Quinone Species Research Articles

All Organic Quinone Solid State Batteries for Environmentally Friendly and Chemical Robust Alternatives Beyond Lithium-Ion Batteries

Introduction: Organic solid-state quinone batteries have unparalleled properties that can meet the most urgent challenges the industry faces. It can create an energy system that is environmentally friendly and electrochemically robust, while being cost efficient enough for industry to adopt and invest in. The inspiration for fully organic solid-state batteries came from extended studies on our all-organic aqueous redox flow batteries, where much of the science of organic redox coupling molecules were understood. Like redox flow batteries, organic solid state quinone batteries utilizes the breaking and reforming of bonds to generate electrical energy. However, it doesn’t require the constant flow of charge carrier solution like the flow batteries. Consequently, this avoids the cost of an extra pumping system and significantly reduce the size of the batteries compared to flow battery systems. Furthermore, the downsized battery system allows for the cell to be implemented into applications such as EV and portable devices. The redox species are directly deposited onto the electrodes. This deposition of active material on carbon paper enables higher surface area for charge transfer, which increases the capacity for fast charge and discharge compared to flow batteries. Additionally, the active materials are of organic quinone nature providing great robustness that other battery systems like lithium-ion batteries don’t allow. The redox chemistry of these quinones still happens in aqueous system, which allows us to use very small amount of aqueous electrolyte instead of the combustible organic solvent used in lithium batteries. Results and discussion: The appropriate quinone species for this solid-state battery must be electrochemically stable and dissolution free in the aqueous system. Various quinones with different substituents were tested. One of the promising redox couples discovered is 2-methylanthraquinone (MAQ) and duroquinone (DQ). The couple displayed a cell voltage of 400 mV (0.4 V) as shown in Figure 1. This value was found to correspond to the redox potential difference between DQ and MAQ. New methods of deposition of active materials onto the electrodes were developed. High conductivity was achieved by introducing CNT with appropriate binder, which resulted in improvements to the cell’s charge and discharge performance (Figure 2). Figure 1. Cyclic voltammetry study of 10 mM 2-Methylanthraquinone (MAQ) and 10 mM Duroquinone (DQ) in 1 M sulfuric acid with 20% ethanol, MSE reference electrode, glassy carbon, 50 mV/s. (Refer to image file) Figure 2: Charge and discharge of solid-state batteries of 2-Methylanthraquinone (MAQ) and Duroquinone (DQ) at 10 mA. (Refer to image file)For the positive side, 0.164 g of duroquinone was deposited on 25 cm2 carbon paper with 0.05 g of CNT. Correspondingly, 0.222 g of 2-Methylantroquinone was deposited for the negative side. The cell was assembled with Nafion 117 as separator and small amount of 1 M sulfuric acid as the supporting electrolyte. The initial charge and discharge curve of this cell showed 97% columbic efficiency. Long-term cycling to test the stability was performed and other redox couples also showed higher cell voltage with high efficiency.The next step for this study is to explore different redox couples that might have better compatibility and higher cell voltage compared to the current redox couple. This will be done through studying the large library of organic compounds including quinones and other redox active organic compounds. Figure 1

Paper-in-Tip Bipolar Electrospray Mass Spectrometry for Real-Time Chemical Reaction Monitoring.

Capturing short-lived intermediates at the molecular level is key to understanding the mechanism and dynamics of chemical reactions. Here, we have developed a paper-in-tip bipolar electrolytic electrospray mass spectrometry platform, in which a piece of triangular conductive paper incorporated into a plastic pipette tip serves not only as an electrospray emitter but also as a bipolar electrode (BPE), thus triggering both electrospray and electrolysis simultaneously upon application of a high voltage. The bipolar electrolysis induces a pair of redox reactions on both sides of BPE, enabling both electro-oxidation and electro-reduction processes regardless of the positive or negative ion mode, thus facilitating access to complementary structural information for mechanism elucidation. Our method enables real-time monitoring of transient intermediates (such as N,N-dimethylaniline radical cation, dopamine o-quinone (DAQ) and sulfenic acid with half-lives ranging from microseconds to minutes) and transient processes (such as DAQ cyclization with a rate constant of 0.15 s-1). This platform also provides key insights into electrocatalytic reactions such as Fe (III)-catalyzed dopamine oxidation to quinone species at physiological pH for neuromelanin formation.

Paper‐in‐Tip Bipolar Electrospray Mass Spectrometry for Real‐Time Chemical Reaction Monitoring

AbstractCapturing short‐lived intermediates at the molecular level is key to understanding the mechanism and dynamics of chemical reactions. Here, we have developed a paper‐in‐tip bipolar electrolytic electrospray mass spectrometry platform, in which a piece of triangular conductive paper incorporated into a plastic pipette tip serves not only as an electrospray emitter but also as a bipolar electrode (BPE), thus triggering both electrospray and electrolysis simultaneously upon application of a high voltage. The bipolar electrolysis induces a pair of redox reactions on both sides of BPE, enabling both electro‐oxidation and electro‐reduction processes regardless of the positive or negative ion mode, thus facilitating access to complementary structural information for mechanism elucidation. Our method enables real‐time monitoring of transient intermediates (such as N,N‐dimethylaniline radical cation, dopamine o‐quinone (DAQ) and sulfenic acid with half‐lives ranging from microseconds to minutes) and transient processes (such as DAQ cyclization with a rate constant of 0.15 s−1). This platform also provides key insights into electrocatalytic reactions such as Fe (III)‐catalyzed dopamine oxidation to quinone species at physiological pH for neuromelanin formation.

Surface-Engineered Cesium Lead Bromide Perovskite Nanocrystals for Enabling Photoreduction Activity.

In recent years, colloidal lead halide perovskite (LHP) nanocrystals (NCs) have exhibited such intriguing light absorption properties to be contemplated as promising candidates for photocatalytic conversions. However, for effective photocatalysis, the light harvesting system needs to be stable under the reaction conditions propaedeutic to a specific transformation. Unlike photoinduced oxidative reaction pathways, photoreductions with LHP NCs are challenging due to their scarce compatibility with common hole scavengers like amines and alcohols. In this contribution, it is investigated the potential of CsPbBr3 NCs protected by a suitably engineered bidentate ligand for the photoreduction of quinone species. Using an in situ approach for the construction of the passivating agent and a halide excess environment, quantum-confined nanocubes (average edge length = 6.0 ± 0.8 nm) are obtained with a low ligand density (1.73 ligand/nm2) at the NC surface. The bifunctional adhesion of the engineered ligand boosts the colloidal stability of the corresponding NCs, preserving their optical properties also in the presence of an amine excess. Despite their relatively short exciton lifetime (τAV = 3.7 ± 0.2 ns), these NCs show an efficient fluorescence quenching in the presence of the selected electron accepting quinones (1,4-naphthoquinone, 9,10-phenanthrenequinone, and 9,10-anthraquinone). All of these aspects demonstrate the suitability of the NCs for an efficient photoreduction of 1,4-naphthoquinone to 1,4-dihydroxynaphthalene in the presence of triethylamine as a hole scavenger. This chemical transformation is impracticable with conventionally passivated LHP NCs, thereby highlighting the potential of the surface functionalization in this class of nanomaterials for exploring new photoinduced reactivities.

O-Semiquinone Radical and o-Benzoquinone Selectively Degrade Aniline Contaminants in the Periodate-Mediated Advanced Oxidation Process.

Advanced oxidation processes (AOPs) often employ strong oxidizing inorganic radicals (e.g., hydroxyl and sulfate radicals) to oxidize contaminants in water treatment. However, the water matrix could scavenge the strong oxidizing radicals, significantly deteriorating the treatment efficiency. Here, we report a periodate/catechol process in which reactive quinone species (RQS) including the o-semiquinone radical (o-SQ•-) and o-benzoquinone (o-Q) were dominant to effectively degrade anilines within 60 s. The second-order reaction rate constants of o-SQ•- and o-Q with aniline were determined to be 1.0 × 108 and 4.0 × 103 M-1 s-1, respectively, at pH 7.0, which accounted for 21% and 79% of the degradation of aniline with a periodate-to-catechol molar ratio of 1:1. The major byproducts were generated via addition or polymerization. The RQS-based process exhibited excellent anti-interference performance in the degradation of aniline-containing contaminants in real water samples in the presence of diverse inorganic ions and organics. Subsequently, we extended the RQS-based process by employing tea extract and dissolved organic matter as catechol replacements as well as metal ions [e.g., Fe(III) or Cu(II)] as periodate replacements, which also exhibited good performance in aniline degradation. This study provides a novel strategy to develop RQS-based AOPs for the highly selective degradation of aniline-containing emerging contaminants.

Convolutional neural network prediction of molecular properties for aerosol chemistry and health effects

AbstractQuinones are chemical compounds commonly found in air particulate matter (PM). Their redox activity can generate reactive oxygen species (ROS) and contribute to the oxidative potential (OP) of PM leading to adverse health effects of aerosols. The quinones' OP and ability to form ROS are linked to their reduction potential (RP, measured in volts), a metric for the tendency to lose electrons in redox reactions. Here, we use convolutional neural networks (CNN) as quantitative structure‐activity relationship (QSAR) models to relate the one‐electron RP of quinones to their molecular structure. For CNN training and testing, a data set of more than 100,000 quinones with associated RP values derived from density functional theory calculations was encoded in simplified molecular input line entry system (SMILES). The best performing CNN model achieved a root mean square error (RMSE) of 0.115 V for an independent test data set and outperformed linear regression models fitted on common molecular descriptors (≥ 0.140 V RMSE). Augmentation methods were newly adapted or applied to support CNN training with smaller data sets, improving RMSE by up to approximately 37% for a data set of 321 molecules. Adjusted for solvent effects, the CNN‐derived RP predictions showed good agreement with experimental data. Using the newly developed method, we identified a subset of atmospherically relevant quinones that are likely to have a high OP and play a role in aerosol health effects, which remains to be further elucidated by experimental studies. We suggest to use the presented machine learning approach in further investigations of atmospheric aerosol chemistry and health effects as well as other studies that require a target‐oriented screening of the properties and effects of large classes of substances.Key Points Convolutional neural networks can be used to estimate unknown physical and chemical properties of chemical substances and outperform additive group contribution methods. Augmentation methods aid in the prevalent problem of data availability. Quinone species detected in the environment are screened for potential relevance in atmospheric chemistry and public health and presented in this study.

Flow System with Liquid Active Sorbents for Electrochemically Mediated Carbon Capture

Within the field of carbon capture, electrochemically driven methods have drawn increasing attention due to their ability to operate at ambient temperature, their efficient scaling, and potentially low energetic cost. An important consideration in such systems is the method of gas contacting to enable efficient CO2 separation from the feed gas. Previous flow-based electrochemical processes that enable large-area gas contacting and desorption of concentrated CO2 at a point location all utilize water as the solvent and can require significant water feeds due to high evaporation rates. Here, we demonstrate the use of liquid, redox-active sorbents in a flow system that can decouple the electrode size from gas contacting area. The concept sorbent is a nonvolatile, liquid quinone species that can be reversibly reduced and oxidized to capture and release CO2, respectively. In this initial study, we employ the liquid quinone with sodium salts to achieve sorbent capacities near 2.5M CO2 and couple this sorbent to a ferrocene-derived counter electrolyte in a continuous capture – release process. Through this, we illustrate considerations in the salt choice, counter-electrolyte, and system design to best enable this concept sorbent, and discuss many opportunities for future optimizations.

Enhancement of peroxymonosulfate activation by sinapic acid accelerating Fe(III)/Fe(II) cycle

Peroxymonosulfate (PMS) is more cost-effective than peroxydisulfate (PDS) and has drawn great attention presently. Low efficiency of Fe(III)/Fe(II) cycle is a great intrinsic drawback of Fenton-like system, which extremely limits its widespread application. In this study, sinapic acid (SA) as a natural and environmental-friendly reductant, was applied to enhance Fe(III)/Fe(II) cycle in PMS/Fe(III) system. The removal efficiency of methyl paraben (MEP) was 98.3% (7.2 × 10−4 s−1) within 90 min in the modified system, and the kobs was 18 times higher than in PMS/Fe(II) system. For the active species identification, SO4−, HO and Fe(Ⅳ) were all responsible for MEP degradation, while SO4− was the dominant radical. The role of SA in SA/PMS/Fe(III) system was investigated, Fe(III) was reduced to Fe(II) and SA was oxidized to quinone species in this reaction process. The concentration of Fe(II) and the activation efficiency of PMS were all improved with SA concentration increasing from 5 to 20 μM, and the contribution of active species for MEP degradation were estimated. The effect of initial pH and common anions were also investigated. For the effect of anions, HCO3− and SO42− presented inhibition effect on MEP removal, and with the HCO3− concentration increasing 1–10 mM the inhibition decreased. Low concentration Cl− promoted MEP degradation while Cl− with higher concentration exhibited inhibition. And NO3− was almost no effect on MEP degradation.

Quinone binding sites of cyt bc complexes analysed by X-ray crystallography and cryogenic electron microscopy.

Cytochrome (cyt) bc1, bcc and b6f complexes, collectively referred to as cyt bc complexes, are homologous isoprenoid quinol oxidising enzymes present in diverse phylogenetic lineages. Cyt bc1 and bcc complexes are constituents of the electron transport chain (ETC) of cellular respiration, and cyt b6f complex is a component of the photosynthetic ETC. Cyt bc complexes share in general the same Mitchellian Q cycle mechanism, with which they accomplish proton translocation and thus contribute to the generation of proton motive force which drives ATP synthesis. They therefore require a quinol oxidation (Qo) and a quinone reduction (Qi) site. Yet, cyt bc complexes evolved to adapt to specific electrochemical properties of different quinone species and exhibit structural diversity. This review summarises structural information on native quinones and quinone-like inhibitors bound in cyt bc complexes resolved by X-ray crystallography and cryo-EM structures. Although the Qi site architecture of cyt bc1 complex and cyt bcc complex differs considerably, quinone molecules were resolved at the respective Qi sites in very similar distance to haem bH. In contrast, more diverse positions of native quinone molecules were resolved at Qo sites, suggesting multiple quinone binding positions or captured snapshots of trajectories toward the catalytic site. A wide spectrum of inhibitors resolved at Qo or Qi site covers fungicides, antimalarial and antituberculosis medications and drug candidates. The impact of these structures for characterising the Q cycle mechanism, as well as their relevance for the development of medications and agrochemicals are discussed.

Studies of pyrroloquinoline quinone species in solution and in lanthanide-dependent methanol dehydrogenases.

Pyrroloquinoline quinone (PQQ) is a redox cofactor in calcium- and lanthanide-dependent alcohol dehydrogenases that has been known and studied for over 40 years. Despite its long history, many questions regarding its fluorescence properties, speciation in solution and in the active site of alcohol dehydrogenase remain open. Here we investigate the effects of pH and temperature on the distribution of different PQQ species (H3PQQ to PQQ3- in addition to water adducts and in complex with lanthanides) with NMR and UV-Vis spectroscopy as well as time-resolved laser-induced fluorescence spectroscopy (TRLFS). Using a europium derivative from a new, recently-discovered class of lanthanide-dependent methanol dehydrogenase (MDH) enzymes, we utilized two techniques to monitor Ln binding to the active sites of these enzymes. Employing TRLFS, we were able to follow Eu(III) binding directly to the active site of MDH using its luminescence and could quantify three Eu(III) states: Eu(III) in the active site of MDH, but also in solution as PQQ-bound Eu(III) and in the aquo-ion form. Additionally, we used the antenna effect to study PQQ and simultaneously Eu(III) in the active site.

In situ DRIFTS combined with GC–MS to identify the catalytic oxidation process of dibenzofuran over activated carbon-supported transition metals oxide catalysts

Emission of polychlorinated dibenzop-dioxins and polychlorinated dibenzofurans (PCDD/Fs) have exerted more and more pressure on humans and the environment. The catalytic oxidation has been a good selection for eliminating dioxin in industries. Carbon-based catalysts were great potential to alleviate dioxin because of their large surface area and low cost. Catalytic oxidation of dioxin over metal oxide catalysts M/AC (M = V, Fe, Cu, Mn) was evaluated, and V/AC showed the highest catalytic activity at 300 °C. The catalysts surface acid amounts were improved through loading metal oxide, especially the Lewis acid, which could promote DBF adsorption on catalysts. Combined in-situ FTIR with GC–MS, two different reaction paths were provided on V/AC and Cu/AC catalyst. The C–C bond of DBF was priority broken to be oxidized on V/AC, and main transformation of DBF was from benzofuran, phenol and maleic acid to final products. The C–H bond of DBF was firstly activated on Cu/AC, and large unstable quinone species were produced. The main transformation of DBF was from DBF- quinone, benzofuran, furan to final products on Cu/AC. In this work, detailed reaction paths and by-products of DBF oxidation were provided.

Stretchable and Bioadhesive Gelatin Methacryloyl-Based Hydrogels Enabled by in Situ Dopamine Polymerization.

Hydrogel patches with high toughness, stretchability, and adhesive properties are critical to healthcare applications including wound dressings and wearable devices. Gelatin methacryloyl (GelMA) provides a highly biocompatible and accessible hydrogel platform. However, low tissue adhesion and poor mechanical properties of cross-linked GelMA patches (i.e., brittleness and low stretchability) have been major obstacles to their application for sealing and repair of wounds. Here, we show that adding dopamine (DA) moieties in larger quantities than those of conjugated counterparts to the GelMA prepolymer solution followed by alkaline DA oxidation could result in robust mechanical and adhesive properties in GelMA-based hydrogels. In this way, cross-linked patches with ∼140% stretchability and ∼19 000 J/m3 toughness, which correspond to ∼5.7 and ∼3.3× improvement, respectively, compared to that of GelMA controls, were obtained. The DA oxidization in the prepolymer solution was found to play an important role in activating adhesive properties of cross-linked GelMA patches (∼4.0 and ∼6.9× increase in adhesion force under tensile and shear modes, respectively) due to the presence of reactive oxidized quinone species. We further conducted a parametric study on the factors such as UV light parameters, the photoinitiator type (i.e., lithium phenyl-2,4,6-trimethylbenzoylphosphinate, LAP, versus 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, Irgacure 2959), and alkaline DA oxidation to tune the cross-linking density and thereby hydrogel compliance for better adhesive properties. The superior adhesion performance of the resulting hydrogel along with in vitro cytocompatibility demonstrated its potential for use in skin-attachable substrates.

A Quinol Anion as Catalytic Intermediate Coupling Proton Translocation With Electron Transfer in E. coli Respiratory Complex I.

Energy-converting NADH:ubiquinone oxidoreductase, respiratory complex I, plays a major role in cellular energy metabolism. It couples NADH oxidation and quinone reduction with the translocation of protons across the membrane, thus contributing to the protonmotive force. Complex I has an overall L-shaped structure with a peripheral arm catalyzing electron transfer and a membrane arm engaged in proton translocation. Although both reactions are arranged spatially separated, they are tightly coupled by a mechanism that is not fully understood. Using redox-difference UV-vis spectroscopy, an unknown redox component was identified in Escherichia coli complex I as reported earlier. A comparison of its spectrum with those obtained for different quinone species indicates features of a quinol anion. The re-oxidation kinetics of the quinol anion intermediate is significantly slower in the D213GH variant that was previously shown to operate with disturbed quinone chemistry. Addition of the quinone-site inhibitor piericidin A led to strongly decreased absorption peaks in the difference spectrum. A hypothesis for a mechanism of proton-coupled electron transfer with the quinol anion as catalytically important intermediate in complex I is discussed.

In situ infrared spectroscopy of dopamine oxidation/reduction reactions on a polycrystalline boron-doped diamond electrode

The oxidation of dopamine (DA) on a boron-doped diamond (BDD) electrode was investigated using in situ attenuated total reflection infrared spectroscopy (ATR-IR) and infrared reflection absorption spectroscopy (IRAS). Voltammogram showed multiple anodic/cathodic peaks for the oxidation/reduction of DA and its oxidized derivatives on the BDD electrode. The oxidation/reduction species on the surface and in solution were assigned using ATR-IR and IRAS, respectively. The anodic oxidation of DA promoted polymerization, and the polymerized DA (PDA) was continuously deposited on BDD without being reduced by potential cycles, which resulted in the irreversible behavior of the voltammogram. A decrease in the oxidation current of DA by potential cycles was due to the deposition of PDA. Some intermediate quinone species, such as dopaminequinone and dopaminechrome, were reversibly reduced to hydroquinone.

Nanocell type Ru@quinone core-shell catalyst for selective oxidation of alcohols to carbonyl compounds

Selective aerobic oxidation of alcohols to corresponding carbonyl compounds is one of the most important challenges in the modern chemical industry. The existing metal based heterogeneous catalysts provide low selectivity due to over-oxidation of aldehydes to acids and esters. We have found that coating of Ru nanoparticles by disodium anthraquinone-2,6-disulfonate (SQ) results in selective oxidation of aliphatic, unsaturated and aromatic alcohols to aldehydes. Analysis of core-shell Ru@SQ catalyst shows strong interaction between Ru and SQ leading to change of their electronic state and structure. In-situ study of alcohol oxidation using FTIR and electrochemistry indicates on hydrogen abstraction by shell quinone species with hydrogen transfer by quinone to Ru core for water generation. Thus, the catalyst behavior mimics nano-electrocell by separation of oxidation reaction over quinone and reduction of oxygen over Ru providing higher selectivity to aldehyde.

A combined first principles and classical molecular dynamics study of clay-soil organic matters (SOMs) interactions

In this study, clay-soil organic matters (SOMs) interactions were investigated by combining first principles molecular dynamics (FPMD) and classical molecular dynamics (CMD) techniques. FPMD was employed to quantify the binding mechanisms of reactive SOMs groups on clay surfaces and to derive parameters for the bonding of the reactive groups on edge surfaces. By integrating the derived parameters with CVFF–CLAYFF force fields, CMD simulations were carried out to investigate the structures of large models of clay-SOMs associations. All possible reactive SOMs groups, including carboxylate, phosphate, quinone species and ammonium groups were taken into account. FPMD results showed that all these groups are important to the complexation of SOMs on clay surfaces under dry conditions but only chemical bonding of carboxylate and phosphate and cation bridging are of significance under wet conditions. pH dependence of carboxylate and phosphate and Eh-pH dependence of quinone species are presented. CMD simulations showed that SOMs bound on clay surfaces via direct bonding of carboxylate and Ca2+ bridging and revealed the effect of water on structures of the clay-SOMs association. Based on the computational results, a procedure was proposed for constructing realistic molecular models for soils. Possible applications and further improvements of these models are discussed.

Observed Daily Profiles of Polyaromatic Hydrocarbons and Quinones in the Gas and PM1 Phases: Sources and Secondary Production in a Metropolitan Area of Mexico

The diel variation of meteorological conditions strongly influences the formation processes of secondary air pollutants. However, due to the complexity of sampling highly reactive chemical compounds, significant information about their transformation and source can be lost when sampling over long periods, affecting the representativeness of the samples. In order to determine the contribution of primary and secondary sources to ambient levels of polyaromatic hydrocarbons (PAHs) and quinones, measurements of gas and PM1 phases were conducted at an urban site in the Guadalajara Metropolitan Area (GMA) using a 4-h sampling protocol. The relation between PAHs, quinones, criteria pollutants, and meteorology was also addressed using statistical analyses. Total PAHs (gas phase + PM1 phase) ambient levels ranged between 184.03 ng m−3 from 19:00 to 23:00 h and 607.90 ng m−3 from 07:00 to 11:00 h. These figures both coincide with the highest vehicular activity peak in the morning and at night near the sampling site, highlighting the dominant role of vehicular emissions on PAHs levels. For the gas phase, PAHs ranged from 177.59 to 595.03 ng m−3, while for PM1, they ranged between 4.81 and 17.44 ng m−3. The distribution of the different PAHs compounds between the gas and PM1 phases was consistent with their vapour pressure (p °L) reported in the literature, the PAHs with vapour pressure ≤ 1 × 10−3 Pa were partitioned to the PM1, and PAHs with vapour pressures ≥ 1 × 10−3 Pa were partitioned to the gas phase. PAHs diagnostic ratios confirmed an anthropogenic emission source, suggesting that incomplete gasoline and diesel combustion from motor vehicles represent the major share of primary emissions. Quinones ambient levels ranged between 18.02 ng m−3 at 19:00–23:00 h and 48.78 ng m−3 at 15:00–19:00 h, with significant increases during the daytime. The distribution of quinone species with vapour pressures (p °L) below 1 × 10−4 Pa were primarily partitioned to the PM1, and quinones with vapour pressures above 1 × 10−4 Pa were mainly partitioned to the gas phase. The analysis of the distribution of phases in quinones suggested emissions from primary sources and their consequent degradation in the gas phase, while quinones in PM1 showed mainly secondary formation modulated by UV, temperature, O3, and wind speed. The sampling protocol proposed in this study allowed obtaining detailed information on PAHs and quinone sources and their secondary processing to be compared to existing studies within the GMA.

Fenton-like degradation of dimethyl phthalate enhanced by quinone species

Fenton-like degradations of dimethyl phthalate (DMP) and phenolic compounds (phenol, catechol, resorcinol, and hydroquinone) in single and binary systems were investigated by focusing on the Fe(III)/Fe(II) redox cycle during the reaction processes. Quinone-like substances were generated and found to be responsible for the autocatalytic transformation of Fe(III) to Fe(II) in the Fenton-like process with DMP or phenolics. Moreover, phenolic compounds could accelerate the Fenton-like degradation of DMP, with an increased efficiency of H2O2 utilization. The effect of phenolic compounds on the degradation of DMP followed the order: catechol ≈ hydroquinone > resorcinol > phenol, which could be attributed to the interaction between quinone-like substances and iron ions. Hydroquinone-like substances accelerated the Fe(III)/(II) redox cycle. The formation of iron complexes between catechol-like substances and iron ions facilitated the release of H+ and regeneration of Fe(II). In addition, a plausible mechanism for enhanced Fenton-like degradation of DMP by phenolics was proposed.

Activity of Spore-Specific Respiratory Nitrate Reductase 1 of Streptomyces coelicolor A3(2) Requires a Functional Cytochrome bcc-aa3 Oxidase Supercomplex.

Spores have strongly reduced metabolic activity and are produced during the complex developmental cycle of the actinobacterium Streptomyces coelicolor Resting spores can remain viable for decades, yet little is known about how they conserve energy. It is known, however, that they can reduce either oxygen or nitrate using endogenous electron sources. S. coelicolor uses either a cytochrome bd oxidase or a cytochrome bcc-aa3 oxidase supercomplex to reduce oxygen, while nitrate is reduced by Nar-type nitrate reductases, which typically oxidize quinol directly. Here, we show that in resting spores the Nar1 nitrate reductase requires a functional bcc-aa3 supercomplex to reduce nitrate. Mutants lacking the complete qcr-cta genetic locus encoding the bcc-aa3 supercomplex showed no Nar1-dependent nitrate reduction. Recovery of Nar1 activity was achieved by genetic complementation but only when the complete qcr-cta locus was reintroduced to the mutant strain. We could exclude that the dependence on the supercomplex for nitrate reduction was via regulation of nitrate transport. Moreover, the catalytic subunit, NarG1, of Nar1 was synthesized in the qcr-cta mutant, ruling out transcriptional control. Constitutive synthesis of Nar1 in mycelium revealed that the enzyme was poorly active in this compartment, suggesting that the Nar1 enzyme cannot act as a typical quinol oxidase. Notably, nitrate reduction by the Nar2 enzyme, which is active in growing mycelium, was not wholly dependent on the bcc-aa3 supercomplex for activity. Together, our data suggest that Nar1 functions together with the proton-translocating bcc-aa3 supercomplex to increase the efficiency of energy conservation in resting spores.IMPORTANCEStreptomyces coelicolor forms spores that respire with either oxygen or nitrate, using only endogenous electron donors. This helps maintain a membrane potential and, thus, viability. Respiratory nitrate reductase (Nar) usually receives electrons directly from reduced quinone species; however, we show that nitrate respiration in spores requires a respiratory supercomplex comprising cytochrome bcc oxidoreductase and aa3 oxidase. Our findings suggest that the Nar1 enzyme in the S. coelicolor spore functions together with the proton-translocating bcc-aa3 supercomplex to help maintain the membrane potential more efficiently. Dissecting the mechanisms underlying this survival strategy is important for our general understanding of bacterial persistence during infection processes and of how bacteria might deal with nutrient limitation in the natural environment.

Evaluation and correction on quinones’ quantification errors: Derived from the coexistence of different quinone species and pH-sensitive feature

Quinones are becoming an essential tool for refractory organics treatment, while their quantification may be not well-considered. In this paper, two kinds of potential errors in quantification were evaluated in multiple pH conditions. They were derived from the coexistence of oxidized/reduced quinone species (Type I) and pH-sensitive feature (Type II), respectively. These errors would remarkably influence the accuracy of quantification while they haven't been emphasized. Thus, to elaborate the relationship between the two types of errors and the absorbance or pH conditions, three typical quinones [Anthraquinone-1-sulfonate (α-AQS), anthraquinone-2,6-disulfonate (AQDS) and lawsone] were selected and their acid dissociation coefficients (pKa) as well as UV–Vis spectra were determined. Results revealed that, for Type I, the relative error (RE) of α-AQS concentration would exceed the limit (5%) when reduced α-AQS was below 48% of total α-AQS. Similar results were found for lawsone. However, the RE can be eliminated by the equation established in this paper. For Type II, the pH-sensitive feature was related to the pKa values of quinones. Absorbances of α-AQS and lawsone would change remarkably with pH variation. Therefore, a model for correction was established. Analog data showed high consistency with experimental data [r = 0.995 (n = 25, p < 0.01) and r = 0.997 (n = 36, p < 0.01), for lawsone and α-AQS respectively]. Especially, the determination of AQDS concentrations was noticed to be pH-independent at 437 nm under pH 4.00 to 9.18 conditions. Based on these features, a comprehensive data solution was proposed for handling these errors.