Photocatalytic reduction of artificial and natural nucleotide co-factors with a chlorophyll-like tin-dihydroporphyrin sensitizer

Fluorinated chlorin chromophores for red-light-driven CO2 reduction

The utilization of low-energy photons in light-driven reactions is an effective strategy for improving the efficiency of solar energy conversion. In nature, photosynthetic organisms use chlorophylls to harvest the red portion of sunlight, which ultimately drives the reduction of CO2. However, a molecular system that mimics such function is extremely rare in non-noble-metal catalysis. Here we report a series of synthetic fluorinated chlorins as biomimetic chromophores for CO2 reduction, which catalytically produces CO under both 630 nm and 730 nm light irradiation, with turnover numbers of 1790 and 510, respectively. Under appropriate conditions, the system lasts over 240 h and stays active under 1% concentration of CO2. Mechanistic studies reveal that chlorin and chlorinphlorin are two key intermediates in red-light-driven CO2 reduction, while corresponding porphyrin and bacteriochlorin are much less active forms of chromophores.

Adsorption and photocatalytic applications of porphyrin-based materials for environmental separation processes: A review

As society progresses and industrializes, the issue of water pollution, caused by a wide array of organic and inorganic pollutants, poses significant risks to both human well-being and the environment. Given its distinctive characteristics, water pollution has become a paramount concern for society, necessitating immediate attention. Numerous studies have been conducted on wastewater treatment, primarily focusing on two key approaches: adsorption and photocatalytic degradation. Adsorption offers unparalleled advantages, including its simplicity, high removal efficiency, and cost-effectiveness. Conversely, photocatalysis harnesses abundant, clean, and non-polluting sunlight, addressing the critical issue of energy scarcity. Porphyrins, which are macrocyclic tetrapyrrole derivatives found widely in nature, have attracted growing interest in recent years. These lipophilic pigments exhibit remarkable chemical stability and have retained their major structural features for up to 1.1 billion years. As such, they are considered vital indicators of life and have been extensively studied, from the remnants of extinct organisms to gain insights into the principles of evolution. Porphyrins are often associated with a central metal ion within their ring system and can be modified through various substituents, including additional rings or ring opening, resulting in a wide range of functionalities. This comprehensive review summarizes recent advancements in the field of porphyrins. It begins by introducing the structures and preparation methods of porphyrins. Subsequently, it delves into notable applications of porphyrins in the context of pollutant adsorption in water and their environmentally friendly photocatalytic degradation.

Photocatalytic Regeneration of a Nicotinamide Adenine Nucleotide Mimic with Water-Soluble Iridium(III) Complexes

Nicotinamide adenine nucleotide (NADH) is involved in many biologically relevant redox reactions, and the photochemical regeneration of its oxidized form (NAD⁺) under physiological conditions is of interest for combined photo- and biocatalysis. Here, we demonstrate that tri-anionic, water-soluble variants of typically very lipophilic iridium(III) complexes can photo-catalyze the reduction of an NAD⁺ mimic in a comparatively efficient manner. In combination with a well-known rhodium co-catalyst to facilitate regioselective reactions, these iridium(III) photo-reductants outcompete the commonly used [Ru(bpy)₃]²⁺ (bpy = 2,2'-bipyridine) photosensitizer in water by up to 1 order of magnitude in turnover frequency. This improved reactivity is attributable to the strong excited-state electron donor properties and the good chemical robustness of the tri-anionic iridium(III) sensitizers, combined with their favorable Coulombic interaction with the di-cationic rhodium co-catalyst. Our findings seem relevant in the greater context of photobiocatalysis, for which access to strong, efficient, and robust photoreductants with good water solubility can be essential.

One-Pot Highly Efficient Synthesis of N-Enrich Graphene Quantum Dots as a Photocatalytic Platform for NAD+/NADP+ Reduction

An efficient photocatalytic regeneration of nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH) has been carried out by two-electron reduction and protonation of NAD⁺ /NADP⁺ , induced by photons in the visible light region. This functional artificial photosynthetic counterpart of the complete energy-trapping occurring in natural photosystem I (PS I) is achieved with nitrogen-enrich graphene quantum dot (N-EGQD) as the light-harvesting photocatalyst. In buffer aqueous solution, this compound photo catalytically recycles a rhodium hydride complex of the type [Cp*Rh(bpy)H]⁺ (Cp* = pentamethylcyclopentadienyl, bpy = 2,2'-bipyridine) which can mediate hydride transfer processes leading to nucleotide co-factor reduction. Very promising yields of 73.31%/78.45% of NADH/NADPH with the excellent thermal stability of N-EGQD photocatalyst is observed. Thus, in this work, an efficient light-harvesting photocatalyst is synthesized for the regeneration of nicotinamide cofactor that has pharmaceuticals application.

Hybrid Chemo-, Bio-, and Electrocatalysis for Atom-Efficient Deuteration of Cofactors in Heavy Water

Deuterium-labeled nicotinamide cofactors such as [4-2H]-NADH can be used as mechanistic probes in biological redox processes and offer a route to the synthesis of selectively [2H] labeled chemicals via biocatalytic reductive deuteration. Atom-efficient routes to the formation and recycling of [4-2H]-NADH are therefore highly desirable but require careful design in order to alleviate the requirement for [2H]-labeled reducing agents. In this work, we explore a suite of electrode or hydrogen gas driven catalyst systems for the generation of [4-2H]-NADH and consider their use for driving reductive deuteration reactions. Catalysts are evaluated for their chemoselectivity, stereoselectivity, and isotopic selectivity, and it is shown that inclusion of an electronically coupled NAD+-reducing enzyme delivers considerable advantages over purely metal based systems, yielding exclusively [4S-2H]-NADH. We further demonstrate the applicability of these types of [4S-2H]-NADH recycling systems for driving reductive deuteration reactions, regardless of the facioselectivity of the coupled enzyme.

Photo-triggered hydrogen atom transfer from an iridium hydride complex to unactivated olefins

Many photoactive metal complexes can act as electron donors or acceptors upon photoexcitation, but hydrogen atom transfer (HAT) reactivity is rare. We discovered that a typical representative of a widely used class of iridium hydride complexes acts as an H-atom donor to unactivated olefins upon irradiation at 470 nm in the presence of tertiary alkyl amines as sacrificial electron and proton sources. The catalytic hydrogenation of simple olefins served as a test ground to establish this new photo-reactivity of iridium hydrides. Substrates that are very difficult to activate by photoinduced electron transfer were readily hydrogenated, and structure-reactivity relationships established with 12 different olefins are in line with typical HAT reactivity, reflecting the relative stabilities of radical intermediates formed by HAT. Radical clock, H/D isotope labeling, and transient absorption experiments provide further mechanistic insight and corroborate the interpretation of the overall reactivity in terms of photo-triggered hydrogen atom transfer (photo-HAT). The catalytically active species is identified as an Ir(ii) hydride with an IrII-H bond dissociation free energy around 44 kcal mol-1, which is formed after reductive 3MLCT excited-state quenching of the corresponding Ir(iii) hydride, i.e. the actual HAT step occurs on the ground-state potential energy surface. The photo-HAT reactivity presented here represents a conceptually novel approach to photocatalysis with metal complexes, which is fundamentally different from the many prior studies relying on photoinduced electron transfer.

Red light-triggered photoreduction on a nucleic acid template

Conjugate Sn(iv)(pyropheophorbide a)dichloride-(peptide nucleic acid) catalyzes reduction of azobenzene derivatives in the presence of complementary nucleic acid (NA) upon irridiation with red light (660 nm). This is the first red light-induced NA-templated photoreduction. It is highly sensitive to single mismatches in the NA-template and can detect down to 5 nM NAs.

Synthesis, singlet oxygen generation and DNA photocleavage of β,β′-conjugated polycationic porphyrins

In this paper, three [Formula: see text],[Formula: see text]-conjugated cationic porphyrin compounds were designed and synthesized. The structure of the intermediates and desired porphyrins were confirmed by UV, IR, 1H NMR, MS and elemental analysis. The interaction modes between these porphyrins and ct-DNA were studied by UV-vis spectroscopy and fluorescence emission spectroscopy. The results showed that PCP 1 had an external binding mode with DNA at low DNA concentration and could intercalate DNA with the increase of concentration. PCP 2 interacted with DNA through an external binding mode, and PCP 3 could insert into DNA. The binding constants ([Formula: see text] between PCP1[Formula: see text]PCP3 and ct-DNA were calculated to be 8.41 × 104, 7.33 × 104 and 4.14 × 104 M[Formula: see text], respectively. The singlet oxygen (1O[Formula: see text] generation of PCP1[Formula: see text]PCP3 was determined by the 1,3-diphenylisobenzofuran (DPBF) method using tetrapyridylporphyrin (H2TMPyP) as a reference. The 1O2 generation rate of PCP1[Formula: see text]PCP3 followed the order of PCP2 >PCP1>H2TMPyP >PCP3. Subsequently, the photocleavage effect of porphyrins on pBR322 plasmid DNA was studied by gel electrophoresis. At 10.0 [Formula: see text]M, PCP1 and PCP2 could cleave DNA completely. At 2.0 [Formula: see text]M, the cleavage rate of DNA by PCP3 was 57.5%, which was significantly higher than that of H2TMPyP (38.8%). These results verified that the amount of cationic ions in the porphyrin structure could affect the binding modes of porphyrins with DNA and their cleavage ability of DNA.

Cooperative Catalysis of an Alcohol Dehydrogenase and Rhodium-Modified Periodic Mesoporous Organosilica

The combined use of a metal-complex catalyst and an enzyme is attractive, but typically results in mutual inactivation. A rhodium (Rh) complex immobilized in a bipyridine-based periodic mesoporous organosilica (BPy-PMO) shows high catalytic activity during transfer hydrogenation, even in the presence of bovine serum albumin (BSA), while a homogeneous Rh complex exhibits reduced activity due to direct interaction with BSA. The use of a smaller protein or an amino acid revealed a clear size-sieving effect of the BPy-PMO that protected the Rh catalyst from direct interactions. A combination of Rh-immobilized BPy-PMO and an enzyme (horse liver alcohol dehydrogenase; HLADH) promoted sequential reactions involving the transfer hydrogenation of NAD⁺ to give NADH followed by the asymmetric hydrogenation of 4-phenyl-2-butanone with high enantioselectivity. The use of BPy-PMO as a support for metal complexes could be applied to other systems consisting of a metal-complex catalyst and an enzyme.

Photoelectrocatalytic reduction of CO2 to methanol over a photosystem II-enhanced Cu foam/Si-nanowire system

A solar-light double illumination photoelectrocatalytic cell (SLDIPEC) was fabricated for autonomous CO₂ reduction and O₂ evolution with the aid of photosystem II (PS-II, an efficient light-driven water-oxidized enzyme from nature) and utilized in a photoanode solution. The proposed SLPEC system was composed of Cu foam as the photoanode and p-Si nanowires (Si-NW) as the photocathode. Under solar irradiation, it exhibited a super-photoelectrocatalytic performance for CO₂ conversion to methanol, with a high evolution rate (41.94mmol/hr), owing to fast electron transfer from PS-II to Cu foam. Electrons were subsequently trapped by Si-NW through an external circuit via bias voltage (0.5V), and a suitable conduction band potential of Si (-0.6eV) allowed CO₂ to be easily reduced to CH₃OH at the photocathode. The constructed Z-scheme between Cu foam and Si-NW can allow the SLDIPEC system to reduce CO₂ (8.03mmol/hr) in the absence of bias voltage. This approach makes full use of the energy band mismatch of the photoanode and photocathode to design a highly efficient device for solving environmental issues and producing clean energy.

Artificial Photosynthesis: Hybrid Systems

Oxidoreductases are promising catalysts for organic synthesis. To sustain their catalytic cycles they require efficient supply with redox equivalents. Today classical biomimetic approaches utilizing natural electron supply chains prevail but artificial regeneration approaches bear the promise of simpler and more robust reaction schemes. Utilizing visible light can accelerate such artificial electron transport chains and even enable thermodynamically unfeasible reactions such as the use of water as reductant.This contribution critically summarizes the current state of the art in photoredoxbiocatalysis (i.e. light-driven biocatalytic oxidation and reduction reactions).

Biocatalytic and Bioelectrocatalytic Approaches for the Reduction of Carbon Dioxide using Enzymes

In the recent decade, CO₂ has increasingly been regarded not only as a greenhouse gas but even more as a chemical feedstock for carbon-based materials. Different strategies have evolved to realize CO₂ utilization and conversion into fuels and chemicals. In particular, biological approaches have drawn attention, as natural CO₂ conversion serves as a model for many processes. Microorganisms and enzymes have been studied extensively for redox reactions involving CO₂. In this review, we focus on monitoring nonliving biocatalyzed reactions for the reduction of CO₂ by using enzymes. We depict the opportunities but also challenges associated with utilizing such biocatalysts. Besides the application of enzymes with co-factors, resembling natural processes, and co-factor recovery, we also discuss implementation into photochemical and electrochemical techniques.

Product Selectivity in Homogeneous Artificial Photosynthesis Using [(bpy)Rh(Cp*)X]n+-Based Catalysts

Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bonds using artificial photosynthesis has been under intensive investigation within the last decades. As the understanding of the underlying working principle of these complex systems continuously grows, more focus will be placed on a catalyst design for highly selective product formation. Recent reports have shown that multifunctional photocatalysts can operate with high chemoselectivity, forming different catalysis products under appropriate reaction conditions. Within this context [(bpy)Rh(Cp*)X]n+-based catalysts are highly relevant examples for a detailed understanding of product selectivity in artificial photosynthesis since the identification of a number of possible reaction intermediates has already been achieved.

Water-soluble metalloporphyrinates with excellent photo-induced anticancer activity resulting from high tumor accumulation

To develop a water-soluble and tumor-targeted photosensitizer for photodynamic therapy (PDT), a porphyrin framework containing the metal ion gallium(III) was combined with platinum(II)-based groups to produce two new pentacationic metalloporphyrinates, Ga-4cisPtTPyP (5,10,15,20-tetrakis{cis-diammine-chloro-platinum(II)}(4-pyridyl)-porphyrinato gallium(III) hydroxide tetranitrate) and Ga-4transPtTPyP (5,10,15,20-tetrakis{trans-diammine-chloro-platinum(II)} (4-pyridyl)-porphyrinato gallium(III) hydroxide tetranitrate). Both complexes exhibited high singlet oxygen quantum yields (Φ_∆) and remarkable photocytotoxicity with appreciable phototoxic indexes (PIs). In particular, Ga-4cisPtTPyP showed a low IC₅₀ value (Colon 26: 0.12μM; Sarcoma 180: 0.08μM) under illumination and its PI up to 1000. With outstanding tumor accumulation (tumor/muscle ratio>9), Ga-4cisPtTPyP almost completely inhibited tumor growth over two weeks in an in vivo PDT assay. These results imply that Ga-4cisPtTPyP could be a promising anticancer agent for use in PDT.

Evidence for photosensitised hydrogen production from water in the absence of precious metals, redox-mediators and co-catalysts

New approaches for sunlight-powered proton reduction and photocatalytic hydrogen evolution from aqueous salt solutions using earth-abundant components and molecular photosensitisers.

Thermodynamic Hydricity of Transition Metal Hydrides

Transition metal hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen.

Synthesis, Characterization, and Reactivity of Functionalized Trinuclear Iron-Sulfur Clusters - A New Class of Bioinspired Hydrogenase Models

The air- and moisture-stable iron-sulfur carbonyl clusters Fe3S2(CO)7(dppm) (1) and Fe3S2(CO)7(dppf) (2) carrying the bisphosphine ligands bis(diphenylphosphanyl)methane (dppm) and 1,1'-bis(diphenylphosphanyl)ferrocene (dppf) were prepared and fully characterized. Two alternative synthetic routes based on different thionation reactions of triiron dodecacarbonyl were tested. The molecular structures of the methylene-bridged compound 1 and the ferrocene-functionalized derivative 2 were determined by single-crystal X-ray diffraction. The catalytic reactivity of the trinuclear iron-sulfur cluster core for proton reduction in solution at low overpotential was demonstrated. These deeply colored bisphosphine-bridged sulfur-capped iron carbonyl systems are discussed as promising candidates for the development of new bioinspired model compounds of iron-based hydrogenases.

Photoinduced charge accumulation by metal ion-coupled electron transfer

An oligotriarylamine (OTA) unit, a Ru(bpy)3(2+) photosensitizer moiety (Ru), and an anthraquinone (AQ) entity were combined to a molecular dyad (Ru-OTA) and a molecular triad (AQ-Ru-OTA). Pulsed laser excitation at 532 nm led to the formation of charge-separated states of the type Ru(-)-OTA(+) and AQ(-)-Ru-OTA(+) with lifetimes of ≤10 ns and 2.4 μs, respectively, in de-aerated CH3CN at 25 °C. Upon addition of Sc(OTf)3, very long-lived photoproducts were observed. Under steady-state irradiation conditions using a flux of (6.74 ± 0.21) × 10(15) photons per second at 450 nm, the formation of twofold oxidized oligotriarylamine (OTA(2+)) was detected in aerated CH3CN containing 0.02 M Sc(3+), as demonstrated unambiguously by comparison with UV-Vis absorption spectra obtained in the course of chemical oxidation with Cu(2+). Photodriven charge accumulation on the OTA unit of Ru-OTA and AQ-Ru-OTA is possible due to the lowering of the O2 reduction potential caused by the interaction of superoxide with the strong Lewis acid Sc(3+). The presence of the anthraquinone unit in AQ-Ru-OTA accelerates the rate-determining reaction step for charge accumulation by a factor of 10 compared to the Ru-OTA dyad. This is attributed to the formation of Sc(3+)-stabilized anthraquinone radical anion intermediates in the triad. Possible mechanistic pathways leading to charge accumulation are discussed. Photodriven charge accumulation is of key importance for solar fuels because their production will have to rely on multi-electron chemistry rather than single-electron reaction steps. Our study is the first to demonstrate that metal ion-coupled electron transfer (MCET) can be exploited to accumulate charges on a given molecular unit using visible light as an energy input. The approach of using a combination of intra- and intermolecular electron transfer reactions which are enabled by MCET is conceptually novel, and the fundamental insights gained from our study are relevant in the greater context of solar energy conversion.

Sn(IV) Metalloporphyrin/Co(III) Complex: An All-Abundant-Element System for the Photocatalytic Production of H2 in Aqueous Solution

A new, molecular system for the light-driven production of hydrogen in aqueous solution was developed by combining a water-soluble tin porphyrin ([Sn(IV)Cl2TPPC], A) acting as photosensitizer with a cobalt-based proton-reduction catalyst ([Co(III)Cl(dmgH)2(py)], C). Under visible light illumination and with triethanolamine (TEOA) as electron source, the system evolves H2 for hours and is clearly catalytic in both dye and catalyst. A detailed analysis of the relevant redox potentials in combination with time-resolved spectroscopy resulted in the development of a Z-scheme type model for the flow of electrons in this system. Key intermediates of the proposed mechanism for the pathway leading to H2 are the porphyrin dye's highly oxidizing singlet excited state (1)A* (E ∼ +1.3 V vs NHE), its strongly reducing isobacteriochlorin analogue (E ∼ +0.95 V), and the Co(I) form of C (E ∼ -0.8 V), acting as catalyst for H2 formation. Among other results, the suggested reaction sequence is supported by the detection of a shortened excited-state lifetime for singlet (1)A* (τ ∼ 1.75 ns) in the presence of TEOA and the ultraviolet-visible detection of the Sn(IV) isobacteriochlorin intermediate at λ = 610 nm. Thus, a molecular, conceptually biomimetic, and precious-metal-free reaction chain was found which photocatalytically generates H2 in a 100% aqueous system from an electron donor with a high oxidation potential (E(TEOA) ∼ +1.1 V). On the other hand, at identical conditions, this photoreaction chain yields H2 markedly slower than a system using the photosensitizer [Re(I)(CO)3(bpy) (py)](+), probably due to the much longer excited-state lifetime (τ ∼ 120 ns) of the rhenium dye and better electron-transfer rates caused by its simple single-electron photoreduction chemistry.

Aluminum Nanoarrays for Plasmon-Enhanced Light Harvesting

The practical limits of coinage-metal-based plasmonic materials demand sustainable, abundant alternatives with a wide plasmonic range of the solar energy spectrum. Aluminum (Al) is an emerging alternative, but its instability in aqueous environments critically limits its applicability to various light-harvesting systems. Here, we report a design strategy to achieve a robust platform for plasmon-enhanced light harvesting using Al nanostructures. The incorporation of mussel-inspired polydopamine nanolayers in the Al nanoarrays allowed for the reliable use of Al plasmonic resonances in a highly corrosive photocatalytic redox solution and provided nanoscale arrangement of organic photosensitizers on Al surfaces. The Al-photosensitizer core-shell assemblies exhibited plasmon-enhanced light absorption, which resulted in a 300% efficiency increase in photo-to-chemical conversion. Our strategy enables stable and advanced use of aluminum for plasmonic light harvesting.

Semi-insulating behaviour of self-assembled tin(IV)corrole nanospheres

Three novel tin(iv)corrole complexes have been prepared and characterized by various spectroscopic techniques including single crystal X-ray structural analysis. Packing diagrams of the tin(iv)corroles revealed that corrolato-tin(iv)-chloride molecules are interconnected by intermolecular C-HCl hydrogen bonding interactions. HCl distances are 2.848 Å, 3.051 Å, and 2.915 Å, respectively, for the complexes. In addition, the C-HCl angles are 119.72°, 144.70°, and 147.08°, respectively, for the complexes. It was also observed that in one of the three synthesized complexes dimers were formed, while in the other two cases 1D infinite polymer chains were formed. Well-defined and nicely organized three-dimensional hollow nanospheres (SEM images on silicon wafers) with diameters of ca. 676 nm and 661 nm are obtained in the complexes, forming 1D polymer chains. By applying a thin layer of tin(iv)corrole nanospheres to an ITO surface (AFM height images of ITO films; ∼200 nm in height), a device was fabricated with the following composition: Ag/ITO-coated glass/tin(iv)corrole nanospheres/ITO-coated glass/Ag. The resistivity (ρ) of the nanostructured film was calculated to be ∼2.4 × 10(8) Ω cm, which falls in the range of semi-insulating semiconductors. CAFM current maps at 10 V bias show bright spots with a 10-20 pA intensity and indicate that the nanospheres (∼250 nm in diameter) are the electron-conducting pathway in the device. The semi-insulating behavior arises from the non-facile electron transfer in the HOMOs of the tin(iv)corrole nanospheres.

Antimony porphyrins as red-light powered photocatalysts for solar fuel production from halide solutions in the presence of air

Stable light-harvesting sensitizers for the two-electron oxidation of halide ions are reported. Photocatalysis is studied in solution, in aqueous micellar medium and with surface immobilized samples for convenient photocatalyst recycling.

Rhodium-coordinated poly(arylene-ethynylene)-alt-poly(arylene-vinylene) copolymer acting as photocatalyst for visible-light-powered NAD⁺/NADH reduction

A 2,2'-bipyridyl-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene) polymer, acting as a light-harvesting ligand system, was synthesized and coupled to an organometallic rhodium complex designed for photocatalytic NAD(+)/NADH reduction. The material, which absorbs over a wide spectral range, was characterized by using various analytical techniques, confirming its chemical structure and properties. The dielectric function of the material was determined from spectroscopic ellipsometry measurements. Photocatalytic reduction of nucleotide redox cofactors under visible light irradiation (390-650 nm) was performed and is discussed in detail. The new metal-containing polymer can be used to cover large surface areas (e.g. glass beads) and, due to this immobilization step, can be easily separated from the reaction solution after photolysis. Because of its high stability, the polymer-based catalyst system can be repeatedly used under different reaction conditions for (photo)chemical reduction of NAD(+). With this concept, enzymatic, photo-biocatalytic systems for solar energy conversion can be facilitated, and the precious metal catalyst can be recycled.

Uniform graphitic carbon nitride nanorod for efficient photocatalytic hydrogen evolution and sustained photoenzymatic catalysis

Uniform graphitic carbon nitride nanorods (CNR) were facilely obtained by a morphology-preserving strategy by templating a chiral mesostructured silica nanorod. The hexagonal mesostructured pore structures of one-dimensional silica nanorods can provide nanoconfinement space for carbon nitride condensation to perfect layered structures. CNR demonstrated excellent photocatalytic capability in generating hydrogen from water even with a small specific surface area, compared with its mesoporous counterpart. For further application demonstration, the CNR was used for photocatalytic regeneration of NAD(+) to NADH, the biological form of hydrogen. The in situ NADH regeneration system was further coupled with l-glutamate dehydrogenase for sustainable generation of l-glutamate from α-ketoglutarate. The high yield and high efficiency obtained here point a high-throughput and sustainable way for practical enzymatic applications.