Decrease In Redox Potential Research Articles

Poly (Ethylene Oxide)-Based Block Copolymer Electrolytes Formed via Ligand-Free Iron-Mediated Atom Transfer Radical Polymerization.

The Br-terminated poly (ethylene oxide) (PEO-Br) is used as a green and efficient macroinitiator in bulk Fe-catalyzed atom transfer radical polymerization (ATRP) without the addition of any organic ligands. The polymerization rate is able to be mediated by PEO-Br with various molecular weights, and the decrease in redox potential of FeBr2 in cyclic voltammetry (CV) curves indicates that an increased coordination effect is deteriorated with the depressing reaction activity in the longer ethylene oxide (EO) chain in PEO-Br. In combination with the study of different catalysts and catalytic contents, the methyl metharylate (MMA) or poly (ethylene glycol) monomethacrylate (PEGMA) was successfully polymerized with PEO-Br as an initiator. This copolymer obtained from PEGMA polymerization can be further employed as a polymer matrix to form the polymer electrolyte (PE). The higher ionic conductivity of PE was obtained by using a high molecular weight of copolymer.

Effects of electron donors on the degradation of hexachlorocyclohexane and microbial community in submerged soils

PURPOSE: Hexachlorocyclohexane (HCH) is a pesticide that is persistent in aerobic but not in anaerobic conditions. The aim of this investigation was to elucidate the impacts of different electron donors on the degradation of hexachlorocyclohexane and their relationships with the microbial community in submerged soils. MATERIALS AND METHODS: Soil samples were collected from a pesticides-polluted site which was previously used for long-term storage of pesticides since the 1960s. Residual amounts of HCHs in submerged soils were assessed to evaluate the efficiency of the added electron donors after incubation. Changes in microbial community were monitored during incubation. RESULTS AND DISCUSSION: The efficiencies of removal of HCHs by Fe⁰, Fe⁰ + straw and glucose treatments were 63.8%, 40.3%, and 22.0%, compared with 5.4% by the control. Soil redox potential decreased rapidly following addition of Fe⁰ and became anaerobic, but there was no significant decrease in redox potential following the addition of glucose. Principal coordinates analysis (PCoA) confirms that the electron donors greatly affected the soil bacterial community. Furthermore, community composition analysis shows that Firmicutes was the dominant phylum after addition of carbon sources (straw and glucose) but Proteobacteria were dominant in the control and the Fe⁰ treatment. Prauserella, Actinobacteria, and Streptomyces showed highly significant increases in the Fe⁰ treatment and were positively correlated with total HCH residues. CONCLUSIONS: These findings indicate that the addition of organic materials (straw and glucose) had a gradual effect on the degradation of HCH while Fe⁰ acted rapidly. Elucidation of the relationships between electron donors and soil microbial communities will help in the bioremediation of HCH-contaminated sites.

Ultramicrobacteria from Nitrate- and Radionuclide-Contaminated Groundwater

The goal of the present work was to investigate the physicochemical and radiochemical conditions and the microbial diversity in groundwater collected near the Lake Karachai (Russia), which was formerly used for the disposal of liquid radioactive waste, to isolate the dominant bacteria, and to determine their taxonomy and the physiological characteristics responsible for their adaptation to this environment. Groundwater samples contained high concentrations of acetate, oxalate, nitrate, and sulfate, as well as radionuclides. High-throughput sequencing and analysis of the clone libraries revealed lower microbial diversity in the most strongly contaminated groundwater and a predominance of bacteria of the genera Polynucleobacter, Pusillimonas, Candidatus Pelagibacter, and of the candidate phylum Parcubacteria; these groups include species with an ultra small cell size. Archaeal sequences in the libraries belonged to ammonium oxidizers of the phylum Thaumarchaeota and methanogens of the phylum Euryarchaeota. Pure cultures of obligate and facultative ultramicrobacteria belonging to the genera Chryseobacterium, Microbacterium, Salinibacterium, Pusillimonas, Roseomonas, and Janibacter were isolated from water samples. In genomes of Pusillimonas and Roseomonas strains the genes associated with nitrate reduction, resistance to heavy metals and metalloids were revealed. Several isolates are able to participate in the geochemical process of nitrate conversion to N2 using acetate; this results in decreasing redox potential, which in turn may stimulate radionuclide reduction and decrease radionuclide migration in groundwater.

Paddy periphyton reduced cadmium accumulation in rice (Oryza sativa) by removing and immobilizing cadmium from the water–soil interface

Periphyton plays a significant role in heavy metal transfer in wetlands, but its contribution to cadmium (Cd) bioavailability in paddy fields remains largely unexplored. The main aim of this study was to investigate the effect of periphyton on Cd behavior in paddy fields. Periphyton significantly decreased Cd concentrations in paddy waters. Non-invasive micro-test technology analyses indicated that periphyton can absorb Cd from water with a maximum Cd2+ influx rate of 394 pmol cm−2 s−1 and periphyton intrusion significantly increased soil Cd concentrations. However, soil Cd bioavailability declined significantly due to soil pH increase and soil redox potential (Eh) decrease induced by periphyton. With periphyton, more Cd was adsorbed and immobilized on organic matter, carbonates, and iron and manganese oxides in soil. Consequently, Cd content in rice decreased significantly. These findings give insights into Cd biogeochemistry in paddy fields with periphyton, and may provide a novel strategy for reducing Cd accumulation in rice.

Temporal Responses of Microbial Communities to Anaerobic Soil Disinfestation

Anaerobic soil disinfestation (ASD) is an organic amendment-based management tool for controlling soil-borne plant diseases and is increasingly used in a variety of crops. ASD results in a marked decrease in soil redox potential and other physicochemical changes, and a turnover in the composition of the soil microbiome. Mechanisms of ASD-mediated pathogen control are not fully understood, but appear to depend on the carbon source used to initiate the process and involve a combination of biological (i.e., release of volatile organic compounds) and abiotic (i.e., lowered pH, release of metal ions) factors. In this study, we examined how the soil microbiome changes over time in response to ASD initiated with rice bran, tomato pomace, or red grape pomace as amendments using growth chamber mesocosms that replicate ASD-induced field soil redox conditions. Within 2 days, the soil microbiome rapidly shifted from a diverse assemblage of taxa to being dominated by members of the Firmicutes for all ASD treatments, whereas control mesocosms maintained diverse and more evenly distributed communities. Rice bran and tomato pomace amendments resulted in microbial communities with similar compositions and trajectories that were different from red grape pomace communities. Quantitative PCR showed nitrogenase gene abundances were higher in ASD communities and tended to increase over time, suggesting the potential for altering soil nitrogen availability. These results highlight the need for temporal and functional studies to understand how pathogen suppressive microbial communities assemble and function in ASD-treated soils.

Association of dissolved organic matter characteristics and trace metals in mountainous streams with sabo dams.

Metals undergo various processes transforming from one phase to another during transportation from head streams to oceans. The major chemical processes in the streams and rivers appear to be strongly dependent on dissolved organic matter (DOM). The mutualistic interactions between DOM and metals are important in determining the fate of many elements. We collected surface water samples from four stations along two mountainous streams in 2015 and analysed DOM quality and quantity and metal concentrations with the aim of understanding how changes in DOM characteristics are associated with dissolved metals along the stream with sabo dams. Both DOM and metal concentration were very low at the upstream site and did not show any significant correlation. However, sites within the dam vicinity (St.2 and St.3) had significantly high concentrations of manganese (Mn) and iron (Fe) which strongly correlated with molecular weight and aromaticity (> 0.6, p ≤ 0.01). Fe, Mn, copper (Cu) and aluminium (Al) significantly varied (p ≤ 0.05) downstream with highest average concentration for Al (17.7 ± 6.0 μg/L) and Cu (0.63 ± 0.3 μg/L). Cu had significant correlation with fluorescence components (fulvic-like, humic-like and protein like) and fluorescence index, while Fe significantly correlated to coloured DOM properties for all the sites. In the midstream section, strong correlations were exhibited by Fe, Cu, Zn and Mn whereas all metals did not show any significant correlation in the upstream site. Additionally, Cu, Mn and lead (Pb) showed strong correlation to DOM properties at the downstream site. The Fe to DOC and Mn to DOC ratios gave significant correlations with aromaticity, molecular weight and fulvic-like component at the midstream sections whereas Cu to DOC ratio lacked significant correlations to DOM at all the stations. Sabo dams enhanced Fe and Mn dissolution, while human activities in the downstream impacted Cu, Al, DOC, Mn and Fe stream concentrations. On the other hand, Fe and Mn were closely associated to DOM properties in regions of changing decreasing redox potential. The significant correlations presented by Mn, Fe and Cu with fluorescence index stresses the role of DOM heterogeneity in natural environments.

Growth of the facultative chemolithoautotroph Ralstonia eutropha on organic waste materials: growth characteristics, redox regulation and hydrogenase activity

BackgroundThe chemolithoautotrophic β-proteobacterium Ralstonia eutropha H16 (Cupriavidus necator) is one of the most studied model organisms for growth on H2 and CO2. R. eutropha H16 is also a biologically significant bacterium capable of synthesizing O2-tolerant [NiFe]-hydrogenases (Hyds), which can be used as anode biocatalysts in enzyme fuel cells. For heterotrophic growth of R. eutropha, various sources of organic carbon and energy can be used.ResultsGrowth, bioenergetic properties, and oxidation–reduction potential (ORP) kinetics were investigated during cultivation of R. eutropha H16 on fructose and glycerol or lignocellulose-containing brewery spent grain hydrolysate (BSGH). BSGH was used as carbon and energy source by R. eutropha H16, and the activities of the membrane-bound hydrogenase (MBH) and cytoplasmic, soluble hydrogenase (SH) were measured in different growth phases. Growth of R. eutropha H16 on optimized BSGH medium yielded ~ 0.7 g cell dry weight L−1 with 3.50 ± 0.02 (SH) and 2.3 ± 0.03 (MBH) U (mg protein)−1 activities. Upon growth on fructose and glycerol, a pH drop from 7.0 to 6.7 and a concomitant decrease of ORP was observed. During growth on BSGH, in contrast, the pH and ORP stayed constant. The growth rate was slightly stimulated through addition of 1 mM K3[Fe(CN)6], whereas temporarily reduced growth was observed upon addition of 3 mM dithiothreitol. The overall and N,N′-dicyclohexylcarbodiimide-sensitive ATPase activities of membrane vesicles were ~ 4- and ~ 2.5-fold lower, respectively, upon growth on fructose and glycerol (FGN) compared with only fructose utilization (FN). Compared to FN, ORP was lower upon bacterial growth on FGN, GFN, and BSGH.ConclusionsOur results suggest that reductive conditions and low ATPase activity might be signals for energy depletion, which, in turn, leads to increased hydrogenase biosynthesis to overcome this unfavorable situation. Addition of fructose or microelements have no, or a negative, influence on hydrogenase activity. Organic wastes (glycerol, BSGH) are promising carbon and energy sources for the formation of biomass harboring significant amounts of the biotechnologically relevant hydrogenases MBH and SH. The results are valuable for using microbial cells as producers of hydrogenase enzymes as catalysts in enzymatic fuel cells.

Замочування насіння сільськогосподарських культур у магнітоактивованій воді

It is possible to increase crop yields, reduce plant incidence, improve agricultural quality without the use of chemical fertilizers when treating seeds before sowing in a magnetic field and soaking them in magnetically activated water. At present, the theory of magnetic treatment of water systems is at the stage of proposing and justifying hypotheses, although it has been experimentally found that magnetic treatment of water alters its physical and chemical properties. Therefore, it is necessary to disclose the mechanisms and patterns of action of the magnetic field on water. The purpose of the work was to determine the regime parameters of water treatment in a magnetic field for soaking seeds of crops. Based on the studies, it was found that the rate of chemical reactions in the aqueous medium, the solubility of the salts, the specific conductivity of the water, the pH and the oxygen concentration increase with the treatment of water in the magnetic field, and the redox potential decreases. This causes an improvement in the sowing quality of the seeds when soaked in magnetically activated water. The effect of magnetic treatment depends on the square of the magnetic induction, the number of magnetizations and the velocity of water movement in the magnetic field. It is established that the most effective mode of treatment of water and seeds in the magnetic field is a magnetic induction of 0.065 T with a fourfold magnetization and a velocity of movement of 0.4 m/s. Under this treatment, when soaking seeds in magnetically activated water, the germination energy of oat seeds increased by 25 % compared to the control, and germination by 19 %. Key words: water, oats, magnetic induction, velocity of movement, germination energy, germination

The use of redox potential to estimate free chlorine in fresh produce washing operations: Possibilities and limitations

Maintaining free chlorine (FC) residual at appropriate pH values is a control approach used to prevent pathogen cross-contamination during tomato dump tank handling and fresh-cut produce washing operations. Oxidation reduction potential (ORP) is a rapid measurement of oxidant-based sanitizer strength, and has been used to estimate FC residual. However, factors, in addition to FC and pH, which influence ORP are not fully understood. This study examined the relationship between ORP and FC under chlorine demand (CLD) free conditions and during fresh produce washing. An equation predictive of FC was developed in the form logFC = f(ORP, ORP2, ORP.pH). A good correlation between ORP and logFC was maintained when other variables changed, but the resulting ORP-logFC curve changed (slope, intercept). A decrease in pH or temperature led to an increase in ORP. Using tap water to wash the produce instead of distilled water significantly changed the ORP. For different types of tested produce, i.e., fresh-cut carrot, onion, romaine and iceberg lettuce, and for whole tomatoes, increasing the product-to-water ratio (i.e., increasing the organics transferred into the water) led to a decrease in ORP for a specific FC residual. The choice of acidulant during washing also influenced ORP. Overall, the correlation of ORP with logFC is more reliable at the lower end (5 mg/L FC) than at the higher end (100 mg/L FC) of the FC range used in fresh produce washing. However, since the ORP in fresh produce wash water is affected significantly in multiple ways by the wash water and process conditions, the predicted FC values with ORP under certain fresh-cut produce washing conditions cannot be generalized for other conditions.

Effect of Bottom Ash and Cow Manure Compost on Chemical Properties of Soil at New-Established Rice Field

<p class="Default">The conversion of dryland to rice field at Sumatra Island, Indonesia was generally developed on marginal lands with Ultisols and Oxisols soil types. Those soil types contained high iron (Fe) and aluminum (Al), but low phosphorus (P) and potassium (K). That is because the changes in the process resulted from submerging the soil. For example, the decrease of redox potential, ion reduction from Fe<sup>3+</sup> to Fe<sup>2+</sup>, and Mn<sup>4+</sup> into Mn<sup>2+</sup>. Those compounds will be dissolved and can be absorbed by plants thus causing toxicity. The objective of the study was to assess the effects of bottom ash and cow manure compost at the various doses on soil chemical properties and rice yield on the new-established rice field. This research used factorial design with two factors in Completely Randomized Design. The factors were a dose of bottom ash and cow manure compost, with three replications. The results showed. The addition of bottom ash and cow manure compost at the dosage in this study was not able to reduce the levels of FeDTPA and MnDTPA at newly established rice fields. However, the application of cow manure compost significantly increased soil pH, exchangeable cation (K, Na, Ca), base saturation and decreased exchangeable-H. The addition of bottom ash does not affect paddy yield, while cow manure compost up to 10 tons ha-1 increased panicle and straw dry weight.</p>

Biogenic Factors of Formation of Geochemical Uranium Anomalies near the Sludge Storage of the Novosibirsk Chemical Concentrate Plant

This paper presents evidence on the possible impact of aerobic and anaerobic microbiological processes on uranium migration in upper aquifers polluted by sulfates and nitrates at the Novosibirsk chemical concentrate plant (PAO NCCP). Uranium can be immobilized in local areas with high contents of organic substances, and the most important microbiological process is a decrease in redox potential owing to aerobic respiration, which can be followed under anaerobic conditions by redox-dependent uranium reduction in areas with negative Eh values. Moreover, in the presence of sufficient amounts of sulfate ions, further anaerobic processes of microbial sulfate and iron reduction result in the formation of iron sulfide, which serves as an antioxidant buffer in the case of oxygen infiltration into the sediment and transforms to molecular sulfur or sulfate preventing uranium oxidation.

Storage Stability and Disinfection Performance on Escherichia coli of Electrolyzed Seawater

The study investigated the effect of storage conditions on the stability of electrolyzed seawater (ESW)’s physicochemical properties (pH, oxidation-reduction potential (ORP), and free chlorine (FC) concentration), and bactericidal efficiency on the fecal coliform Escherichia coli for 30 days. Preliminary experiments were conducted to determine the optimal current and electrolysis time. Two batches of 2750 mL filtered seawater were electrolyzed using 50 mm × 192 mm platinum–titanium mesh electrodes at a current of 1.5 A for 20 min. One hundred milliliters of electrolyzed solution was transferred into each amber glass and high-density polyethylene (HDPE) bottles. The bottles were stored in a dark area at ambient temperature. The results showed an increase in pH and a decrease in ORP and FC concentration through time. Hypochlorous acid remained as the dominant component since the pH levels of the solutions remained below 7.5. FC decay was investigated using Chick’s Law. It was determined that the decay in HDPE bottles (k = −0.066 day−1) was faster compared to amber glass bottles (k = −0.046 day−1). Nonetheless, HDPE bottles could still be used as an alternative container for 30 days only due to observed instability beyond 30 days. ESW remained effective since no surviving population of E. coli was observed throughout the experimentation.

Methane emission and soil microbial communities in early rice paddy as influenced by urea-N fertilization

Urea is widely used in rice farming systems to improve the nitrogen (N) availability and crop yield, yet its influence on CH4 emissions remains unclear. The present study aimed to identify the potential microbial mechanisms resulting in the N fertilizer-induced effects on CH4 emissions from paddies. A field experiment was conducted with (N1, 100 kg N ha−1) and without (N0) N fertilization. CH4 emission rate was measured every 3–7 day using the static chamber-gas chromatography method. Quantitative PCR (qPCR) and Illumina MiSeq sequencing approaches were employed to investigate the community composition and structure of methanogenic archaea and methanotrophic bacteria in rice rhizosphere soil at three time points (tillering stage 17d, heading stage 47d and mature stage 67 d). Urea application significantly stimulated the CH4 emissions from paddies, partially due to the decrease of redox potential (Eh) around the root region and the reduction of dissolved oxygen (DO) concentration at the soil-water interface. qPCR indicated a sharp increase in methanogenic archaeal 16S rRNA and methanotrophic bacterial pmoA gene copies with urea fertilization. Next-generation sequencing of these amplicons revealed that the diversity of both methanogenic and methanotrophic communities was decreased by urea input. Additionally, urea fertilization stimulated the genera Methanoregula (methanogen) and Methylococcus (type I methanotrophs) and inhibited the genus Methylocystis (type II methanotrophs). Urea fertilization changed oxygen state of the paddy soil and water and thus changed the community structure of methanogens and methanotrophs, which resulted in increased CH4 emissions.

Short Research Report: high level of soil carbon addition causes possible manganese and aluminium phytotoxicity

SummaryA restoration trial of grassy woodland on former agricultural land applied carbon at a standard rate (840 g C/m2/year) and at a high rate (4,200 g C/m2/year), to test whether further benefits to native plants and suppression of exotics would emerge. Carbon addition at the high rate reduced plant cover further than the standard rate but led to severe loss of plant species; it also reduced soil pH. Soil Al, Fe and Mn levels increased across the gradient of C addition, which would be consistent with the reduction in soil pH for Al and Mn, and a decrease in soil redox potential for Mn and Fe. Nutrient analysis of leaf tissue confirmed that uptake of Fe and Mn increased over the range of C addition, with the concentration of Mn in the high carbon treatment exceeding the threshold for toxicity for a range of species. The soil and plant tissue data are consistent with the induction of increased soil acidity and of stronger reducing conditions in the soil by high level of carbon addition and localised soil flooding. Plant uptake of Mn to toxic levels occurred subsequently, leading to negative effects on plants; aluminium phytotoxicity may also have occurred.

Срастания корунда и шпинели из месторождения Турейн-Таунг (Мьянма)

The article displays data on formation conditions and features of unique corundum-spinel aggregates from the Thurein-Taung deposit in Myanmar (Burma). Chemical composition of corundum and spinel is given, and there is traced the effect of iron admixture on the coloring of spinel and parameters of its crystal lattice on the base of X-ray diffraction analysis. The surface of corundum on contact with spinel was studied in detail with aid of the color cathodoluminescence; it is shown that the process of overgrowing by spinel was preceded by resorption of corundum surface. Mineral and fluid inclusions in these minerals have been studied with use of microprobe analysis and the Raman spectroscopy. The temperatures of homogenization have been determined for liquid carbon dioxide in fluid inclusions inside corundum. On the base of mineral equilibria analysis in the Al—Mg—O—CO 2 —H 2 S—C system there were determined the optimal activities of magnesium and calcium and the fugacity of carbon dioxide. They are equal to а Mg = 10 –5 ; а Ca = 10 –1 and f CO 2 = 10 –4 . It was found that corundum-spinel aggregates formed at temperature about 400 oС as a result of partial dissolution of corundum protocrystal by high-temperature solutions containing Mg and Ca. Crystallization of the spinel took place with increasing pH (>3.5) and a decrease of redox potential (Eh ≤ –0.3 V).

Varying redox potential affects P release from stream bank sediments.

Sediments in streams that drain agricultural watersheds may be sinks that can adsorb P from the stream or sources that can release P to the stream. Sediment characteristics and environmental factors, including the oxidation-reduction (redox) potential of the water associated with the sediment, determine whether P will be adsorbed or released by the sediment. We investigated P adsorption and release by four sediments [three Holocene-age sediments (Camp Creek, Roberts Creek and Gunder) as well as Pre-Illinoian-age Till] that occur in Walnut Creek, a second-order stream in Jasper County, Iowa, that is representative of many small streams in the glaciated upper Midwest of the US. The effects of two redox potentials on phosphorus buffering capacity (PBC) and equilibrium phosphorus concentration (EPC) were evaluated in batch adsorption experiments. We also simulated aerobic and anerobic conditions over a 24-day period and measured solution-phase P concentrations in stirred systems where the sediments were isolated from the water by dialysis tubing. The batch experiment indicated that the EPCs of the three Holocene-age sediments were similar to one another and increased with decreasing redox potential. In the stirred flow reactors, more dissolved P was released from the Camp Creek and Roberts Creek sediments under anaerobic conditions than from the other sediments. This observation suggests that these two sediments, which are younger and higher in the stratigraphic sequence, are more likely to be P sources in suboxic settings. The P buffering capacity was greatest in the till. Where it is in contact with the stream water, the till is likely to serve as an adsorbing sink for P in the water column.

Revisiting structural and photocatalytic properties of g-C3N4/TiO2: Is surface modification of TiO2 by calcination with urea an effective route to “solar” photocatalyst?

g-C3N4/TiO2 derived from the surface modification of TiO2 by calcination with urea has been widely studied as a “visible-light-active” photocatalyst for environmental remediation. However, few attentions have been paid to the structure characterization and the photocatalytic properties of the resultant nanocomposite photocatalysts under a practical sunlight irradiation. Here we employ various characterization techniques, including TGA, XRD, TEM, XPS, UV–vis spectrum, and N2-sorption analysis to characterize the evolutions in phase crystal structure, microstructure and optical properties of g-C3N4/TiO2 nanohybrids synthesized through calcining a mechanical mixture of urea and Evonik Aeroxide P-25 TiO2 (P25) at 350–500 °C. The thermal pyrolysis of urea leads to the surface decoration of TiO2 with graphitic carbon nitrate (g-C3N4) at temperatures above 400 °C. The photocatalytic properties of the resultant g-C3N4/TiO2 nanoparticles are evaluated through photocatalytic decoloration of methylene blue (MB) and reduction of Cr (VI) to Cr (III) under visible (420 nm), UV (365 nm), and simulated solar light irradiations. The nanohybrid photocatalysts, as most previous studies reported, show much higher photocatalytic activity under visible light irradiation than the single-component counterparts, i.e. P25 or g-C3N4. However, under solar and UV irradiation, no considerable improvements are found, which is caused by the decrease in redox potential upon interfacial charge carrier transfer between g-C3N4 and TiO2. Moreover, g-C3N4/TiO2 shows an ultralow photocatalytic activity in Cr (VI) reduction. The surface modification with organic g-C3N4 is assumed to tune the surface properties (e.g. hydrophilicity) of TiO2. Our results demonstrate that photocatalytic activity in UV range is as important as that in visible range, and developing efficient “solar” photocatalysts should balance the photocatalytic activities at both ranges since they might be incompatible with each other.

Efficient hydrogen generation of indium doped BaTiO3 decorated with CdSe quantum dots: Novel understanding of the effect of doping strategy

Doping has been widely utilized as an effective method of semiconductor modification to enhance photocatalytic efficiency. Most researches focus only on the effect of doping on decreasing band gap and inhibiting carriers recombination, however, the proximity of conduction band minimum (CBM) and valence band maximum (VBM) indicates the decrease of energy level and redox potential. Therefore, to further investigate the effect of doping on photocatalytic activity, the composite structure consisted of CdSe quantum dots (QDs) and indium doped BaTiO3 is synthesized by plain hydrothermal and chemical bath means. Under the condition of maintaining CdSe QDs optimal load ratio of 7.5 mol.%, doping 2.5% indium maximizes hydrogen production (0.437 mmol g–1 h–1) compared to undoped composite structure (0.258 mmol g–1 h–1), which originates from the increase of photo-induced electron reductive activity. The results suggest that we can use doping in reverse thinking to provide a new tactics for the design of semiconductor photocatalytic materials.

Arsenic phytotoxicity and accumulation in rice seedlings grown in arsenic‐contaminated soils as influenced by the characteristics of organic matter amendments and soils

AbstractOrganic matter (OM) application into soils is a common agricultural practice. Previous studies have shown that in arsenic (As)‐contaminated paddy soils, OM has the potential to alter the behavior of As and affects the growth and As accumulation of rice plants. In this study, pot experiments were conducted to investigate the differences in the amounts of As released into soil solutions, its toxicity, and accumulation in rice seedlings caused by application of three different OM amendments [soybean meal (SB), sugarcane dreg compost (SC), and cattle‐dung compost (CD)]. These OM amendments were each applied to three As‐contaminated soils, Guandu (Gd), Pinchen (Pc), and Chengchung (Cf), which have different characteristics. The results indicate that after addition of two easily decomposable OMs (SB and SC), the As toxicity and concentrations increased in rice plants, especially in As‐spiked Cf soils which had low As retention capacity. This was the result of elevated As concentration in soil solutions due to a decrease in soil redox potential and competition between dissolved organic carbon (DOC) and As for sorption sites, as well as the formation of As–DOC complexes. However, there were no significant effects on plant growth and As accumulation in rice seedlings after treatments with CD (not easily decomposable OM). Another important finding was that the amount of iron plaque on the surface of rice roots increased with OM amendments in the Gd soils rich in iron oxides and hydroxides, thus reducing the As uptake by rice plants. These results suggest that the characteristics of OM and soils should be considered when OM amendments are applied to As‐contaminated soils.

X-ray structural analyses of azide-bound cytochrome c oxidases reveal that the H-pathway is critically important for the proton-pumping activity

Cytochrome c oxidase (CcO) is the terminal oxidase of cellular respiration, reducing O2 to water and pumping protons. X-ray structural features have suggested that CcO pumps protons via a mechanism involving electrostatic repulsions between pumping protons in the hydrogen-bond network of a proton-conducting pathway (the H-pathway) and net positive charges created upon oxidation of an iron site, heme a (Fea2+), for reduction of O2 at another iron site, heme a3 (Fea32+). The protons for pumping are transferred to the hydrogen-bond network from the N-side via the water channel of the H-pathway. Back-leakage of protons to the N-side is thought to be blocked by closure of the water channel. To experimentally test this, we examined X-ray structures of the azide-bound, oxidized bovine CcO and found that an azide derivative (N3−–Fea33+, CuB2+–N3−) induces a translational movement of the heme a3 plane. This was accompanied by opening of the water channel, revealing that Fea3 and the H-pathway are tightly coupled. The channel opening in the oxidized state is likely to induce back-leakage of pumping protons, which lowers the proton level in the hydrogen-bond network during enzymatic turnover. The proton level decrease weakens the electron affinity of Fea, if Fea electrostatically interacts with protons in the hydrogen-bond network. The previously reported azide-induced redox-potential decrease in Fea supports existence of the electrostatic interaction. In summary, our results indicate that the H-pathway is critical for CcO's proton-pumping function.