Redox Interactions Research Articles

Enhanced oxidation of tetrachloroethylene by Fenton reaction during interaction between nano-hematite and glutathione

The enhancement of oxidation of tetrachloroethylene (PCE) by the redox interaction between nano-hematite (nano-Fe2O3) and glutathione(GSH) was investigated. This study revealed the oxidation of PCE by the nano-Fe2O3-GSH occurred via Fenton-like reaction to initiate the formation of OH• and O2‾• radicals. The oxidation kinetic of PCE by the nano-Fe2O3-GSH was enhanced by 600 times greater (0.014 ± 0.003 hr−1) than that by the nano-Fe2O3 alone (0.00023 ± 0.00008 hr−1). The GSH played an important role as the catalyst to enhance redox reaction of Fe3+ to Fe2+ and promoted the formation of OH• and O2‾• radicals at netural and alkaline conditions. The reactivity of GSH was significantly increased at alkaline condition due to the high nucleophilicity of -SH. PCE was completely transformed to oxalic acid in the nano-Fe2O3-GSH suspension. This study provides new knowledge on the redox interaction between nano-Fe2O3 and GSH as a significant reaction mechanism to enhance the oxidation of PCE.

Pharmacokinetic profiles, cytotoxicity, and redox metabolism of free and nanoencapsulated curcumin

To analyze the biodistribution, pharmacokinetics, and toxicity of curcumin, we made in silico predictions and performed in vitro tests to demonstrate the differences in the behavior of two cells types (peripheral blood mononuclear cells, PBMCs, and fibroblasts, HFF-1 cell line) treated with curcumin nanocapsule formulations and curcumin solution with respect to cytotoxic effects and redox metabolism. We generated in silico, ADME/Tox profile predictions of curcumin using computational tools. We produced and characterized Eudragit® L-100 and PCL nanocapsules containing curcumin using interfacial deposition of preformed polymer, evaluation of hemolytic potential in erythrocytes, cytotoxic capacity (MTT and dsDNA PicoGreen® assay), and influence on redox metabolism (nitric oxide and DCF production) of PBMCs and HFF-1 treated with curcumin nanoformulations and solution response curves. Computational results showed low biodistribution, no permeation at of the blood-brain barrier (BBB), discreet gastrointestinal absorption, a potential inhibitor of cytochrome P450 isoforms (CYP2C9 and CYP3A4), toxicity class IV, and immunomodulatory action. In vitro tests showed that cell type influenced curcumin behavior. For cytotoxicity, PBMCs showed a concentration-dependent standard, while HFF-1 cells showed that incubation time was an important variable. Redox interactions showed that nanocapsules induced NO production, and all treatments reduced DCF levels. We highlight the pleiotropic biological activities of curcumin and drug release models so that the therapeutic properties of this polyphenol might be better used. Finally, we emphasize that pharmacological safety must always be evaluated in drug delivery systems and, especially, for substances with multiple interaction pathways.

Mechano-Redox Control of Integrins in Thromboinflammation.

Significance: How mechanical forces and biochemical cues are coupled remains a miracle for many biological processes. Integrins, well-known adhesion receptors, sense changes in mechanical forces and reduction-oxidation reactions (redox) in their environment to mediate their adhesive function. The coupling of mechanical and redox function is a new area of investigation. Disturbance of normal mechanical forces and the redox balance occurs in thromboinflammatory conditions; atherosclerotic plaques create changes to the mechanical forces in the circulation. Diabetes induces redox changes in the circulation by the production of reactive oxygen species and vascular inflammation. Recent Advances: Integrins sense changes in the blood flow shear stress at the level of focal adhesions and respond to flow and traction forces by increased signaling. Talin, the integrin-actin linker, is a traction force sensor and adaptor. Oxidation and reduction of integrin disulfide bonds regulate their adhesion. A conserved disulfide bond in integrin αlpha IIb beta 3 (αIIbβ3) is directly reduced by the thiol oxidoreductase endoplasmic reticulum protein 5 (ERp5) under shear stress. Critical Issues: The coordination of mechano-redox events between the extracellular and intracellular compartments is an active area of investigation. Another fundamental issue is to determine the spatiotemporal arrangement of key regulators of integrins' mechanical and redox interactions. How thromboinflammatory conditions lead to mechanoredox uncoupling is relatively unexplored. Future Directions: Integrated approaches, involving disulfide bond biochemistry, microfluidic assays, and dynamic force spectroscopy, will aid in showing that cell adhesion constitutes a crossroad of mechano- and redox biology, within the same molecule, the integrin. Antioxid. Redox Signal. 37, 1072-1093.

Redox Interaction between Selenite and Mackinawite in Cement Pore Water.

In cement-rich radioactive waste repositories, mackinawite (FeS) forms at the steel corrosion interface within reinforced concrete and potentially retards the transport of redox-sensitive radionuclides (e.g., 79Se) in porous cement media. Redox interactions between selenite and mackinawite under hyperalkaline conditions remain unclear and require further investigations. Here, using comprehensive characterization on both aqueous and solid speciation, we successfully monitored the whole interaction process between selenite and mackinawite under hyperalkaline conditions. The results show similar chemical environments for SeO32- and S2-/Sn2- at the mackinawite-water interface, verifying an immediate reduction. After 192 h of reaction, SeO32- was reduced to solid Se0 and SeS2 species, accompanied by the oxidation of S2-/Sn2- to S2O32- and Fe(II) to Fe(III) in mackinawite. Aqueous speciation results showed that ∼99% of aqueous selenium was present as Se4S nanoparticles due to the dissolution of Se from the solid. In parallel, ∼62% of S2-/Sn2- was released into the solution, with mackinawite transforming into magnetite, Fe(OH)3 and FeS2O3+ complexed to Cl- or OH- species, and magnetite subsequently dispersed in the solution. This study provides valuable data about the retardation mechanisms of redox-sensitive radionuclides by soluble iron sulfides, which is critical to advance our understanding of reactive concrete barriers used in nuclear waste disposal systems.

Electroactive biofilms: how microbial electron transfer enables bioelectrochemical applications.

Microbial biofilms are ubiquitous. In marine and freshwater ecosystems, microbe–mineral interactions sustain biogeochemical cycles, while biofilms found on plants and animals can range from pathogens to commensals. Moreover, biofouling and biocorrosion represent significant challenges to industry. Bioprocessing is an opportunity to take advantage of biofilms and harness their utility as a chassis for biocommodity production. Electrochemical bioreactors have numerous potential applications, including wastewater treatment and commodity production. The literature examining these applications has demonstrated that the cell–surface interface is vital to facilitating these processes. Therefore, it is necessary to understand the state of knowledge regarding biofilms’ role in bioprocessing. This mini-review discusses bacterial biofilm formation, cell–surface redox interactions, and the role of microbial electron transfer in bioprocesses. It also highlights some current goals and challenges with respect to microbe-mediated bioprocessing and future perspectives.

Psoriasis between Autoimmunity and Oxidative Stress: Changes Induced by Different Therapeutic Approaches.

Psoriasis is defined as chronic, immune-mediated disease. Regardless of the development of new therapeutic approaches, the precise etiology of psoriasis remains unknown and speculative. The aim of this review was to systematize the results of previous research on the role of oxidative stress and aberrant immune response in the pathogenesis of psoriasis, as well as the impact of certain therapeutic modalities on the oxidative status in patients with psoriasis. Complex immune pathways of both the innate and adaptive immune systems appear to be major pathomechanisms in the development of psoriasis. Oxidative stress represents another important contributor to the pathophysiology of disease, and the redox imbalance in psoriasis has been reported in skin cells and, systemically, in plasma and blood cells, and more recently, also in saliva. Current immune model of psoriasis begins with activation of immune system in susceptible person by some environmental factor and loss of immune tolerance to psoriasis autoantigens. Increased production of IL-17 appears to be the most prominent role in psoriasis pathogenesis, while IL-23 is recognized as master regulator in psoriasis having a specific role in cross bridging the production of IL-17 by innate and acquired immunity. Other proinflammatory cytokines, including IFN-γ, TNF-α, IL-1β, IL-6, IL-22, IL-26, IL-29, or IL-36, have also been reported to play important roles in the development of psoriasis. Oxidative stress can promote inflammation through several signaling pathways. The most noticeable and most powerful antioxidative effects exert various biologics compared to more convenient therapeutic modalities, such as methotrexate or phototherapy. The complex interaction of redox, immune, and inflammatory signaling pathways should be focused on further researches tackling the pathophysiology of psoriasis, while antioxidative supplementation could be the solution in some refractory cases of the disease.

Cu- and Ce-promoted nano-heterostructures on vanadate catalysts for low-temperature NH3–SCR activity with improved SO2 and water resistance

The objective of this study was to demonstrate a facile strategy for vanadate-based catalysts having high NOx conversion efficiency (∼96% @ 220 °C) and improved SO2 resistance by impregnating highly-dispersed CuO–CeO2 nano-heterostructures to V2O5–CeO2–WO3/TiO2 catalysts. The key design of catalysts was based on the maximization of interface chemistry towards synergetic effects of catalytic and redox reactions between Cu and Ce species. The impregnation of 0.1 wt% CuO–CeO2 possessed more surface acid sites and enhanced redox ability at low temperatures (180–220 °C). Based on Gibbs energy calculation and XPS results, thermodynamically favorable reaction of Cu2+ + Ce3+ → Cu+ + Ce4+ made it a perfect candidate for an excellent redox system with V4+/V5+ charge imbalance proportion through electron migration at the adjacent interface. The strong redox interaction and facile electron transfer could also restrain the formation of surface sulfate species and showed an excellent SO2 and water tolerance.

Generation of Strong Basicity in Metal-Organic Frameworks: How Do Coordination Solvents Matter?

Solid strong bases with an ordered pore structure (OPS-SSBs) have attracted much attention because of their high catalytic activity and shape selectivity as heterogeneous catalysts in various reactions. Nevertheless, high temperatures are required to fabricate OPS-SSBs by using traditional methods. Herein, we report for the first time that the coordination solvents affect basicity generation in metal-organic frameworks (MOFs) greatly and that strong basicity can be formed at comparatively low temperatures. A typical MOF, MIL-53, was employed, and three different solvents, namely, water, methanol, and N,N-dimethylformamide (DMF), were coordinated, respectively, by means of solvent exchange. Thermogravimetry-mass spectrometer analysis shows that the conversion temperature of base precursor KNO3 is quite different on MIL-53 coordinated with different solvents. The conversion of KNO3 to basic sites takes place at 350, 300, and 250 °C on MIL-53 coordinated with water, methanol, and DMF, respectively. It is fascinating to observe the generation temperature of strongly basic sites at 250 °C, which is noticeably lower than that on various supports, such as mesoporous silica SBA-15 (600 °C), zeolite Y (700 °C), and metal oxide ZrO2 (730 °C). This is due to the redox interaction between coordination solvents and KNO3, leading to a significant decrease in the temperature for KNO3 conversion. Consequently, OPS-SSBs were prepared successfully with an ordered pore structure and strong basicity. The obtained OPS-SSBs show good shape selectivity in Knoevenagel condensation of aromatic aldehydes with different active methylene compounds. Moreover, these solid bases are highly active in the synthesis of dimethyl carbonate through transesterification reaction. This work might open up a new avenue for the fabrication of various functional materials at low temperatures through redox interactions.

Amyloid beta peptides electrochemistry: A review

Alzheimer disease is a progressive age-related neurodegenerative disorder estimated to affect up to 107 million people by 2050, its pathology is associated with the dysfunction of the amyloid beta (Aβ) peptide mechanism, among others. Electrochemical methods were successfully applied for Aβ electrochemical characterisation and have received increased attention in Aβ research. This review discusses the recent advances on the direct electrochemical detection of Aβ redox mechanisms, fibrilization and interaction with metal ions based on the electrochemical detection of the Aβ′s , and amino acid residues oxidation peaks.

Investigating the adsorption behavior and mechanism of Eu(III) and Au(III) on β-cyclodextrin/polyethylenimine functionalized waste paper

A bio-adsorbent (DAWP-PEI-β-CD) was facilely prepared by introducing polyethylenimine (PEI) and β-cyclodextrin (β-CD) into dialdehyde waste paper (DAWP) via a facile two-step method. The structures, morphologies and compositions of the as-prepared adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), solid state nuclear magnetic resonance spectrometry (NMR) and X-ray photoelectron spectroscopy (XPS) techniques. Results showed that the pH values, adsorption temperature and contact time played a vital role in uptake of Eu(III) and Au(III). Meanwhile, the adsorption behavior of Eu(III) and Au(III) could be fitted felicitously with the Langmuir and the pseudo-second-order models, and the maximum adsorption capacities of Eu(III) (pH = 6.0) and Au(III) (pH = 2.0) onto DAWP-PEI-β-CD were 424.2 and 241.3 mg/g, respectively. Further advanced spectroscopy analysis revealed that the elimination of Eu(III) was attributed to host-guest inclusion and surface complexation interaction, while adsorption of Au(III) might stem from a combination of electrostatic attraction, chelation, host-guest inclusion and redox interaction. This study demonstrated that DAWP-PEI-β-CD was a promising environmental functional material to separation and enrichment of Eu(III) and Au(III) from contaminated water.

Solvent-Free Method for Nanoparticles Synthesis by Solid-State Combustion Using Tetra(Imidazole)Copper(II) Nitrate

The development of solvent-free techniques for nanoparticles synthesis is one of the challenges of Green chemistry. In this work, the principled opportunity to obtain copper-containing nanosized particles without use of any solvents was shown. The copper complexes were prepared as precursors by the melting-assisted solvent-free synthesis. The formation of tetra(imidazole)copper(II) nitrate complex was confirmed by XRD, elemental analysis, FTIR spectroscopy, and thermal analysis. It was noted that their thermal decomposition occurs in two stages: (I) the low-temperature step may be related to redox interaction between organic ligands and nitrate-anions; (II) the high-temperature step may be related to the oxidation of the products of incomplete imidazole decomposition. TEM and XRD studies of solid products of complex combustion have shown that they are oxides with particle size less than 40 nm. Thus, the combustion of [Cu(Im)4](NO3)2 complex under air can be considered as a new approach to prepare nanosized particles of copper oxides without the use of solvents.

Способ очистки почвы и воды от тяжелых металлов и устройства для его осуществления

The work is based on the results of studies conducted on the effectiveness of the application for the purposeful transformation of the composition of harmful emissions by neutralizing the impurities included in them. And also researched and developed the process of cleaning and neutralizing the soil from heavy metals, by exposure to strong electric fields and discharges. The results of a quantitative analysis of soil samples taken from oil fields, bottom sediments of the Aras River cleaned before and after ordinary water are presented. According to the results, the content of heavy metals in the initial soils exceeds the maximum permissible concentration (MPC). The content of Mn, Mo, Cu, Al in the waters and bottom sediments of the Aras River also exceeds the MPC. The possibility of cleaning the soil from a certain name of heavy metals by exposure to ozone water has been revealed. Experiments on soil and water ozonation at voltages of 8 kV and 14 kV for 30 minutes showed a significant decrease in the concentration of heavy metals. The results of cleaning soil samples before and after treatment with ozonated water were checked with an inductively coupled plasma mass spectrometer.мThe process of chemical oxidation of pollutants in soils, soils, underground and surface waters is based on the release of electrons from the outer unstable layer of the electron shell of atoms of substances and elements, which leads to the transition of the pollutant into a less toxic and reactive form. Atoms of elements that have a small number of electrons in the outer electron layer tend to give up electrons. The process is an integral part of the redox interaction between the contaminant and the chemical or reactive surface.

HOCH2CH2NH2 – TROPEOLIN OOO – H2O SYSTEM ACID-BASIC PROPERTIES IN THE PRESENCE OF HCl, HClO4, H2SO4 AND SO2H2O

The influence of hydrochloric, chloric, sulfuric and sulfurous acids (HCl, HClO4, H2SO4 and SO2×H2O, respectively) on protolytic equilibria in the system monoethanolamine (MEA) – tropeolin OOO (TrOOO) – water (CMEA = 0.1 M; pH = 1.0 ÷ 9.5) was studied by pH-metric, spectrophotometric and colorimetric methods. The acid-base behavior of the HOCH2CH2NH2 – TrOOO – H2O system was investigated at CTrOOO = 1,12 ×10-4 М, CMEA = 1,0×10-4 ÷ 1,0 М (pH = 8,25 ÷ 12,05), T = 293 K. TrOOO in this system exists in two tautomeric forms due to acid-base dissociation of the 4-OH group and associates formed by H-bonding with MEA molecules. There is a direct ratio between the pH values ​​of solutions and the total color difference (ΔE76), in contrast to the specific color difference (SCD). The difference in the behavior of the H2SO4 – HOCH2CH2NH2 – TrOOO – H2O system from the systems with HCl and HClO4 is due to the fact that the interaction of the first acid with MEA (8,0 £ pH) forms an ionic associate [HOCH2СH2NH3]2(SO4), which is more stable than ionic pairs [[HOCH2СH2NH3](HSO4), [HOCH2СH2NH3](ClO4), [HOCH2СH2NH3]Cl и [HOCH2СH2NH3](O3S-C­10H6-N=N-C6H4-SO3)[H3NCH2СH2OH]. Acid-base dissociation constants in systems significantly depend on the structure and physicochemical parameters of the mineral acid. In the electronic absorption spectra of the SO2 – MEA – TrOOO – H2O system (pH £ 7,5), there is a pronounced isobestic point at 415 nm, due to the dynamic equilibrium between ion-molecular forms. The coincidence of the maxima on the curves ΔE76 = f(pH) and SCD = f(pH) for the indicated system, in contrast to others studied in this work, was stated. The difference between the spectrophotometric and colorimetric behavior of the SO2 – MEA – TrOOO – H2O system from behavior of the systems with HCl, HClO4, and H2SO4 systems is due to the sulfur(IV)oxyanions with an azo indicator redox interaction.

Fluorescent porous organic cage with good water solubility for ratiometric sensing of gold(III) ion in aqueous solution

Fluorescent porous organic cage with good water solubility is of great interest but still challenging for its fluorescent sensing application. Poor water solubility and single signal of most previous probes are unfavorable for the monitoring of Au3+ generated from the potential dissociation of gold nanoparticles in environmental and biological samples. Here we report a water-soluble porous organic cage as a ratiometric fluorescent probe for Au3+ in aqueous solution. The prepared porous organic cage with good water solubility showed specific redox interaction with Au3+ in pH 5, leading to the change of dual emission at 420 and 484 nm. Based on the change of fluorescence ratio, a simple ratiometric sensing method for Au3+ from the dissociation of gold nanoparticles in aqueous solution was developed. The proposed method gave a calibration function of F484/F420 = 0.0370[Au3+] + 0.5689 (where F484/F420 is the intensity ratio of fluorescence at 484 nm to that at 420 nm; [Au3+] in μM) (R2 = 0.9975) in the concentration range of 1–60 μM, the limit of detection (3s) of 8 nM, and the relative standard deviation of 0.26% for 10 replicate detections of 50 μM Au3+. The recoveries of spiked Au3+ in domestic wastewater and human serum samples ranged from 94.66% to 105.61%.

Sharp luminescent violet- and blue-emitting stable (Eu3+ → Eu2+: PPA):SiO2 sonogel hybrid glasses: Synthesis, structural and overall photophysical characterizations

Nanostructured Eu2O3:Polyphenylacetylene (Eu2O3:PPA) complexes prepared at different lanthanide content were synthesized as active ligand–to–metal charge–transfer (LMCT) systems. These phosphors were embedded into mesoporous a–SiO2 sonogel hosting networks at different dopant ratios to obtain luminescent (Eu2O3:PPA):SiO2 monolith glasses. The electroactive sonochemical medium of the colloidal sol–phase activates massive Eu3+→Eu2+ self–reduction processes along the polycondensation reaction of the doped emulsions, giving rise to sharp violet (407 nm) and blue (470 nm) PL–emission bands (FWHM ≤18 nm). The unusual violet–lines arise from the 4f65d1→4f7 transitions of Eu2+ ions to produce intense 6P7/2 → 8S7/2 emissions, while the blue–lines are ascribed to overlapping 5D2→7Fj (j = 0, 1) transitions of remanent Eu3+ ions assisted by LMCT and interionic energy transfers. The CIE coordinates of these composites lay within the light violet/blue region and the bandgap energy was reduced up to 2.16 eV for increasing Eu2O3 concentration. Our experimental approach shows that the Eu3+→Eu2+ process occurs at room temperature material processing, without the use of reducing atmospheres, stimulated UV photoreduction, or post–doping functionalization. Results suggest that guest–host redox interactions and Eu/SiO2 surface–assisted mechanisms are responsible for accomplishing a homogeneous self–reduction and the structuring of steady Eu2+–silicates. Extensive morphological, structural, linear and NLO spectroscopic characterizations, CIE–chromaticity, and energy bandgap evaluations, were performed to explore these novel nanostructured composites' physicochemical and photophysical properties, pointing out potential applications in tunable phosphor devices.

The Damaging Outcome of the POLAR Phase III Trials Was Due to Avoidable Time-Dependent Redox Interaction between Oxaliplatin and PledOx.

On 2 July 2021, highly negative results were reported from the POLAR A and M phase III trials in patients with colorectal cancer, treated with an oxaliplatin-based regimen and co-treated with calmangafodipir (CaM; PledOx®; PledPharma AB/Egetis Therapeutics AB) or placebo. The results revealed persistent chemotherapy-induced peripheral neuropathy (CIPN) in 54.8% of the patients treated with PledOx, compared with 40.0% of the patients treated with the placebo (p < 0.05), i.e., a 37% increase in incidence of the side effect that the trial was aimed to prevent. The damaging outcome of the trials differed diametrically from an in-parallel conducted mice study and from a clinical trial with mangafodipir, the active ingredient of CaM. According to the authors of the POLAR report, the etiology of the profound increase in CIPN in the PledOx arm is unclear. However, these devastating effects are presumably explained by intravenous administrations of PledOx and oxaliplatin being too close in time and, thereby, causing unfavorable redox interactions between Mn2+ and Pt2−. In the mice study as well as in the preceding phase II clinical trial (PLIANT), PledOx was administered 10 min before the start of the oxaliplatin infusion; this was clearly an administration procedure, where the devastating interactions between PledOx and oxaliplatin could be avoided. However, when it comes to the POLAR trials, PledOx was administered, for incomprehensible reasons, “on Top of Modified FOLFOX6” at day one, i.e., after the two-hour oxaliplatin infusion instead of before oxaliplatin. This is a time point when the plasma concentration of oxaliplatin and Pt2+-metabolites is at its highest, and where the risk of devastating redox interactions between PledOx and oxaliplatin, in turn, is at its highest.

Experimental Modeling of Ankerite–Pyrite Interaction under Lithospheric Mantle P–T Parameters: Implications for Graphite Formation as a Result of Ankerite Sulfidation

Experimental modeling of ankerite–pyrite interaction was carried out on a multi-anvil high-pressure apparatus of a “split sphere” type (6.3 GPa, 1050–1550 °C, 20–60 h). At T ≤ 1250 °C, the formation of pyrrhotite, dolomite, magnesite, and metastable graphite was established. At higher temperatures, the generation of two immiscible melts (carbonate and sulfide ones), as well as graphite crystallization and diamond growth on seeds, occurred. It was established that the decrease in iron concentration in ankerite occurs by extraction of iron by sulfide and leads to the formation of pyrrhotite or sulfide melt, with corresponding ankerite breakdown into dolomite and magnesite. Further redox interaction of Ca,Mg,Fe carbonates with pyrrhotite (or between carbonate and sulfide melts) results in the carbonate reduction to C0 and metastable graphite formation (±diamond growth on seeds). It was established that the ankerite–pyrite interaction, which can occur in a downgoing slab, involves ankerite sulfidation that triggers further graphite-forming redox reactions and can be one of the scenarios of the elemental carbon formation under subduction settings.

Oxidation of V(IV) by Birnessite: Kinetics and Surface Complexation.

Vanadium is a redox-active metal that has been added to the EPA's Contaminant Candidate List with a notification level of 50 μg L-1 due to mounting evidence that VV exposure can lead to adverse health outcomes. Groundwater V concentration exceeds the notification level in many locations, yet geochemical controls on its mobility are poorly understood. Here, we examined the redox interaction between VIV and birnessite (MnO2), a well-characterized oxidant and a scavenger of many trace metals. In our findings, birnessite quickly oxidized sparingly soluble VIV species such as häggite [V2O3(OH)2] into highly mobile and toxic vanadate (HnVO4(3-n)-) in continuously stirred batch reactors under neutral pH conditions. Synchrotron X-ray absorption spectroscopic (XAS) analysis of in situ and ex situ experiments showed that oxidation of VIV occurs in two stages, which are both rapid relative to the measured dissolution rate of the VIV solid. Concomitantly, the reduction of birnessite during VIV oxidation generated soluble MnII, which led to the formation of the MnIII oxyhydroxide feitknechtite (β-MnOOH) upon back-reaction with birnessite. XAS analysis confirmed a bidentate-mononuclear edge-sharing complex formed between VV and birnessite, although retention of VV was minimal relative to the aqueous quantities generated. In summary, we demonstrate that Mn oxides are effective oxidants of VIV in the environment with the potential to increase dissolved V concentrations in aquifers subject to redox oscillations.

Redox transformation of structural iron in nontronite induced by quinones under anoxic conditions

In natural anoxic subsurface environments, the geochemical cycles of iron are largely associated with the migration and transformation of organic matter. Intensive attention has been paid to the redox interaction of organic matter with aqueous Fe and iron (hydr)oxides. Whereas, the abiotic redox cycling of structural Fe in clay minerals induced by quinones has not been well understood. In this study, we selected nontronite (NAu-2) as a model Fe-bearing phyllosilicate clay mineral and 1,4-hydroquinone (H2Q)/1,4-benquinone (BQ) as a model quinone couple. Our results show that the structural Fe(III) in NAu-2, with tetrahedral Fe(III) priority, can oxidize H2Q into BQ, and octahedral Fe(II) in NAu-2 can reduce BQ to H2Q, with semiquinone radicals (SQ−) as intermediate. The extent of the redox reactions depends on the reduction potential difference between NAu-2 and H2Q/BQ. However, a fraction of Fe(II)-Fe(III)-OH and Fe(II)-Fe(II)-OH groups in the octahedral sheet are difficult to be oxidized by BQ, because the reduction potential gradient decreases to a low level as the reaction proceeds. And the structure of NAu-2 can only partially restored upon re-oxidation with tetrahedral Fe(III) irreversibility. Output of this study replenishes the understanding regarding redox cycling of structural Fe in clay minerals induced by quinones.

Specificity of Small c-Type Cytochromes in Anaerobic Ammonium Oxidation

Anaerobic ammonium oxidation (anammox) is a bacterial process in which ammonium and nitrite are combined into dinitrogen gas and water, yielding energy for the cell. This process relies on a series of redox reactions catalyzed by a set of enzymes, with electrons being shuttled to and from these enzymes, likely by small cytochrome c proteins. For this system to work productively, these electron carriers require a degree of specificity toward the various possible redox partners they encounter in the cell. Here, we compare two cytochrome c proteins from the anammox model organism Kuenenia stuttgartiensis. We show that they are highly homologous, are expressed at comparable levels, share the same fold, and display highly similar redox potentials, yet one of them accepts electrons from the metabolic enzyme hydroxylamine oxidase (HAO) efficiently, whereas the other does not. An analysis of the crystal structures supplemented by Monte Carlo simulations of the transient redox interactions suggests that this difference is at least partly due to the electrostatic field surrounding the proteins, illustrating one way in which the electron carriers in anammox could attain the required specificity. Moreover, the simulations suggest a different “outlet” for electrons on HAO than has traditionally been assumed.