatives were prepared with yields of up to 98% under mild reaction conditions by a simple operation. The photoorgano catalyst rose Bengal (rB) was employed to oxyfunctionalise alcohols to aldehydes. Compared with aldehydes, alcohols with more stable properties and lower cost, thus we used photocatalysis to oxidize alcohols into aldehydes. Next, the enzyme was used to further catalyze the reaction of Biginelli to produce the target product of 4H-pyrimidine [2,1-b] benzothiazole. Experimental results show that this method provides a more efficient and eco-friendly strategy for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives.

Photo-biohydrogen Production by Photosensitization with Biologically Precipitated Cadmium Sulfide in Hydrogen-Forming Recombinant Escherichia coli

An inorganic-biological hybrid system that integrates features of both stable and efficient semiconductors and selective and efficient enzymes is attractive for facilitating the conversion of solar energy to hydrogen. In this study, we aimed to develop a new photocatalytic hydrogen-production system based on Escherichia coli whole-cell genetically engineered as a biocatalysis for highly active hydrogen formation. The photocatalysis part was obtained by bacterial precipitation of cadmium sulfide (CdS), which is a visible-light-responsive semiconductor. The recombinant E. coli cells were sequentially subjected to CdS precipitation and heterologous [FeFe]-hydrogenase synthesis to yield a CdS@E. coli hybrid capable of light energy conversion and hydrogen formation in a single cell. The CdS@E. coli hybrid achieved photocatalytic hydrogen production with a sacrificial electron donor, thus demonstrating the feasibility of our system and expanding the current knowledge of photosensitization using a whole-cell biocatalyst with a bacterially precipitated semiconductor.

Water-soluble chlorophyll-binding proteins from Brassica oleracea allow for stable photobiocatalytic oxidation of cellulose by a lytic polysaccharide monooxygenase

BACKGROUND

Lytic polysaccharide monooxygenases (LPMOs) are indispensable redox enzymes used in industry for the saccharification of plant biomass. LPMO-driven cellulose oxidation can be enhanced considerably through photobiocatalysis using chlorophyll derivatives and light. Water soluble chlorophyll binding proteins (WSCPs) make it is possible to stabilize and solubilize chlorophyll in aqueous solution, allowing for in vitro studies on photostability and ROS production. Here we aim to apply WSCP-Chl a as a photosensitizing complex for photobiocatalysis with the LPMO, TtAA9.

RESULTS

We have in this study demonstrated how WSCP reconstituted with chlorophyll a (WSCP-Chl a) can create a stable photosensitizing complex which produces controlled amounts of H2O2 in the presence of ascorbic acid and light. WSCP-Chl a is highly reactive and allows for tightly controlled formation of H2O2 by regulating light intensity. TtAA9 together with WSCP-Chl a shows increased cellulose oxidation under low light conditions, and the WSCP-Chl a complex remains stable after 24 h of light exposure. Additionally, the WSCP-Chl a complex demonstrates stability over a range of temperatures and pH conditions relevant for enzyme activity in industrial settings.

CONCLUSION

With WSCP-Chl a as the photosensitizer, the need to replenish Chl is greatly reduced, enhancing the catalytic lifetime of light-driven LPMOs and increasing the efficiency of cellulose depolymerization. WSCP-Chl a allows for stable photobiocatalysis providing a sustainable solution for biomass processing.

Active-Site Environmental Factors Customize the Photophysics of Photoenzymatic Old Yellow Enzymes

The development of non-natural photoenzymatic systems has reinvigorated the study of photoinduced electron transfer (ET) within protein active sites, providing new and unique platforms for understanding how biological environments affect photochemical processes. In this work, we use ultrafast spectroscopy to compare the photoinduced electron transfer in known photoenzymes. 12-Oxophytodienoate reductase 1 (OPR1) is compared to Old Yellow Enzyme 1 (OYE1) and morphinone reductase (MR). The latter enzymes are structurally homologous to OPR1. We find that slight differences in the amino acid composition of the active sites of these proteins determine their distinct electron-transfer dynamics. Our work suggests that the inside of a protein active site is a complex/heterogeneous dielectric network where genetically programmed heterogeneity near the site of biological ET can significantly affect the presence and lifetime of various intermediate states. Our work motivates additional tunability of Old Yellow Enzyme active-site reorganization energy and electron-transfer energetics that could be leveraged for photoenzymatic redox approaches.

Decarboxylative Alkyl Coupling Promoted by NADH and Blue Light

Photoexcited dihydronicotinamides like NADH and analogues have been found to generate alkyl radicals upon reductive decarboxylation of redox-active esters without auxiliary photocatalysts. This principle allowed aliphatic photocoupling between redox-active carboxylate derivatives and electron-poor olefins, displaying surprising water and air-tolerance and unusually high coupling rates in dilute conditions. The orthogonality of the reaction in the presence of other carboxylic acids and its utility in the functionalization of DNA is presented, notably using visible light in combination with NADH, the ubiquitous reductant of life.

Construction of Thiazolo[5,4-d]thiazole-based Two-Dimensional Network for Efficient Photocatalytic CO2 Reduction

The efficient conversion of CO₂ to chemical fuels driven by solar energy is still a challenging research area in photosynthesis, in which the conversion efficiency greatly relies on photocatalytic coenzyme NADH regeneration. Herein, a photocatalyst/biocatalyst synergetic system based on a conjugated microporous polymer (CMP) was prepared for sustainable and highly selective photocatalytic reduction of CO₂ to methanol. Two thiazolo[5,4-d]thiazole-linked CMPs (TZTZ-TA and TZTZ-TP) were designed and synthesized as photocatalysts. Slight skeleton modification led to a great difference in their photocatalytic performance. Triazine-based TZTZ-TA exhibited an unprecedentedly high NADH regeneration efficiency of 82.0% yield within 5 min. Furthermore, the in situ photocatalytic NADH regeneration system could integrate with three consecutive enzymes for efficient conversion of CO₂ into methanol. This CMP-enzyme hybrid system provides a new avenue for accomplishing the liquid sunshine from CO₂.

Evolution of Glucose Dehydrogenase for Cofactor Regeneration in Bioredox Processes with Denaturing Agents

Glucose dehydrogenase (GDH) is a general tool for driving nicotinamide (NAD(P)H) regeneration in synthetic biochemistry. An increasing number of synthetic bioreactions are carried out in media containing high amounts of organic cosolvents or hydrophobic substrates/products, which often denature native enzymes, including those for cofactor regeneration. In this work, we attempted to improve the chemical stability of Bacillus megaterium GDH (BmGDH_M0 ) in the presence of large amounts of 1-phenylethanol by directed evolution. Among the resulting mutants, BmGDH_M6 (Q252L/E170K/S100P/K166R/V72I/K137R) exhibited a 9.2-fold increase in tolerance against 10 % (v/v) 1-phenylethanol. Moreover, BmGDH_M6 was also more stable than BmGDH_M0 when exposed to hydrophobic and enzyme-inactivating compounds such as acetophenone, ethyl 2-oxo-4-phenylbutyrate, and ethyl (R)-2-hydroxy-4-phenylbutyrate. Coupled with a Candida glabrata carbonyl reductase, BmGDH_M6 was successfully used for the asymmetric reduction of deactivating ethyl 2-oxo-4-phenylbutyrate with total turnover number of 1800 for the nicotinamide cofactor, thus making it attractive for commercial application. Overall, the evolution of chemically robust GDH facilitates its wider use as a general tool for NAD(P)H regeneration in biocatalysis.

Green Catalysts: Applied and Synthetic Photosynthesis

The biological process of photosynthesis was critical in catalyzing the oxygenation of Earth’s atmosphere 2.5 billion years ago, changing the course of development of life on Earth. Recently, the fields of applied and synthetic photosynthesis have utilized the light-driven protein–pigment supercomplexes central to photosynthesis for the photocatalytic production of fuel and other various valuable products. The reaction center Photosystem I is of particular interest in applied photosynthesis due to its high stability post-purification, non-geopolitical limitation, and its ability to generate the greatest reducing power found in nature. These remarkable properties have been harnessed for the photocatalytic production of a number of valuable products in the applied photosynthesis research field. These primarily include photocurrents and molecular hydrogen as fuels. The use of artificial reaction centers to generate substrates and reducing equivalents to drive non-photoactive enzymes for valuable product generation has been a long-standing area of interest in the synthetic photosynthesis research field. In this review, we cover advances in these areas and further speculate synthetic and applied photosynthesis as photocatalysts for the generation of valuable products.

Water-Soluble Anthraquinone Photocatalysts Enable Methanol-Driven Enzymatic Halogenation and Hydroxylation Reactions

Peroxyzymes simply use H₂O₂ as a cosubstrate to oxidize a broad range of inert C–H bonds. The lability of many peroxyzymes against H₂O₂ can be addressed by a controlled supply of H₂O₂, ideally in situ. Here, we report a simple, robust, and water-soluble anthraquinone sulfonate (SAS) as a promising organophotocatalyst to drive both haloperoxidase-catalyzed halogenation and peroxygenase-catalyzed oxyfunctionalization reactions. Simple alcohols, methanol in particular, can be used both as a cosolvent and an electron donor for H₂O₂ generation. Very promising turnover numbers for the biocatalysts of up to 318 000 have been achieved.

Construction of Functionally Compartmental Inorganic Photocatalyst-Enzyme System via Imitating Chloroplast for Efficient Photoreduction of CO2 to Formic Acid

Inorganic photocatalyst-enzyme systems are a prominent platform for the photoreduction of CO₂ to value-added chemicals and fuels. However, poor electron transfer kinetics and enzyme deactivation by reactive oxygen species in the photoexcitation process severely limit catalytic efficiency. In chloroplast, enzymatic CO₂ reduction and photoexcitation are compartmentalized by the thylakoid membrane, which protects enzymes from photodamage, while the tightly integrated photosystem facilitates electron transfer, promoting photocatalysis. By mimicking this strategy, we constructed a novel functionally compartmental inorganic photocatalyst-enzyme system for CO₂ reduction to formate. To accomplish efficient electron transfer, we first synthesized an integrated artificial photosystem by conjugation of the cocatalyst (a Rh complex) onto thiophene-modified C₃N₄ (TPE-C₃N₄), demonstrating an NADH regeneration rate of 9.33 μM·min^-1, 2.33 times higher than that of a homogeneous counterpart. The enhanced NADH regeneration activity was caused by the tightly conjugated structure of the artificial photosystem, enabling rapid electron transfer from TPE-C₃N₄ to the Rh complex. To protect formate dehydrogenase (FDH) from photoinduced deactivation, FDH was encapsulated into MAF-7, a metal-organic framework (MOF) material, to compartmentalize FDH from the toxic photoexcitation process, similar to the function of the thylakoid membrane. Moreover, the triazole linkers of MAF-7 possess both hydrophilicity and pH-buffering capacity providing a stable microenvironment for FDH, which could enhance enzyme stability in photosynthesis. The synergy between the enhanced electron transfer of TPE-C₃N₄ for NADH cofactor regeneration and MOF-protection of the redox enzyme enables the construction of a functionally compartmental inorganic photocatalyst-enzyme association system, promoting CO₂ photoconversion to formic acid with a yield of 16.75 mM after 9 h of illumination, 3.24 times greater than that of the homogeneous reaction counterpart.

Thermal, electrochemical and photochemical reactions involving catalytically versatile ene reductase enzymes

Successful exploitation of biocatalytic processes employing flavoproteins requires the implementation of cost-effective solutions to circumvent the need to supply costly nicotinamide coenzymes as reducing equivalents. Chemical syntheses harnessing the power of the flavoprotein ene reductases will likely increase the range and/or optical purity of available fine chemicals and pharmaceuticals due to their ability to catalyze asymmetric bioreductions. This review will outline current progress in the design of alternative routes to ene reductase flavin activation, most notably within the Old Yellow Enzyme family. A variety of chemical, enzymatic, electrochemical and photocatalytic routes have been employed, designed to eliminate the need for nicotinamide coenzymes or provide cost-effective alternatives to efficient recycling. Photochemical approaches have also enabled novel mechanistic routes of ene reductases to become available, opening up the possibility of accessing a wider range of non-natural chemical diversity.

Light-Driven Catalytic Regulation of Enzymes at the Interface with Plasmonic Nanomaterials

Regulation of enzymes is highly relevant toward orchestrating cell-free and stepwise biotransformations, thereby maximizing their overall performance. Plasmonic nanomaterials offer a great opportunity to tune the functionality of enzymes through their remarkable optical properties. Localized surface plasmon resonances (LSPR) can be used to modify chemical transformations at the nanomaterial's surface, upon light irradiation. Incident light can promote energetic processes, which may be related to an increase of local temperature (photothermal effects) but also to effects triggered by generated hotspots or hot electrons (photoelectronic effects). As a consequence, light irradiation of the protein-nanomaterial interface affects enzyme functionality. To harness these effects to finely and remotely regulate enzyme activity, the physicochemical features of the nanomaterial, properties of the incident light, and parameters governing molecular interactions must be optimized. In this Perspective, we discuss relevant examples that illustrate the use of plasmonic nanoparticles to control enzyme function through LSPR excitation. Finally, we also highlight the importance of expanding the use of plasmonic nanomaterials to the immobilization of multienzyme systems for light-driven regulation of cell-free biosynthetic pathways. Although this concept is living its infancy, we encourage the scientific community to advance in the development of novel light-controlled biocatalytic plasmonic nanoconjugates and explore their application in biosensing, applied biocatalysis, and biomedicine.

Light-driven catalysis with engineered enzymes and biomimetic systems

Efforts to drive catalytic reactions with light, inspired by natural processes like photosynthesis, have a long history and have seen significant recent growth. Successfully engineering systems using biomolecular and bioinspired catalysts to carry out light-driven chemical reactions capitalizes on advantages offered from the fields of biocatalysis and photocatalysis. In particular, driving reactions under mild conditions and in water, in which enzymes are operative, using sunlight as a renewable energy source yield environmentally friendly systems. Furthermore, using enzymes and bioinspired systems can take advantage of the high efficiency and specificity of biocatalysts. There are many challenges to overcome to fully capitalize on the potential of light-driven biocatalysis. In this mini-review, we discuss examples of enzymes and engineered biomolecular catalysts that are activated via electron transfer from a photosensitizer in a photocatalytic system. We place an emphasis on selected forefront chemical reactions of high interest, including CH oxidation, proton reduction, water oxidation, CO₂ reduction, and N₂ reduction.

Deazaflavin reductive photocatalysis involves excited semiquinone radicals

Flavin-mediated photocatalytic oxidations are established in synthetic chemistry. In contrast, their use in reductive chemistry is rare. Deazaflavins with a much lower reduction potential are even better suited for reductive chemistry rendering also deazaflavin semiquinones as strong reductants. However, no direct evidence exists for the involvement of these radical species in reductive processes. Here, we synthesise deazaflavins with different substituents at C5 and demonstrate their photocatalytic activity in the dehalogenation of p-halogenanisoles with best performance under basic conditions. Mechanistic investigations reveal a consecutive photo-induced electron transfer via the semiquinone form of the deazaflavin as part of a triplet-correlated radical pair after electron transfer from a sacrificial electron donor to the triplet state. A second electron transfer from the excited semiquinone to p-halogenanisoles triggers the final product formation. This study provides first evidence that the reductive power of excited deazaflavin semiquinones can be used in photocatalytic reductive chemistry.

Flavins and deazaflavins are well suited for photoredox processes but their application in photoreductions is challenging. Here, the authors provide direct evidence of the high reductive power of excited deazaflavin semiquinones and their application in catalytic photodehalogenations.

Mimic of the Cellular Antioxidant Defense System for a Sustainable Regeneration of Nicotinamide Adenine Dinucleotide (NAD)

The prolonged use of enzymes under oxidative stress is a major challenge in enabling effective enzymatic reaction pathways. Herein, we report a biomimetic antioxidant defensive strategy capable of providing adequate protection of enzymes against superoxide-mediated oxidation. Superoxide dismutase (SOD) and catalase (CAT) were chosen as scavengers and covalently encapsulated into silica nanoreactors, together with glucose dehydrogenase (GDH), which simultaneously should produce the coenzyme nicotinamide adenine dinucleotide (NADH, reduced form). By the enzymatic reactions of SOD and CAT, the interior of silica nanoreactors becomes a "ROS safe zone" to protect the glucose-dependent NADH production of coencapsulated GDH. We further combined this protected NADH-producing module with photocatalytic nanoparticles that enable the light-triggered oxidation of NADH back to NAD⁺ (oxidized form). In combination, these two modules allow interconversion between NAD⁺ and NADH by the addition of glucose or by light irradiation (LED lamp or sunlight). This protection and regeneration strategy is a versatile tool for enzyme applications for biological reactors, catalysis, or prototypes of artificial organelles or building blocks that contains fragile biomolecules and rely on the coenzyme NAD⁺/NADH.

A host-guest approach to combining enzymatic and artificial catalysis for catalyzing biomimetic monooxygenation

Direct transfer of protons and electrons between two tandem reactions is still a great challenge, because overall reaction kinetics is seriously affected by diffusion rate of the proton and electron carriers. We herein report a host–guest supramolecular strategy based on the incorporation of NADH mimics onto the surface of a metal-organic capsule to encapsulate flavin analogues for catalytic biomimetic monooxygenations in conjunction with enzymes. Coupling an artificial catalysis and a natural enzymatic catalysis in the pocket of an enzyme, this host–guest catalyst–enzyme system allows direct proton and electron transport between two catalytic processes via NADH mimics for the monooxygenation of both cyclobutanones and thioethers. This host–guest approach, which involves the direct coupling of abiotic and biotic catalysts via a NADH-containing host, is quite promising compared to normal catalyst–enzyme systems, as it offers the key advantages of supramolecular catalysis in integrated chemical and biological synthetic sequences.

Combining artificial and natural enzymes is a strategy to mimic biocatalytic processes with high efficiency and selectivity. This study reports a dual catalytic system composed of flavin adenine dinucleotide model and NADH mimics to catalyze the monooxygenation of cyclobutanones and thioethers.

CO2 -Reductive, Copper Oxide-Based Photobiocathode for Z-Scheme Semi-Artificial Leaf Structure

Green plants convert sunlight into high-energy chemicals by coupling solar-driven water oxidation in the Z-scheme and CO₂ fixation in the Calvin cycle. In this study, formate dehydrogenase from Clostridium ljungdahlii (ClFDH) is interfaced with a TiO₂ -coated CuFeO₂ and CuO mixed (ClFDH-TiO₂ |CFO) electrode. In this biohybrid photocathode, the TiO₂ layer enhances the photoelectrochemical (PEC) stability of the labile CFO photocathode and facilitates the transfer of photoexcited electrons from the CFO to ClFDH. Furthermore, inspired by the natural photosynthetic scheme, the photobiocathode is combined with a water-oxidizing, FeOOH-coated BiVO₄ (FeOOH|BiVO₄ ) photoanode to assemble a wireless Z-scheme biocatalytic PEC device as a semi-artificial leaf. The leaf-like structure effects a bias-free biocatalytic CO₂ -to-formate conversion under visible light. Its rate of formate production is 2.45 times faster than that without ClFDH. This work is the first example of a wireless solar-driven semi-biological PEC system for CO₂ reduction that uses water as an electron feedstock.

"Waste to Wealth": Lignin as a Renewable Building Block for Energy Harvesting/Storage and Environmental Remediation

Lignin is the second most earth-abundant biopolymer having aromatic unit structures, but it has received less attention than other natural biomaterials. Recent advances in the development of lignin-based materials, such as mesoporous carbon, flexible thin films, and fiber matrix, have found their way into applications to photovoltaic devices, energy-storage systems, mechanical energy harvesters, and catalytic components. In this Review, we summarize and suggest another dimension of lignin valorization as a building block for the synthesis of functional materials in the fields of energy and environmental applications. We cover lignin-based materials in the photovoltaic and artificial photosynthesis for solar energy conversion applications. The most recent technological evolution in lignin-based triboelectric nanogenerators is summarized from its fundamental properties to practical implementations. Lignin-derived catalysts for solar-to-heat conversion and oxygen reduction are discussed. For energy-storage applications, we describe the utilization of lignin-based materials in lithium-ion rechargeable batteries and supercapacitors (e.g., electrodes, binders, and separators). We also summarize the use of lignin-based materials as heavy-metal adsorbents for environmental remediation. This Review paves the way to future potentials and opportunities of lignin as a renewable material for energy and environmental applications.

Flavin-Conjugated Iron Oxide Nanoparticles as Enzyme-Inspired Photocatalysts for Azo Dye Degradation

In this work, a new photocatalytic system consisting of iron oxide nanoparticles (IONPs), coated with a catechol-flavin conjugate (DAFL), is synthesized and explored for use in water remediation. In order to test the efficiency of the catalyst, the photodegradation of amaranth (AMT), an azo dye water pollutant, was performed under aerobic and anaerobic conditions, using either ethylenediaminetetraacetic acid (EDTA) or 2-(N-morpholino)ethanesulfonic acid (MES) as electron donors. Depending on the conditions, either dye photoreduction or photooxidation were observed, indicating that flavin-coated iron-oxide nanoparticles can be used as a versatile enzyme-inspired photocatalysts.

Artificial Light-Harvesting Complexes Enable Rieske Oxygenase Catalyzed Hydroxylations in Non-Photosynthetic cells

In this study, we coupled a well-established whole-cell system based on E. coli via light-harvesting complexes to Rieske oxygenase (RO)-catalyzed hydroxylations in vivo. Although these enzymes represent very promising biocatalysts, their practical applicability is hampered by their dependency on NAD(P)H as well as their multicomponent nature and intrinsic instability in cell-free systems. In order to explore the boundaries of E. coli as chassis for artificial photosynthesis, and due to the reported instability of ROs, we used these challenging enzymes as a model system. The light-driven approach relies on light-harvesting complexes such as eosin Y, 5(6)-carboxyeosin, and rose bengal and sacrificial electron donors (EDTA, MOPS, and MES) that were easily taken up by the cells. The obtained product formations of up to 1.3 g L-1 and rates of up to 1.6 mm h-1 demonstrate that this is a comparable approach to typical whole-cell transformations in E. coli. The applicability of this photocatalytic synthesis has been demonstrated and represents the first example of a photoinduced RO system.

Electron Transfer from Semiconductor Nanocrystals to Redox Enzymes

This review summarizes progress in understanding electron transfer from photoexcited nanocrystals to redox enzymes. The combination of the light-harvesting properties of nanocrystals and the catalytic properties of redox enzymes has emerged as a versatile platform to drive a variety of enzyme-catalyzed reactions with light. Transfer of a photoexcited charge from a nanocrystal to an enzyme is a critical first step for these reactions. This process has been studied in depth in systems that combine Cd-chalcogenide nanocrystals with hydrogenases. The two components can be assembled in close proximity to enable direct interfacial electron transfer or integrated with redox mediators to transport charges. Time-resolved spectroscopy and kinetic modeling have been used to measure the rates and efficiencies of the electron transfer. Electron transfer has been described within the framework of Marcus theory, providing insights into the factors that can be used to control the photochemical activity of these biohybrid systems. The range of potential applications and reactions that can be achieved using nanocrystal-enzyme systems is expanding, and numerous fundamental and practical questions remain to be addressed.

Femtomolar sensing of Alzheimer's tau proteins by water oxidation-coupled photoelectrochemical platform

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. A key pathogenic event of AD is the formation of intracellular neurofibrillary tangles that are mainly composed of tau proteins. Here, we report on ultrasensitive detection of total tau (t-tau) proteins using an artificial electron donor-free, BiVO₄-based photoelectrochemical (PEC) analysis. The platform was constructed by incorporating molybdenum (Mo) dopant and iron oxyhydroxide (FeOOH) ad-layer into the BiVO₄ photoelectrode and employing a signal amplifier formed by horseradish peroxidase (HRP)-triggered oxidation of 3,3'-diaminobenzidine (DAB). Despite the absence of additional electron suppliers, the FeOOH/Mo:BiVO₄ conjugated with the Tau5 antibody produced strong current signals at 0 V (vs. Ag/AgCl, 3 M NaCl) under the illumination of a white light-emitting diode. The Mo extrinsic dopants increased the charge carrier density of BiVO₄-Tau5 by 1.57 times, and the FeOOH co-catalyst promoted the interfacial water oxidation reaction of Mo:BiVO₄-Tau5 by suppressing charge recombination. The introduction of HRP-labeled Tau46 capture antibodies to the FeOOH/Mo:BiVO₄-Tau5 platform produced insoluble precipitation on the transducer by accelerating the oxidation of DAB, which amplified the photocurrent signal of FeOOH/Mo:BiVO₄-Tau5 by 2.07-fold. Consequently, the water oxidation-coupled, FeOOH/Mo:BiVO₄-based PEC sensing platform accurately and selectively recognized t-tau proteins down to femtomolar concentrations; the limit of detection and limit of quantification were determined to be 1.59 fM and 4.11 fM, respectively.

Examination of abiotic cofactor assembly in photosynthetic biomimetics: site-specific stereoselectivity in the conjugation of a ruthenium(II) tris(bipyridine) photosensitizer to a multi-heme protein

To understand design principles for assembling photosynthetic biohybrids that incorporate precisely-controlled sites for electron injection into redox enzyme cofactor arrays, we investigated the influence of chirality in assembly of the photosensitizer ruthenium(II)bis(2,2'-bipyridine)(4-bromomethyl-4'-methyl-2,2'-bipyridine), Ru(bpy)2(Br-bpy), when covalently conjugated to cysteine residues introduced by site-directed mutagenesis in the triheme periplasmic cytochrome A (PpcA) as a model biohybrid system. For two investigated conjugates that show ultrafast electron transfer, A23C-Ru and K29C-Ru, analysis by circular dichroism spectroscopy, CD, demonstrated site-specific chiral discrimination as a factor emerging from the close association between [Ru(bpy)3]2+ and heme cofactors. CD analysis showed the A23C-Ru and K29C-Ru conjugates to have distinct, but opposite, stereoselectivity for the Λ and Δ-Ru(bpy)2(Br-bpy) enantiomers, with enantiomeric excesses of 33.1% and 65.6%, respectively. In contrast, Ru(bpy)2(Br-bpy) conjugation to a protein site with high flexibility, represented by the E39C-Ru construct, exhibited a nearly negligible chiral selectivity, measured by an enantiomeric excess of 4.2% for the Λ enantiomer. Molecular dynamics simulations showed that site-specific stereoselectivity reflects steric constraints at the conjugating sites and that a high degree of chiral selectivity correlates to reduced structural disorder for [Ru(bpy)3]2+ in the linked assembly. This work identifies chiral discrimination as means to achieve site-specific, precise geometric positioning of introduced photosensitizers relative to the heme cofactors in manner that mimics the tuning of cofactors in photosynthesis.

Coupling natural systems with synthetic chemistry for light-driven enzymatic biocatalysis

Visible light-driven redox reactions have been widely adopted for the production of chemicals to combat energy shortage and global warming. Key elements of such a reaction system include a photosensitizer, a catalyst, and an electron source. In this review, we introduce the small molecules and nanoparticles that are widely used as photosensitizers, as well as the development of a photosensitizer protein that is based on the expansion of genetic code, with a fluorescent protein that is used as a scaffold. Visible light-driven enzymes using proteins as photosensitizers or as catalysts such as carbon monoxide dehydrogenase (CODH), formic acid dehydrogenase (FDH), hydrogenase, nitrogenase, cytochrome P450 BM3, and alkane synthase are then described. CODH can be coupled with photosensitizing nanoparticles to reduce CO₂ to CO, and hydrogenase can produce H₂ using high-energy electrons produced from dye-sensitized nanoparticles. When water-soluble zinc porphyrin is coupled with FDH, visible light drives CO₂ to produce formic acid. Nitrogenase can reduce N₂ to NH₃ using CdS nanoparticle as photosensitizer. Cytochrome P450 BM3 can be enhanced by a visible light-driven redox system and thus by hydroxylate lauric acid or fatty acids. CvFAP, an alkane synthase, can decarboxylate palmitic acid to pentadecane under blue light excitation. Moreover, we describe a genetically encoded photosensitive protein, which mimics the function of natural photosynthesis and catalyzes the conversion of CO₂ to CO when covalently attached with a Ni-terpyridine complex.

Integration of a Hydrogenase in a Lead Halide Perovskite Photoelectrode for Tandem Solar Water Splitting

Lead halide perovskite solar cells are notoriously moisture-sensitive, but recent encapsulation strategies have demonstrated their potential application as photoelectrodes in aqueous solution. However, perovskite photoelectrodes rely on precious metal co-catalysts, and their combination with biological materials remains elusive in integrated devices. Here, we interface [NiFeSe] hydrogenase from Desulfovibrio vulgaris Hildenborough, a highly active enzyme for H₂ generation, with a triple cation mixed halide perovskite. The perovskite-hydrogenase photoelectrode produces a photocurrent of -5 mA cm^-2 at 0 V vs RHE during AM1.5G irradiation, is stable for 12 h and the hydrogenase exhibits a turnover number of 1.9 × 10⁶. The positive onset potential of +0.8 V vs RHE allows its combination with a BiVO₄ water oxidation photoanode to give a self-sustaining, bias-free photoelectrochemical tandem system for overall water splitting (solar-to-hydrogen efficiency of 1.1%). This work demonstrates the compatibility of immersed perovskite elements with biological catalysts to produce hybrid photoelectrodes with benchmark performance, which establishes their utility in semiartificial photosynthesis.

The rise of continuous flow biocatalysis – fundamentals, very recent developments and future perspectives

Very recent developments in the field of biocatalysis in continuously operated systems. Special attention on the future perspectives in this key emerging technological area ranging from process analytical technologies to digitalization.

Facile assembly of a graphitic carbon nitride film at an air/water interface for photoelectrochemical NADH regeneration

A graphitic carbon nitride film electrode could be assembled at an air/water interface from nanosheets which exhibits improved photoelectrochemical coenzyme regeneration by further coupling with graphene during the interfacial self-assembly.

Visible light-driven, external mediator-free H2 production by a combination of a photosensitizer and a whole-cell biocatalyst: Escherichia coli expressing [FeFe]-hydrogenase and maturase genes

A new visible light-driven, external mediator-free, and highly efficient H₂ production system is developed based on the combination of a photosensitizer and a living whole-cell biocatalyst: genetically engineered Escherichia coli.

Chemical sensing platforms for detecting trace-level Alzheimer's core biomarkers

This review provides an overview of recent advances in optical and electrical detection of Alzheimer's disease biomarkers in clinically relevant fluids.

Light-driven carbon-carbon bond formation via CO2 reduction catalyzed by complexes of CdS nanorods and a 2-oxoacid oxidoreductase

Redox enzymes are capable of catalyzing a vast array of useful reactions, but they require redox partners that donate or accept electrons. Semiconductor nanocrystals provide a mechanism to convert absorbed photon energy into redox equivalents for enzyme catalysis. Here, we describe a system for photochemical carbon-carbon bond formation to make 2-oxoglutarate by coupling CO₂ with a succinyl group. Photoexcited electrons from cadmium sulfide nanorods (CdS NRs) transfer to 2-oxoglutarate:ferredoxin oxidoreductase from Magnetococcus marinus MC-1 (MmOGOR), which catalyzes a carbon-carbon bond formation reaction. We thereby decouple MmOGOR from its native role in the reductive tricarboxylic acid cycle and drive it directly with light. We examine the dependence of 2-oxoglutarate formation on a variety of factors and, using ultrafast transient absorption spectroscopy, elucidate the critical role of electron transfer (ET) from CdS NRs to MmOGOR. We find that the efficiency of this ET depends strongly on whether the succinyl CoA (SCoA) cosubstrate is bound at the MmOGOR active site. We hypothesize that the conformational changes due to SCoA binding impact the CdS NR-MmOGOR interaction in a manner that decreases ET efficiency compared to the enzyme with no cosubstrate bound. Our work reveals structural considerations for the nano-bio interfaces involved in light-driven enzyme catalysis and points to the competing factors of enzyme catalysis and ET efficiency that may arise when complex enzyme reactions are driven by artificial light absorbers.