Quinone Redox Mediators Research Articles

Molecular Unravelling of the Structural Effect of Quinone Redox Mediators on Oxygen Reduction Reaction in Aprotic Lithium-Oxygen Batteries.

Redox mediators (RMs) provide tantalizing solutions to unlock the energy capabilities of aprotic lithium-oxygen (Li-O2) batteries by driving solution-mediated Li2O2 growth. However, the structural effect of RMs on the catalytic efficiency of the oxygen reduction reaction remains incompletely understood. Herein, we present the interplay between the structure of RMs and their discharge capabilities by a comparative study of model quinone (Q)-based RMs. Specifically, at low current densities, incorporating electron-withdrawing groups onto the Q ring can positively move the discharge potential and deliver larger discharge capacity by extending the lifespan of the LiQO2 intermediate and allowing for Li2O2 growth into deeper electrolyte regions. Conversely, at high current densities, the absence of electron-withdrawing groups facilitates homogeneous reaction kinetics from LiQ to regenerate Q (i.e., decreased lifespan of LiQO2), mitigating electrode potential polarization and preserving catalytic activity of Q for higher discharge capacity. The work establishes structure-property relationships that guide the rational design of RMs toward next-generation Li-O2 batteries.

Probing Carboxylate Anolytes for Photo-Biofuel Cells through Combination of Bioinformatics and Electrochemistry

Photoheterotrophic purple bacterium Rhodobacter capsulatus has recently gained attention for its high halotolerance and its photo-enhanced extracellular electron transfer via exogenous quinone redox mediators, opening opportunity for self-powered decontamination of saline wastewater. Biodegradation of malate and succinate in R. capsulatus electrochemical systems has undergone prior examination, although a consistent bioelectrochemical system to comparatively study multiple carbon sources has not previously been developed. In this study, electrochemical techniques, biological assays, and computational tools were combined to evaluate malate, succinate, propionate, and lactate as oxidizable fuels in photo-enhanced microbial electrochemical systems. Specifically, cyclic voltammetry and amperometry data demonstrated that R. capsulatus generates distinctive photo-enhanced current densities dependent on both fuel identity and concentration. Bacterial growth curve studies were in agreement with the electrochemical data, indicating that lactate, which yielded the greatest bio-anodic current density (9.5 ± 1.9 µA cm-2), allowed the bacteria to grow more rapidly than the other substrates, suggesting its effectiveness as a fuel. Moreover, propionate appeared to be the fuel least efficiently utilized by R. capsulatus, having the slowest growth curve and the lowest current density generation (1.3 ± 0.2 µA cm-2). Finally, high-throughput differential gene expression analysis allowed for illuminating the physiological underpinnings of the observed differences between substrates. Most remarkably, cells grown in lactate were found to overexpress light harvesting complex II proteins and to underexpress flagellar motility proteins, which both correspond to the high photo-enhanced current density in lactate bioanodes compared to malate and propionate.

Evaluating Organic Acids As Oxidizable Fuels in R. Capsulatus-Based Bioelectrochemical Systems

The development of microbial fuel cells (MFCs) for wastewater treatment has recently gained significant attention in the bioremediation and renewable energy industries. Bacteria can be integrated into the anodes of MFCs to oxidize organic wastes, simultaneously producing electrical current and decontaminating wastewater. The photoheterotrophic purple bacterium Rhodobacter capsulatus has demonstrated photo-catalyzed electron transfer to carbon electrodes via exogenous quinone redox mediators, and tolerance to high salinity, opening opportunities for solar-powered MFC systems for treatment of saline wastewater. While the consumption of malate by R. capsulatus has been electrochemically analyzed previously, in this project, alternative target carbon sources were examined in order to improve electrochemical performance of these R. capsulatus systems. A combination of electrochemical techniques and biological assays were used to evaluate the relative viability of malate, lactate, succinate and propionate as oxidizable fuels. Specifically, cyclic voltammetry and amperometry data demonstrated that R. capsulatus generates distinctive bio-photocurrent densities depending on the fuel metabolized. Bioanodes with immobilized R. capsulatus cells oxidizing lactate (9.49 ± 1.89 µA cm-2) as the fuel yielded the greatest mediated bio-photocurrent densities compared to the other fuels, while those metabolizing propionate (1.33 ± 0.18 µA cm-2) generated the smallest current densities. In tandem with electrochemistry methods, growth curve assays and RNA sequencing were performed to further delve into the biological effects of altering the carbon source.

The Effects of Adding Quinone Redox Mediator on TEMPO-Immobilizing Cathode for Lithium Oxygen Batteries

The lithium oxygen battery has received much attention for its high specific capacity (3505 mAh cm-2). However, it has many issues such as the high charge/discharge overpotential and associated by-product formation. To solve this problem, Redox Mediators (RMs) have been widely proposed. RMs were reported to reduce overpotential on charging or discharging and improve cycle performance. However, oxidized RMs may diffuse or migrate from cathode side to anode side and they may be reduced by Li anode (Redox shuttle phenomenon). This phenomenon will lead overcharge and also lead RM’s decomposition. For this reason, the methodology that prevents RMs from diffusing to Li anode is required.In our previous research [1], TEMPO which is known for charge RM was immobilized on carbon paper by silane coupling. This cathode can reduce charge overpotential at very early cycles. However, decreasing charge capacity after several cycles was confirmed. One of possible causes of this problem might be the accumulation of by-product (such as Li2CO3) during discharge/charge cycle and deteriorate immobilized cathode. In this study, quinone RMs which are supposed to suppress the formation of by-product were introduced [2] As quinone RMs, 2,5-Di-tert-butl-1,4-benzoquinone(DBBQ) and Anthraquinone(AQ) are examined.Figure 1 shows 1st charge and discharge curves of O2 cathodes using TEMPO immobilized with/without quinone RMs. As shown Fig.1, with quinone RMs, the effect of reducing discharge overvoltage was confirmed. Moreover, the by-product suppression effect was also confirmed from XPS measurements. SEM images (Figure 2 (b), (d)) illustrates the difference in the morphology of the discharge product by the added quinone RMs. With DBBQ (Figure 2 (b)) about 250 nm particle-like precipitate was confirmed, while, with AQ (Figure 2 (d)) film-like precipitate was confirmed. This difference was considered to be derived from the difference is deposit mechanism [3].The addition of quinone RM also was found to affect charging behavior. In Fig. 1, when using DBBQ, insufficient amount of charge capacity compared to that of without additives, in contrast, when using AQ, sufficient amount of charge capacity was demonstrated. The reason for this was explained in the model shown in Figure 2 (a) and (c). When precipitates occurred in particle form (using DBBQ), the decomposition proceeded preferentially at the contact point between the immobilized TEMPO and the precipitate. For this reason, some of the precipitates may flow to bulk electrolyte without being decomposed, and resulting in insufficient charge capacity.On the other hands, when precipitates occurred in film form (using AQ), immobilized TEMPO could continuously react with precipitate. So, the almost precipitates could be decomposed, and sufficient charge capacity could achieve. However, the deterioration of the TEMPO-immobilized cathode, which was the original purpose, with the cycling was not suppressed. Therefore, there is need to examine other methods to suppress deterioration.In summary, suppress deterioration of TEMPO-immobilizing cathode could not be achieved by the addition of quinone RM, while, the finding as the relationship between the form of discharge product and the charge capacity obtained in this study would be useful knowledge for RM-immobilized cathode. Reference [1] Takuya Naruse, Kae Miyashiro, Toshiyuki Momma, “Immobilization of TEMPO to Carbon Paper Cathode for Li-O2 battery”, The 60th Battery Symposium in Japan, 2019/11/13.[2] Xiang wen Gao, Yuhui Chen, Lee Johnson and Peter G. Bruce, Nature Materials, volume 15, pages882–888(2016).[3] Peng Zhang, Liangliang Liu, Xiaofeng He, Xiao Liu, Hua Wang, Jinling He, and Yong Zhao, J. Am. Chem. Soc. 2019, 141, 6263−6270. Figure 1

Enhanced dissimilatory perchlorate reduction in the presence of humic acids or 2,6-anthraquinone disulfonate as quinone redox mediators

Humic acids (HA) and anthraquinone-2,6-Disulfonate (AQDS) are conceived as quinone-based redox mediators (QRM) in contaminant transformation processes, however, their effects on perchlorate (ClO4−) reduction remain unclear. This study explored the efficacy of quinone-mediated perchlorate reduction and the redox reactions occurred in QRM-amended systems. Relative to the average perchlorate reduction rate (k) in the control system, k was increased by 1.8, 1.9, and 2.3-fold in the presence of 100 mg/L commercial HA, extracted HA, and AQDS, respectively. Moreover, in AQDS-amended systems, k was further increased by 66.3% and 158.6%, respectively, with the addition of 0.003 g and 0.032 g hematite to the 200 mL culture. The critical redox reactions implying the electron transferring mechanism were explored and proven to be enzymatically driven. The presence of AQDS shortened the nitrate-induced lag of perchlorate reduction by stimulating nitrate exhaustion rate (2.83 mM NO3− h−1 compared to 1.26 mM NO3− h−1 in the control). Also, the inhibition of the 5-h aeration was alleviated (36.6% compared to 52.5% in the control) due to the higher redox-buffer capacity in AQDS-amended systems. Thaeura was predominant in all perchlorate-acclimated inocula, while the presence of QRM contributed to the enrichment of Desulfuromonas and Geobacter.

The Effect of Water on Quinone Redox Mediators in Nonaqueous Li-O2 Batteries.

The parasitic reactions associated with reduced oxygen species and the difficulty in achieving the high theoretical capacity have been major issues plaguing development of practical nonaqueous Li-O2 batteries. We hereby address the above issues by exploring the synergistic effect of 2,5-di-tert-butyl-1,4-benzoquinone and H2O on the oxygen chemistry in a nonaqueous Li-O2 battery. Water stabilizes the quinone monoanion and dianion, shifting the reduction potentials of the quinone and monoanion to more positive values (vs Li/Li+). When water and the quinone are used together in a (largely) nonaqueous Li-O2 battery, the cell discharge operates via a two-electron oxygen reduction reaction to form Li2O2, with the battery discharge voltage, rate, and capacity all being considerably increased and fewer side reactions being detected. Li2O2 crystals can grow up to 30 μm, more than an order of magnitude larger than cases with the quinone alone or without any additives, suggesting that water is essential to promoting a solution dominated process with the quinone on discharging. The catalytic reduction of O2 by the quinone monoanion is predominantly responsible for the attractive features mentioned above. Water stabilizes the quinone monoanion via hydrogen-bond formation and by coordination of the Li+ ions, and it also helps increase the solvation, concentration, lifetime, and diffusion length of reduced oxygen species that dictate the discharge voltage, rate, and capacity of the battery. When a redox mediator is also used to aid the charging process, a high-power, high energy density, rechargeable Li-O2 battery is obtained.

An approach for electrochemical functionalization of carbon nanotubes/1-amino-9,10-anthraquinone electrode with catechol derivatives for the development of NADH sensors

A new type of modified electrode, consisting of electro generated quinone redox mediator and carbon nanotubes (CNT) for electrocatalytic oxidation of reduced form of β-nicotinamide adenine dinucleotide (NADH) has been developed. The CNT functionalized with 1-amino-9,10-anthraquinone electrodes (GC/CNT/AAQ) were subjected to cyclic voltammetry in the presence of selected 1,2-dihydroxybenzene derivatives (catechol, 3-methoxycatechol and 4-methylcatechol). As a result, the electroactive quinone adducts were synthesized directly on the electrode surface via Michael addition mechanism. The structures of novel compounds were established using complementary computational studies and then were confirmed by HPLC-ESI-MS method. Electrochemical characterization of the electrodes after modification was carried out by cyclic voltammetry in broad range of pH. The heterogeneous electron transfer rate constants (ks) for the studied quinone modified electrodes were estimated and the obtained values (between 9.8 and 16.7 s−1) suggest moderate electron transfer kinetics. The electrodes displayed remarkable catalytic activity toward NADH oxidation in neutral phosphate buffer (pH = 7.4). The incorporation of quinone moieties onto electrode surface resulted in significantly decreased oxidation potential and enhanced current as compared to unmodified electrodes. NADH has been successfully determined at 0.1 V vs. Ag/AgCl, on all developed electrodes. The established method is characterized by linearity, low limits of detection (from 0.63 to 1.15 μM) and quantitation (from 1.9 to 3.47 μM), high sensitivity, suitable accuracy, repeatability and precision.

Decolorization of azo dyes by a salt-tolerant Staphylococcus cohnii strain isolated from textile wastewater

The salt-tolerant Staphylococcus cohnii strain, isolated from textile wastewater, has been found effective on decolorizing several kinds of azo dyes with different structures. The optimal conditions for azo dye acid red B (ARB) decolorization by S. cohnii were determined to be pH = 7.0 and 30°C. The decolorization efficiency increased with the increase of the salinity concentration, and around 90% of ARB (100 mg·L−1) could be decolorized in 24 h when the salinity concentration was up to 50 g·L−1. Moreover, the strain could still decolorize 19% of ARB in 24 h even when the NaCl concentration was increased to 150 g·L−1. Meanwhile, the dependence of the specific decolorization rate by S. cohnii on the ARB concentration could be described with Michaelis-Menten kinetics (Km = 585.7mg·L−1, Vmax = 109.8 mg·g cell−1·h−1). The addition of quinone redox mediator, named 2-hydroxy-1,4-naphthoquinone and anthraquinone-2,6-disulfonate, significantly accelerated the decolorization performance of S. cohnii. Furtherly, the activities of azoreductase (0.55 μmol·mg protein−1·min−1) and Nicotineamide adenine dinucleotide-dichlorophenol indophenol (NADH-DCIP) reductase (8.9 μmol·mg protein−1·min−1) have been observed in the crude cell extracts of S. cohnii. The decolorization products of ARB were analyzed by HPLC-MS, and the results indicated the reductive pathway was responsible for azo dye decolorization by S. cohnii.

Quinone-mediated reduction of selenite and tellurite by Escherichia coli

The reduction of selenite (Se(IV)) and tellurite (Te(IV)) by Escherichia coli was significantly enhanced by various quinone redox mediators (lawsone, menadione, anthraquinone-2-sulfonate, and anthraquinone-2,6-disulfonate). In the presence of 0.2mM lawsone, over 99.1% Se(IV) and around 96.4% Te(IV) were reduced in 8 h, at average reduction rates of 9.1 and 7.6 mM g cell(-1) h(-1), respectively. Better mediated reduction of Se(IV) and Te(IV) were observed when lawsone concentration increased from 0.1 to 0.4 mM and cell concentration increased from 0.1 to 0.6 g l(-1), respectively. Transmission electron microscopy analysis revealed the formation of both intracellular and extracellular Se(0) nanospheres or Te(0) nanorods, and the presence of lawsone increased the formation and accumulation of extracellular precipitates. The efficient mediated microbial reduction of Se(IV)/Te(IV) may be exploited for pollution removal and biological nanomaterials production.

Enhanced chromate reduction by resting Escherichia coli cells in the presence of quinone redox mediators

The reduction of Cr(VI) by resting Escherichia coli cells was significantly enhanced by the quinone redox mediators, lawsone, menadione, anthraquinone-2-sulfonate and anthraquinone-2,6-disulfonate. In the presence of 0.2 mM lawsone, over 97.5% Cr(VI) (100 mg l −1) was reduced in 4 h. The mediated reduction occurred at initial Cr(VI) concentrations of 50–250 mg l −1, and increased with increasing initial biomass concentrations from 0.05 to 1.2 g l −1. The addition of glucose as electron donor promoted the reduction process. Cu 2+, Ni 2+ and Co 2+ inhibited, whereas Mn 2+ and Pb 2+ stimulated reduction. Four rounds of mediated reduction were completed in 19 h, suggesting its stability and persistence. The efficient mediated microbial reduction of Cr(VI) is promising for rapid anaerobic removal of chromate.

Acceleration of azo dye decolorization by using quinone reductase activity of azoreductase and quinone redox mediator

This study demonstrated the effective application of intracellular azoreductase in mediated decolorization of azo dyes. Using the quinone reductase activity of overexpressed azoreductase AZR and quinone redox mediators, the decolorization performance of the recombinant strain Escherichia coli YB was significantly enhanced. In the presence of 0.2 mM lawsone, 75% acid red 27 (1 mM) was decolorized by E. coli YB in only 2 h, which was the highest bacterial decolorization rate ever reported. Compared to lawsone, menadione was a less effective redox mediator. Glucose was found to be the best carbon source for mediated decolorization by E. coli YB. The recombinant strain could complete four rounds of mediated decolorization repeatedly in 12 h. In addition, a 10-min pre-incubation of E. coli JM109 and activated sludge with 2-methylhydroquinone resulted in great improvement of mediated decolorization performance, which may be applied in practical treatment.

Reduction of nitroaromatic pesticides with zero-valent iron

Reduction of eleven nitroaromatic pesticides was studied with zero-valent iron powder. Average half-lives ranged from 2.8 to 6.3 h and the parent compounds were completely reduced after 48–96 h. The di-nitro groups of the 2,6-dinitroaniline herbicides were rapidly reduced to the corresponding diamines, with a negligible amount of partially reduced monoamino or nitroso products. Low levels of de-alkylated products were observed after 10 days. The nitro group of the organophosphorus insecticides was reduced dominantly to the monoamines but in a slower rate than the 2,6-dinitroanilines. A trace amount of oxon products was found. Reduction of nitro to amino was also the predominant reaction for the diphenyl ether herbicides. Aromatic de-chlorination and de-alkylation were minor reactions. These amine products were more stable than the parent compounds and 60% or more of the amines were detected after two weeks. Humic acid decreased the reduction rates of pendimethalin, and dichlone (a known quinone redox mediator) counteracted the effect of humic acid on the reactivity. Storage of iron powder under air decreased the reactivity very rapidly due to iron oxidation. Repeated use of iron powder also showed similar results. The reduced activity of air-oxidized iron was recovered by purging with hydrogen, but not nitrogen. Integration of iron powder with hydrogen- and quinone-producing microbial technologies may be a viable mean for remediation of highly oxidized xenobiotics in the environment.

Role of quinones in the biodegradation of priority pollutants: a review

Evidence is accumulating that inert humic substances can play important roles in the anaerobic degradation of priority pollutants by shuttling electrons. This paper reviews the roles of humus and quinone analogues as electron acceptors, redox mediators and electron donors for microbial and abiotic degradation processes. An eventual technology based on pumping quinones as terminal electron acceptors into aquifers and sediments to stimulate xenobiotic degradation offers promising potential. Also quinone redox mediators can be considered to accelerate reductive transformations (e.g. dechlorination, azo cleavage) of priority pollutants.