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[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]

[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]

Plants and cyanobacteria are promising heterologous hosts for metabolic engineering, and particularly suited for expression of cytochrome P450 (P450s), enzymes that catalyse key steps in biosynthetic pathways leading to valuable natural products such as alkaloids, terpenoids and phenylpropanoids. P450s are often difficult to express and require a membrane-bound NADPH-dependent reductase, complicating their use in metabolic engineering and bio-production. We previously demonstrated targeting of heterologous P450s to thylakoid membranes both in N. benthamiana chloroplasts and cyanobacteria, and functional substitution of their native reductases with the photosynthetic apparatus via the endogenous soluble electron carrier ferredoxin. However, because ferredoxin acts as a sorting hub for photosynthetic reducing power, there is fierce competition for reducing equivalents, which limits photosynthesis-driven P450 output. This study compares the ability of four electron carriers to increase photosynthesis-driven P450 activity. These carriers, three plant ferredoxins and a flavodoxin-like engineered protein derived from cytochrome P450 reductase, show only modest differences in their electron transfer to our model P450, CYP79A1 in vitro. However, only the flavodoxin-like carrier supplies appreciable reducing power in the presence of competition for reduced ferredoxin, because it possesses a redox potential that renders delivery of reducing equivalents to endogenous processes inefficient. We further investigate the efficacy of these electron carrier proteins in vivo by expressing them transiently in N. benthamiana fused to CYP79A1. All but one of the fusion enzymes show improved sequestration of photosynthetic reducing power. Fusion with the flavodoxin-like carrier offers the greatest improvement in this comparison - nearly 25-fold on a per protein basis. Thus, this study demonstrates that synthetic electron transfer pathways with optimal redox potentials can alleviate the problem of endogenous competition for reduced ferredoxin and sets out a new metabolic engineering strategy useful for producing valuable natural products. • Photosynthesis can supply reducing power for cytochrome P450 catalysis directly. • Competing host metabolism limits the amount of reducing power channeled towards heterologous P450s. • Four soluble electron carriers were tested as partners for a plant P450 expressed in N. benthamiana thylakoids. • All carriers could reduce the P450 in vitro , but had different electron transfer efficiencies with photosystem I and P450. • A flavodoxin-like carrier greatly enhanced in vivo flux of reducing power to the P450 when carrier and P450 were fused. [ABSTRACT FROM AUTHOR]

• Develop micro-kinetic models of electrocatalytic PCET reactions. • Propose theory for optimizing catalysts and reaction conditions for PCET. • Validate the theory by experiment on model catalysts for CO 2 reduction. Understanding the effects of pH and potential on proton-coupled electron transfer (PCET) steps and optimizing the reaction activity are of key importance for efficient applications of energy conversion processes. In this work, we develop a simple theory to optimize the electrocatalytic PCET reactions, in which electron and proton transfer take place in sequential steps, by combining an energy level diagram and micro-kinetic theories. Our theory suggests matching conditions on PCET energetics (redox potentials and p K a 's) and reaction environments (potential and pH) in order to achieve maximum kinetics. Consequently, a descriptor representing deviation from the ideal condition, i.e. |Δ U re |+ 2.30 k B T/ e |Δp K a |, is proposed to measure catalyst (in)activity. To test our theory, we further investigate CO 2 electroreduction on a model catalyst both computationally and experimentally, and show that the activity for CO 2 reduction on FePc (Iron Phthalocyanine) molecule is higher than H 2 evolution at near neutral condition. Our theory not only identifies the individual contribution of electron and proton transfer to overpotentials but also provides simple guidelines for optimizing the experimental conditions and searching for efficient catalysts. [ABSTRACT FROM AUTHOR]

Aldehyde-functionalized α-Fe 2 O 3 /graphitic carbon nitride (α-Fe 2 O 3 -DBD/g-C 3 N 4) was successfully synthesized through Schiff-based reaction between aromatic aldehydes in 3,4-dihydroxybenzaldehyde and NH 2 groups in urea. The 3,4-dihydroxybenzaldehyde around α-Fe 2 O 3 were advantageous to in situ growth of graphitic carbon nitride on α-Fe 2 O 3 to form the contact interface by chemical bonds and beneficial to the electron transfer, leading to the formation of Z-scheme photocatalytic system. The α-Fe 2 O 3 -DBD/g-C 3 N 4 photocatalysts exhibited a remarkable improvement in the degradation of bisphenol A (BPA) compared with bulk g-C 3 N 4. The enhanced photocatalytic activity was attributed to the enhanced charge separation efficiency and higher redox potential. This study presents a simple and efficient method to construct all-solid-state Z-scheme photocatalytic system with the formation of tight contact interface and nonmetal materials (aromatic rings) as electron mediators for the removal of complex pollutants. [ABSTRACT FROM AUTHOR]

The synthesis of gold nanoparticles decorated poly(3,4-ethylenendioxythiophene) loaded on reduced graphene oxide (AuNPs/PEDOT/rGO) was carried out by one-pot method as a potential cathode catalyst in fuel cells. The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and thermogravimetric analysis (TGA). From the SEM and TEM; it was found that AuNPs and PEDOT have a uniform distribution on rGO sheets. Meanwhile, FTIR and Raman spectroscopy results confirmed the existence of vibrational and adsorption bond of PEDOT on rGO sheets, while XRD pattern revealed the formation of AuNPs/PEDOT/rGO composite by characteristic of crystallographic structure. The nitrogen adsorption isotherm study indicated that the composites have both mesopores and macropores particle size. The analysis of thermogravimetric showed the synthesized composites are stable, where the decomposition step was below than 400 °C with a slightly mass loss. For the fabrication of electrode, the composite's suspension was drop-casted on glassy carbon electrode (GCE) and characterized using cyclic voltammetry (CV) technique and electrochemical impedance spectroscopy. AuNPs/PEDOT/rGO modified GCE exhibits better electron transfer, good capacitive and control-diffuse behaviour. The electrocatalytic activity toward oxygen reduction reaction was investigated by cyclic voltammetry in the presence of O 2 -saturated 0.1 M KOH solution. The results demonstrated that AuNPs/PEDOT/rGO/GCE has a good response toward catalytic of O 2. Therefore, this work gives support that the AuNPs/PEDOT/rGO composite has a potential for cathode materials in fuel cells. Image 1 • AuNPs was successfully deposited onto PEDOT/rGO sheet by facile chemical method. • A very low concentration of AuNPs were loaded on PEDOT/rGO sheets. • AuNPs/PEDOT/rGO modified electrode presented better electron transfer, good capacitive and control-diffusive behaviour. • AuNPs/PEDOT/rGO modified electrode exhibited high electrocatalytic activity toward ORR by four electron transfer pathway. [ABSTRACT FROM AUTHOR]

Several commercial assay kits exist with limited explanation of the kit components and reagent constituents, which greatly increases potential incompatibility issues resulting in the loss of samples, time, and data. Herein we explore such issues via the redox ion [Fe(CN) 6 ]3/4- in two commercial l -lactate and pyruvate assay kits. We clearly demonstrate significant interference from redox compounds with the l -lactate and pyruvate assays; a significance in signal inhibition/mechanism restriction, and false/mechanism exhaustion, respectively. Potential mechanisms are explored to explain interference. The need for transparency is crucial for consistency of assay kit performance from lab to lab. There is a need for suppliers to list the components of kits and/or list the potential for interference from specific agents to ensure that results obtained from these kits are reliable and reproducible. [Display omitted] • Discusses the growing field of bioelectronics and implementation of electrochemistry to detect and quantify biomarkers. • Demonstrates how components of assay kits interfere with electron facilitating compounds resulting in inaccurate data. • Discusses potential electron transfer kinetics between assay kits and underlying reactions responsible for inaccurate data. • Discusses the need for transparency regarding interference; a wider problem in the scientific community. [ABSTRACT FROM AUTHOR]

High-potential iron-sulfur proteins (HiPIPs) from extremely acidophilic chemolithotrophic non-photosynthetic Acidithiobacillus commonly play a crucial role in ferrous or sulfurous biooxidation. Acidithiobacillus exhibit important industrial applications for bioleaching valuable metals from sulfide ores. In this study, two HiPIP genes from thermophilic Acidithiobacillus caldus SM-1 were cloned and successfully expressed, and their proteins were purified. The proteins displayed a brownish color with an optical absorbance peak at approximately 385 nm and an electronic paramagnetic resonance (EPR) g value of approximately 2.01, which confirmed that the iron-sulfur cluster was correctly inserted into the active site when the proteins were generated in E. coli. The proteins were more thermostable than HiPIPs from mesophilic Acidithiobacillus. The direct electron transfer (DET) between HiPIPs and electrode was achieved by the 2-mercaptopyrimidine (MP) surface-modified gold electrodes; the redox potentials of the HiPIP1 and HiPIP2 measured by cyclic voltammetry were approximately 304.5 mV and 400.5 mV, respectively. The electron transfer rate constant was estimated to be 0.75 s−1 and 0.66 s−1, respectively. The MP/Au electrode and Au electrode showed consistent differences in heterogeneous electron transfer rates and electron transfer resistances. Bioinformatics and molecular simulations further explained the direct electron transfer between the proteins and surface-modified electrode. [Display omitted] • HiPIPs from A. caldus were cloned and successfully expressed in E. coli. • The [Fe 4 S 4 ] cluster of the HiPIPs were inserted into the active site. • HiPIPs from thermophilic A. caldus exhibit a more thermostability. • Direct electrochemistry of HiPIPs was achieved by SAM electrode. • Molecular simulation analyzed the electron transfer from HiPIPs to electrode. [ABSTRACT FROM AUTHOR]

Despite lacking mitochondria and a known pathway for heme biosynthesis the micro-aerotolerant anaerobic protozoan parasite Giardia intestinalis encodes four members of the cytochrome b 5 family of electron transfer proteins, three of which are small, single-domain proteins. While these are similar in size and fold to their better-known mammalian counterparts the Giardia proteins have distinctly lower reduction potentials, ranging from −140 to −171 mV compared to +6 mV for the bovine microsomal protein. This difference is accounted for by a more polar heme environment in the Giardia proteins, as mutation of a conserved heme pocket tyrosine residue to phenylalanine in the Giardia cytochrome b 5 isotype-I (gCYTb5-I Y61F) raises its reduction potential by nearly 100 mV. All three isotypes have UV–visible spectra consistent with axial coordination of the heme by a pair of histidine residues, but electron paramagnetic spectroscopy indicates that the planes of their imidazole rings are nearly perpendicular rather than coplanar as observed in mammalian cytochrome b 5 , which may be due to geometrical constraints imposed by a one-residue shorter spacing between the ligand pair in the Giardia proteins. Although no function has yet to be ascribed to any Giardia cytochrome b 5 , the presence of similar sequences in many other eukaryotes indicates that these represent an under-characterized class of low reduction potential family members. [ABSTRACT FROM AUTHOR]

Redox reactions between humic substances and Fe(III) compounds play a critical role in the biogeochemical cycle of pollutants. Most humic substances in soils and sediments are in a solid form (i.e. humin (HM)). In order to assess the contribution of electron shuttling via HM within the electron transfer network in natural environments and to predict environmental fate of pollutants associated with iron oxides, it is necessary to understand the electron transfer processes from HM to the environmentally relevant Fe(III) minerals, and to examine the redox reversibility of HM. The results of this study demonstrated that non-reduced HMs could only donate electrons to dissolved ferric citrate and poorly crystalline ferrihydrite, but reduced HMs could also reduce hematite and magnetite that had high crystallinity. The degree of reduction depended on the difference in redox potential and the crystallinity of the Fe(III) compounds. The electron-accepting capacities of different HMs correlated well with their organic carbon content, and quinones and Fe-bound organic component were important electron-accepting groups in HMs. Furthermore, the redox reversibility experiments demonstrated that HMs could maintain stable electron transfer capacities over three reduction-oxidation cycles, indicating that the HM could be an environmentally sustainable electron shuttle. Our results suggest that (1) HM may play an unrecognized and important role in biogeochemical cycles of pollutants in Fe(III) mineral-rich environments; (2) electron shuttling through HM to ferric citrate and ferrihydrite can occur even in the presence of O 2 ; and (3) HM would be a promising material for environmental remediation. [Display omitted] • H 2 /Pd reduced HMs could reduce hematite and magnetite. • Apparent redox potentials of native HMs were in a range from −287 to 0 mV. • HM extracted from riparian wetland exhibited the highest EAC value. • All HMs were fully reversible over three reduction−oxidation cycles. [ABSTRACT FROM AUTHOR]

Cytochrome c is a prototypical multifunctional protein that is implicated in a variety of processes that are essential both for sustaining and for terminating cellular life. Typically, alternative functions other than canonical electron transport in the respiratory chain are associated to alternative conformations. In this work we apply a combined experimental and computational study of Cyt c variants to assess whether the parameters that regulate the canonical electron transport function of Cyt c are correlated with those that determine the transition to alternative conformations, using the alkaline transition as a model conformational change. The results show that pK a values of the alkaline transition correlate with the activation energies of the frictionally-controlled electron transfer reaction, and that both parameters are mainly modulated by the flexibility of the Ω-loop 70–85. Reduction potentials and non-adiabatic ET reorganization energies, on the other hand, are both modulated by the flexibilities of the Ω-loops 40–57 and 70–85. Finally, all the measured thermodynamic and kinetic parameters that characterize both types of processes exhibit systematic variations with the dynamics of the hydrogen bond between the axial ligand Met80 and the second sphere ligand Tyr67, thus highlighting the critical role of Tyr67 in controlling canonical and alternative functions of Cyt c. Image 1 [ABSTRACT FROM AUTHOR]