Electron Transfer Mediator Research Articles

Insights into the biocorrosion of Q235A steel influenced by the electron transfer process between iron and methanogenic microbiota

Anaerobic microbiologically influenced corrosion (MIC) of Fe (0) metals causes great harm to the environment and economy, which depends on the key electron transfer process between anaerobic microorganisms and Fe (0) metals. However, the key electron transfer process in microbiota dominating MIC remains unclear, especially for methanogenic microbiota wildly distributed in the environment. Herein, three different methanogenic microbiota (Methanothrix, Methanospirillum, and Methanobacterium) were acclimated to systematically investigate electron transfer pathways on corroding Q235A steel coupons. Results indicated that microbiota dominated by Methanothrix, Methanospirillum, or Methanobacterium accelerated the steel corrosion mainly through direct electron transfer (DET) pathway, H2 mediated electron transfer (HMET) pathway, and combined DET and HMET pathways, respectively. Compared with Methanospirillum dominant microbiota, Methanothrix or Methanobacterium dominant microbiota caused more methane production, higher weight loss, corrosion pits with larger areas, higher corrosion depth, and smaller corrosion pits density. Such results reflected that the DET process between microbiota and Fe (0) metals decided the biocorrosion degree and behavior of Fe (0) metals. This study insightfully elucidates the mechanisms of methanogenic microbiota on corroding steels, in turn providing new insights for anti-corrosion motives.

Direct transformation of rice straw to electricity and hydrogen by a single yeast strain: Performance and mechanism

Lignocellulosic waste is one of the most abundant renewable energy sources. However, pretreatment or complex microbial consortia are usually required for the biological transformation into energy products. This study demonstrates the direct transformation of raw rice straw biomass into electricity and hydrogen without any pretreatment by employing a single yeast strain, Cystobasidium slooffiae JSUX1, in microbial fuel cells (MFCs). The yeast-MFCs exhibit a maximum power density of 28.56 ± 2.54 mW/m2 with simultaneous production of hydrogen gas (4.9 ± 0.52 L/m3) from raw straw. Further analysis reveals that enzymes secreted by the yeast strain degraded rice straw into sugars or organic acids, serving as fuel for electricity and hydrogen production. In addition, humic acid (HA) and Fe-HA derived from biomass consumption serve as electron mediators for extracellular electron transfer (EET) in MFCs. This study demonstrates the power of the yeast strain for renewable energy recovery from straw, diversifying the toolbox for the lignocellulose industry.

In-situ electrochemical upcycling ammonia from wastewater-level nitrate with a natural hematite electrode: Regulation, performance, and application

Electrochemical reduction of nitrate (NO3-RR) to ammonia (NH4+/NH3) offers promising prospects for NO3- treatment. However, this process still suffers from NH4+ causing secondary pollution and catalyst deactivation in high-concentration NO3- wastewater. Herein, a high-performance system comprising a hematite (α-Fe2O3) electrode and a water-resistant membrane achieved 97.6 % NO3- removal and 81.6 % NH4+ as (NH4)2SO4in situ recovery at wastewater-level NO3-. The system exhibited an energy consumption of 62.2 kWh·KgNH3−1 and a Faradaic efficiency of 85.9 %. In-situ spectroscopy and electrochemical measurements revealed that α-Fe2O3 acted as both an electron transfer mediator for reducing NO3- to NO2- and an active center for NH3 formation via NO2-/Fe(Ⅱ) redox. Density functional theory calculations identified *HNO3 to *NO2 as potential-determining step of NO3-RR. Natural hematite-based system exhibited 74.8 % total inorganic nitrogen removal and 77.1 % NH4+ recovery for actual photovoltaic wastewater. This study provides insights into the development of electrochemical systems for resourcefully treating NO3--containing wastewater.

Triton X-100 Mediated Electron Transfer Reactions between Iron(III) Polypyridyl Complexes and Phenylsulfinylacetic Acids

Triton X-100 Mediated Electron Transfer Reactions between Iron(III) Polypyridyl Complexes and Phenylsulfinylacetic Acids

Palladium‐Catalyzed Aerobic γ‐C(sp3)−H Lactamization Using a NOx‐based Redox Mediator

AbstractHerein, we report a Pd‐catalyzed aerobic lactamization of unactivated γ‐C(sp3)−H bonds of aliphatic carboxylic acids and amino acids derivatives. The utilization of Pd(OAc)2 as a catalyst, along with catalytic AgNO2 as an electron transfer mediator, circumvents the need for stoichiometric oxidants and demonstrates significant practicality.

Biomimetic Activation of N‐Nitrosamides with Red Light‐Triggered Nitric Oxide Release via Mediated Electron Transfer

Mediated electron transfer (MET) is fundamental to many biological functions, including cellular respiration, photosynthesis, and enzymatic catalysis. However, leveraging the MET process to enable the release of therapeutic gases has been largely unexplored. Herein, we report the bio‐inspired activation of a series of UV‐absorbing N‐nitrosamide derivatives (NOA) under red light exposure, enabling the quantitative release of nitric oxide (NO) gasotransmitter via an MET process. The cornerstone of our design is the covalent linkage of a 2,4‐dinitroaniline moiety, which acts as an electron mediator to the N‐nitrosamide groups. This facilitates efficient electron transfer from the excited palladium(II) meso‐tetraphenyltetrabenzoporphyrin (PdTPTBP) photocatalyst and the selective activation of NOA. Our approach has been validated with distinct photocatalysts and various N‐nitrosamides, including those derived from carbamates, amides, and ureas. Notably, the modulation of the linker length between the electron mediator and N‐nitrosamide groups serves as a regulatory mechanism for controlling NO release kinetics. Moreover, this biomimetic NO release platform demonstrates effective operation under both normoxic and hypoxic conditions, and it enables localized delivery of NO under physiological conditions, exhibiting significant anticancer efficacy within the phototherapeutic window and enhanced selectivity towards tumor cells.

Biomimetic Activation of N-Nitrosamides with Red Light-Triggered Nitric Oxide Release via Mediated Electron Transfer.

Mediated electron transfer (MET) is fundamental to many biological functions, including cellular respiration, photosynthesis, and enzymatic catalysis. However, leveraging the MET process to enable the release of therapeutic gases has been largely unexplored. Herein, we report the bio-inspired activation of a series of UV-absorbing N-nitrosamide derivatives (NOA) under red light exposure, enabling the quantitative release of nitric oxide (NO) gasotransmitter via an MET process. The cornerstone of our design is the covalent linkage of a 2,4-dinitroaniline moiety, which acts as an electron mediator to the N-nitrosamide groups. This facilitates efficient electron transfer from the excited palladium(II) meso-tetraphenyltetrabenzoporphyrin (PdTPTBP) photocatalyst and the selective activation of NOA. Our approach has been validated with distinct photocatalysts and various N-nitrosamides, including those derived from carbamates, amides, and ureas. Notably, the modulation of the linker length between the electron mediator and N-nitrosamide groups serves as a regulatory mechanism for controlling NO release kinetics. Moreover, this biomimetic NO release platform demonstrates effective operation under both normoxic and hypoxic conditions, and it enables localized delivery of NO under physiological conditions, exhibiting significant anticancer efficacy within the phototherapeutic window and enhanced selectivity towards tumor cells.

Revisiting the role of algal biocathodes in microbial fuel cells for bioremediation and value-addition

Algal-microbial fuel cells (A-MFC) offers a sustainable solution for wastewater treatment and energy recovery. The performance of a typical MFC is affected by the oxidative-reductive reactions occurring in it. The cathodic reduction is facilitated by electron acceptors such as oxygen and ferricyanide. However, higher operational cost is incurred from their application. Algae owing to its phototrophic metabolism, oxygenates the cathode photosynthetically and acts as a mediator for cathodic electron transfer. Mixotrophic metabolism of algae enable their adaptation and growth in pollutant-rich toxic environments, making them suitable for wastewater treatment and remediation. A-MFCs enable the generation of algal biomass, a rich source of carbohydrates, lipids, proteins, pigments, and many more for commercial applications. Algal-based CO2 sequestration, nutrient and heavy metal removal via assimilation and carbon capture pathways make A-MFC systems a promising approach for bioenergy generation and wastewater remediation. Hence, this review offers an overview on the principles and applications of A-MFC and their relevance in developing a waste-centered-circular economy.

Photocatalytic performance of TiO2 modified with graphene derivatives and Fe (Ⅲ) at different thermal reduction temperatures

ABSTRACT To further investigate the synergistic effects of Fe (Ⅲ) and graphene derivatives with varying degrees of oxidation for photocatalysis, commercial titanium dioxide nanoparticles and graphene oxide were employed as precursors to synthesize the catalyst in this study. Graphene oxygenated derivatives and Fe (Ⅲ)-modified titanium dioxide photocatalysts with different oxidation degrees were prepared using a simple one-step solvothermal method. The results demonstrated that the photocatalytic performance in degrading rhodamine B and sulfamethoxazole was enhanced with an increase in the oxidation degrees of graphene materials. Through the combined action of delocalized conjugated π electrons as electron transfer mediators, Fe (Ⅲ) as an electron trap, and photosensitization reactions, titanium dioxide exhibited exceptional photocatalytic properties with the assistance of graphene derivatives and Fe (Ⅲ) co-catalysts in the degradation of organic compounds.

Simultaneous removal of nitrate nitrogen and ammonium nitrogen by partial denitrification coupled with anammox synergy by zero-valent iron

The implications of zero-valent iron (ZVI) on performance of partial denitrification (PD) coupled with anammox process (PD-anammox) and microbial community structures were assessed in present investigation. The results indicated that removal efficiencies of nitrate nitrogen, ammonium nitrogen and total nitrogen (TN) reached 86.28 ± 0.04%, 81.05 ± 0.06% and 82.90 ± 0.80%, respectively, with 30-day addition of ZVI under ratio of ZVI to nitrate (ZVI/N), carbon to nitrate (C/N) respectively for 3 and 2.3. Moreover, the content of extracellular polymer substance elevated by ZVI, and which could substitute carbon sources, mediated electron transfer and promoted nitrogen removal efficiency. Additionally, microbiological analysis revealed that ZVI enhanced nitrogen removal process by promoting the growth of genus Ignavibacterium and Denitratisoma, which coexist with anaerobic ammonia oxidation bacterium (AnAOB) and also induced other nitrogen removal process such as heterotrophic nitrate reduction to ammonium (DNRA), nitrate-dependent anaerobic ferrous oxide (NAFO), and iron-based anammox (Feammox) process. This study offers new insights into the enhancement of the nitrogen removal process by ZVI in PD-anammox process.

Enhanced hydrogen peroxide production under visible light via pyrimidine and glucose polymer modified graphitic carbon nitride in pure water

Photocatalytic H2O2 production by g-C3N4 (CN) has drawn intense research attention in the past decade. However, it suffers from drawbacks of weak light absorption capacity and rapid recombination of photogenerated electron-hole pairs. Here, we report a 4, 6-diamino-2-mercaptomidine (DAMP) and glucose (GLU) polymer modified CN (CN-DAMP-GLU) to enhance the photocatalytic performance of CN. The reported modified CN shows a high H2O2 production rate of 284.0 μmol g−1h−1 in pure water, surpassing most of the reported modified g-C3N4 catalysts. The mechanistic study confirms that the rapid conversion of •O2− is the key step in the visible-light-driven 2e− oxygen reduction reaction. This step favors efficient H2O2 generation and ensures the stable photocatalytic performance of the system. Experimental and DFT results further reveal that the donor-mediator-acceptor structure (polyfuran-DAMP-CN) with DAMP as the electron transfer mediator can inhibit the electron-hole recombination. We also demonstrate that this photocatalytic H2O2 production system can effectively degrade ciprofloxacin (CIP) through Fenton reaction. This work will promote the development of g-C3N4 for efficient photocatalytic production of H2O2 and possible applications in organic pollutant removal.

Synthesis of TiO2 nanoplate decorated by Co particles immobilized on porous Polycalix[4]resorcinarene for enhancing photocatalytic degradation of drug acetaminophen by light Emitting Diode

The sustainability and feasibility of using visible irradiation in photocatalysis is a promising approach for water purification. In this study, photocatalytic degradation of a widely used analgesic and antipyretic drug, acetaminophen (ACM), with metal-loaded an efficient photocatalyst (TiO2NPs-Co/Polycalix (Christen et al., 2010) [4]resorcinarene (TCP)) was inv estigated using visible light. photocatalyst structural, surface, and morphological features were characterized using FTIR, XRD, TEM, EDX, PL, and DRS analyses. Considering various sites of Polycalix (Christen et al., 2010) [4]resorcinarene in the TCP, studied by trapping experiments. A novel charge transfer bridge for electron-hole recombination is made possible by using Co and TiO2 as electron transfer mediators with electronic conductivity. This results in efficient process and energy optimization, which makes it easier for ACM to degrade throughout the absorption process. The ACM (15 and 40 mg/L) achieved complete degradation under visible light irradiation with 0.6 g/L of TCP at pH = 5.0 during 120 min reaction because of the good synergetic effect of the catalyst systems. Additionally, the intermediates generated by photo electrocatalytic activities were identified, and two potential paths for degradation were suggested. Some of these organic products were identified by High-Performance Liquid Chromatography (HPLC).

Interfacial bonding of Co3O4 and oxygen vacancies engineering on ZnO induced efficient peroxymonosulfate activation and pollutants degradation

A heterojunction of trace Co3O4 bonded on oxygen vacancies (OVs)-rich ZnO (OVs-ZnO/Co3O4) was synthesized via defect-assisted method to promote peroxymonosulfate (PMS) activation and pollutants degradation. Experiments and theoretical calculations demonstrated that electrons could efficiently transfer from OVs-ZnO to Co3O4. OVs-ZnO and Co3O4 played different roles in activating PMS. PMS was easily adsorbed on the OVs-ZnO to form PMS* complex and mediated electron transfer to oxide ciprofloxacin (CIP), whereas, Co3O4 facilitated breakup of peroxide bond to produce radicals. The optimal OVs-ZnO/Co3O4 with Co content of 1.34% exhibited good PMS decomposition ability (94.2% in 30 min) compared to unmodified ZnO (24.2%), stability and anti-interference feature in removing CIP, 96.9% CIP (10 ppm) and 79.6% of total organic carbon were removed in 30 min. Moreover, the OVs-ZnO/Co3O4 achieved 91.2% CIP removal ratio with 1.0 mM PMS via a flow-through device in 180 min. This study proposes a new strategy to enhance PMS activation of ZnO and provides new viewpoint in PMS activation way.

Unraveling the Electron Transfer in Cupriavidus necator – Insights Into Mediator Reduction Mechanics

AbstractCupriavidus necator, despite lacking direct electron transfer capabilities, demonstrates efficient reduction of various redox mediators in oxygen‐free cultivation within bioelectrochemical systems. This study investigates the reduction site of ferricyanide through inhibition and expression rate analysis of oxygen and nitrate respiration chain complexes, comparing aerobic cultivation conditions with fructose as carbon and electron donor to autotrophic (CO2/H2/O2) and anodic cultivation conditions (fructose/anode). Azide inhibition identified cytochrome c oxidase as the primary complex facilitating electron transfer to ferricyanide, with a secondary role proposed for nitrite reductase NirS, demonstrating a 3.9±1.1‐fold higher expression when exposed to anodic conditions. The 2.9±0.6‐fold increase in the expression of the natural porin OmpA under anodic conditions implies its potential involvement in ferricyanide uptake. Additionally, chemically permeabilizing cell membranes with cetyltrimethylammonium bromide doubles ferricyanide reduction rates without an anode present, offering insights for optimizing redox mediation in C. necator based bioelectrochemical systems. This study opens up new possibilities for the targeted optimization of mediated electron transfer in C. necator and other organisms.

Thymoquinone as an electron transfer mediator to convert Type II photosensitizers to Type I photosensitizers

The development of Type I photosensitizers (PSs) is of great importance due to the inherent hypoxic intolerance of photodynamic therapy (PDT) in the hypoxic microenvironment. Compared to Type II PSs, Type I PSs are less reported due to the absence of a general molecular design strategy. Herein, we report that the combination of typical Type II PS and natural substrate carvacrol (CA) can significantly facilitate the Type I pathway to efficiently generate superoxide radical (O2–•). Detailed mechanism study suggests that CA is activated into thymoquinone (TQ) by local singlet oxygen generated from the PS upon light irradiation. With TQ as an efficient electron transfer mediator, it promotes the conversion of O2 to O2–• by PS via electron transfer-based Type I pathway. Notably, three classical Type II PSs are employed to demonstrate the universality of the proposed approach. The Type I PDT against S. aureus has been demonstrated under hypoxic conditions in vitro. Furthermore, this coupled photodynamic agent exhibits significant bactericidal activity with an antibacterial rate of 99.6% for the bacterial-infection female mice in the in vivo experiments. Here, we show a simple, effective, and universal method to endow traditional Type II PSs with hypoxic tolerance.

Engineering Electron Transfer Pathway of Cytochrome P450s.

Cytochrome P450s (P450s), a superfamily of heme-containing enzymes, existed in animals, plants, and microorganisms. P450s can catalyze various regional and stereoselective oxidation reactions, which are widely used in natural product biosynthesis, drug metabolism, and biotechnology. In a typical catalytic cycle, P450s use redox proteins or domains to mediate electron transfer from NAD(P)H to heme iron. Therefore, the main factors determining the catalytic efficiency of P450s include not only the P450s themselves but also their redox-partners and electron transfer pathways. In this review, the electron transfer pathway engineering strategies of the P450s catalytic system are reviewed from four aspects: cofactor regeneration, selection of redox-partners, P450s and redox-partner engineering, and electrochemically or photochemically driven electron transfer.

Dual single atomic Fe-Ni sites in N‑doped nanoporous carbon for high-efficiency potassium periodate activation toward pollutant abatement

Diatomic catalysts (DACs) with atomically isolated metal pairs hold the potential for activating potassium periodate (PI) in sustainable pollution control, yet their synthesis poses a significant challenge. In this study, Fe/Ni species anchored to a nitrogen-doped carbon as diatomic catalysts (FeNi-NC DACs) were precisely synthesized by direct carbonization of metal–organic frameworks (MOFs) assembled by Fe/Ni-doped ZnO nanoparticles and used for the effective decomposition of organic pollutants through PI activation. As anticipated, FeNi-NC exhibited superior catalytic properties due to the abundance of adjacent bimetallic active sites (Fe/Ni-Nx), rich doped nitrogen, high specific surface area, and electron transport conductivity, surpassing single-atom Fe-NC and Ni-NC, as well as nonmetallic NC catalysts. Free radical quenching, electron paramagnetic resonance, and electrochemical experiments have shown that the FeNi-NC/PI system can oxidize organic compounds through non-free radical oxidation pathways, including singlet oxygen (1O2) oxidation and mediated electron transfer processes. Electron transfer mediated by FeNi-NC/PI* complexes is the primary mechanism for organic oxidation. Additionally, the FeNi-NC catalyst demonstrated remarkable stability in both inorganic-containing and real water samples, as well as in continuous-flow microreactors. This study introduces a novel approach for designing highly efficient DACs and offers fundamental insights into the mechanism of PI-activated oxidation of organic pollutants.

A novel nanozyme doped ZnO/r-GO-based sensor for highly sensitive electrochemical determination of muscle-relaxant drug: cyclobenzaprine HCl.

A nanocomposite of Ce-doped ZnO/r-GO was synthesized using a conventional hydrothermal method. The synthesized nanocomposites were utilized for the purpose of sensitive and selective detection of cyclobenzaprine hydrochloride (CBP). The properties of the composite were extensively analyzed, including its morphology, structure, and electrochemical behavior. This study investigates the application of a modified glassy carbon electrode for the detection of CBP, a muscle relaxant used to treat musculoskeletal diseases that cause muscle spasms. The electrode is modified with Ce-doped ZnO/r-GO. Various detection methods, such as cyclic voltammetric and square wave techniques (SWV), were utilized. The composite material showed high effectiveness as an electron transfer mediator in the oxidation of CBP. The electrode showed a good response for SWV evaluations in CBP identification, with a minimum detection limit of 1.6 × 10-8M and a wide linear range from 10 × 10-6 M to 0.6 × 10-7 M, under ideal conditions. The rate constant for charge transfer (ks) and the estimation of the electrochemical active surface area were obtained. A developed sensor exhibited desirable selectivity, long-lasting stability, and remarkable reproducibility. A sensor was used to analyze water, human serum, and urine samples, resulting in positive recovery results.

A Coupled System of Ni3S2 and Rh Complex with Biomimetic Function for Electrocatalytic 1,4-NAD(P)H Regeneration.

NAD(P)H cofactor is a critical energy and electron carrier in biocatalysis and photosynthesis, but the artificial reduction of NAD(P)+ to regenerate bioactive 1,4-NAD(P)H with both high activity and selectivity is challenging. Herein, we found that a coupled system of a Ni3S2 electrode and a Rh complex in an electrolyte (denoted as Ni3S2-Rh) can catalyze the reduction of NAD(P)+ to 1,4-NAD(P)H with superior activity and selectivity. The optimized selectivity in 1,4-NADH can be up to 99.1%, much higher than that for Ni3S2 (80%); the normalized activity of Ni3S2-Rh is about 5.8 times that of Ni3S2 and 13.2 times that of the Rh complex. The high performance of Ni3S2-Rh is attributed to the synergistic effect between metal sulfides and Rh complex. The NAD+ reduction reaction proceeds via a concerted electron-proton transfer (CEPT) mechanism in the Ni3S2-Rh system, in which Ni3S2 acts as a proton and electron-transfer mediator to accelerate the formation of Rh hydride (Rh-H), and then the Rh-H regioselectively transfers the hydride to NAD+ to form 1,4-NADH. The artificial system Ni3S2-Rh essentially mimics the functions of ferredoxin-NADP+ reductase in nature.

Unraveling the intrinsic activity origin of sludge-derived biochar for boosted chlorination of diclofenac: Key role of persistent free radicals

Economical and eco-friendly chlorine-based advanced oxidation processes (AOPs) have been urgently demanded to enhance the green abatement of emerging micropollutants. Herein, sludge-derived biochar (SBC) was innovatively introduced to activate free available chlorine (FAC) to enhance the elimination of diclofenac (DCF) among pH 5.0–11.0. Pyrolysis of municipal sludge endowed biochar with superior structure, various chemical compositions, and electronic properties, among which carbon-centered persistent free radicals (PFRs) were verified as the dominant active sites for enhanced chlorination based on correlation analysis. Electron spin resonance and electrochemical tests firstly verified that PFRs could mediate electron transfer toward FAC and dissolved oxygen to generate multiple reactive species of •OH, ClO•, 1O2, and O2•−. Further investigation revealed that enhanced DCF chlorination relied on both radical attack by •OH, ClO•, O2•− and direct electron transfer. Meanwhile, the regeneration of PFRs mediated by FAC and electron-rich DCF greatly promoted the reusability of SBC800. SBC800/FAC system was much superior to sole chlorination in terms of toxicity reduction and anti-interference capacity. This study innovatively introduced SBC as a green and sustainable catalyst to enhance chlorination efficiency, and provided new insights into the activation potential and mechanism of PFRs for chlorination.