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

Intermarrying MOF Glass and Lead Halide Perovskites for Artificial Photosynthesis

The development of efficient artificial photosynthesis systems is crucial for sustainable chemical production, as they mimic natural processes to convert solar energy into chemical products, thereby addressing both energy and environmental challenges. The main bottlenecks in current research include fabricating highly selective, stable, and scalable catalysts, as well as effectively harnessing the full spectrum of light, particularly the low-energy, long-wavelength portion. Herein, we report a novel composite photocatalyst system based on lead halide perovskites embedded in functionalized MOF glass. The construction of a well-defined interface between the light-harvesting perovskite and stable Rh single-atom-containing MOF glass mimics the functions of photosystem I (PS I). This facilitates efficient photoinduced electron generation under visible light and subsequent electron transfer for coenzyme (NADH) regeneration with high selectivity. The regenerated NADH can then be consumed by immobilized enzymes for CO2 reduction, realizing the artificial photosynthesis process for formic acid generation. This work also elucidates the interactions and optoelectronic responses between MOF glass and perovskites, offering insights into the design and fabrication of nanocomposite photocatalysts for other advanced chemical syntheses.

Organometallic Iridium-Complex-Functionalized Nanographene Catalysts for Low-Temperature Hydrogenation of Carbonyl Derivatives

An organometallic iridium (Ir)-complex-functionalized nanographene catalyst Ir-PyPh-GC was prepared via a two-step strategy involving amide ligand modification and metal Ir coordination. Ir-PyPh-GC showed ultrahigh hydrogenation capability, good recyclability, and selectivity for carbonyl derivatives (ketones, aldehydes, and quinones) at a low temperature (40 °C). The as-prepared Ir-complex-based catalyst is less expensive, making it feasible for industrial application.

Visible light-driven oxidation of non-native substrate by laccase attached on Ru-based metal-organic frameworks

Light-induced electron transfer can broaden the substrate range of metalloenzyme. However, the efficiency of photo-enzyme coupling is limited by the poor combination of photosensitizer or photocatalyst with enzyme. Herein, we prepared the nano-photocatalyst MIL-125-NH2@Ru(bpy) by in site embedding ruthenium pyridine-diimine complex [Ru(bpy)3]2+ into metal organic frameworks MIL-125-NH2 and associated it with multicopper oxidase (MCO) laccase. Compared to [Ru(bpy)3]2+, the coupling efficiency of MIL-125-NH2@Ru(bpy)3 for enzymatic oxygen reduction increased by 35.7%. A series of characterizations confirmed that the amino group of laccase formed chemical bonds with the surface defects or hydrophobic groups of MIL-125-NH2@Ru(bpy)3. Consequently, the tight binding accelerated the quenching process and electron transfer between laccase and the immobilized ruthenium pyridine-diimine complex. This work would open an avenue for the synthesis of MOFs photocatalyst towards photo-enzyme coupling.

Redox Biocatalysis: Quantitative Comparisons of Nicotinamide Cofactor Regeneration Methods

Enzymatic processes, particularly those capable of performing redox reactions, have recently been of growing research interest. Substrate specificity, optimal activity at mild temperatures, high selectivity, and yield are among the desirable characteristics of these oxidoreductase catalyzed reactions. Nicotinamide adenine dinucleotide (phosphate) or NAD(P)H-dependent oxidoreductases have been extensively studied for their potential applications like biosynthesis of chiral organic compounds, construction of biosensors, and pollutant degradation. One of the main challenges associated with making these processes commercially viable is the regeneration of the expensive cofactors required by the enzymes. Numerous efforts have pursued enzymatic regeneration of NAD(P)H by coupling a substrate reduction with a complementary enzyme catalyzed oxidation of a co-substrate. While offering excellent selectivity and high total turnover numbers, such processes involve complicated downstream product separation of a primary product from the coproducts and impurities. Alternative methods comprising chemical, electrochemical, and photochemical regeneration have been developed with the goal of enhanced efficiency and operational simplicity compared to enzymatic regeneration. Despite the goal, however, the literature rarely offers a meaningful comparison of the total turnover numbers for various regeneration methodologies. This comprehensive Review systematically discusses various methods of NAD(P)H cofactor regeneration and quantitatively compares performance across the numerous methods. Further, fundamental barriers to enhanced cofactor regeneration in the various methods are identified, and future opportunities are highlighted for improving the efficiency and sustainability of commercially viable oxidoreductase processes for practical implementation.

Photocatalytic Reduction of Nicotinamide Co-factor by Perylene Sensitized RhIII Complexes

The ambitious goal of artificial photosynthesis is to develop active systems that mimic nature and use light to split water into hydrogen and oxygen. Intramolecular design concepts are particularly promising. Herein, we firstly present an intramolecular photocatalyst integrating a perylene-based light-harvesting moiety and a catalytic rhodium center (RhIII phenPer). The excited-state dynamics were investigated by means of steady-state and time-resolved absorption and emission spectroscopy. The studies reveal that photoexcitation of RhIII phenPer yields the formation of a charge-separated intermediate, namely RhII phenPer⋅+ , that results in a catalytically active species in the presence of protons.

Chiral NADH Model: Design, Synthesis, Asymmetric Reduction Reaction and Fluorescence Characteristics

Abstract:

A new type of NADH model compound, which has six asymmetric carbon centers, has been synthesized by an efficient and convenient method. We preliminarily attempted that NADH models combined with enzyme were used in the asymmetric reduction. It is the first time that dehydrogenase with NADH models instead of inorganic catalysts such as MgCl2 were used in the asymmetric reduction. Furthermore, the experimental results showed that the new NADH model has the strongest fluorescence emission properties compared with previous reported models.

The Efficient Synthesis of 2-(3-Carbamoylpyridine-2-yl) Nicotinamide Pyridine Salts

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The synthesis of axially chiral compounds has attracted a great deal of attention in recent years. Herein, an efficient and economical synthetic route has been developed for 2-(3- carbamoylpyridin-2-yl) nicotinamide pyridine salts, axially chiral compounds. The starting material 1,10-phenanthroline is readily available. In this study, 2-(3-carbamoylpyridin-2-yl) nicotinamide pyridine salts are obtained in moderate to good yields. This protocol includes simple operations and has easy scalability. In addition, the axial chirality of the products is also preliminary studied.

Photocatalyst-enzyme hybrid systems for light-driven biotransformation

Enzymes catalyse target reactions under mild conditions with high efficiency, as well as excellent regional-, stereo-, and enantiomeric selectivity. Photocatalysis utilises sustainable and environment-friendly light power to realise efficient chemical conversion. By combining the interdisciplinary advantages of photo- and enzymatic catalysis, the photocatalyst-enzyme hybrid systems have proceeded various light-driven biotransformation with high efficiency under environmentally benign conditions, thus, attracting unparalleled focus during the last decades. It has also been regarded as a promising pathway towards green chemistry utilising ubiquitous solar energy. This systematic review gives insight into this research field by classifying the existing photocatalyst-enzyme hybrid systems into three sections based on different hybridizing modes between photo- and enzymatic catalysis. Furthermore, existing challenges and proposed strategies are discussed within this context. The first system summarised is the cofactor-mediated hybrid system, in which natural/artificial cofactors act as reducing equivalents that connect photocatalysts with enzymes for light-driven enzymatic biotransformation. Second, the direct contact-based photocatalyst-enzyme hybrid systems are described, including two different kinds of electron exchange sites on the enzyme molecules. Third, some cases where photocatalysts and enzymes are integrated into a reaction cascade with specific intermediates will be discussed in the following chapter. Finally, we provide perspective concerning the future of this field.

Advances in electrochemical cofactor regeneration: enzymatic and non-enzymatic approaches

Nicotinamide adenine dinucleotide(NAD(P)H) is a metabolically interconnected redox cofactor serving as a hydride source for the majority of oxidoreductases, and consequently constituting a significant cost factor for bioprocessing. Much research has been devoted to the development of efficient, affordable, and sustainable methods for the regeneration of these cofactors through chemical, electrochemical, and photochemical approaches. However, the enzymatic approach using formate dehydrogenase is still the most abundantly employed in industrial applications, even though it suffers from system complexity and product purity issues. In this review, we summarize non-enzymatic and enzymatic electrochemical approaches for cofactor regeneration, then discuss recent developments to solve major issues. Issues discussed include Rh-catalyst mediated enzyme mutual inactivation, electron-transfer rates, catalyst sustainability, product selectivity and simplifying product purification. Recently reported remedies are discussed, such as heterogeneous metal catalysts generating H⁺ as the sole byproduct or high activity and stability redox-polymer immobilized enzymatic systems for sustainable organic synthesis.

Enzyme-Loaded Nanoreactors Enable the Continuous Regeneration of Nicotinamide Adenine Dinucleotide in Artificial Metabolisms

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme for numerous biocatalytic pathways. While in nature, NAD+ is continuously regenerated from NADH by enzymes, all synthetic NAD+ regeneration strategies require a continuous supply of expensive reagents and generate byproducts, making these strategies unattractive. In contrast, we present an artificial enzyme combination that produces NAD+ from oxygen and water continuously; no additional organic substrates are required once a minimal amount pyruvate is supplied. Three enzymes, i.e., LDH, LOX, and CAT, are covalently encapsulated into a substrate-permeable silica nanoreactor by a mild fluoride-catalyzed sol-gel process. The enzymes retain their activity inside of the nanoreactors and are protected against proteolysis and heat. We successfully used NAD+ from the nanoreactors for the continuous production of NAD+ i) to sense glucose in artificial glucose metabolism, and ii) to reduce the non-oxygen binding methemoglobin to oxygen-binding hemoglobin. This latter conversion might be used for the treatment of Methemoglobinemia. We believe that this versatile tool will allow the design of artificial NAD+ -dependent metabolisms or NAD+ -mediated redox-reactions.

ZnO Materials as Effective Anodes for the Photoelectrochemical Regeneration of Enzymatically Active NAD. ACS APPLIED MATERIALS & INTERFACES 2021;13:10719-10727. [PMID: 33645209 DOI: 10.1021/acsami.0c20630]

This work reports the study of ZnO-based anodes for the photoelectrochemical regeneration of the oxidized form of nicotinamide adenine dinucleotide (NAD⁺). The latter is the most important coenzyme for dehydrogenases. However, the high costs of NAD⁺ limit the use of such enzymes at the industrial level. The influence of the ZnO morphologies (flower-like, porous film, and nanowires), showing different surface area and crystallinity, was studied. The detection of diluted solutions (0.1 mM) of the reduced form of the coenzyme (NADH) was accomplished by the flower-like and the porous films, whereas concentrations greater than 20 mM were needed for the detection of NADH with nanowire-shaped ZnO-based electrodes. The photocatalytic activity of ZnO was reduced at increasing concentrations of NAD⁺ because part of the ultraviolet irradiation was absorbed by the coenzyme, reducing the photons available for the ZnO material. The higher electrochemical surface area of the flower-like film makes it suitable for the regeneration reaction. The illumination of the electrodes led to a significant increase on the NAD⁺ regeneration with respect to both the electrochemical oxidation in dark and the only photochemical reaction. The tests with formate dehydrogenase demonstrated that 94% of the regenerated NAD⁺ was enzymatically active.

Intensifying Electron Utilization by Surface-Anchored Rh Complex for Enhanced Nicotinamide Cofactor Regeneration and Photoenzymatic CO2 Reduction

Solar-driven photocatalytic regeneration of cofactors, including reduced nicotinamide adenine dinucleotide (NADH), reduced nicotinamide adenine dinucleotide phosphate (NADPH), and reduced flavin adenine dinucleotide (FADH₂), could ensure the sustainable energy supply of enzymatic reactions catalyzed by oxidoreductases for the efficient synthesis of chemicals. However, the elevation of cofactor regeneration efficiency is severely hindered by the inefficient utilization of electrons transferred on the surface of photocatalysts. Inspired by the phenomenon of ferredoxin-NADP⁺ reductase (FNR) anchoring on thylakoid membrane, herein, a homogeneous catalyst of rhodium (Rh) complex, [Cp∗Rh(bpy)H₂O]²⁺, was anchored on polymeric carbon nitride (PCN) mediated by a tannic acid/polyethyleneimine (TA/PEI) adhesive layer, acquiring PCN@TA/PEI-Rh core@shell photocatalyst. Illuminated by visible light, electrons were excited from the PCN core, then transferred through the TA/PEI shell, and finally captured by the surface-anchored Rh for instant utilization during the regeneration of NADH. The TA/PEI-Rh shell could facilitate the electron transfer from the PCN core and, more importantly, achieved ~1.3-fold elevation of electron utilization efficiency compared with PCN. Accordingly, the PCN@TA/PEI-Rh afforded the NADH regeneration efficiency of 37.8% after 20 min reaction under LED light (405 nm) illumination, over 1.5 times higher than PCN with free Rh. Coupling of the NADH regeneration system with formate dehydrogenase achieved continuous production of formate from carbon dioxide (CO₂). Our study may provide a generic and effective strategy to elevate the catalytic efficiency of a photocatalyst through intensifying the electron utilization.

Early instability of MIL-125-NH2 in aqueous solution and mediation of the visible photogeneration of an NADH cofactor

MIL-125-NH₂ hydrolysis can be minimized by regulating the pH of the medium, thus defining a stability window where it is possible to use it as a photocatalyst for visible light-driven production of NADH.

A PMMA-based heterogeneous photocatalyst for visible light-promoted [4 + 2] cycloaddition

Macromolecular organic photocatalysts consisting of a PMMA network with integrated conjugated moiety have broad and promising applications in visible light-promoted photoredox catalysis.

Visible-light photooxidation in water by 1O2-generating supramolecular hydrogels

An aqueous photocatalytic system exploits photophysical properties arising from the formation of supramolecular hydrogels, with properties and assembly modulated by the amino acids appended to an organic chromophore.

Catalytic recycling of NAD(P)H

A large number of industrially relevant enzymes depend upon dihydronicotinamide adenine dinucleotide (NADH) and dihydronicotinamide adenine dinucleotide phosphate (NADPH) cofactors, which are too expensive to be added in stoichiometric amounts. Existing NAD(P)H-recycling systems suffer from low activity, or the generation of side products. This review focuses on NAD(P)H cofactor regeneration catalyzed by transition metal complexes such as rhodium, ruthenium and iridium complexes using cheap reducing agents such as hydrogen (H₂) and ethanol, which have attracted increasing attention as sustainable energy carriers. The catalytic mechanisms for the regioselective reduction of NAD(P)⁺ are discussed with emphasis on identification of catalytically active intermediates such as transition metal hydride complexes. Applications of NAD(P)H-recycling systems to develop artificial photosynthesis are also discussed.

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.

Metallopolymers for advanced sustainable applications

Since the development of metallopolymers, there has been tremendous interest in the applications of this type of materials. The interest in these materials stems from their potential use in industry as catalysts, biomedical agents in healthcare, energy storage and production as well as climate change mitigation. The past two decades have clearly shown exponential growth in the development of many new classes of metallopolymers that address these issues. Today, metallopolymers are considered to be at the forefront for discovering new and sustainable heterogeneous catalysts, therapeutics for drug-resistant diseases, energy storage and photovoltaics, molecular barometers and thermometers, as well as carbon dioxide sequesters. The focus of this review is to highlight the advances in design of metallopolymers with specific sustainable applications.

Effect of sulfonamidoethylenediamine substituents in RuII arene anticancer catalysts on transfer hydrogenation of coenzyme NAD+ by formate

A series of neutral pseudo-octahedral RuII sulfonamidoethylenediamine complexes [(η6-p-cym)Ru(N,N')Cl] where N,N' is N-(2-(R1,R2-amino)ethyl)-4-toluenesulfonamide (TsEn(R1,R2)) R1,R2 = Me,H (1); Me,Me (2); Et,H (3); benzyl,H (Bz, 4); 4-fluorobenzyl,H (4-F-Bz, 5) or naphthalen-2-ylmethyl,H (Naph, 6), were synthesised and characterised including the X-ray crystal structure of 3. These complexes catalyse the reduction of NAD+ regioselectively to 1,4-NADH by using formate as the hydride source. The catalytic efficiency depends markedly on the steric and electronic effects of the N-substitutent, with turnover frequencies (TOFs) increasing in the order: 1 < 2 < 3, 6 < 4, 5, achieving a TOF of 7.7 h-1 for 4 with a 95% yield of 1,4-NADH. The reduction rate was highest between pH* (deuterated solvent) 6 and 7.5 and improved with an increase in formate concentration (TOF of 18.8 h-1, 140 mM formate). The calculations suggested initial substitution of an aqua ligand by formate, followed by hydride transfer to RuII and then to NAD+, and indicated specific interactions between the aqua complex and both NAD+ and NADH, the former allowing a preorganisation involving interaction between the aqua ligand, formate anion and the pyridine ring of NAD+. The complexes exhibited antiproliferative activity towards A2780 human ovarian cancer cells with IC50 values ranging from 1 to 31 μM, the most potent complex, [(η6-p-cym)Ru(TsEn(Bz,H))Cl] (4, IC50 = 1.0 ± 0.1 μM), having a potency similar to the anticancer drug cisplatin. Co-administration with sodium formate (2 mM), increased the potency of all complexes towards A2780 cells by 20-36%, with the greatest effect seen for complex 6.

New Insight into the Mechanism of NADH Model Oxidation by Metal Ions in Nonalkaline Media

For a long time, it has been controversial that the three-step (e-H⁺-e) or two-step (e-H^•) mechanism was used for the oxidation of nicotinamide adenine dinucleotide coenzyme (NADH) and its models by metal ions in nonalkaline media. The latter mechanism has been accepted by the majority of researchers. In this work, 1-benzyl-1,4-dihydronicotinamide (BNAH) and 1-phenyl-l,4-dihydronicotinamide are used as NADH models and ferrocenium (Fc⁺) metal ion as an electron acceptor. The kinetics for oxidation of the NADH models by Fc⁺ in pure acetonitrile was monitored by using UV-vis absorption and a quadratic relationship between k_obs and the concentrations of NADH models was found for the first time. The rate expression of the reactions developed according to the three-step mechanism is quite consistent with the quadratic curves. The rate constants, thermodynamic driving forces, and kinetic isotope effects of each elementary step for the reactions were estimated. All results supported the three-step mechanism. The intrinsic kinetic barriers of the proton transfer from BNAH^+• to BNAH and the hydrogen-atom transfer from BNAH^+• to BNAH^+• were estimated by using Zhu equation; the results showed that the former is 11.8 kcal/mol and the latter is larger than 24.3 kcal/mol. It is the large intrinsic kinetic barrier of the hydrogen-atom transfer that makes the reactions choose the three-step rather than two-step mechanism. Further investigation of the factors affecting the intrinsic kinetic barrier of chemical reactions indicated that the large intrinsic kinetic barrier of the hydrogen-atom transfer originated from the repulsion of positive charges between BNAH^+• and BNAH^+•. The greatest contribution of this work is the discovery of the quadratic dependence of k_obs on the concentrations of the NADH models, which is inconsistent with the conventional viewpoint of the "two-step mechanism" on the oxidation of NADH and its models by metal ions in the nonalkaline media.

Anticancer Activity and Catalytic Potential of Ruthenium(II)-Arene Complexes with N,O-Donor Ligands

The special ability of organometallic complexes to catalyze various transformations might offer new effective mechanisms for the treatment of cancer. Studies that report both the biological properties and the ability of metallic complexes to promote therapeutically relevant catalytic reactions are limited. Herein, we report the anticancer activity and catalytic potential of some ruthenium(II)-arene complexes bearing bidentate Schiff base ligands (2a and 2b) and their reduced analogues (5a and 5b, respectively). In comparison to their Schiff base counterparts 2a and 2b, we demonstrate that amine complexes 5a and 5b display (i) a higher in vitro antiproliferative activity on different human cancer cell lines, (ii) a lower rate of hydrolysis, and (iii) an improved initial catalytic rate for the reduction of NAD⁺ to NADH. In contrast to their imine analogues 2a and 2b, we also show that amine complexes 5a and 5b induce the generation of intracellular reactive oxygen species (ROS) in MCF-7 breast cancer cells. Our results highlight the impact that a simple ligand modification such as the reduction of an imine moiety can have on both the catalytic and biological activities of metal complexes. Moreover, the ruthenium complexes reported here display some antiproliferative activity against T47D breast cancer cells, known for their cis-platin resistance.

The effect of the functional ionic group of the viologen derivative on visible-light driven CO2 reduction to formic acid with the system consisting of water-soluble zinc porphyrin and formate dehydrogenase

The effect of the functional ionic group of 4,4′-bipyridinium salt on the visible-light driven CO₂ conversion to formic acid with the system consisting of zinc porphyrin and formate dehydrogenase was investigated.

From sequential chemoenzymatic synthesis to integrated hybrid catalysis: taking the best of both worlds to open up the scope of possibilities for a sustainable future

Here an overview of all pathways that integrate chemical and biological catalysis is presented. We emphasize the factors to be considered in order to understand catalytic synergy.

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.

Catalytic Hydroxylation of Benzene to Phenol by Dioxygen with an NADH Analogue

Hydroxylation of benzene by molecular oxygen (O2 ) occurs efficiently with 10-methyl-9,10-dihydroacridine (AcrH2 ) as an NADH analogue in the presence of a catalytic amount of Fe(ClO4 )3 or Fe(ClO4 )2 with excess trifluoroacetic acid in a solvent mixture of benzene and acetonitrile (1:1 v/v) to produce phenol, 10-methylacridinium ion and hydrogen peroxide (H2 O2 ) at 298 K. The catalytic oxidation of benzene by O2 with AcrH2 in the presence of a catalytic amount of Fe(ClO4 )3 is started by the formation of H2 O2 from AcrH2 , O2 , and H(+) . Hydroperoxyl radical (HO2 (.) ) is produced from H2 O2 with the redox pair of Fe(3+) /Fe(2+) by a Fenton type reaction. The rate-determining step in the initiation is the proton-coupled electron transfer from Fe(2+) to H2 O2 to produce HO(.) and H2 O. HO(.) abstracts hydrogen rapidly from H2 O2 to produce HO2 (.) and H2 O. The Fe(3+) produced was reduced back to Fe(2+) by H2 O2 . HO2 (.) reacts with benzene to produce the radical adduct, which abstracts hydrogen from AcrH2 to give the corresponding hydroperoxide, accompanied by generation of acridinyl radical (AcrH(.) ) to constitute the radical chain reaction. Hydroperoxyl radical (HO2 (.) ), which was detected by using the spin trap method with EPR analysis, acts as a chain carrier for the two radical chain pathways: one is the benzene hydroxylation with O2 and the second is oxidation of an NADH analogue with O2 to produce H2 O2 .

Microfluidic chip-based one-step fabrication of an artificial photosystem I for photocatalytic cofactor regeneration

We report a one-step strategy for the formation of an artificial photosystem I, with an enhanced coenzyme regeneration rate.

Generation of a stable supramolecular hydrogen evolving photocatalyst by alteration of the catalytic center

The change of the catalytic center from MX₂ to RhCp*Cl leads to a stability boost in [(tbbpy)₂Ru(tpphz)] based supramolecular photocatalysts.

A Petal-type Chiral NADH Model: Design, Synthesis and its Asymmetric Reduction

A new type of NADH model compound has been synthesized by an efficient and convenient method. This model compound exhibits high reactivity and enantioselectivity in asymmetric reduction reactions. The results show that chiral NADH model S could be effectively combined with Mg²⁺ to form ternary complexes. This novel C₃ symmetrical NADH model is capable of fluorescence emission at 460 nm when excited at 377 nm.

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.

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.