Mediated Redox Reactions Research Articles

A highly stretchable and self-adhesive cellulose complex hydrogels based on PDA@Fe3+ mediated redox reaction for strain sensor

As the application of conductive hydrogels in the field of wearable smart devices is gradually deepening, a variety of hydrogel sensors with high mechanical properties, strong adhesion, fast self-healing, and excellent conductivity are emerging. However, it is still a great challenge to manufacture hydrogel sensors combining multiple properties. Herein, we leveraged the dynamic redox reaction occurring between polydopamine (PDA) and Fe3+ to induce ammonium persulfate (APS) to generate free radicals, thereby initiating the copolymerization of hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) monomers. Then, polypyrrole-encapsulated cellulose nanofibers (PPy@CNF) and carboxymethylcellulose (CMC) were incorporated as conductive reinforced nanofillers and interpenetrating network skeleton. The obtained hydrogel cross-linked through reversible metal-ligand bonds, π-π stacking and abundant hydrogen bonding demonstrated great mechanical properties (strength 240.4 kPa, strain 1175 %) and self-healing ability (88.96 %). Particularly, the gel displayed ultrahigh durability and skin adhesive ability (75 kPa after 10 cycles), surpassing previous skin adhesion hydrogels. Furthermore, through the synergistic conductive effect of PPy@CNF and Fe3+, the prepared hydrogel sensor possessed high sensitivity (GF = 1.89) with a wide sensing range (~1000 %), which could realize the human body's daily motion detection, and had a promising application in flexible wearable electronics.

Organic carbon oxidation and the associated pyrite formation in deep sediments at the Nankai subduction zone

The preservation of organic carbon (OC) in marine sediments is crucial for Earth's climate by sequestering CO2. While OC is mostly remineralized before it reaches the seafloor, a notable fraction is buried in deep-sea sediments, particularly at subduction zones known for their enhanced sedimentation rates that promote OC burial. The mechanisms behind OC recycling and decomposition within subduction zone sediments are governed by biologically mediated redox reactions involving a range of electron acceptors, which facilitate the sequential oxidation of OC. However, direct evidence regarding such effects on OC in deep sediments remains limited. In this study, we examine the contents of pyrite and trace metals of molybdenum (Mo), vanadium (V), and cesium (Cs) in organic-rich deep sediments from the Nankai subduction zone. We find that the pyrite, sulfate, diagenetic illite, and OC contents covary in Unit V, highlighting the important role of organoclastic sulfate reduction and biotic smectite-to-illite reaction at 60–70 °C in OC oxidation and pyrite formation. The profiles of Mo, V, and Cs also align with these processes in the same interval. Our findings contribute to an in-depth understanding of OC dynamics in subduction zones, emphasizing the complex interactions within deep sediments that may influence the global carbon cycle.

Nano-wired polyaniline/VS2 composite materials for quasi-solid-state supercapacitor and zinc-ion battery applications

A nano-wired polyaniline/VS2 network morphology mediated redox reactions of V and improved the overall conductivity to deliver a promising capacity and long-term cyclability in energy storage devices (QSSCs and ZIBs).

Bacteria-derived topologies of Cu2O nanozymes exert a variable antibacterial effect.

The ability of bacteria to facilitate fabrication of nanomaterials has been adapted towards bacterial sensing applications. In this work, we fabricate spherical, cubic and truncated octahedron topologies of Cu2O nanoparticles via E. coli-facilitated redox reaction in an electrochemical setup. The Cu2O nanoparticles exhibit cytochrome c oxidase-like activity with the spherical topology displaying higher catalytic rate compared to the other geometries. The topology-dependent catalytic behavior of Cu2O nanoparticles has not been reported previously. The Cu2O nanozymes also display E. coli killing activity in a topology-correlated manner. The E. coli mediated redox reaction in an electrochemical setup is being reported for the first time for synthesis of different topologies of Cu2O which also exert a variable antibacterial effect.

Semi-rational engineering membrane binding domain of L-amino acid deaminase from Proteus vulgaris for enhanced α-ketoisocaproate

α-Keto acids are important raw materials for pharmaceuticals and functional foods, which could be produced from cheap feed stock by whole cell biocatalysts containing L-amino acid deaminases (L-AADs). However, the production capacity is limited by the low activity of L-AADs. The L-AAD mediated redox reaction employs the electron transport chain to transfer electrons from the reduced FADH2 to O2, implying that the interaction between L-AAD and the cell membrane affects its catalytic activity. To improve the catalytic activity of L-AAD from Proteus vulgaris, we redesigned the membrane-bound hydrophobic insertion sequences (INS, residues 325–375) by saturation mutagenesis and high-throughput screening. Mutants D340N and L363N exhibited higher affinity and catalytic efficiency for L-leucine, with half-life 1.62-fold and 1.28-fold longer than that of wild-type L-AAD. D340N catalyzed L-leucine to produce 81.21 g⋅L–1 α-ketoisocaproate, with a bioconversion rate of 89.06%, which was 17.57% higher than that of the wild-type. It is predicted that the mutations enhanced the interaction between the protein and the cell membrane.

Synthesis and characterization of new multiferroic (BiBa)(FeTi2)O8

The present communication reports the study of various properties (i.e., structural, electrical, dielectric, ferroelectric, and magnetic) of new multiferroic: (BiBa)(FeTi2)O8 synthesized by a mixed oxide reaction route. The analysis of the X-ray diffraction profile at room temperature ensures its phase formation in the orthorhombic crystal structure. The micrographic study divulges irregular shape grains (mostly rectangular) with an average grain size of 3.5 μm. The compositional study displays the desired stoichiometry. The study of electrical (impedance, modulus, and conductivity) and dielectric properties (dielectric constant and tangent loss) of the sample at different temperatures (RT – 773 K) and electric field frequency (1 kHz-1MHz) provides many new experimental data, and insight mechanisms. The temperature dependence of the dielectric constant exhibits a dielectric anomaly around 523 K that may be due to the combined effect of oxygen vacancy mediated redox reaction (Fe3+→Fe2+ and Ti4+→Ti3+) and Maxwell-Wagner polarization. The loss tangent follows a similar trend to that of the dielectric constant except for an additional low-frequency relaxation peak of about 543 K. The dielectric loss tangent exhibits low value in low temperature and high-frequency regions, indicating that the sample can be a potential candidate for data storage devices. The ferroelectric recording shows a non-linear PE loop at room temperature. The room temperature magnetic recordings show evidence of weak ferromagnetism due to suppression of spiral spin structure as opposed to the antiferromagnetic nature of BiFeO3. The coexistence of these unique features enables the synthesized sample to be used in voltage-controlled data storage devices.

Correlation Between Fe/S/As Speciation Transformation and Depth Distribution of Acidithiobacillus ferrooxidans and Acidiphilium acidophilum in Simulated Acidic Water Column.

It is well known that speciation transformations of As(III) vs. As(V) in acid mine drainage (AMD) are mainly driven by microbially mediated redox reactions of Fe and S. However, these processes are rarely investigated. In this study, columns containing mine water were inoculated with two typical acidophilic Fe/S-oxidizing/reducing bacteria [the chemoautotrophic Acidithiobacillus (At.) ferrooxidans and the heterotrophic Acidiphilium (Aph.) acidophilum], and three typical energy substrates (Fe2+, S0, and glucose) and two concentrations of As(III) (2.0 and 4.5 mM) were added. The correlation between Fe/S/As speciation transformation and bacterial depth distribution at three different depths, i.e., 15, 55, and 105 cm from the top of the columns, was comparatively investigated. The results show that the cell growth at the top and in the middle of the columns was much more significantly inhibited by the additions of As(III) than at the bottom, where the cell growth was promoted even on days 24–44. At. ferrooxidans dominated over Aph. acidophilum in most samples collected from the three depths, but the elevated proportions of Aph. acidophilum were observed in the top and bottom column samples when 4.5 mM As(III) was added. Fe2+ bio-oxidation and Fe3+ reduction coupled to As(III) oxidation occurred for all three column depths. At the column top surfaces, jarosites were formed, and the addition of As(III) could lead to the formation of the amorphous FeAsO4⋅2H2O. Furthermore, the higher As(III) concentration could inhibit Fe2+ bio-oxidation and the formation of FeAsO4⋅2H2O and jarosites. S oxidation coupled to Fe3+ reduction occurred at the bottom of the columns, with the formations of FeAsO4⋅2H2O precipitate and S intermediates. The formed FeAsO4⋅2H2O and jarosites at the top and bottom of the columns could adsorb to and coprecipitate with As(III) and As(V), resulting in the transfer of As from solution to solid phases, thus further affecting As speciation transformation. The distribution difference of Fe/S energy substrates could apparently affect Fe/S/As speciation transformation and bacterial depth distribution between the top and bottom of the water columns. These findings are valuable for elucidating As fate and toxicity mediated by microbially driven Fe/S redox in AMD environments.

Enhancing the electrochemical performance of Fe3O4 nanoparticles layered carbon electrodes in microbial electrolysis cell

The present study assesses the performance of microbial electrolysis cell (MEC) to generate electric current using (I) uncoated/untreated electrodes and (II) Fe3O4 nanoparticles (FNPs) coated electrodes. The cyclic voltammetry (CV) reports highest conductivity of 58 Sm−1 in (II) while lowest (0.18 Sm−1) in (I) electrodes. The impedance spectroscopy confirms bulk resistivity of 375 kΩ in (I) electrodes while relatively lowest resistivity of 0.4 kΩ in (II) electrodes. Two sets of single chamber membraneless MECs is operated simultaneously at different applied voltage (300 mV, 500 mV and 700 mV): RI (uncoated electrodes) and RII, (FNP coated electrodes). The RII attains maximum current density and power density of 15.2 mAcm−1 and 10.6 mWcm−2 respectively at 0.7 V while RI achieves the maximum current density and power density of 4.03 mAcm−2 and 2.8 mWcm−2 respectively at same voltage. Moreover, the current density recorded in electrodes (II) is significantly higher compared to electrodes (I) measured using CV. The result suggests FNP to be an excellent catalyst which improves biosynthesis of electric current. The biologically active environment consisting of anaerobic electrogenic microbes supported biosynthesis/generation of high electric current along with other metabolites produced from the microbes mediated redox reaction.

Spin‐Regulated Electron Transfer and Exchange‐Enhanced Reactivity in Fe4S4‐Mediated Redox Reaction of the Dph2 Enzyme During the Biosynthesis of Diphthamide

AbstractThe [4Fe‐4S]‐dependent radical S‐adenosylmethionine (SAM) proteins is one of large families of redox enzymes that are able to carry a panoply of challenging transformations. Despite the extensive studies of structure–function relationships of radical SAM (RS) enzymes, the electronic state‐dependent reactivity of the [4Fe‐4S] cluster in these enzymes remains elusive. Using combined MD simulations and QM/MM calculations, we deciphered the electronic state‐dependent reactivity of the [4Fe‐4S] cluster in Dph2, a key enzyme involved in the biosynthesis of diphthamide. Our calculations show that the reductive cleavage of the S−C(γ) bond is highly dependent on the electronic structure of [4Fe‐4S]. Interestingly, the six electronic states can be classified into a low‐energy and a high‐energy groups, which are correlated with the net spin of Fe4 atom ligated to SAM. Due to the driving force of Fe4−C(γ) bonding, the net spin on the Fe4 moiety dictate the shift of the opposite spin electron from the Fe1‐Fe2‐Fe3 block to SAM. Such spin‐regulated electron transfer results in the exchange‐enhanced reactivity in the lower‐energy group compared with those in the higher‐energy group. This reactivity principle provides fundamental mechanistic insights into reactivities of [4Fe‐4S] cluster in RS enzymes.

Spin-Regulated Electron Transfer and Exchange-Enhanced Reactivity in Fe4 S4 -Mediated Redox Reaction of the Dph2 Enzyme During the Biosynthesis of Diphthamide.

The [4Fe-4S]-dependent radical S-adenosylmethionine (SAM) proteins is one of large families of redox enzymes that are able to carry a panoply of challenging transformations. Despite the extensive studies of structure-function relationships of radical SAM (RS) enzymes, the electronic state-dependent reactivity of the [4Fe-4S] cluster in these enzymes remains elusive. Using combined MD simulations and QM/MM calculations, we deciphered the electronic state-dependent reactivity of the [4Fe-4S] cluster in Dph2, a key enzyme involved in the biosynthesis of diphthamide. Our calculations show that the reductive cleavage of the S-C(γ) bond is highly dependent on the electronic structure of [4Fe-4S]. Interestingly, the six electronic states can be classified into a low-energy and a high-energy groups, which are correlated with the net spin of Fe4 atom ligated to SAM. Due to the driving force of Fe4-C(γ) bonding, the net spin on the Fe4 moiety dictate the shift of the opposite spin electron from the Fe1-Fe2-Fe3 block to SAM. Such spin-regulated electron transfer results in the exchange-enhanced reactivity in the lower-energy group compared with those in the higher-energy group. This reactivity principle provides fundamental mechanistic insights into reactivities of [4Fe-4S] cluster in RS enzymes.

Effect of Sb on precipitation of biogenic minerals during the reduction of Sb-bearing ferrihydrites

Antimony (Sb) is a naturally occurring element; it is enriched in the environment by anthropogenic activities. Like other metalloid species, Sb partitions to mineral phases such as oxyhydroxides. In reducing environments, Fe(III) may serve as a terminal electron acceptor during dissimilatory iron reduction leading to its transformation. Relatively little is known concerning the effect of Sb(V) on the precipitation of biogenic minerals in relation to microbiologically mediated redox reactions. To further our understanding, Sb-bearing ferrihydrites (0.5 g) with variable Sb/(Fe + Sb) molar ratios of 0.04, 0.06 and 0.1, were incubated in the presence of Shewanella oneindensis MR-1 (1 × 108 cell mL−1) under N2 atmosphere. Additionally, we synthesized abiotic GR1(CO32−) in the presence of Sb(V) to examine the effect of Sb(V) on this mineral formation and stabilization. A combination of wet chemistry and solid analysis techniques (XRD, Mössbauer and Raman spectroscopies) was used to characterize the reactions.The Sb loading affected the rate and the extent of bio-reduction compared with pure ferrihydrite. Only a minor fraction of the total Sb, less than 0.5%, was released into the solution by the end of the incubation period, suggesting that the metalloid partitioned mainly in a newly formed phase. Furthermore, XPS analyses showed the presence of Sb(V) and Sb(III) species on the biogenic minerals. Magnetite was the main biogenic precipitate (91%) in the absence of Sb(V). Increasing of the molar ratios [Sb/(Fe + Sb)] to 0.1 resulted mainly in the precipitation of carbonated green (47%) rust and goethite (37%). Abiotic green rust synthesis carried out in the presence of Sb(V) indicated the latter’s stabilizing effect on the green rust structure, as for phosphate species. Thus, it is likely that Sb(V) preserve biogenic green rust, hindering its transformation to more thermodynamically stable phases.

Measurement Time Reduction by Means of Mathematical Modeling of Enzyme Mediated RedOx Reaction in Food Samples Biosensors.

The possibility of measuring in real time the different types of analytes present in food is becoming a requirement in food industry. In this context, biosensors are presented as an alternative to traditional analytical methodologies due to their specificity, high sensitivity and ability to work in real time. It has been observed that the behavior of the analysis curves of the biosensors follow a trend that is reproducible among all the measurements and that is specific to the reaction that occurs in the electrochemical cell and the analyte being analyzed. Kinetic reaction modeling is a widely used method to model processes that occur within the sensors, and this leads to the idea that a mathematical approximation can mimic the electrochemical reaction that takes place while the analysis of the sample is ongoing. For this purpose, a novel mathematical model is proposed to approximate the enzymatic reaction within the biosensor in real time, so the output of the measurement can be estimated in advance. The proposed model is based on adjusting an exponential decay model to the response of the biosensors using a nonlinear least-square method to minimize the error. The obtained results show that our proposed approach is capable of reducing about 40% the required measurement time in the sample analysis phase, while keeping the error rate low enough to meet the accuracy standards of the food industry.

The Auxiliary NADH Dehydrogenase Plays a Crucial Role in Redox Homeostasis of Nicotinamide Cofactors in the Absence of the Periplasmic Oxidation System in Gluconobacter oxydans NBRC3293.

Gluconobacter oxydans has the unique property of a glucose oxidation system in the periplasmic space, where glucose is oxidized incompletely to ketogluconic acids in a nicotinamide cofactor-independent manner. Elimination of the gdhM gene for membrane-bound glucose dehydrogenase, the first enzyme for the periplasmic glucose oxidation system, induces a metabolic change whereby glucose is oxidized in the cytoplasm to acetic acid. G. oxydans strain NBRC3293 possesses two molecular species of type II NADH dehydrogenase (NDH), the primary and auxiliary NDHs that oxidize NAD(P)H by reducing ubiquinone in the cell membrane. The substrate specificities of the two NDHs are different from each other: primary NDH (p-NDH) oxidizes NADH specifically but auxiliary NDH (a-NDH) oxidizes both NADH and NADPH. We constructed G. oxydans NBRC3293 derivatives defective in the ndhA gene for a-NDH, in the gdhM gene, and in both. Our ΔgdhM derivative yielded higher cell biomass on glucose, as reported previously, but grew at a lower rate than the wild-type strain. The ΔndhA derivative showed growth behavior on glucose similar to that of the wild type. The ΔgdhM ΔndhA double mutant showed greatly delayed growth on glucose, but its cell biomass was similar to that of the ΔgdhM strain. The double mutant accumulated intracellular levels of NAD(P)H and thus shifted the redox balance to reduction. Accumulated NAD(P)H levels might repress growth on glucose by limiting oxidative metabolisms in the cytoplasm. We suggest that a-NDH plays a crucial role in redox homeostasis of nicotinamide cofactors in the absence of the periplasmic oxidation system in G. oxydansIMPORTANCE Nicotinamide cofactors NAD+ and NADP+ mediate redox reactions in metabolism. Gluconobacter oxydans, a member of the acetic acid bacteria, oxidizes glucose incompletely in the periplasmic space-outside the cell. This incomplete oxidation of glucose is independent of nicotinamide cofactors. However, if the periplasmic oxidation of glucose is abolished, the cells oxidize glucose in the cytoplasm by reducing nicotinamide cofactors. Reduced forms of nicotinamide cofactors are reoxidized by NADH dehydrogenase (NDH) on the cell membrane. We found that two kinds of NDH in G. oxydans have different substrate specificities: the primary enzyme is NADH specific, and the auxiliary one oxidizes both NADH and NADPH. Inactivation of the latter enzyme in G. oxydans cells in which we had induced cytoplasmic glucose oxidation resulted in elevated intracellular levels of NAD(P)H, limiting cell growth on glucose. We suggest that the auxiliary enzyme is important if G. oxydans grows independently of the periplasmic oxidation system.

3D Printing of an Oil/Water Mixture Separator with In Situ Demulsification and Separation.

Currently, many meshes, membranes, and fabrics with extreme wettability of superhydrophobicity/superoleophilicity, or superhydrophilicity and underwater superoleophobicity are promising candidates for oil/water mixture separation. Nevertheless, a facile yet effective way to design and fabricate porous mesh still remains challenging. In this work, fused deposition modeling (FDM) 3D printing of Fe/polylactic acid (PLA) composites was employed to fabricate superhydrophilic and underwater superoleophobic mesh (S-USM) with hydrogel coatings via the surface polymerization of Fe(II)-mediated redox reaction. In addition, salt of aluminum chloride was incorporated within the hydrogel coating, which was attributed to strengthening the demulsification of oil-in-water emulsions, resulting in efficient separation of oil-in-water mixtures. The S-USM was efficient for a wide range of oil-in-water mixtures, such as dodecane, diesel, vegetable oil, and even crude oil, with a separation efficiency of up to 85%. In this study, the flexible design and fabrication of 3D printing were used for the facile creation of spherical oil skimmers with hydrogel coatings that were capable of removing the floating oil. Most importantly, this work is expected to promote post-treatment processes using 3D printing as a new manufacturing technology and, in this way, a series of devices of specific shape and function will be expanded to satisfy desired requirements and bring great convenience to personal life.

Spatial and Temporal Patterns of Pore Water Chemistry in the Inter-Tidal Zone of a High Energy Beach

Submarine groundwater discharge (SGD) is a ubiquitous source of meteoric fresh groundwater and recirculating seawater to the coastal ocean. Due to the hidden distribution of SGD, as well as the hydraulic- and stratigraphy-driven spatial and temporal heterogeneities, one of the biggest challenges to date is the correct assessment of SGD-driven constituent fluxes. Here, we present results from a 3-dimensional seasonal sampling campaign of a shallow subterranean estuary in a high-energy, meso-tidal beach, Spiekeroog Island, Northern Germany. We determined beach topography and analyzed physico-chemical and biogeochemical parameters such as salinity, temperature, dissolved oxygen, Fe(II) and dissolved organic matter fluorescence (FDOM). Overall, the highest gradients in pore water chemistry were found in the cross-shore direction. In particular, a strong physico-chemical differentiation between the tidal high water and low water line was found and reflected relatively stable in- and exfiltrating conditions in these areas. Contrastingly, in between, the pore water compositions in the existing foreshore ridge and runnel system were very heterogeneous on a spatial and temporal scale. The reasons for this observation may be the strong morphological changes that occur throughout the entire year, which affect the exact locations and heights of the ridge and runnel structures and associated flow paths. Further, seasonal changes in temperature and inland hydraulic head, and the associated effect on microbial mediated redox reactions likely overprint these patterns. In the long-shore direction the pore water chemistry varied less than the along the cross-shore direction. Variation in long-shore direction was probably occurring due to topography changes of the ridge-runnel structure and a physical heterogeneity of the sediment, which produced non-uniform groundwater flow conditions. We conclude that on meso-tidal high energy beaches, the rapidly changing beach morphology produces zones with different approximations to steady-state conditions. Therefore, we suggest that zone-specific endmember sampling is the optimal strategy to reduce uncertainties of SGD-driven constituent fluxes.

Continuous Surface Polymerization via Fe(II)‐Mediated Redox Reaction for Thick Hydrogel Coatings on Versatile Substrates

The development of versatile generalized strategies for easy surface modification is of immense scientific interest. Herein, a novel mechanism to form functional hydrogel coatings on a wide variety of substrate materials including polymers, polymeric resins, ceramics, and intermetallic compounds, enabling easy change of the surface wettability and lubrication property, is reported. In situ polymerization and hydrogel coating formation is initiated by free radicals generated through the redox reaction between Fe2+ and S2 O8 2- at the solid-liquid interface, which shows controllable growth kinetics. Hydrogel modification is fast, controllable, and performed in mild conditions at room temperature. The chemical components, thickness, and network structure of the hydrogel coating can be well controlled. The surface catalytically initiated radical polymerization method allows reinitiation of the polymerization when the grafted hydrogel coating is polished away, and allows continuous surface polymerization to form multi-interpenetrating network hydrogel coatings. Interestingly, it is fully compatible with 3D-printing technology, and by using 3D-printed composites as the catalytic template, it demonstrates an extreme advantage for engineering 3D hollow hydrogel objects with various complex structures. The versatility of this method makes it generate potential applications in the field of surface/interface and biological engineering.

Microbial mediated sedimentary phosphorus mobilization in emerging and eroding wetlands of coastal Louisiana

The interactions between the microbial reduction of Fe (III) oxides and sediment geochemistry are poorly understood and mostly unknown for the Louisiana deltaic plain. This study evaluates the potential of P mobilization for this region during bacterially mediated redox reactions. Samples were collected from two wetland habitats (forested wetland ridge, and marsh) characterized by variations in vegetation structure and elevation in the currently prograding Wax Lake Delta (WLD) and two habitats (wetland marsh, and benthic channel) in degrading Barataria Bay in Lake Cataouatche (BLC). Our results show that PO43− mobilization from WLD and BLC habitats were negligible under aerobic condition. Under anaerobic condition, there is a potential for significant release of PO43− from sediment and wetland soils. PO43− release in sediments spiked with Fe reducing bacteria Shewanella putrefaciens (Sp-CN32) were significantly higher in all cases with respect to a control treatment. In Wax Lake delta, PO43− release from sediment spiked with Sp-CN32 increased significantly from 0.064 ± 0.001 to 1.460 ± 0.005 μmol g−1 in the ridge and from 0.079 ± 0.007 to 2.407 ± 0.001 μmol g−1 in the marsh substrates. In Barataria bay, PO43− release increased from 0.103 ± 0.006 μmol g−1 to 0.601 ± 0.008 μmol g−1 in the channel and 0.050 ± 0.000 to 0.618 ± 0.026 μmol g−1 in marsh substrates. The PO43− release from sediment slurries spiked with Sp-CN32 was higher in the WLD habitats (marsh 30-fold, ridge 22-fold) compared to the BLC habitats (marsh 12-fold, channel 6-fold). The increase in PO43− release was significantly correlated with the Fe bound PO43− in sediments from different habitats but not with their organic matter content. This study contributes to our understanding of the release mechanism of PO43− during bacterial mediated redox reaction in wetland soils undergoing pulsing sediment deposition and loss.

Dissolved Mineral Ash Generated by Vegetation Fire Is Photoactive under the Solar Spectrum.

Vegetation fire generates vast amounts of mineral ash annually that can be readily mobilized by water or wind erosion. Little is known about the photoactivity of dissolved mineral ash in aquatic systems and its ability to mediate redox reactions of environmental pollutants. This study reports that dissolved mineral ash derived from pyrolysis of biomass is photoactive under simulated sunlight, generating reactive oxygen species. It can mediate the photoreduction of hexavalent chromium (Cr(VI)) in the presence of electron donors; for example, phenols and dissolved organic matter, at pH 4.7. The reaction kinetics followed the Langmuir-Hinshelwood model, suggesting a heterogeneous photocatalytic reaction. The enhancement of reduction efficiency was linearly correlated with the one-electron reduction potential of phenols. The synergy between dissolved mineral ash and phenols is attributed to the inhibition of electron-hole recombination. The reduction rate decreases with increasing solution pH, owing to the decreased reduction potential and surface adsorption of Cr(VI). The silicon and silicon carbide components are most likely responsible for the photocatalytic activity of dissolved mineral ash. Our results suggest that dissolved mineral ash is a natural photocatalyst that can mediate redox reactions of pollutants in sunlit aquatic systems, playing an overlooked role in natural attenuation and aquatic photochemistry.

Iron Homeostasis and Diabetes Risk

Iron binds to protein in the form of heme and functions as co-factor of enzymes that mediate redox reactions for energy production and intermediate of metabolism. Individual iron status is reflected as the combination of nutritional and pathological diseases. Iron overload (IO) and iron deficiency anemia (IDA) are the risk factor for diabetes. The association of iron and diabetes was investigated in i ¢-thalassemia patients, in high dietary iron levels, and in iron deficiency anemia were also associated with diabetes risk.

Considering a Threshold Energy in Reactive Transport Modeling of Microbially Mediated Redox Reactions in an Arsenic-Affected Aquifer

The reductive dissolution of Fe-oxide driven by organic matter oxidation is the primary mechanism accepted for As mobilization in several alluvial aquifers. These processes are often mediated by microorganisms that require a minimum Gibbs energy available to conduct the reaction in order to sustain their life functions. Implementing this threshold energy in reactive transport modeling is rarely used in the existing literature. This work presents a 1D reactive transport modeling of As mobilization by the reductive dissolution of Fe-oxide and subsequent immobilization by co-precipitation in iron sulfides considering a threshold energy for the following terminal electron accepting processes: (a) Fe-oxide reduction, (b) sulfate reduction, and (c) methanogenesis. The model is then extended by implementing a threshold energy on both reaction directions for the redox reaction pairs Fe(III) reduction/Fe(II) oxidation and methanogenesis/methane oxidation. The optimal threshold energy fitted in 4.50, 3.76, and 1.60 kJ/mol e− for sulfate reduction, Fe(III) reduction/Fe(II) oxidation, and methanogenesis/methane oxidation, respectively. The use of models implementing bidirectional threshold energy is needed when a redox reaction pair can be transported between domains with different redox potentials. This may often occur in 2D or 3D simulations.