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Modifying redox potential of substrates and intermediates to balance pairs of redox steps are important stages for multistep photosynthesis but faced marked challenges. Through co‐clathration of iridium photosensitizer and imine substrate within one packet of a metal‐organic capsule to shift the redox potentials of substrate, herein, we reported a multiphoton enzymatic strategy for the generation of heterocycles by intramolecular C−X hydrogen evolution cross‐couplings. The cage facilitated a pre‐equilibrium substrate‐involving clathrate that cathodic shifts the oxidation potential of the substrate‐dye‐host ternary complex and configuration inversion of substrate via spatial constraints in the confined space. The new two photon excitation strategy enabled the precise control of the multistep electron transfer between each pair (photosensitizer, substrate and the capsule), endowing the catalytic system proceeding smoothly with an enzymatic fashion. Three kinds of 2‐subsituted (−OH, −NH2, and −SH) imines and N‐aryl enamines all give the corresponding cyclization products efficiently under visible light irradiation, demonstrating the promising of the microenvironment driven thermodynamic activation in the host‐dye‐substrate ternary for synergistic combination of multistep photocatalytic transformations. [ABSTRACT FROM AUTHOR]

Modifying redox potential of substrates and intermediates to balance pairs of redox steps are important stages for multistep photosynthesis but faced marked challenges. Through co‐clathration of iridium photosensitizer and imine substrate within one packet of a metal‐organic capsule to shift the redox potentials of substrate, herein, we reported a multiphoton enzymatic strategy for the generation of heterocycles by intramolecular C−X hydrogen evolution cross‐couplings. The cage facilitated a pre‐equilibrium substrate‐involving clathrate that cathodic shifts the oxidation potential of the substrate‐dye‐host ternary complex and configuration inversion of substrate via spatial constraints in the confined space. The new two photon excitation strategy enabled the precise control of the multistep electron transfer between each pair (photosensitizer, substrate and the capsule), endowing the catalytic system proceeding smoothly with an enzymatic fashion. Three kinds of 2‐subsituted (−OH, −NH2, and −SH) imines and N‐aryl enamines all give the corresponding cyclization products efficiently under visible light irradiation, demonstrating the promising of the microenvironment driven thermodynamic activation in the host‐dye‐substrate ternary for synergistic combination of multistep photocatalytic transformations. [ABSTRACT FROM AUTHOR]

Using our recent relevant results, this account shows the featured reactivities of two‐molecule photoredox systems compared to one‐molecule photoredox systems. The low efficiency of electron transfer processes, such as photoinduced and back‐electron transfer, in the two‐molecule photoredox system, furnishes unique products through different pathways. The facile replacement of photoredox catalysts with appropriate oxidation/reduction potentials in this system provides valuable insights into photoredox reactions. [ABSTRACT FROM AUTHOR]

The sensitizing ability of a catalytic system is closely related to the visible‐light absorption ability, excited‐state lifetime, redox potential, and electron‐transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO2 photoreduction. Herein, a series of Ir(III)‐based PSs (Ir‐1–Ir‐6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO2 photoreduction. Among them, less efficient visible‐light absorption capacity results in lower CO yields of Ir‐1, Ir‐2 or Ir‐4. Ir‐3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the Kobs of Ir‐3 is ≈10 times higher than that of Ir‐5, the CO yield of Ir‐3 is slightly higher than that of Ir‐5 due to the compensation of Ir‐5's strong visible‐light‐absorbing ability. Ir‐6 exhibits excellent photocatalytic performance due to the strong visible‐light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO2 photoreduction to CO with Ir‐6 can achieve 91.5 μmol, over 54 times higher than Ir‐1, and the optimized TONC‐1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO2 photoreduction. [ABSTRACT FROM AUTHOR]

The sensitizing ability of a catalytic system is closely related to the visible‐light absorption ability, excited‐state lifetime, redox potential, and electron‐transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO2 photoreduction. Herein, a series of Ir(III)‐based PSs (Ir‐1–Ir‐6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO2 photoreduction. Among them, less efficient visible‐light absorption capacity results in lower CO yields of Ir‐1, Ir‐2 or Ir‐4. Ir‐3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the Kobs of Ir‐3 is ≈10 times higher than that of Ir‐5, the CO yield of Ir‐3 is slightly higher than that of Ir‐5 due to the compensation of Ir‐5's strong visible‐light‐absorbing ability. Ir‐6 exhibits excellent photocatalytic performance due to the strong visible‐light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO2 photoreduction to CO with Ir‐6 can achieve 91.5 μmol, over 54 times higher than Ir‐1, and the optimized TONC‐1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO2 photoreduction. [ABSTRACT FROM AUTHOR]

The key to type 1 copper (T1Cu) function lies in the fine tuning of the CuII/I reduction potential (E°′T1Cu) to match those of its redox partners, enabling efficient electron transfer in a wide range of biological systems. While the secondary coordination sphere (SCS) effects have been used to tune E°′T1Cu in azurin over a wide range, these principles are yet to be generalized to other T1Cu‐containing proteins to tune catalytic properties. To this end, we have examined the effects of Y229F, V290N and S292F mutations around the T1Cu of small laccase (SLAC) from Streptomyces coelicolor to match the high E°′T1Cu of fungal laccases. Using ultraviolet‐visible absorption and electron paramagnetic resonance spectroscopies, together with X‐ray crystallography and redox titrations, we have probed the influence of SCS mutations on the T1Cu and corresponding E°′T1Cu. While minimal and small E°′T1Cu increases are observed in Y229F‐ and S292F‐SLAC, the V290N mutant exhibits a major E°′T1Cu increase. Moreover, the influence of these mutations on E°′T1Cu is additive, culminating in a triple mutant Y229F/V290N/S292F‐SLAC with the highest E°′T1Cu of 556 mV vs. SHE reported to date. Further activity assays indicate that all mutants retain oxygen reduction reaction activity, and display improved catalytic efficiencies (kcat/KM) relative to WT‐SLAC. [ABSTRACT FROM AUTHOR]

The key to type 1 copper (T1Cu) function lies in the fine tuning of the CuII/I reduction potential (E°′T1Cu) to match those of its redox partners, enabling efficient electron transfer in a wide range of biological systems. While the secondary coordination sphere (SCS) effects have been used to tune E°′T1Cu in azurin over a wide range, these principles are yet to be generalized to other T1Cu‐containing proteins to tune catalytic properties. To this end, we have examined the effects of Y229F, V290N and S292F mutations around the T1Cu of small laccase (SLAC) from Streptomyces coelicolor to match the high E°′T1Cu of fungal laccases. Using ultraviolet‐visible absorption and electron paramagnetic resonance spectroscopies, together with X‐ray crystallography and redox titrations, we have probed the influence of SCS mutations on the T1Cu and corresponding E°′T1Cu. While minimal and small E°′T1Cu increases are observed in Y229F‐ and S292F‐SLAC, the V290N mutant exhibits a major E°′T1Cu increase. Moreover, the influence of these mutations on E°′T1Cu is additive, culminating in a triple mutant Y229F/V290N/S292F‐SLAC with the highest E°′T1Cu of 556 mV vs. SHE reported to date. Further activity assays indicate that all mutants retain oxygen reduction reaction activity, and display improved catalytic efficiencies (kcat/KM) relative to WT‐SLAC. [ABSTRACT FROM AUTHOR]

The manuscript discloses a methoxylation reaction to an aromatic carbonyl function that carries out a CPET reaction oxidizing a transition metal ion. Spontaneous methoxylation of a redox non‐innocent fragment coordinated to a high spin cobalt(II) ion, promoted concerted proton electron transfer (CPET) reaction oxidizing cobalt(II) to cobalt(III) in air and subsequent demethoxylation induced reduction of cobalt(III) to cobalt(II) producing H2O2 are authenticated. The cobalt(III)/cobalt(II) electron transfer (ET) potential of the designed complex in CH2Cl2 is −0.27 V vs Fc+/Fc redox couple. However, in presence of MeOH the reduction potential decreases to −1.02 V due to CPET involving MeOH proton. In CH2Cl2/CHCl3 spontaneous demethoxylation occurs giving back the original complex and reactive methoxyl radical that reacts with O2 producing H2O2. Overall one molecule of MeOH produces one molecule of H2O2. To analyze the involvement of the proton, the rate constants of the CPET reactions in CH2Cl2‐MeOH (2 : 1) and CH2Cl2‐CD3OD (2 : 1) and the demethoxylation reaction in CHCl3 at 330 K were determined by time drive UV‐Vis spectroscopy. [ABSTRACT FROM AUTHOR]

The anaerobic region of the gastrointestinal (GI) tract has been replicated in the anaerobic chamber of a microbial fuel cell (MFC). Electroactive biomolecules released by the facultative anaerobes (Providencia rettgeri) under anoxic conditions have been studied for their potential role for redox balance. MALDI study reveals the presence of vitamin B9 (folate), 6-methylpterin, para-aminobenzoic acid (PABA) and pteroic acid called pterin pool. ATR-FTIR studies further confirm the presence of the aromatic ring and side chains of folate, 6-methylpterin and PABA groups. The photoluminescence spectra of the pool exhibit the maximum emission at 420, 425, 440, and 445 nm when excited by 310, 325, 350, and 365 nm wavelengths (day 20 sample) highlighting the presence of tunable bands. The cyclic voltammetric studies indicate the active participation of pterin pool molecules in the transfer of electrons with redox potentials at − 0.2 V and − 0.4 V for p-aminobenzoate and pterin groups, respectively. In addition, it is observed that under prolonged conditions of continuous oxidative stress (> 20 days), quinonoid tetrahydrofolate is formed, leading to temporary storage of charge. The results of the present study may potentially be useful in designing effective therapeutic strategies for the management of various GI diseases by promoting or blocking folate receptors. [ABSTRACT FROM AUTHOR]

Plasmonic materials are promising photocatalysts as they are well suited to convert light into hot carriers and heat. Hot electron transfer is suggested as the driving force in many plasmon-driven reactions. However, to date, there are no direct molecular measures of the rate and yield of plasmon-to-molecule electron transfer or energy of these electrons on the timescale of plasmon decay. Here, we use ultrafast and spectroelectrochemical surface-enhanced Raman spectroscopy to quantify electron transfer from a plasmonic substrate to adsorbed methyl viologen molecules. We observe a reduction yield of 2.4 to 3.5% on the picosecond timescale, with plasmon-induced potentials ranging from -3.1 to -4.5 mV. Excitingly, some of these reduced species are stabilized and persist for tens of minutes. This work provides concrete metrics toward optimizing material-molecule interactions for efficient plasmon-driven photocatalysis. [ABSTRACT FROM AUTHOR]

Molecules containing a difluoromethyl group or a propargylic stereocenter are widely used in pharmaceuticals and agrochemicals, and 1,2‐functionalization of olefins is an important method for introducing the two groups into molecules simultaneously. The construction of the propargylic stereocenter with terminal alkynes usually requires bases. However, difluoromethylating agents with high reduction potentials often decompose in the presence of bases because of their acidities, and those with low reduction potentials are stable but difficult to undergo the desired single electron transfer (SET) reduction. Using the linear relationship between reduction potential differences (ΔE) and Hammett substituent constants (σ) of difluoromethyl aryl sulfones, we solved the dilemma between acidities and reduction potentials of difluoromethylating agents. Herein, we report the first enantioselective difluoromethylation‐alkynylation of olefins with difluoromethyl 4‐chlorophenyl sulfone with high enantioselectivity (>90 % ee). We also extended this asymmetric fluoroalkylation‐alkynylation reaction with other fluoroalkyl sulfones, which enabled efficient installation of trifluoromethyl, difluoroalkyl, difluorobenzyl, (benzenesulfonyl)‐difluoromethyl and monofluoromethyl groups into products. [ABSTRACT FROM AUTHOR]

Molecules containing a difluoromethyl group or a propargylic stereocenter are widely used in pharmaceuticals and agrochemicals, and 1,2‐functionalization of olefins is an important method for introducing the two groups into molecules simultaneously. The construction of the propargylic stereocenter with terminal alkynes usually requires bases. However, difluoromethylating agents with high reduction potentials often decompose in the presence of bases because of their acidities, and those with low reduction potentials are stable but difficult to undergo the desired single electron transfer (SET) reduction. Using the linear relationship between reduction potential differences (ΔE) and Hammett substituent constants (σ) of difluoromethyl aryl sulfones, we solved the dilemma between acidities and reduction potentials of difluoromethylating agents. Herein, we report the first enantioselective difluoromethylation‐alkynylation of olefins with difluoromethyl 4‐chlorophenyl sulfone with high enantioselectivity (>90 % ee). We also extended this asymmetric fluoroalkylation‐alkynylation reaction with other fluoroalkyl sulfones, which enabled efficient installation of trifluoromethyl, difluoroalkyl, difluorobenzyl, (benzenesulfonyl)‐difluoromethyl and monofluoromethyl groups into products. [ABSTRACT FROM AUTHOR]

Flavodoxins are enzymes that contain the redox-active flavin mononucleotide (FMN) cofactor and play a crucial role in numerous biological processes, including energy conversion and electron transfer. Since the redox characteristics of flavodoxins are significantly impacted by the molecular environment of the FMN cofactor, the evaluation of the interplay between the redox properties of the flavin cofactor and its molecular surroundings in flavoproteins is a critical area of investigation for both fundamental research and technological advancements, as the electrochemical tuning of flavoproteins is necessary for optimal interaction with redox acceptor or donor molecules. In order to facilitate the rational design of biomolecular devices, it is imperative to have access to computational tools that can accurately predict the redox potential of both natural and artificial flavoproteins. In this study, we have investigated the feasibility of using non-equilibrium thermodynamic integration protocols to reliably predict the redox potential of flavodoxins. Using as a test set the wild-type flavodoxin from Clostridium Beijerinckii and eight experimentally characterized single-point mutants, we have computed their redox potential. Our results show that 75% (6 out of 8) of the calculated reaction free energies are within 1 kcal/mol of the experimental values, and none exceed an error of 2 kcal/mol, confirming that non-equilibrium thermodynamic integration is a trustworthy tool for the quantitative estimation of the redox potential of this biologically and technologically significant class of enzymes. [ABSTRACT FROM AUTHOR]

Sediment microbial fuel cell (SMFC) is a type of MFC without a proton exchange membrane. However, SMFC have had problems with low-power production performance. In this paper, the effects of native bacteria (K1) in oily sludge and their electro-oil-induced domestication on the power generation and oil removal performance of SMFC were studied. The results showed that K1 belonged to Ochrobactrum intermedium. During the domestication process, an upward trend was shown in the OD600 and ORP values in the culture medium, and it grown best at 0.7 V. Ochrobactrum intermedium K1 significantly increased the average output voltage, electromotive force, and maximum power density of SMFC and reduced the apparent internal resistance of the battery. The maximum power density was 169.43 mW/m3, which was 8.59 times higher than that of the control group. Ochrobactrum intermedium K1 improved the degradation of crude oil by SMFC. Ochrobactrum intermedium K1 enhanced the degradation of high-carbon alkanes and even-carbon alkanes in n-alkanes. Cyclic voltammetry and chronoamperometry tests showed that after acclimation, Ochrobactrum intermedium K1 improved the extracellular electron transfer efficiency (EET) mediated by c-Cyts and flavin by increasing the surface protein redox potential. [ABSTRACT FROM AUTHOR]

Extracellular electron transfer (EET) is a bioelectrochemical process performed by electrochemically active bacteria (EAB) found in host-associated environments, including plant and animal ecosystems and fermenting plant- and animal-derived foods. Through direct or mediated electron transfer pathways, certain bacteria use EET to enhance ecological fitness with host-impacting effects. In the plant rhizosphere, electron acceptors support the growth of EAB such as Geobacter , cable bacteria, and some clostridia that can result changing iron and heavy metal uptake by plants. In animal microbiomes, EET is associated with diet-derived iron in the intestines of soil-dwelling termites, earthworms, and beetle larvae. EET is also associated with the colonization and metabolism of some bacteria in human and animal microbiomes, such as Streptococcus mutans in the mouth, Enterococcus faecalis and Listeria monocytogenes in the intestine, and Pseudomonas aeruginosa in the lungs. During the fermentation of plant tissues and bovine milk, lactic acid bacteria like Lactiplantibacillus plantarum and Lactococcus lactis may use EET to increase their growth and food acidification, as well as decrease environmental oxidation–reduction potential. Thus, EET is likely an important metabolic pathway for host-associated bacteria and has implications for ecosystem function, health and disease, and biotechnological applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Photocatalytic technology is of great significance in environmental purification due to its eco-friendly and cost-effective operations. However, low charge-transfer efficiency restricts the photocatalytic activity of the catalyst. Herein, we report Cs 2 SnBr 6 /C 3 N 4 composite catalysts that exhibit a robust interfacial electron exchange thereby enhancing photocatalytic nitric oxide (NO) oxidation. A comprehensive study has demonstrated the S-scheme electron transfer mechanism. Benefiting from the interfacial internal electric field, the C-Br bond serves as a direct electron transfer channel, resulting in enhanced charge separation. Furthermore, the S-scheme heterojunction effectively traps high redox potential electrons and holes, leading to the production of abundant reactive oxygen radicals that enhance photocatalytic NO abatement. The NO removal rate of the Cs 2 SnBr 6 /C 3 N 4 heterogeneous system can reach 86.8 %, which is approximately 3-fold and 18-fold that of pristine C 3 N 4 and Cs 2 SnBr 6 , respectively. The comprehensive understanding of the electron transfer between heterojunction atomic interfaces will provide a novel perspective on efficient environmental photocatalysis. [ABSTRACT FROM AUTHOR]

Fluoroarenes are abundant and readily available feedstocks. However, due to the high reduction potentials of mono‐fluoroarenes, their photoreduction remains a continuing challenge, motivating the development of efficient activation modes to address this issue. This report presents the blue light‐induced N‐heterocyclic carbene (NHC)‐catalyzed single electron reduction of mono‐fluoroarenes for biaryl cross‐couplings. We discovered that under blue light irradiation, NHC/tBuOK combination could construct powerful photoactive architectures to promote single electron transfer for Caryl−F bond reduction via forming highly reducing NHC radical anion. Notably, the strategy was also successful to reduce Caryl−O, Caryl−N, and Caryl−S bonds for biaryl cross‐couplings. [ABSTRACT FROM AUTHOR]

Fluoroarenes are abundant and readily available feedstocks. However, due to the high reduction potentials of mono‐fluoroarenes, their photoreduction remains a continuing challenge, motivating the development of efficient activation modes to address this issue. This report presents the blue light‐induced N‐heterocyclic carbene (NHC)‐catalyzed single electron reduction of mono‐fluoroarenes for biaryl cross‐couplings. We discovered that under blue light irradiation, NHC/tBuOK combination could construct powerful photoactive architectures to promote single electron transfer for Caryl−F bond reduction via forming highly reducing NHC radical anion. Notably, the strategy was also successful to reduce Caryl−O, Caryl−N, and Caryl−S bonds for biaryl cross‐couplings. [ABSTRACT FROM AUTHOR]

This investigation reports the extraction of UO2Cl42− and MoO22+via neutral (R4N)2UO2Cl4 and cationic MoO2(Ph)+ complexes (following 'solvation' and 'cation exchange' mechanisms), using a task-specific ionic liquid (TSIL). The processes were found to be spontaneous and endothermic in nature. The formation of an inner sphere complex resulted in the release of several water molecules during complexation, making the extractive mass transfer entropically driven. The ionic liquid was found to be highly radiolytically stable. Multiple contacts with aqueous carbonate solution were required for back extraction of U and Mo from the ionic liquid phase. Cyclic voltammmetry analysis was used to probe mechanistic insight into the extraction process and to understand the nature of complexation of the ionic liquid with U ions. An interesting observation related to a change in the redox physicochemical parameters of U in ionic liquid was observed compared to that in aqueous medium, indicating the complexation of the U species with the TSIL. The shift in redox potential of U after complexation evidenced the difference in its speciation during mass transfer. The redox thermodynamic (peak and formal potential), diffusion coefficient, and heterogeneous electron transfer kinetic parameters (αn and k0) of U in the TSIL were reported. The higher viscosity of ionic liquid was found to slow down the rate of mass transfer during extraction, which can be optimized by proper dilution. A trade-off between extraction efficiency and extraction kinetics was evidenced. [ABSTRACT FROM AUTHOR]

Visible‐light photocatalytic carboxylation with CO2 is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C−N bonds in cyclic amines with CO2 via consecutive photo‐induced electron transfer (ConPET). It is also the first photocatalytic reductive ring‐opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β‐, γ‐, δ‐ and ϵ‐amino acids in moderate‐to‐excellent yields. Moreover, the method also features mild and transition‐metal‐free conditions, high selectivity, good functional‐group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates. [ABSTRACT FROM AUTHOR]

Visible‐light photocatalytic carboxylation with CO2 is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C−N bonds in cyclic amines with CO2 via consecutive photo‐induced electron transfer (ConPET). It is also the first photocatalytic reductive ring‐opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β‐, γ‐, δ‐ and ϵ‐amino acids in moderate‐to‐excellent yields. Moreover, the method also features mild and transition‐metal‐free conditions, high selectivity, good functional‐group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates. [ABSTRACT FROM AUTHOR]

The accurate measurement of redox potentials of small molecules is a relatively straightforward task using electrochemical methods such as cyclic voltammetry. However, proteins, in most cases, are not amenable to the same approach due to slow heterogeneous electron transfer and the possibility of denaturing at the electrode surface. This necessitates the use of small molecular weight redox mediators to facilitate electron transfer. This leads to spectroelectrochemical techniques where the applied electrochemical potential is coupled to a spectroscopic signal of the protein. Traditionally this is done at different applied (fixed) potentials akin to an electrochemical titration, but the time required for electrochemical equilibrium to be established, and its consistent application, are major sources of experimental error. Here we have utilised a continuously scanning potential synchronised with time‐resolved UV‐vis spectroscopy to provide an automated approach that can be used to measure protein redox potentials accurately in an expedient manner. The test cases are the heme proteins cytochrome c and myoglobin. The scope and limitations of the method are discussed. [ABSTRACT FROM AUTHOR]

Nitrate (NO3−-N) and nitrites (NO2−-N) are common pollutants in various water bodies causing serious threats not only to aquatic, but also to animals and human beings. In this study, we developed a strategy for efficiently reducing nitrates in microbial fuel cells (MFCs) powered by a granular activated carbon (GAC)-biocathode. GAC was developed by acclimatizing and enriching denitrifying bacteria under a redox potential (0.3 V) generated from MFCs. Thus, using the formed GAC-biocathode we continued to study their effect on denitrification with different cathode materials and circulation speeds in MFCs. The GAC-biocathode with its excellent capacitive property can actively reduce nitrate for over thirty days irrespective of the cathode material used. The stirring speed of GAC in the cathode showed a steady growth in potential generation from 0.25 V to 0.33 V. A rapid lag phase was observed when a new carbon cathode was used with enriched GAC. While a slow lag phase was seen when a stainless-steel cathode was replaced. These observations showed that effective storage and supply of electrons to the GAC plays a crucial role in the reduction process in MFCs. Electrochemical analysis of the GAC properties studied using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and zeta potential showed distinct properties with different abiotic and biocathode conditions. We found that the enrichment of electrotrophic bacteria on GAC facilitates the direct electron transfer in the cathode chamber for reducing NO3−-N in MFCs as observed by scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Samarium diiodide is a versatile single electron transfer (SET) agent with various applications in organic chemistry. Lewis structures regularly insinuate the existence of a ketyl radical when samarium diiodide binds a carbonyl group. The study presented here investigates this electron transfer by the means of computational chemistry. All electron CASPT2 calculations with the inclusion of scalar relativistic effects predict an endotherm electron transfer from samarium diiodide to acetone. Energies calculated with the PBE0-D3(BJ) functional and a small core pseudopotential are in good agreement with CASPT2. The calculations confirm the experimentally measured increase of the samarium diiodide reduction potential through the addition of hexamethylphosphoramide also known as HMPA. [ABSTRACT FROM AUTHOR]

Electron harvesting bacteria are key targets to develop microbial electrosynthesis technologies, which are valid alternatives for the production of value‐added compounds without utilization of fossil fuels. Geobacter sulfurreducens, that is capable of donating and accepting electrons from electrodes, is one of the most promising electroactive bacteria. Its electron transfer mechanisms to electrodes have been progressively elucidated, however the electron harvesting pathways are still poorly understood. Previous studies showed that the periplasmic cytochromes PccH and GSU2515 are overexpressed in current‐consuming G. sulfurreducens biofilms. PccH was characterized, though no putative partners have been identified. In this work, GSU2515 was characterized by complementary biophysical techniques and in silico simulations using the AlphaFold neural network. GSU2515 is a low‐spin monoheme cytochrome with a disordered N‐terminal region and an α‐helical C‐terminal domain harboring the heme group. The cytochrome undergoes a redox‐linked heme axial ligand switch, with Met91 and His94 as distal axial ligands in the reduced and oxidized states, respectively. The reduction potential of the cytochrome is negative and modulated by the pH in the physiological range: −78 mV at pH 6 and −113 mV at pH 7. Such pH‐dependence coupled to the redox‐linked switch of the axial ligand allows the cytochrome to drive a proton‐coupled electron transfer step that is crucial to confer directionality to the respiratory chain. Biomolecular interactions and electron transfer experiments indicated that GSU2515 and PccH form a redox complex. Overall, the data obtained highlight for the first time how periplasmic proteins bridge the electron transfer between the outer and inner membrane in the electron harvesting pathways of G. sulfurreducens. [ABSTRACT FROM AUTHOR]

[Display omitted] Catalytic hydrogenation reduction provides a potential route to detoxify nitro compounds. Spinel NiFe 2 O 4 (NiFeO) serves as a natural abundance and low-cost catalyst but suffers from low catalytic activity due to poor redox nature and limited active sites. Herein, defective MNiFeO (M = Cu, Zn, Co, Mn) nanorods (NRs) were synthesized by pyrolysis of cation-exchanged Fe 2 Ni-MOFs. The introduction of M modified the electronic structure of NiFeO and thus accelerated the electron transfer and proton transport in the hydrogenation of nitro aromatics. CuNiFeO exhibited the highest catalytic activity with a turn frequency of 2.89 × 105h−1, giving 308- and 422-fold larger than that of NiFeO-V o and NiFeO in the reduction of 4-nitrophenol (4-NP). CuNiFeO NRs also presented exceptional performances in the reduction of the other nitroarenes. The remarkable improvement in activity of mesoporous CuNiFeO may be attributed to its ternary composites, and increased oxygen vacancies. This work not only provides a simple route to constructing mesoporous MNiFeO NRs with oxygen vacancies, but also further discusses the effects of metal component and oxygen defects in the catalytic reduction of 4-NP. [ABSTRACT FROM AUTHOR]

Ferredoxins (Fds) are small proteins which shuttle electrons to pathways like biological nitrogen fixation. Physical properties tune the reactivity of Fds with different pathways, but knowledge on how these properties can be manipulated to engineer new electron transfer pathways is lacking. Recently, we showed that an evolved strain of Rhodopseudomonas palustris uses a new electron transfer pathway for nitrogen fixation. This pathway involves a variant of the primary Fd of nitrogen fixation in R. palustris , Fer1, in which threonine at position 11 is substituted for isoleucine (Fer1T11I). To understand why this substitution in Fer1 enables more efficient electron transfer, we used in vivo and in vitro methods to characterize Fer1 and Fer1T11I. Electrochemical characterization revealed both Fer1 and Fer1T11I have similar redox transitions (−480 mV and − 550 mV), indicating the reduction potential was unaffected despite the proximity of T11 to an iron‑sulfur (Fe S) cluster of Fer1. Additionally, disruption of hydrogen bonding around an Fe S cluster in Fer1 by substituting threonine with alanine (T11A) or valine (T11V) did not increase nitrogenase activity, indicating that disruption of hydrogen bonding does not explain the difference in activity observed for Fer1T11I. Electron paramagnetic resonance spectroscopy studies revealed key differences in the electronic structure of Fer1 and Fer1T11I, which indicate changes to the high spin states and/or spin-spin coupling between the Fe S clusters of Fer1. Our data implicates these electronic structure differences in facilitating electron flow and sets a foundation for further investigations to understand the connection between these properties and intermolecular electron transfer. A recently characterized laboratory-evolved strain of Rhodopseudomonas palustris requires two single-residue variants, AadNC38W and Fer1T11I, to form an alternative electron transfer pathway for nitrogenase. Here we characterize Fer1, a ferredoxin involved in electron transfer to nitrogenase and a variant of Fer1, Fer1T11I, to explore how this single substitution changed the flow of electrons between different pathways. [Display omitted] • A single substitution in a ferredoxin alters activity but not midpoint potential. • Residue 11 variants in a 2[4Fe 4S] Fds have different in vivo activity. • Differences in electron structure may impact intermolecular electron transfer. [ABSTRACT FROM AUTHOR]

Metal-dependent, nicotine adenine dinucleotide (NAD+)-dependent formate dehydrogenases (FDHs) are complex metalloenzymes coupling biochemical transformations through intricate electron transfer pathways. Rhodobacter capsulatus FDH is a model enzyme for understanding coupled catalysis, in that reversible CO 2 reduction and formate oxidation are linked to a flavin mononuclotide (FMN)-bound diaphorase module via seven iron-sulfur (Fe S) clusters as a dimer of heterotetramers. Catalysis occurs at a bis-metal-binding pterin (Mo) binding two molybdopterin guanine dinucleotides (bis-MGD), a protein-based Cys residue and a participatory sulfido ligand. Insights regarding the proposed electron transfer mechanism between the bis-MGD and the FMN have been complicated by the discovery that an alternative pathway might occur via intersubunit electron transfer between two [4Fe 4S] clusters within electron transfer distance. To clarify this difference, the redox potentials of the bis-MGD and the Fe S clusters were determined via redox titration by EPR spectroscopy. Redox potentials for the bis-MGD cofactor and five of the seven Fe S clusters could be assigned. Furthermore, substitution of the active site residue Lys295 with Ala resulted in altered enzyme kinetics, primarily due to a more negative redox potential of the A1 [4Fe 4S] cluster. Finally, characterization of the monomeric FdsGBAD heterotetramer exhibited slightly decreased formate oxidation activity and similar iron-sulfur clusters reduced relative to the dimeric heterotetramer. Comparison of the measured redox potentials relative to structurally defined Fe S clusters support a mechanism by which electron transfer occurs within a heterotetrameric unit, with the interfacial [4Fe 4S] cluster serving as a structural component toward the integrity of the heterodimeric structure to drive efficient catalysis. The metal-dependent formate dehydrogenase from Rhodobacter capsulatus is a complex, molybdenum-containing iron-sulfur flavoenzyme. Herein, the redox potentials for five of the seven iron-sulfur clusters and the Mo(VI) → Mo(V) and Mo(V) → Mo(IV) reduction couples have been determined, and evidence for electron transfer through the monomeric heterotetramer unit is presented. [Display omitted] • Redox potentials of Mo active site and five of seven iron-sulfur clusters determined. • Use of Eu-based reductant improved discernment of cofactor redox potentials. • Alteration of an active site residue reveals identity of an iron-sulfur cluster. • Comparable monomer vs dimer activity and iron-sulfur cluster reduction observed. [ABSTRACT FROM AUTHOR]

Lactate oxidation with NAD+ as electron acceptor is a highly endergonic reaction. Some anaerobic bacteria overcome the energetic hurdle by flavin- based electron bifurcation/confurcation (FBEB/FBEC) using a lactate dehydrogenase (Ldh) in concert with the electron-transferring proteins EtfA and EtfB. The electron cryo-microscopically characterized (Ldh- EtfAB)2 complex of Aceto-bacterium woodii at 2.43 Å resolution consists of a mobile EtfAB shuttle domain located between the rigid central Ldh and the peripheral EtfAB base units. The FADs of Ldh and the EtfAB shuttle domain contact each other thereby forming the D (dehydrogenation-connected) state. The intermediary Glu37 and Glu139 may harmonize the redox potentials between the FADs and the pyruvate/ lactate pair crucial for FBEC. By integrating Alphafold2 calculations a plausible novel B (bifurcation- connected) state was obtained allowing electron transfer between the EtfAB base and shuttle FADs. Kinetic analysis of enzyme variants suggests a correlation between NAD+ binding site and D-to-B-state transition implicating a 75° rotation of the EtfAB shuttle domain. The FBEC inactivity when truncating the ferredoxin domain of EtfA substantiates its role as redox relay. Lactate oxidation in Ldh is assisted by the catalytic base His423 and a metal center. On this basis, a comprehensive cata- lytic mechanism of the FBEC process was proposed. [ABSTRACT FROM AUTHOR]

Biocatalysts are widely used in industry, but few examples of the use of oxidoreductases, in which enzymatic function often requires electrons, have been reported. NADPH is a cofactor that supplies an electron to oxidoreductases, but is consequently inactivated and no longer able to act as an electron donor. NADP+ can not receive electrons from electrodes through straightforward electrochemistry owing to its complicated three-dimensional structure. This study reports that bipyridines effectively mediate electron transfer between an electrode and NADP+, allowing them to serve as electron mediators for NADPH production. Using bipyridines, quinones, and anilines, which have negative oxidation–reduction potentials, an electrochemical investigation was conducted into whether electrons were transferred to NADP+. Only bipyridines with a reduction potential near -1.0 V exhibited electron transfer. Furthermore, the NADPH production level was measured using spectroscopy. NADPH was efficiently produced using bipyridines, such as methyl viologen and ethyl viologen, in which the bipyridyl 1- and 1'-positions bear small substituents. However, methyl viologen caused a dehydrogenation reaction of NADPH, making it unsuitable as an electron mediator for NADPH production. The dehydrogenation reaction did not occur using ethyl viologen. These results indicated that NADP+ can be reduced more effectively using substituents that prevent a dehydrogenation reaction at the bipyridyl 1- and 1'-positions while maintaining the reducing power. [ABSTRACT FROM AUTHOR]

Simple Summary: Many biological systems contain iron–sulfur clusters, which are typically found as components of electron transport proteins. Continuum electrostatic calculations were used to investigate the effect of protein environment on the redox properties of the three iron–sulfur clusters in the cyanobacterial photosystem I. Our results show a good correlation between the estimated and the measured reduction potential. Moreover, the results indicate that the low potential of FX is shown to be due to the interactions with the surrounding residues and ligating sulfurs. Our results will help in understanding the electron transfer reaction in photosystem I. Photosystem I is a light-driven electron transfer device. Available X-ray crystal structure from Thermosynechococcus elongatus showed that electron transfer pathways consist of two nearly symmetric branches of cofactors converging at the first iron–sulfur cluster FX, which is followed by two terminal iron–sulfur clusters FA and FB. Experiments have shown that FX has lower oxidation potential than FA and FB, which facilitates the electron transfer reaction. Here, we use density functional theory and Multi-Conformer Continuum Electrostatics to explain the differences in the midpoint E m potentials of the FX, FA and FB clusters. Our calculations show that FX has the lowest oxidation potential compared to FA and FB due to strong pairwise electrostatic interactions with surrounding residues. These interactions are shown to be dominated by the bridging sulfurs and cysteine ligands, which may be attributed to the shorter average bond distances between the oxidized Fe ion and ligating sulfurs for FX compared to FA and FB. Moreover, the electrostatic repulsion between the 4Fe-4S clusters and the positive potential of the backbone atoms is lowest for FX compared to both FA and FB. These results agree with the experimental measurements from the redox titrations of low-temperature EPR signals and of room temperature recombination kinetics. [ABSTRACT FROM AUTHOR]

• The rate constant of Fe(II) release and generation correlated with cysteine. • A low pH thermodynamically enhanced electron transfer from cysteine to goethite. • Organic ligands only kinetically promoted release of the less available Fe(II). • Electron transfer from cysteine to goethite was via S-S complexation on goethite. Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils, while the roles of pH and organic ligands in this process are poorly understood. Herein, the reductive dissolution process of goethite by cysteine were explored in the presence of organic ligands. Our results showed that cysteine exhibited a strong reactivity towards goethite – a typical iron minerals in paddy soils with a rate constant ranging from 0.01 to 0.1 hr−1. However, a large portion of Fe(II) appeared to be "structural species" retained on the surface. The decline of pH was favorable to generate more Fe(II) ions and enhancing tendency of Fe(II) release to solution. The decline of generation of Fe(II) by increasing pH was likely to be caused by a lower redox potential and the nature of cysteine pH-dependent adsorption towards goethite. Interestingly, the co-existence of oxalate and citrate ligands also enhanced the rate constant of Fe(II) release from 0.09 to 0.15 hr−1; nevertheless, they negligibly affected the overall generation of Fe(II) in opposition to the pH effect. Further spectroscopic evidence demonstrated that two molecules of cysteine could form disulfide bonds (S-S) to generate cystine through oxidative dehydration, and subsequently, inducing electron transfer from cysteine to the structural Fe(III) on goethite; meanwhile, those organic ligands act as Fe(II) "strippers". The findings of this work provide new insights into the understanding of the different roles of pH and organic ligands on the generation and release of Fe induced by electron shuttles in soils. [Display omitted] [ABSTRACT FROM AUTHOR]

Anaerobic microbial respiration in suboxic and anoxic environments often involves particulate ferric iron (oxyhydr-)oxides as terminal electron acceptors. To ensure efficient respiration, a widespread strategy among iron-reducing microorganisms is the use of extracellular electron shuttles (EES) that transfer two electrons from the microbial cell to the iron oxide surface. Yet, a fundamental understanding of how EES-oxide redox thermodynamics affect rates of iron oxide reduction remains elusive. Attempts to rationalize these rates for different EES, solution pH, and iron oxides on the basis of the underlying reaction free energy of the two-electron transfer were unsuccessful. Here, we demonstrate that broadly varying reduction rates determined in this work for different iron oxides and EES at varying solution chemistry as well as previously published data can be reconciled when these rates are instead related to the free energy of the less exergonic (or even endergonic) first of the two electron transfers from the fully, two-electron reduced EES to ferric iron oxide. We show how free energy relationships aid in identifying controls on microbial iron oxide reduction by EES, thereby advancing a more fundamental understanding of anaerobic respiration using iron oxides. [ABSTRACT FROM AUTHOR]

The efficient visible light-driven photoelectrocatalyst (denoted as g-C 3 N 4 -CO-TETA-Pr-SiW 11) was designed through the organic linker strategy by combination of polyoxometalate (POM) (cluster of [SiW 11 O 39 ]−8 (SiW 11)) with graphitic carbon nitride (g-C 3 N 4). For this purpose, a reactive tetradentate NH 2 linker was introduced by oxidation and subsequently amidation reactions on the surface of g-C 3 N 4 frameworks then SiW 11 was bonded to the organic linker to generate g-C 3 N 4 -CO-TETA-Pr-SiW 11. In this study, for the first time, this organic linker strategy was applied for covalent combination of POM and g-C 3 N 4 to design a stable photocatalyst with high-performance. Photoelectrocatalytic performance of prepared catalysts was investigated under visible light irradiation. The photocurrent density of 0.17 mA cm−2 for g-C 3 N 4 -CO-TETA-Pr-SiW 11 compared with 0.077 mA cm−2 for g-C 3 N 4 was achieved. Investigation of the transient open circuit potential decay and photoluminescence showed the efficient electron-hole separation for g-C 3 N 4 -CO-TETA-Pr-SiW 11. The arc diameter in Nyquist plots indicated the improved charge transfer and charge carrier's lifetimes after decorating of g-C 3 N 4 with POM. Mott−Schottky plots demonstrated a greater electron transfer at the photo electrode/electrolyte interface for g-C 3 N 4 -CO-TETA-Pr-SiW 11 2.8 in compared to g-C 3 N 4. Also, the photoconversion efficiency exhibited more than 2.4 time enhancement for g-C 3 N 4 -CO-TETA-Pr-SiW 11 photoanode compared to g-C 3 N 4. [Display omitted] • Designing an efficient photoelectrocatalyst by organic linker strategy. • The high performance of synthesized photocatalyst through covalent bonding of SiW 11 and g-C 3 N 4. • Achieving the photocurrent density of 0.17 mA cm−2 for g-C 3 N 4 -CO-TETA-Pr-SiW 11 at the redox potential of O 2 /H 2 O. • Band bending for g-C 3 N 4 -CO-TETA-Pr-SiW 11 is deeper than pristine g-C 3 N 4. [ABSTRACT FROM AUTHOR]

Azaphenalenes are nitrogen substituted analogues of the phenalene ring system, and their radicals have attracted significant attention because of the novel electronic and magnetic properties. In the previous study, the neutral tris(tert-butyl) 1,3-diazaphenalenyl radical has been synthesized by chemical oxidation of the parent compound with PbO 2. In this study, we focused on electrochemical proton-coupled electron transfer (PCET) process leading to the formation of neutral unsubstituted 1,3-diazaphenalenyl radical from 1,3-diazaphenalene (DAP) in solution. Additionally, this electrochemical approach was extended to study the redox behavior of newly synthesized 1,4,7-triazaphenalene (TAP) giving the access to the 1,4,7-triazaphenalenyl radical. Electrochemical oxidation potentials vs. pH plots (Pourbaix diagram) for DAP and TAP revealed that their one-electron oxidation to the corresponding neutral radicals occurred by a PCET process over a wide pH range. From the analysis of Pourbaix diagrams, the p K a values of the protonated radicals were determined to be p K a = 2.57 and 2.39 for the DAP and TAP radicals, respectively. Cyclic voltammograms of azaphenalenes in MeCN and MeCN/buffer solutions showed a characteristic ECE process, in which electrochemical oxidative dimerization took place following the electron transfer. The dimerization reaction pathway was rationalized by the digital simulations, DFT calculations and crystallization of a DAP dimer after chemical oxidation with PbO 2. The spectroscopic properties of azaphenalenes and their dimerized products were characterized by in-situ UV–Vis and EPR spectroelectrochemistry techniques. The fundamental information about the p K a and redox potentials for a series of azaphenalenes (DAP, TAP, as well as 1,3,4,6,7,9-hexaazaphenalene, HAP) could be fed back into the molecular design of redox-active conductive coordination networks based on multi-interactive ligands. [Display omitted] [ABSTRACT FROM AUTHOR]

The multiredox reactivity of bioinorganic cofactors is often coupled to proton transfers. Here we investigate the structural, thermochemical, and electronic structure of ruthenium‐amino/amido complexes with multi‐ proton‐coupled electron transfer reactivity. The bis(amino)ruthenium(II) and bis(amido)ruthenium(IV) complexes [RuII(bpy)(en*)2]2+ (RuII‐H0) and [RuIV(bpy)(en*‐H2)2]2+ (RuIV‐H2) interconvert reversibly with the transfer of 2e−/2H+ (bpy=2,2'‐bipyridine, en*=2,3‐diamino‐2,3‐dimethylbutane). X‐ray structures allow correlations between the structural and electronic parameters, and the thermochemical data of the 2e−/2H+ multi‐square grid scheme. Redox potentials, acidity constants and DFT calculations reveal potential intermediates implicated in 2e−/2H+ reactivity with organic reagents in non‐protic solvents, which shows a strong inverted redox potential favoring 2e−/2H+ transfer. This is suggested to be an attractive system for potential one‐step (concerted) transfer of 2e−and 2H+ due to the small changes of the pseudo‐octahedral geometries and the absence of charge change, indicating a relatively small overall reorganization energy. [ABSTRACT FROM AUTHOR]

Tethering metal complexes, like [Ru(bpy)2Cl2] (bpy = 2,2′-bipyridine), which are redox-active at low reduction potentials and have the ability to transfer electrons to another complex, to a [Ni(cyclen)]2+ electrocatalyst enhanced the reduction of CO2 to CO at low overpotentials. The [Ni(cyclen)]2+ electrocatalyst was modified by tethering redox-active metal complexes via 4-methylpyridyl linkers. The redox-active metal complexes were reduced after CO2 bound to the active site. In controlled potential electrolysis (CPE) experiments in 95 : 5 (v/v) CH3CN/H2O, [{([Ru]pic)4cyclen}NiCl]5+ ([Ru]+ = {Ru(bpy)2Cl}+; pic = 4-methylpyridyl) could be used to reduce CO2 into CO at a turnover frequency (TOF) of 708 s−1 with a faradaic efficiency (FE) of 80% at an onset potential of −1.60 V vs. NHE. At the same time, this electrocatalyst was active at an onset potential of −1.25 V vs. NHE, which is the reduction potential of one of the bpy ligands of the [Ru]+ moieties, with FE = 84% and TOF = 178 s−1. When the electrocatalysis was performed using [bn4cyclenNiCl]Cl (bn = benzyl) without tethered redox-active metal complexes, the TOF value was determined to be 8 s−1 with FE = 77% at an onset potential of −1.45 V vs. NHE. The results show that tethering redox-active metal complexes significantly improves the electrocatalytic activities by lowering the potential needed to reduce CO2. [ABSTRACT FROM AUTHOR]

Geobacter sulfurreducens utilizes extracellular electron acceptors such as Mn(IV), Fe(III), syntrophic partners, and electrodes that vary from +0.4 to −0.3 V versus standard hydrogen electrode (SHE), representing a potential energy span that should require a highly branched electron transfer chain. Here we describe CbcBA, a bc‐type cytochrome essential near the thermodynamic limit of respiration when acetate is the electron donor. Mutants‐lacking cbcBA ceased Fe(III) reduction at −0.21 V versus SHE, could not transfer electrons to electrodes between −0.21 and −0.28 V, and could not reduce the final 10%–35% of Fe(III) minerals. As redox potential decreased during Fe(III) reduction, cbcBA was induced with the aid of the regulator BccR to become one of the most highly expressed genes in G. sulfurreducens. Growth yield (CFU/mM Fe(II)) was 112% of WT in ∆cbcBA, and deletion of cbcL (an unrelated bc‐cytochrome essential near −0.15 V) in ΔcbcBA increased yield to 220%. Together with ImcH, which is required at high redox potentials, CbcBA represents a third cytoplasmic membrane oxidoreductase in G. sulfurreducens. This expanding list shows how metal‐reducing bacteria may constantly sense redox potential to adjust growth efficiency in changing environments. [ABSTRACT FROM AUTHOR]

Intervalence charge transfer (IVCT), a phenomenon observed in molecular systems comprised of two redox centers differing in oxidation states by one unit, is reported in a novel, newly synthesized, multi‐modular donor‐acceptor system comprised of central bis(thienyl)diketopyrrolopyrrole (TDPP) hosting two phenothiazine‐tetracyanobutadiene (PTZ‐TCBD) entities on the opposite sides. One‐electron reduction of TCBD promoted electron exchange between the two TCBD resulting in IVCT transition in the near‐infrared region. The stabilization energy, −ΔGcom and comproportionation equilibrium constant, Kcom calculated from peak potentials of the split reduction waves were found to be 1.06×104 J mol−1, and 72.3 M−1, respectively. Further, the IVCT transition was also witnessed during the process of thermodynamically feasible electron transfer upon excitation of the TDPP entity in the system, and served as a diagnostic marker to characterize the electron transfer product. Subsequent transient absorption spectral studies and data analysis by Global and Target analyses revealed occurrence of ultrafast charge separation (kcs≈1010 s−1) owing to the close proximity and good communication between the entities of the multi‐modular donor‐acceptor system. The role of central TDPP in promoting IVCT is borne out from the present investigation. [ABSTRACT FROM AUTHOR]

Proton‐coupled electron transfer (PCET) is of key importance in modern synthetic chemistry. Redox‐active guanidines were established by our group as valuable alternatives to toxic high‐potential benzoquinones in a variety of different PCET reactions. In this work, the PCET reactivity of a series of 1,4‐bisguanidino‐benzenes varying in their redox potentials and proton affinities is evaluated. The relevant redox and protonation states are fully characterized, and the compounds sorted with respect to their PCET reactivity by comparative PCET experiments supplemented by quantum‐chemical calculations. Depending on the studied reactions, the driving force is either electron transfer or proton transfer; thereby the influence of both processes on the overall reactivity could be assessed. Then, two of the PCET reagents are applied in representative oxidative aryl‐aryl coupling reactions, namely the intramolecular coupling of 3,3"‐4,4"‐tetramethoxy‐o‐terphenyl to give the corresponding triphenylene, the intermolecular coupling of N‐ethylcarbazole to give N,N'‐diethyl‐3,3'‐bicarbazole, and in the oxidative lactonization of 2‐[(4‐methoxyphenyl)methyl]‐benzoic acid. Under mild conditions, the reactions proceed fast and efficient. Only small amounts of acid are needed, in clear contrast to the corresponding coupling reactions with traditional high‐potential benzoquinones such as DDQ or chloranil requiring a large excess of a strong acid. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anthrarufin (AN) chosen as anolyte as it shows 2 electron reduction and low redox potential • Extended conjugation of AN reduces redox potential and improves the cell voltage • Negligible cross-over due to repulsion of charged analytes by sulfonate of Nafion membrane Among the aqueous organic redox flow batteries, quinone derivatives based redox molecules are commonly explored, due to their facile electron transfer ability. In this work, we have screened three redox active quinones (anthrarufin (AN), naphthazarin (NN), and juglone (JN)) for anolyte and cells were fabricated against K 4 Fe(CN) 6 catholyte. The anolyte with more number of aromatic rings, i.e., AN is capable of better delocalizing the electrons and show more negative redox potential, thereby enhancing the operating voltage of the battery. AN exhibited a single step two-electron reduction process and delivered a capacity of 1.32 Ah L−1 at 20 mA cm-2 current density. [ABSTRACT FROM AUTHOR]

Optimized synthetic procedures for pyridinium ions featuring iminophosphorano (−N=PR3; R=Ph, Cy) π‐donor substituents in the 2‐ and 4‐ positions are described. Crystallographic and theoretical studies reveal that the strongly donating substituents severely polarize the π‐electrons of the pyridyl ring at the expense of aromaticity. Moreover, the pyridinium ions are readily deprotonated to generate powerful bispyridinylidene (BPY) organic electron donors. Electrochemical studies show exceptionally low redox potentials for the two‐electron BPY/BPY2+ couples, ranging from −1.71 V vs the saturated calomel electrode for 3PhPh (with four Ph3P=N− groups) to −1.85 V for 3CyCy (with four Cy3P=N− groups). These new compounds represent the most reducing neutral organic electron donors (OEDs) currently known. Some preliminary reductions involving 3CyCy showed enhanced capability owing to its low redox potential, such as the thermally activated reduction of an aryl chloride, but purification challenges were often encountered. [ABSTRACT FROM AUTHOR]

Neutral complexes [MII(C5Me5)(Q2−)(NO+)] with M=Ru or Os and the catecholates Q2− with 3,5‐di‐tert‐butyl (dtbc) or 3,4,5,6‐tetrachloro substituents (tcc) were identified with the oxidation and charge states indicated. Reversible electron transfer was analyzed spectroelectrochemically (EPR, UV‐vis‐NIR, IR), supported by DFT calculations. Reversible reduction was observed for [Ru(C5Me5)(tcc)(NO)] to occur on the nitrosyl ligand to yield the NO radical complex [RuII(C5Me5)(tcc2−)(NO.)]−, whereas the stepwise oxidation yielded o‐semiquinone cations, [MII(C5Me5)(Q.−)(NO+)]+, and dications. The metals remained in the stable low‐spin d6 states, RuII and OsII, respectively. Redox potentials were found to depend strongly on the donor or acceptor substitution pattern at Qn. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of boron subphthalocyanines (BsubPcs) has been investigated using cyclic voltammetry in the presence of various solvents, internal standards, supporting electrolytes, working electrodes, and sweep voltage scan rates. We have focused on halogenated BsubPcs (Cl−Cl6BsubPc, Cl−Cl12BsubPc, F−F6BsubPc, F−F12BsubPc) and a non‐halogenated baseline (Cl−BsubPc). Halogenated BsubPcs are of interest to the field due to their promising advances as organic electronic materials for applications based on redox or electron transfer processes. We had pre‐established a standard operating procedure (SOP) for electrochemical data acquisition, but it was timely to consider alternative variables, their impact on the electrochemical data and re‐establish an alternative SOP. We observed modest shifts (up to 49 mV) of the BsubPc redox potentials when changing the internal standard, working electrode and/or the electrolyte concentration. In scan rate range between 20 and 250 mV s−1, the peak (ir)reversibility for F−F6BsubPc and F−F12BsubPc remained unchanged and the electron transfers at the surface electrode remained diffusion‐controlled. [ABSTRACT FROM AUTHOR]

The role of oxidative stress in male infertility has been broadly recognised, and the search for a new marker to determine the redox environment in semen has gained considerable interest. Oxidation–reduction potential (ORP) or redox potential, is a measure of the electron transfer from antioxidants to oxidants and provides information on the redox balance. In this review, the benefits of ORP as a new oxidative stress marker, the protocol for its evaluation and the importance of its measurement in the context of male infertility are discussed. In association with the standard semen analysis, seminal ORP has been analysed to evaluate semen quality and male fertility status. However, further studies are required to establish its use in assisted reproductive techniques (ART) practice. [ABSTRACT FROM AUTHOR]

Photo‐induced electron transfer chemistry between molecules is a central theme in several fields including biology, physics and chemistry. Specifically, in photoredox catalysis, greater use has been made of iridium(III) complexes as they exhibit ground‐ and excited‐state redox potentials that span a very large range. Unfortunately, most of these complexes suffer from limited visible light absorption properties. This concept article highlights recent developments in the synthesis of iridium(III) complexes with increased visible light absorption properties and their use as candidates for visible light driven redox catalysis. Fundamental tools are provided to enable the independent tuning of the HOMO and LUMO energy levels. Recent examples are given with the hope that this concept article will foster further developments of iridium(III)‐based sensitizers for visible light driven reactivity. [ABSTRACT FROM AUTHOR]

Green colored mononuclear copper(II) complexes viz. [Cu(L)(bpy)](ClO4) (1) or [Cu(L)(phen)](ClO4) (2) (where H(L) is 2-((2-dimethylamino)ethyliminomethyl)naphthol) show distorted square pyramidal (4 + 1) geometry with CuN4O chromophore. The existence of self-assembled molecular associations indicates the formation of the dimer. Dimeric nature in solution is retained due to the binding of the substrate, encourages steric match between substrate and Cu(II) active site, which favors electron transfer. Interestingly, both the complexes exhibit high-positive redox potential. Therefore, the presence of self-assembled molecular association along with the positive redox potential enhances the catalytic oxidation of ascorbic acid to dehydroascorbic acid or benzylamine to benaldehyde or catechol to o-quinone thereby model the functional properties of type 2 and type 3 copper oxidases. Notably, catalytic activity is effective when compared with other reported mononuclear copper(II) complexes and even superior to many binuclear copper(II) complexes. Existence of self-assembled molecular association in solution along with high-positive redox potential favors electron transfer process in mononuclear copper(II) complexes and models the functional properties of type 2 and type 3 copper oxidases. [ABSTRACT FROM AUTHOR]

The flavin‐based electron bifurcation (FBEB) system from Acidaminococcus fermentans is composed of the electron transfer flavoprotein (EtfAB) and butyryl‐CoA dehydrogenase (Bcd). α‐FAD binds to domain II of the A‐subunit of EtfAB, β‐FAD to the B‐subunit of EtfAB and δ‐FAD to Bcd. NADH reduces β‐FAD to β‐FADH−, which bifurcates one electron to the high potential α‐FAD•− semiquinone followed by the other to the low potential ferredoxin (Fd). As deduced from crystal structures, upon interaction of EtfAB with Bcd, the formed α‐FADH− approaches δ‐FAD by rotation of domain II, yielding δ‐FAD•−. Repetition of this process leads to a second reduced ferredoxin (Fd−) and δ‐FADH−, which reduces crotonyl‐CoA to butyryl‐CoA. In this study, we measured the redox properties of the components EtfAB, EtfaB (Etf without α‐FAD), Bcd, and Fd, as well as of the complexes EtfaB:Bcd, EtfAB:Bcd, EtfaB:Fd, and EftAB:Fd. In agreement with the structural studies, we have shown for the first time that the interaction of EtfAB with Bcd drastically decreases the midpoint reduction potential of α‐FAD to be within the same range of that of β‐FAD and to destabilize the semiquinone of α‐FAD. This finding clearly explains that these interactions facilitate the passing of electrons from β‐FADH− via α‐FAD•− to the final electron acceptor δ‐FAD•− on Bcd. The interactions modulate the semiquinone stability of δ‐FAD in an opposite way by having a greater semiquinone stability than in free Bcd. [ABSTRACT FROM AUTHOR]

Reduction of β-diketiminato nickel(II) complexes (LtBuNiII) to the corresponding nickel(I) compounds does not require alkali metal compounds but can also be performed with the milder cobaltocenes. LtBuNiBr and Cp2Co have rather similar redox potentials, so that the equilibrium with the corresponding electron transfer compound [LtBuNiIBr][Cp2CoIII] (ETC) clearly lies on the side of the starting materials. Still, the ETC portion can be used to activate CO2 yielding a mononuclear nickel(II) carbonate complex and ETC can be isolated almost quantitatively from the solutions through crystallisation. The more negative reduction potential of Cp*2Co shifts the equilibrium formed with LtBuNiBr strongly towards the ETC and accordingly the reaction of such solutions with CO2 is much faster. [ABSTRACT FROM AUTHOR]

The synthesis, electrochemical and spectroscopic characterization of five copper triarylcorroles bearing one, two or three meso-nitroaryl substituents is reported. Redox potentials and spectroscopic properties of the neutral Cu(II) corrole cation radicals and singly reduced formof the complexes are reported in CH2Cl2 and the ability of the initial noninnocent derivatives to be chemically reduced via anion induced electron transfer (AIET) is explored using cyanide (CN-) or fluoride (F-) anions in the form of tetra-n-butylammonium salts. UV--visible spectra of the singly reduced corroles and the species generated after addition of CN- or F- to solutions of the neutral compounds are identical, thus confirming the AIET event in these systems. This result, when combined with the facile electrochemical reduction, provides strong indirect evidence for the presence of noninnocence in these systems. [ABSTRACT FROM AUTHOR]