Anthraquinone-2,6-disulfonate Research Articles

Charge assisted hydrogen bonded assemblies and unconventional O···O dichalcogen bonding interactions in pyrazole-based isostructural Ni(II) and Mn(II) compounds involving anthraquinone disulfonate: Antiproliferative evaluation and theoretical studies

Two new isostructural coordination compounds of Ni(II) and Mn(II) viz. [Ni(H2O)4(Hdmpz)2]ADS (1) and [Mn(H2O)4(Hdmpz)2]ADS (2) (where, Hdmpz = 3,5-dimethylpyrazole, ADS = anthraquinone-1,5-disulfonate) have been synthesized in aqueous medium at room temperature and characterized them using elemental analysis, TGA, FT-IR, electronic spectroscopy and single crystal X-ray diffraction techniques. Coordination compounds involving ADS anions in the crystal lattice are scarcely reported in the literature. Crystal structure analysis reveals the presence of unconventional O···O dichalcogen bonding interaction between the O-atoms of neighbouring ADS moieties of the compounds. Aromatic π-stacking and unusual charge assisted O‒H···O and C‒H···O hydrogen bonds (CAHBs) are also involved in the stabilization of the crystal structures. Theoretical calculations have been performed to analyze the CAHBs, π-stacking and O···O dichalcogen bonding interactions observed in the solid-state structures of 1 and 2 using DFT calculations, MEP surface analysis, QTAIM and NCI plot index computational tools. The relatively larger interaction energy observed for Ni(II) compound can be attributed to the higher contribution of the CAHBs than that for the Mn(II) complex. The energy associated to the O···O dichalcogen bonding interaction is small (0.6 kcal/mol) and comparable with the weak C‒H···O contact observed in compound 2. In vitro antiproliferative activities of the compounds considering cell cytotoxicity and apoptosis reveal the cytotoxic potential of the compounds in Dalton's Lymphoma (DL) cancer cells with negligible cytotoxicity in normal PBMC cells. Molecular docking simulation of the compounds with antiapoptotic proteins reveals significant affinity of the compounds with the active sites of the antiapoptotic proteins.

Reductive Transformation of 3-Nitro-1,2,4-triazol-5-one (NTO) by Leonardite Humic Acid and Anthraquinone-2,6-disulfonate (AQDS).

3-Nitro-1,2,4-triazol-5-one (NTO) is a major and the most water-soluble constituent in the insensitive munition formulations IMX-101 and IMX-104. While NTO is known to undergo redox reactions in soils, its reaction with soil humic acid has not been evaluated. We studied NTO reduction by anthraquinone-2,6-disulfonate (AQDS) and Leonardite humic acid (LHA) reduced with dithionite. Both LHA and AQDS reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO), stoichiometrically at alkaline pH and partially (50-60%) at pH ≤ 6.5. Due to NTO and hydroquinone speciation, the pseudo-first-order rate constants (kObs) varied by 3 orders of magnitude from pH 1.5 to 12.5 but remained constant from pH 4 to 10. This distinct pH dependency of kObs suggests that NTO reactivity decreases upon deprotonation and offsets the increasing AQDS reactivity with pH. The reduction of NTO by LHA deviated continuously from first-order behavior for >600 h. The extent of reduction increased with pH and LHA electron content, likely due to greater reactivity of and/or accessibility to hydroquinone groups. Only a fraction of the electrons stored in LHA was utilized for NTO reduction. Electron balance analysis and LHA redox potential profile suggest that the physical conformation of LHA kinetically limited NTO access to hydroquinone groups. This study demonstrates the importance of carbonaceous materials in controlling the environmental fate of NTO.

Chemistry and Isotope Fractionation of Divalent Mercury during Aqueous Reduction Mediated by Selected Oxygenated Organic Ligands.

We have investigated the chemistry and Hg isotope fractionation during the aqueous reduction of HgII by oxalic acid, p-quinone, quinol, and anthraquinone-2,6-disulfonate (AQDS), a derivate of anthraquinone (AQ) that is found in secondary organic aerosols (SOA) and building blocks of natural organic matter (NOM). Each reaction was examined for the effects of light, pH, and dissolved O2. Using an excess of ligand, UVB photolysis of HgII was seen to follow pseudo-first-order kinetics, with the highest rate of ∼10-3 s-1 observed for AQDS and oxalic acid. Mass-dependent fractionation (MDF) occurs by the normal kinetic isotope effect (KIE). Only the oxalate ion, rather than oxalic acid, is photoreactive when present in HgC2O4, which decomposes via two separate pathways distinguishable by isotope anomalies. Upon UVB photolysis, only the reduction mediated by AQDS results in a large odd number mass-independent fractionation (odd-MIF) signified by enrichment of odd isotopes in the reactant. Consistent with the rate, MDF, and odd-MIF reported for fulvic acid, our AQDS result confirms previous assumptions that quinones control HgII reduction in NOM-rich waters. Given the magnitude of odd-MIF triggered via a radical pair mechanism and the significant rate in the presence of air, reduction of HgII by photoproducts of AQDS may help explain the positive odd-MIF observed in ambient aerosols depleted of HgII.

Humic substances improve the co-production of hydrogen and carboxylic acids by anaerobic mixed cultures

The addition of external redox mediators (e.g., humic substances) as a strategy to enhance the production of H2 and carboxylic acids through mixed-culture dark fermentation was investigated. Pahokee Peat and Leonardite humic substances along the anthraquinone-2,6-disulfonate (AQDS) humic model compound were evaluated. The use of Pahokee peat into dark fermentation assays reached an H2 potential of 618.2 ± 28.9 mL H2/L, equivalent to an increase of 8% compared with the control experiment. In contrast, the addition of Leonardite (in its basal redox state) as a redox mediator increased the H2 potential by up to 14.5% and achieved 655.8 mL H2/L-d, which was higher than the control's H2 production of 572.6 mL H2/L-d. Moreover, the use of chemically reduced Leonardite led to the highest H2 potential (1158.6 mL H2/L-d) which was about 1.8-fold the H2 potential found in the control. Overall, experimental and production-modeling results suggest that external redox mediators not only served as an additional source of electrons for dark-fermentative pathways but also as electron acceptors. Electrons from redox mediators were likely transported through membrane proteins and could be used to reduce NAD+ and Fdox. Results indicated that electrons were preferably channeled through the butyrate pathway when reduced substances were applied.

Sulfate differentially stimulates but is not respired by diverse anaerobic methanotrophic archaea.

Sulfate-coupled anaerobic oxidation of methane (AOM) is a major methane sink in marine sediments. Multiple lineages of anaerobic methanotrophic archaea (ANME) often coexist in sediments and catalyze this process syntrophically with sulfate-reducing bacteria (SRB), but the potential differences in ANME ecophysiology and mechanisms of syntrophy remain unresolved. A humic acid analog, anthraquinone 2,6-disulfonate (AQDS), could decouple archaeal methanotrophy from bacterial sulfate reduction and serve as the terminal electron acceptor for AOM (AQDS-coupled AOM). Here in sediment microcosm experiments, we examined variations in physiological response between two co-occurring ANME-2 families (ANME-2a and ANME-2c) and tested the hypothesis of sulfate respiration by ANME-2. Sulfate concentrations as low as 100 µM increased AQDS-coupled AOM nearly 2-fold matching the rates of sulfate-coupled AOM. However, the SRB partners remained inactive in microcosms with sulfate and AQDS and neither ANME-2 families respired sulfate, as shown by their cellular sulfur contents and anabolic activities measured using nanoscale secondary ion mass spectrometry. ANME-2a anabolic activity was significantly higher than ANME-2c, suggesting that ANME-2a was primarily responsible for the observed sulfate stimulation of AQDS-coupled AOM. Comparative transcriptomics showed significant upregulation of ANME-2a transcripts linked to multiple ABC transporters and downregulation of central carbon metabolism during AQDS-coupled AOM compared to sulfate-coupled AOM. Surprisingly, genes involved in sulfur anabolism were not differentially expressed during AQDS-coupled AOM with and without sulfate amendment. Collectively, this data indicates that ANME-2 archaea are incapable of respiring sulfate, but sulfate availability differentially stimulates the growth and AOM activity of different ANME lineages.

Microbial analysis and enrichment of anaerobic phenol and p-cresol degrading consortia with addition of AQDS.

Quinones and humus are ubiquitous in the biosphere and play an important role in the anaerobic biodegradation and biotransformation of organic acids, poisonous compounds as well as inorganic compounds. The impact of humic model compound, anthraquinone-2, 6-disulfonate (AQDS) on anaerobic phenol and p-cresol degradation were studied. Four methanogenic AQDS-free phenol and p-cresol enrichments and two phenol-AQDS enrichments were obtained using two sludges with potential biodegradability of phenol and cresol isomers as inoculum. 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that syntrophic aromatic compound degrading bacterium Syntrophorhabdus aromaticivorans was dominant in four AQDS-free enrichments, whereas phenol degrading Cryptanaerobacter phenolicus was dominant in two phenol-AQDS enrichments. Neither co-culture of S. aromaticivorans with Methanospirillum hungatei nor two phenol-AQDS enrichments could metabolize phenol using AQDS as the terminal electron acceptor. Further degradation experiments suggested that C. phenolicus related microbes in two phenol-AQDS enrichments were responsible for the conversion of phenol to benzoate, and benzoate was further degraded by benzoate degraders of Syntrophus aciditrophicus or Sporotomaculum syntrophicum to acetate.

Simulating the synergy of electron donors and different redox mediators on the anaerobic decolorization of azo dyes: Can AQDS-chitosan globules replace the traditional redox mediators?

During anaerobic treatment of azo dye wastewater, the decolorization efficiency is low and dissolved redox mediators (RMs) added to the system are easy lost. In order to solve these issues, immobilized RMs have been a hot area of research. In this study a novel immobilized RM material, disodium anthraquinone-2,6-disulfonate (AQDS)-chitosan globules, which is natural, highly efficient and environmentally friendly, was prepared. Compared with natural immobilized RMs (activated carbon) and dissolved RMs (AQDS), it can be considered that it has a significant strengthening effect on the anaerobic biological degradation and decolorization of azo dye wastewater. An electron donor (ED, glucose) or RM (AQDS solution) was dosed into an anaerobic reactor to determine the enhancing effect and appropriate concentration for the decolorization treatment. The results indicate that a certain concentration of ED or RM [300 mg/L (1.667 mmol/L) glucose or 200 μmol/L AQDS solution] can improve effectively the anaerobic biological degradation and decolorization effect of azo dye wastewater. While by adding both 300 mg/L (1.667 mmol/L) glucose and 300 μmol/L AQDS (the concentrations were the initial reactive concentrations) together the decolorization efficiency was improved further. At the same time, the synergy of ED (glucose) and RM (AQDS solution) on the anaerobic decolorization of azo dye was simulated by the central combination design. A mathematical model for the decolorization efficiency has been established. According to this model, the hydraulic retention time of the best decolorization speed and efficiency has been obtained.

Enhancement of nitrite reduction and enrichment of Methylomonas via conductive materials in a nitrite-dependent anaerobic methane oxidation system

Nitrite-dependent anaerobic methane-oxidizing (n-damo) process has a promising prospect in anaerobic wastewater treatment, utilizing methane as the sole electron source to remove nitrite. However, the metabolic activity of n-damo bacteria is too low for practical application. This study aimed to stimulate n-damo process by introducing conductive nano-magnetite and/or electron shuttle anthraquinone-2,6-disulfonate (AQDS), and also set a comparative treatment of adding insulated ferrihydrite. The results showed that the nitrite reduction rate was enhanced the most significantly in treatment with nano-magnetite, approximately 1.6 times higher than that of the control without any supplement. While ferrihydrite application showed an adverse effect on n-damo process. The well-known aerobic methane oxidizer Methylomonas spp. was found to be enriched under n-damo condition with the supplementation of nano-magnetite and/or AQDS, but abundance of n-damo bacteria did not exhibit significant increase. It was hypothesized that Methylomonas spp. could be survived under anaerobic n-damo condition using oxygen produced by n-damo bacteria for the self-growth, and the nitrite reduction could be promoted through the enhancement of microbial interspecies electron transfer triggered by the introduction of conductive materials. It opens a new direction for the stimulation of n-damo activity, which needs more evidences to verify the hypothetic mechanism.

Quinone-mediated dissimilatory iron reduction of hematite: Interfacial reactions on exposed {0 0 1} and {1 0 0} facets

Although quinone-mediated bioreduction of iron oxides has been investigated extensively, little is known about the interfacial interactions between quinone and various exposed facets. In this study, the reduction of hematite {001} and {100} by Shewanella putrefaciens CN-32 with anthraquinone-2,6-disulfonate (AQDS) was investigated. The added AQDS can enhance the bioreduction of both hematite {001} and {100}, with hematite {001} showing a higher reduction degree than hematite {100}. No significant secondary iron oxides were found, but defects were observed in HR-TEM images. AQDS sorption was higher on hematite {001} (0.13 μM m−2) than hematite {100} (0.1 μM m−2). Electron transfer rate between hematite {001} and AQDS (19.6 s−1) was higher than hematite {100} (18.2 s−1). Tafel curves revealed that hematite {001} possesses lower resistance (3.5–2.4 Ω) than hematite {100} (4.1–2.9 Ω) with AQDS from 0 to 400 μM, indicating that hematite {001} is more favorable for electron transfer from cells or anthrahydroquinone-2,6,-disulfonate (AH2QDS) to Fe oxide. In addition to the well-known electron shuttling role of AQDS, the higher adsorption sites and electrochemical activity of hematite {001} over {100} jointly contributed to the enhanced iron bioreduction. The findings provide a mechanistic understanding of the interactions between quinone and various facets of iron oxides.

Redox mediator, microaeration, and nitrate addition as engineering approaches to enhance the biotransformation of antibiotics in anaerobic reactors

The present work assessed some engineering approaches, such as the addition of the redox mediator anthraquinone-2,6-disulfonate (AQDS) (50 and 100 μM), microaeration (1 mL air min−1), and nitrate (100−400 mg L−1), for enhancing the biotransformation of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) (200 μg L−1 each) in anaerobic reactors operated at a short hydraulic retention time (7.4 h). Initially, very low removal efficiencies (REs) of SMX and TMP were obtained under anaerobic conditions (∼6%). After adding AQDS, the anaerobic biotransformation of these antibiotics significantly improved, with an increase of approximately 70% in the REs with 100 μM of AQDS. Microaeration also enhanced the biotransformation of SMX and TMP, especially when associated with AQDS, which provided REs above 70%, particularly for TMP (∼91% with 1 mL air min−1 and 50 μM of AQDS). Concerning nitrate, the higher the added concentration, the higher the REs of the antibiotics (∼86% with 400 mg L−1). Therefore, all the assessed approaches were demonstrated to be very effective in improving the limited biotransformation of SMX and TMP in anaerobic reactors, ensuring REs comparable to those found in higher-cost wastewater treatment technologies, such as conventional activated sludge, membrane bioreactors, and hybrid processes.

Effects of the antibiotics trimethoprim (TMP) and sulfamethoxazole (SMX) on granulation, microbiology, and performance of aerobic granular sludge systems

This work assessed the effect of the antibiotics trimethoprim (TMP) and sulfamethoxazole (SMX) on the granulation process, microbiology, and organic matter and nutrient removal of an aerobic granular sludge (AGS) system. In addition, after the maturation stage, the impact of the redox mediator anthraquinone-2,6-disulfonate (AQDS) (25 μM) on the biotransformation of the antibiotics was evaluated. The reactor R1 was maintained as a control, and the reactor R2 was supplemented with TMP and SMX (200 μg L−1). The ability to remove C, N, and P was similar between the reactors. However, the structural integrity of the AGS was impaired by the antibiotics. Low TMP (∼30%) and SMX (∼60%) removals were achieved when compared to anaerobic or floccular biomass aerobic systems. However, when the system was supplemented with AQDS, an increase in the removal of TMP (∼75%) and SMX (∼95%) was observed, possibly due to the catalytic action of the redox mediator on cometabolic processes. Regarding the microbial groups, whereas Proteobacteria and Bacterioidetes increased, Planctomycetes decreased in both reactors. However, TMP and SMX presence seemed to inhibit or favor some genera during the formation of the granules, possibly due to their bactericidal action.

Redox mediator-modified biocathode enables highly efficient microbial electro-synthesis of methane from carbon dioxide

Regulating cathodic interface properties towards highly effective CH4 production from CO2 is of great importance for energy storage using microbial electro-synthesis (MES). Herein, the feasibility and mechanism of two typical redox mediators, neutral red (NR) and anthraquinone-2, 6-disulfonate (AQDS), were evaluated for the improvement of CH4 formation from CO2 reduction in mixed-culture biocathodes of MESs. Results showed that the CH4 formation rates of biocathodes after modification with NR and AQDS were 5.8 and 3.5 times higher than that of unaltered cathodes. Moreover, the coulombic efficiency of CH4 formation improved from 44.27 ± 4.01% of the control cathode to 64.30 ± 4.83% and 62.26 ± 2.87% after modification with NR and AQDS, respectively. Consequently, the energy efficiency of MESs after cathode modification with NR and AQDS increased to 58.33 ± 3.17% and 53.21 ± 4.11% compared to 38.20 ± 3.12% without modification. Such improvements were likely attributed to the enhanced extracellular electron transfer of microbes, the reduction in internal resistances and the enrichment of hydrogenotrophic methanogens in the mixed-culture biocathodes after modification with NR and AQDS. This study provides an alternative strategy to regulate cathodic interface in MESs for renewable energy storage and biomethane production from CO2.

Exploring the reactivity of β-cyclodextrin-encapsulated anthraquinone-2,6-disulfonate

The intracomplex reaction of anthraquinone-2,6-disulfonate (AQDS) in triplet excited state (3AQDS) with beta-cyclodextrin (CD) and the reaction of 3AQDS:CD complex with external quencher, N-Acetyl-l-Tyrosine (TyrO−), have been studied using laser flash photolysis, 1H NMR and 1H CIDNP. The two reactions were found to be competing with each other. The intracomplex hydrogen abstraction previously proposed for 3AQDS:CD complex may represent a two-step process, where at first stage an electron is transferred from the –OH group of CD to 3AQDS followed by a proton transfer and recombination of AQDS and CD radicals resulting in a stable AQDS-CD product. The rate constant of the intracomplex electron transfer from CD to 3AQDS was found to be 6 ± 1 × 106 s−1 and the rate of subsequent proton transfer is 1 ± 0.1 × 106 s−1. The rate constant of electron transfer between TyrO− and 3AQDS:CD complex (0.4 ± 0.1 × 109 M−1 s−1) drops approx. by half compared to that in the reaction between TyrO− and free 3AQDS (0.8 ± 0.1 × 109 M−1 s−1).

AQDS and Redox-Active NOM Enables Microbial Fe(III)-Mineral Reduction at cm-Scales

Redox-active organic molecules such as anthraquinone-2,6-disulfonate (AQDS) and natural organic matter (NOM) can act as electron shuttles thus facilitating electron transfer from Fe(III)-reducing bacteria (FeRB) to terminal electron acceptors such as Fe(III) minerals. In this research, we examined the length scale over which this electron shuttling can occur. We present results from agar-solidified experimental incubations, containing either AQDS or NOM, where FeRB were physically separated from ferrihydrite or goethite by 2 cm. Iron speciation and concentration measurements coupled to a diffusion-reaction model highlighted clearly Fe(III) reduction in the presence of electron shuttles, independent of the type of FeRB. Based on our fitted model, the rate of ferrihydrite reduction increased from 0.07 to 0.19 μmol d-1 with a 10-fold increase in the AQDS concentration, highlighting a dependence of the reduction rate on the electron-shuttle concentration. To capture the kinetics of Fe(II) production, the effective AQDS diffusion coefficient had to be increased by a factor of 9.4. Thus, we postulate that the 2 cm electron transfer was enabled by a combination of AQDS molecular diffusion and an electron hopping contribution from reduced to oxidized AQDS molecules. Our results demonstrate that AQDS and NOM can drive microbial Fe(III) reduction across 2 cm distances and shed light on the electron transfer process in natural anoxic environments.

Anthraquinone-2,6-disulfonate enhanced biodegradation of dibutyl phthalate: Reducing membrane damage and oxidative stress in bacterial degradation

Plasticizer dibutyl phthalate (DBP) pollution has received more and more attention. In this study, a DBP degrading bacteria Enterobacter sp. DNB-S2 was found to suffer membrane damage and oxidative stress during DBP degradation. Physiological and transcriptome analysis showed that 100 μmol L−1 anthraquinone-2,6-disulfonate (AQDS) could enhance the ability of strain DNB-S2 for biodegradation of DBP. AQDS adjusted the cell surface structure, including increase levels of hydrophobic and unsaturated fatty acids. These changes increased the chemotactic ability of the strain DNB-S2 to the hydrophobic pollutant DBP and the fluidity of the cell membrane. The expression of methyl chemotactic protein and genes associated with cell membrane-fixed components were up-regulated. AQDS also improved the scavenging ability of ·OH and H2O2 of DNB-S2 by promoting expression genes related to glutathione metabolism, thereby reducing oxidative stress. These results will provide new insights into the biodegradation of DBP.

Biofilm microbial composition changes due to different surface chemical modifications of activated carbon cloths in the biotransformation of 4-nitrophenol

Activated carbon cloths (ACCs) were used as biofilms supports in the anaerobic biotransformation of 4-nitrophenol (4NP). As received ACC material (AW) was oxidized with HNO3 (OX) and then functionalized with anthraquinone-2,6-disulfonate (AQ). The three ACCs were packed in hybrid UASB reactors and seeded with anaerobic granular sludge for biotransformation experiments. The results indicated that ACC-packed bioreactors improved the biotransformation of 4NP by twofold as compared to the control reactor without support materials. However, the biotransformation effciency of AW, OX and AQ was very similar (59%), indicating the role of ACC as biofilm support and not as redox mediator. After 4NP biotransformation several physicochemical and biological changes were observed like (1) the point of zero charge (pHPZC) shift from acidic values (AW = 5.0, OX = 3.4, AQ = 3.1) to neutral values (pHPZC = 7.6 on average), (2) increase in the concentration of acidic and basic surface functional groups over ACC materials and the amount of supported biomass on ACCs due to biofilm formation, and (3) enrichment of exoelectrogenic microorganisms belonging to the genera Geobacter over carbonyl-rich ACC surface as revealed by 16S rRNA amplicon sequencing. Overall, the results suggest that chemical modifications of ACCs changed the microbial composition of the biofilm, but the higher concentration of carbonyl groups on ACC did not affect the biotransformation of 4NP.

Electrochemical properties of the interaction between cytochrome c and a hematite nanowire array electrode

We investigate the interaction of horse heart cytochrome c (cyt c) with hematite nanowire array electrodes by cyclic voltammetry to study the electron transfer between redox active proteins and mineral surfaces. Using this model system, we quantify electron transfer rates between cyt c and hematite under varying electric potential and pH conditions. The results are consistent with two cyt c conformations adsorbed at the hematite surface: the native and a partially unfolded form. The partially unfolded protein maintained redox activity, but at a lower redox potential than the native protein. Adsorption of cyt c allowed direct electron transfer between cyt c and hematite, with an interfacial electron transfer rate, k°ET, of 0.4 s−1 for the native form and 0.55 s−1 for the partially unfolded protein at pH 7.07. At pH 4.66, protein adsorption decreased compared to neutral pH and the fraction of partially unfolded protein increased. Additionally, the diffusion controlled electron transfer rate between hematite and the electron shuttling compound anthraquinone-2,6-disulfonate (AQDS) was determined to be k°ET = 8.0·10−3 cm·s−1 at pH 7.07. Modulation of electron transfer rates as a result of conformational changes by redox active proteins has broad implications for describing chemical transformations at biological-mineral interfaces.

The Study of Electron Transfer at the Interface of Cytochromes and Iron Oxide Minerals

Molecular-scale protein-mineral interactions are central to understanding electron transfer mechanisms and microbial processes in subsurface environments. Although, the electron transfer between c-type cytochrome and hematite has been investigated many factors impacting the electron transfer rate have not been determined. We investigated the interactions of horse heart cytochrome c (cyt c) with hematite nanowire array electrodes by cyclic voltammetry to study the electron transfer between redox active proteins and mineral surfaces. Using this model system, specific interactions of cyt c with hematite as a function of electrical potential and pH were examined. We observed direct electron transfer between cyt c and hematite with an interfacial electron transfer rate of kº ET = 0.6 s-1. show buffer pH has an apparent effect on the conformational and adsorption-induced change on the cyt c. Moreover, in the presence of the electron shuttling compound, anthraquinone-2,6-disulfonate (AQDS), electron transfer rate between cyt c and hematite increased to kº ET = 2 s-1, which is more than three times of the rate determined in absence of AQDS. This study provides into biomolecular factors controlling the complex interactions and electron transfer processes between redox-active proteins and minerals, which has broader implications for describing chemical transformations at biological-mineral interfaces at the molecular scale.

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.

The role of electron shuttle enhances Fe(III)-mediated reduction of Cr(VI) by Shewanella oneidensis MR-1.

Chromate is one of the hazardous toxic pollutants. Reduction of Cr(VI) to Cr(III) has shown to reduce the toxicity of chromate. This work examined the reduction of Cr(VI) using an anaerobic batch cultures of Shewanella oneidensis MR-1 containing Fe(III). To do so, 10mg/L Cr(VI) was reduced to Cr(III) within 3days along with the oxidization of Fe(II) to Fe(III). The removal rate of Cr(VI) increased with increasing the concentration of Fe(III). In the absence of Cr(VI), the Fe(II) concentration of the batch culture increased with the growth of S. oneidensis MR-1. These data showed that S. oneidensis MR-1 could reduce Fe(III) into Fe(II), resulting in reduction of Cr(VI) to Cr(III). During this process, the anthraquinone-2,6-disulfonate (AQDS) acted as an electron shuttle. Microscopic analysis showed that Cr(VI) had toxic effects on S. oneidensis MR-1 due to the appearance of Cr species on the bacterial surface. Cr2O3 or Cr(OH)3 precipitates formed during Cr(VI) reduction was identified using X-ray photoelectron spectroscopy. The AQDS as an electron shuttle enhanced the Cr(VI) reduction by S. oneidensis MR-1. Microbial reduction of Cr(VI) can be a useful technique for Cr detoxification.