Weak Oxidation Research Articles

PH significantly affects removal of trace antibiotics in chlorination of municipal wastewater

The effect of pH on chlorination behaviors of 12 antibiotics, including β-lactams, sulfonamides, fluoroquinolones, tetracyclines, macrolides, and others at environmentally relevant concentrations was systematically examined in the effluent matrix of activated sludge process. The removal of most antibiotics (except cefalexin and tetracycline) significantly depended on pH in the range of 5.5–8.5. The elimination rates of ciprofloxacin, norfloxacin, anhydro-erythromycin, and roxithromycin increased while that of sulfamethoxazole decreased significantly with the increase of pH. Sulfadiazine, ofloxacin, and trimethoprim exhibited the highest reactivity with free available chlorine under the pH of 6–7, 7, and 7.5, respectively. Not only the free available chlorine species (HOCl and OCl−), but also the antibiotics species (cationic, neutral and anionic) affected the overall reaction rate. Anionic antibiotic species are usually much more reactive (1–3 orders of magnitude greater) than cationic antibiotic species toward free available chlorine. Although OCl− is a weaker oxidant than HOCl, chlorination of sulfadiazine, sulfamethoxazole, ciprofloxacin, norfloxacin, and trimethoprim with OCl− became significant at pH>7.5. The observed kinetics rate constants calculated from species-specific rate constants could accurately (0.91<R2<0.99) predict the antibiotic removal in chlorination of activated sludge effluent with similar DOC and ammonia concentration to this study at a given pH value.

Electrochemical Behavior of Metal-Supported SOFCs Under High Fuel Utilization and Their Durability

The aim of this project was to study whether the oxidation resistance of cells is affected while working under high fuel utilization. A previous study measured the weak oxidation resistance for very porous samples (measured porosity ∼ 70%) in H2 with high H2O content (over 50%) in the interval from 600 to 800 °C. Thus, additional tests were carried out with cells. Crofer22APU-supported solid oxide fuel cells (SOFCs) were produced by scalable cost competitive routes. One of the highly porous cells (calculated porosity 45%) was run under high fuel utilization conditions (calculated fuel utilization 56%), and a further two in H2-50%H2O. Another cell, with low porosity (calculated porosity 20%), was kept working in the same H2-50%H2O atmosphere for many hours. Durability tests with cells of different porosities confirmed that this is the main variable concerning degradation issues while working under high fuel utilization.

Oxidation of aniline with strong and weak oxidants

Oxidative polymerization of aniline by the action of a strong oxidant, ammonium peroxodisulfate, and a weak oxidant, silver nitrate, was studied in media with different acidities. Depending on the reaction conditions, the organic fraction of the products contained either nonconducting aniline oligomers or conducting high-molecular polyaniline. The effect of the oxidation potential on the oxidation process and formation of supramolecular structures by oxidation products was discussed on the basis of analysis of the kinetics and products of aniline oxidation by spectroscopic, conductometric, thermogravimetric, chromatographic (gel permeation), and electron microscopic methods. A relation was revealed between the morphology of composite materials and their electric conductivity.

Easy modification of pencil graphite electrode for discrimination and determination of morphine in biological and street samples

The electrochemical sensor was developed for discrimination and determination of morphine (MO) using an electrochemically pretreated pencil graphite electrode (PPGE). A potentiostatic strategy was employed for the electrochemical pretreatment of the electrode. The PPGE has displayed very good electrochemical catalytic activities as compared with the non-pretreated PGE (NPGE). At the PPGE, two well-defined anodic peaks of morphine at about 0.35 V and +0.80 V were observed. There is only a weak oxidation peak at +0.50 V at NPGE at the same morphine concentration, while the peak cannot be found at +0.80 V. The pretreatment of the polished PGE by electrostatic procedure at 1.80 V for 5 min in 0.50 M phosphate buffer solution of pH 7.0 was proposed as the optimum pretreatment procedure. Differential pulse voltammetry (DPV) and hydrodynamic amperometry were used for determination of MO. A calibration graph plotted by the variation of anodic peak currents as a function of MO concentration was linear in the range of 1–100 μM. The detection limit calculated from calibration graph was 0.26 μM. The PPGE was used for determination of MO in real samples, including human urine and street drug samples such as opium, heroin and heroin-crack, and the results were quite promising.

A polyphenol-enriched cocoa extract reduces free radicals produced by mycotoxins

Polyphenols are characterized by the presence of phenol units in the molecules. These compounds may show antioxidant ability by scavenging reactive oxygen species (ROS) of the free radical type. A polyphenol enriched cocoa extract (PECE) was obtained from cocoa seeds with 28% of procyanidins which were mainly epicatechin oligomers. PECE was very active as free radical scavenger against 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl (HNTTM) radicals; and the tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl (TNPTM) assay showed that the PECE might not be pro-oxidant. Thus it was considered a good candidate to be tested in in vitro models. It showed mild cytotoxic power on Hep G2 cells and induced ROS in a dose-dependent manner being weak oxidant only at high concentrations near the limit of solubility. The antioxidant properties were assayed in Hep G2 treated with the mycotoxins ochratoxin A (OTA) and/or aflatoxin B1 (AFB1). The PECE was not effective against AFB1 but it increased the cell viability and reduced significantly the amounts of ROS in cells treated with OTA or mixtures of AFB1+OTA. These results are coherent with the role of oxidative pathways in the mechanism of OTA and indicate that polyphenols extracted from cocoa may be good candidates as antioxidant agents.

Encapsulation of Perchlorate Salts within Metal Oxides for Application as Nanoenergetic Oxidizers

AbstractIn this work, high‐oxygen‐content strong oxidizer perchlorate salts were successfully incorporated into current nanothermite composite formulations. The perchlorates were encapsulated within mild oxidizer particles through a series of thermal decomposition, melting, phase segregation, and recrystallization processes, which occurred within confined aerosol droplets. This approach enables the use of hygroscopic materials by stabilizing them within a matrix. Several samples, including Fe2O3/KClO4, CuO/KClO4 and Fe2O3/NH4ClO4 composite oxidizer particles, have been created. The results show that these composite systems significantly outperform the single metal oxide system in both pressurization rate and peak pressure. The ignition temperatures for these mixtures are significantly lower than those of the metal oxides alone, and time‐resolved mass spectrometry shows that O2 release from the oxidizer also occurs at a lower temperature and with high flux. The results are consistent with O2 release being the controlling factor in determining the ignition temperature. High‐speed imaging clearly shows a much more violent reaction. The results suggest that a strategy of encapsulating a very strong oxidizer, which may not be environmentally compatible, within a more stable weak oxidizer offers the opportunity to both tune reactivity and employ materials that previously could not be considered.

MgZnO synthesis employing weak oxidants for accurate Mg incorporation control

MgZnO films with different Mg contents were synthesized on c-plane sapphire by metal organic chemical vapor deposition, using diethyl zinc (DEZn) and bis(cyclopentadienyl) magnesium (Cp 2Mg) as Zn and Mg precursors, respectively. Tertiary butanol (t-BuOH) was used as a weak oxidant in order to enhance the accuracy of Mg incorporation when varying DEZn/Cp 2Mg flow rates. As a result the Mg contents in the range of 1–9% were confirmed by time-of-flight elastic recoil detection analysis, which is known to be specifically sensitive to detect light elements. Thus, independently and accurately determined composition in the samples was correlated with structural and optical properties as measured by x-ray diffraction and photoluminescence.

Lipoteichoic acid from Lactobacillus plantarum induces nitric oxide production in the presence of interferon-γ in murine macrophages

Lipoteichoic acid (LTA) is a major immuno-stimulating component of Gram-positive bacteria. LTA from the beneficial bacterium Lactobacillus plantarum induces weak nitric oxide (NO) production in murine macrophages. Currently, it is not clear if LTA from L. plantarum is able to stimulate the innate immune response, even in the presence of inflammation. In the present study, we prepared highly pure and structurally intact LTA from L. plantarum and investigated its ability to induce NO in the presence of interferon (IFN)-γ in the RAW 264.7 murine macrophage cell line and bone marrow-derived macrophages (BMMs) from mice. L. plantarum LTA alone was unable to induce NO production, even at 30μg/ml. However, LTA in the presence of IFN-γ significantly induced NO production in RAW 264.7 cells. The observed NO production was inhibited by a NO synthase (NOS) inhibitor l-NAME and an inducible NOS (iNOS) inhibitor l-NIL, suggesting that iNOS is specifically required for this action. Western blot analysis and reverse transcription and polymerase chain reaction further confirmed that L. plantarum LTA increased protein and mRNA levels of iNOS, respectively. However, such induction was substantially inhibited in BMMs from Toll-like receptor 2 (TLR2)-deficient mice and the macrophages treated with an inhibitor blocking platelet-activating factor receptor. In addition, L. plantarum LTA plus IFN-γ induced IFN-β expression and STAT1 phosphorylation, which are key pathways for inducing iNOS expression. Electrophoretic mobility shift assay demonstrated that L. plantarum LTA in the presence of IFN-γ remarkably increased the DNA-binding activity of NF-κB transcription factor, which is known to be involved in the iNOS gene expression. Collectively, these results suggest that LTA from L. plantarum alone has no inflammatory potential but does induce NO production under conditions of inflammation, such as the presence of IFN-γ.

Copper-mediated synthesis of PdI2 colloidal spheres

A novel copper-mediated solvothermal method was proposed for synthesizing colloidal spheres of a new composition, palladium iodide (PdI2). Typical procedure was designed to involve the introduction of cupric chloride (CuCl2) as weak oxidant. CuCl2 was found to be essential for preventing the easy formation of palladium deposits as well as facilitating the synthesis and assembly. Under the co-effect of CuCl2 and the surfactant of polyvinylpyrrolidone (PVP), neutral PdI2 colloidal spheres with narrow size distribution were successfully produced. Such ion-assisted synthetic method is believed to be prospective in producing well-constructed nanostructures.

Interactions of synthetic Fe(II)–Fe(III) green rusts with pentachlorophenol under various experimental conditions

Sorption of pentachlorophenol (PCP) to three different green rusts (GRs) was studied versus time and initial PCP concentration at neutral pH. A competitive adsorption occurred when salicylate or silicate was present in the reaction medium. The monitoring of chloride formation and PCP byproducts indicated the absence of any possible reductive pathway in the PCP removal. All solid characterization showed that the PCP sorption in the presence or absence of foreign ligands did not alter the GR structure. Addition of nitrate (weak oxidant) involved a gradual release of PCP in solution from the sorbent solid. This is probably due to the oxidative transformation of GR into magnetite that sorbs less PCP. However, reaction with a strong oxidant (H 2O 2) involved both dechlorination and mineralization of PCP via oxidation reaction. HPLC and ion chromatography analysis, TOC and dissolved iron measurements showed that PCP had been degraded by heterogeneous Fenton-like reaction. Both X-ray diffraction analysis and Raman spectroscopy showed that the oxidation of GR may lead to magnetite (Fe 3O 4) or goethite (α-FeOOH), depending on the oxidant type. As green rusts have considerable potential in environmental applications, the influence of naturally occurring ligands and/or oxidants on the reactivity of green rusts should be considered.

Significant spin polarization of Co2MnGa Heusler thin films on MgO(100) measured by ultraviolet photoemission spectroscopy

The spin dependent valence band structure of the Heusler compound Co2MnGa grown on MgO(100) is investigated by spin resolved ultraviolet photoemission spectroscopy (SRUPS). Using a vacuum suitcase, epitaxial thin film samples are transferred from a deposition chamber into an SRUPS chamber with a highly efficient spin detector. The transport results only in weak oxidation of the moderately reactive compound Co2MnGa. A spin polarization of 34% is obtained at the Fermi energy. The energy dependence of the spin polarization including a sign change at E−EF=−0.6 eV is in good agreement with theoretical predictions of the bulk properties of the Heusler compound.

Identification of a Gene Essential for the First Committed Step in the Biosynthesis of Bacteriochlorophyll c

Bacteriochlorophylls (BChls) c, d, and e are the major chlorophylls in chlorosomes, which are the largest and one of the most efficient antennae produced by chlorophototrophic organisms. In the biosynthesis of these three BChls, a C-13(2)-methylcarboxyl group found in all other chlorophylls (Chls) must be removed. This reaction is postulated to be the first committed step in the synthesis of these BChls. Analyses of gene neighborhoods of (B)Chl biosynthesis genes and distribution patterns in organisms producing chlorosomes helped to identify a gene (bciC) that appeared to be a good candidate to produce the enzyme involved in this biochemical reaction. To confirm that this was the case, a deletion mutant of an open reading frame orthologous to bciC, CT1077, was constructed in Chlorobaculum tepidum, a genetically tractible green sulfur bacterium. The CT1077 deletion mutant was unable to synthesize BChl c but still synthesized BChl a and Chl a. The deletion mutant accumulated large amounts of various (bacterio)pheophorbides, all of which still had C-13(2)-methylcarboxyl groups. A C. tepidum strain in which CT1077 was replaced by an orthologous gene, Cabther_B0081 [corrected] from "Candidatus Chloracidobacterium thermophilum" was constructed. Although the product of Cabther_B0081 [corrected] was only 28% identical to the product of CT1077, this strain synthesized BChl c, BChl a, and Chl a in amounts similar to wild-type C. tepidum cells. To indicate their roles in the first committed step of BChl c, d, and e biosynthesis, open reading frames CT1077 and Cabther_B0081 [corrected] have been redesignated bciC. The potential mechanism by which BciC removes the C-13(2)-methylcarboxyl moiety of chlorophyllide a is discussed.

Photocatalytic Oxidation of Arsenite over TiO2: Is Superoxide the Main Oxidant in Normal Air-Saturated Aqueous Solutions?

TiO(2) photocatalytic oxidation (PCO) of As(III) in the normal air-saturated aqueous solutions has been widely studied. Yet no consensus has been achieved on the mechanism whether superoxide is the main oxidant, although many approaches have been taken. (Photo)electrochemical method can minimize changes to TiO(2) surface and could therefore not alter the normal mechanism. In this Article, both this approach and As(III) oxidation kinetic measurements were performed to clarify the disputed mechanism. Under a sufficient cathodic bias potential, the dark oxidation of As(III) by superoxide could occur, but both the reaction rate and the columbic efficiency were rather low, suggesting that it is a weak oxidant. However, under UV light, both the reaction rate and the columbic efficiency were greatly enhanced even at potentials negative enough to eliminate photohole participation, indicating that more efficient oxidants than superoxide were produced. Under UV illumination and enough positive potential where superoxide was absent, the As(III) oxidation was the most highly efficient. The columbic efficiency of photoholes was much higher than that of superoxide. In the normal aerated aqueous solutions and at open circuit, although the total contribution of superoxide and its derivates to the PCO of As(III) was considerably high (up to 43%), it was not more than that of photohole (57%). In addition, the reported various approaches taken to elucidate the mechanism were discussed, and the resulting disputes can be clarified by these findings. It was demonstrated that (photo)electrochemical method could provide direct and undisputed evidence to reveal the truth mechanics issues.

Plasma synthesis of nanostructures for improved thermoelectric properties

The utilization of silicon-based materials for thermoelectrics is studied with respect to the synthesis and processing of doped silicon nanoparticles from gas phase plasma synthesis. It is found that plasma synthesis enables the formation of spherical, highly crystalline and soft-agglomerated materials. We discuss the requirements for the formation of dense sintered bodies, while keeping the crystallite size small. Small particles a few tens of nanometres and below that are easily achievable from plasma synthesis, and a weak surface oxidation, both lead to a pronounced sinter activity about 350 K below the temperature usually needed for the successful densification of silicon. The thermoelectric properties of our sintered materials are comparable to the best results found for nanocrystalline silicon prepared by methods other than plasma synthesis.

Enteric neurons of the adult mouse; successful isolation through immunoselection and immunocytochemical and electrophysiological characterization

The enteric nervous system (ENS) is often referred to as the ‘second brain’ and plays an essential role in gastrointestinal peristalsis. However, isolation of individual neurons from adult mice has proven difficult. In this study we isolated mouse enteric neurons by immunoselection. Neurons from digested longitudinal muscle myenteric plexus preparations were labeled with an extracellular p75NTRantibody coupled to modified biotin and selected by streptavidin-coated magnetic beads. Cells were cultured for up to 2 weeks in modified Neurobasal A media. All neurons positively stained for the neuronal marker βIII-tubulin, and many grew in clusters. Immunocytochemistry revealed positive membrane staining for the μ opioid receptor and β-arrestin 2. Select neurons showed positive staining for choline acetyltransferase and weak nitric oxide synthase immunoreactivity. Electrophysiological studies of these neurons suggest at least two distinct neuronal populations. One population displays strong outward rectifying 4-aminopyridine-sensitive K+ currents. In a second set of neurons, current injection elicited action potentials. Robust Na+ currents are seen in tandem with these regenerative action potentials. We have developed a methodology for the successful isolation and study of viable adult mouse enteric neurons for systematic electrophysiological investigation. Supported by NIH DA024009.

Neokomagataeagen. nov., with Descriptions ofNeokomagataea thailandicasp. nov. andNeokomagataea tanensissp. nov., Osmotolerant Acetic Acid Bacteria of the α-Proteobacteria

Isolates AH11(T) and AH13(T) were isolated from flowers of lantana and candle bush respectively collected in Thailand. In phylogenetic trees based on 16S rRNA gene sequences, the two isolates formed an independent cluster, which was then connected to the type strain of Saccharibacter floricola. The calculated pair-wise 16S rRNA gene sequence similarities of isolate AH11(T) were 95.7-92.3% to the type strains of the type species of the 12 genera of acetic acid bacteria. The DNA base composition was from 51.2 to 56.8 mol % G+C, with a range of 5.6 mol %. When isolate AH11(T) was labeled, DNA-DNA similarities were 100, 12, 4, 5, and 4% respectively to isolates AH11(T) and AH13(T) and the type strains of Saccharibacter floricola, Gluconobacter oxydans, and Acetobacter aceti. The two isolates were non-motile and did not oxidize either acetate or lactate. No growth was found in the presence of 0.35% acetic acid w/v. The two isolates were not osmophilic but osmotolerant, produced 2,5-diketo-D-gluconate from D-glucose, and did not oxidize lactate, thus differing from strains of Saccharibacter floricola, which showed weak lactate oxidation. The two isolates contained unsaturated C(18:1)ω7c fatty acid as the major fatty acid, and were unique in the presence of a considerable amount of straight-chain C(18:1)2OH fatty acid. Q-10 was present as the major isoprenoid quinone. Neokomagataea gen. nov. was proposed with the two species, Neokomagataea thailandica sp. nov. for isolate AH11(T) (=BCC 25710(T)=NBRC 106555(T)), which has 56.8 mol % G+C, and Neokomagataea tanensis sp. nov. for isolate AH13(T) (=BCC 25711(T)=NBRC 106556(T)), which has 51.2 mol % G+C.

Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles

In this study, magnetite-maghemite nanoparti- cles were used to treat arsenic-contaminated water. X-ray photoelectron spectroscopy (XPS) studies showed the presence of arsenic on the surface of magnetite-maghemite nanoparticles. Theoretical multiplet analysis of the mag- netite-maghemite mixture (Fe3O4-cFe2O3) reported 30.8% of maghemite and 69.2% of magnetite. The results show that redox reaction occurred on magnetite-maghemite mixture surface when arsenic was introduced. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on contact time and ini- tial concentration of arsenic. Equilibrium was achieved in 3 h in the case of 2 mg/L of As(V) and As(III) concen- trations at pH 6.5. The results further suggest that arsenic adsorption involved the formation of weak arsenic-iron oxide complexes at the magnetite-maghemite surface. In groundwater, arsenic adsorption capacity of magnetite- maghemite nanoparticles at room temperature, calculated from the Langmuir isotherm, was 80 lmol/g and Gibbs free energy (DG 0 , kJ/mol) for arsenic removal was -35 kJ/mol, indicating the spontaneous nature of adsorp- tion on magnetite-maghemite nanoparticles.

Nanoparticle Modification by Weak Polyelectrolytes for pH-Sensitive Pickering Emulsions

The affinity of weak polyelectrolyte coated oxide particles to the oil-water interface can be controlled by the degree of dissociation and the thickness of the weak polyelectrolyte layer. Thereby the oil in water (o/w) emulsification ability of the particles can be enabled. We selected the weak polyacid poly(methacrylic acid sodium salt) and the weak polybase poly(allylamine hydrochloride) for the surface modification of oppositely charged alumina and silica colloids, respectively. The isoelectric point and the pH range of colloidal stability of both particle-polyelectrolyte composites depend on the thickness of the weak polyelectrolyte layer. The pH-dependent wettability of a weak polyelectrolyte-coated oxide surface is characterized by contact angle measurements. The o/w emulsification properties of both particles for the nonpolar oil dodecane and the more polar oil diethylphthalate are investigated by measurements of the droplet size distributions. Highly stable emulsions can be obtained when the degree of dissociation of the weak polyelectrolyte is below 80%. Here the average droplet size depends on the degree of dissociation, and a minimum can be found when 15 to 45% of the monomer units are dissociated. The thickness of the adsorbed polyelectrolyte layer strongly influences the droplet size of dodecane/water emulsion droplets but has a less pronounced impact on the diethylphthalate/water droplets. We explain the dependency of the droplet size on the emulsion pH value and the polyelectrolyte coating thickness with arguments based on the particle-wetting properties, the particle aggregation state, and the oil phase polarity. Cryo-SEM visualization shows that the regularity of the densely packed particles on the oil-water interface correlates with the degree of dissociation of the corresponding polyelectrolyte.

Highly efficient photocatalytic oxygenation reactions using water as an oxygen source

The effective utilization of solar energy requires photocatalytic reactions with high quantum efficiency. Water is the most abundant reactant that can be used as an oxygen source in efficient photocatalytic reactions, just as nature uses water in an oxygenic photosynthesis. We report that photocatalytic oxygenation of organic substrates such as sodium p-styrene sulfonate occurs with nearly 100% quantum efficiency using manganese(III) porphyrins as an oxygenation catalyst, [Ru(II)(bpy)(3)](2+) (bpy = 2,2'-bipyridine) as a photosensitized electron-transfer catalyst, [Co(III)(NH(3))(5)Cl](2+) as a low-cost and weak one-electron oxidant, and water as an oxygen source in a phosphate buffer solution (pH 7.4). A high-valent manganese-oxo porphyrin is proposed as an active oxidant that effects the oxygenation reactions.

Photocatalytic Oxidation Mechanism of As(III) on TiO2: Unique Role of As(III) as a Charge Recombinant Species

Using TiO(2) photocatalyst, arsenite, As(III), can be rapidly oxidized to arsenate, As(V), which is less toxic and less mobile in the aquatic environment. Therefore, the TiO(2)/UV process can be employed as an efficient pretreatment method for arsenic contaminated water. Since we first reported in 2002 that the superoxide (or hydroperoxyl radical) plays the role of main oxidant of As(III) in the TiO(2)/UV process, there has been much debate over the true identity of the major photooxidant among superoxides, holes, and OH radicals. The key issue is centered on why the much stronger OH radicals cannot oxidize As(III), and it has been proposed that the unique role of As(III) as an external charge recombination center on the UV-excited TiO(2) particle is responsible for this eccentric mechanism. Although the proposed mechanism has been supported by many experimental evidences, doubts on it were not clearly removed. In this study, we provided direct and undisputed evidence to support the role of As(III) in the charge recombination dynamics using time-resolved transient absorption spectroscopy. The presence of As(III) indeed mediated the charge recombination in TiO(2). Under this condition, the role of the OH radical is suppressed because of the null cycle, and the weaker oxidant, superoxide, should prevail. The role of the superoxide has been previously doubted on the basis of the observation that the addition of excess formic acid (hole scavenger that should enhance the production of superoxides) inhibited the photocatalytic oxidation of As(III). However, this study proved that this was due to the photogeneration of reducing radicals (HCO(2)·) that recycle As(V)/As(IV) back to As(III). It was also demonstrated that the 4-chlorophenol/TiO(2) system under visible light that cannot generate neither OH radicals nor valence band holes converted As(III) to As(V) through the superoxide pathway.