Increase In Redox Potential Research Articles

Are High-Potential Cobalt Tris(bipyridyl) Complexes Sufficiently Stable to Be Efficient Mediators in Dye-Sensitized Solar Cells? Synthesis, Characterization, and Stability Tests

We report the synthesis of three new, high-oxidation-potential cobalt complexes. The ligand lability of cobalt complexes, especially those of higher redox potential, has been scantly addressed in the current literature on the use of these complexes in dye-sensitized solar cells (DSSCs). In characterizing our high-potential complexes, multiple pieces of evidence reveal a trend of decreasing complex stability with increasing redox potential. These include the appearance of multiple waves in the cyclic voltammetry, a color change upon addition of 4-tert-butylpyridine indicating the formation of a new species, direct NMR evidence of free dissociated ligand in acetonitrile solution, and potential-independent DSSC recombination currents paralleling the stability trends as determined by NMR. We take advantage of a simple quantitative NMR experiment to determine the approximate ligand-binding equilibrium (stability) constants of our complexes in acetonitrile at room temperature. With the above information, we propose alternative, clathrochelating ligand structures for the future study of high potential cobalt mediators for application in DSSCs.

Lithium-Ion Battery Based on LiMn0.5Fe0.5PO4 Cathode and Lithium Alloying Anode

Polyanion framework olivine materials have attracted large attention as cathodes in LIBs. Recently, the attention of the scientific community has been focused on the substitution of iron by manganese, cobalt or nickel within the olivine lattice [1]. Indeed, Mn3+/Mn2+, Co3+/Co2+ and Ni3+/Ni2+ couples show increasing redox potentials compared to Fe3+/Fe2+, thus leading to an increased energy density. However, the latter two exhibit redox potential of about 4.8 and 5.2 V vs. Li+/Li, respectively, i.e. a value exceeding the conventional carbonate-based electrolytes stability limit [2]. LiMnPO4 has instead an operating voltage of about 4.1 V vs. Li+/Li, still within the working electrochemical window of conventional electrolytes, thus leading to a theoretical energy density of about 700 Wh kg-1 [3]. LiMnPO4 suffers from poor electric conductivity in comparison to LiFePO4 [4]. Several approaches have been studied to improve LiMnPO4 electrochemical activity in lithium cell. Incorporation of conductive additives, such as carbon, by post-synthesis ball milling or formation of a carbon layer on particle surface can increase the electronic conductivity [5, 6]. Significant decrease of the lithium diffusion pathway and consequent conductivity increase may be reached by reduction of particle size by proper synthetic procedures leading to nano-morphologies [7, 8]. Soft-chemistry methods allow more controlled tailoring of morphologies and size than the conventional solid-state approaches [9]. In particular, hydro- and solvo-thermal methods are simple techniques allowing the precipitation of olivines at low temperature and controlled crystal growth [10]. Further improvement of the cathode performance may be reached by mixed compositions, LiMn1-xFexPO4. Iron incorporation in the olivine lattice has proven to enhance the electrochemical activity of the Mn3+/Mn2+ redox reaction by increasing both electronic and ionic conductivity, and by reducing lattice strain due to Jahn-Teller active ion Mn3+ [11, 12].Herein we report the synthesis and characterization of LiMnPO4, LiFePO4 and mixed LiMn0.5Fe0.5PO4 materials through solvothermal approach. Careful analysis of the electrochemical properties by potentiodynamic cycling with galvanostatic acceleration and galvanostatic cycling techniques were carried out in order to investigate the features of the Fe3+/Fe2+ and Mn3+/Mn2+ redox couples in the olivine structure. In addition, an advanced lithium-ion battery formed by combining a LiMn0.5Fe0.5PO4 cathode with a Sn-C anode is reported. The figure shows the galvanostatic cycling results of a Sn-C/LiMn0.5Fe0.5PO4 cell.

Iron L-edge and sulfur K-edge XANES spectroscopy analysis of pyrite leached by Acidianus manzaensis

Iron L-edge and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy analysis of pyrite leached by extreme thermophilic Archaea strain Acidianus manzaensis (A. manzaensis) was carried out. Leaching experiments show that the oxidation of pyrite can be accelerated by A. manzaensis. Leaching results show that with the increase of leaching time, pH value in the leaching solution gradually decreases, redox potential increases rapidly from day 0 to day 3, and then increases slowly. The SEM results show that the pyrite surfaces are corroded gradually by A. manzaensis, and the XRD results show that the leaching residues contain new compositions of jarosite and elemental sulfur (S0). The iron L-edge XANES spectroscopy analysis of pyrite during biooxidation indicates that pyrite is gradually converted to Fe(III)-containing species. The sulfur K-edge XANES spectroscopy analysis indicates that elemental sulfur is produced during bioleaching and maintains mass fractions of 3.2%–5.9%. Sodium thiosulfate was also detected from day 2 to day 4, indicating the existence of thiosulfate during biooxidation of pyrite.

Complex Interactions Between the Macrophyte Acorus Calamus and Microbial Fuel Cells During Pyrene and Benzo[a]Pyrene Degradation in Sediments.

This study investigated the interaction of the macrophyte Acorus calamus and sediment microbial fuel cells (SMFC) during the degradation of high molecular weight-polycyclic aromatic hydrocarbons (HMW-PAHs) in sediments. Over 367-days, the combination of macrophyte and SMFC led to an increase in pyrene and benzo[a]pyrene degradation rates by at least 70% compared to SMFC or macrophyte alone. While either the macrophyte or SMFC increased redox potential in sediments, redox potentials near the anode (approximately 6 cm depth) in the macrophyte-SMFC combination were markedly lower than that in the only macrophyte treatment. Moreover, rhizospheric bacterial communities in macrophyte-SMFC and macrophyte treatments were distinctly different. Aerobic genera (Vogesella, Pseudomonas, Flavobacterium and Rhizobium) and anaerobic genera (Longilinea, Bellilinea, Desulfobacca and Anaeromyxobacter) became dominant in the rhizosphere in macrophyte and macrophyte-SMFC treatments, respectively. In addition, the macrophyte-SMFC combination improved the numbers of not only aerobic but anaerobic PAHs degraders in sediments. So, the SMFC employment facilitated the formation of anoxic zones in sediments with oxygen loss and exudates from the roots. As a result, cooperation of anaerobic/aerobic microbial metabolism for accelerating HMW-PAHs removal occurred within sediments after combining macrophytes with SMFC.

Hydrothermal chloritization processes from biotite in the Toki granite, Central Japan: Temporal variations of of the compositions of hydrothermal fluids associated with chloritization

This paper describes the biotite chloritization process with a focus on mass transfer in the Toki granitic pluton, Central Japan, and also depicts the temporal variations in chemical characteristics of hydrothermal fluid associated with chloritization during the sub-solidus cooling of the pluton. Singular value decomposition (SVD) analysis results in chloritization reaction equations for eight mineral assemblages, leading to the quantitative assessment of mass transfer between the reactant and product minerals, and inflow and outflow of components through the hydrothermal fluid. The matrices for SVD analysis consist of arbitrary combinations of molar volume and closure component in the reactant and product minerals. The eight reactions represent the temporal variations of chemical characteristics of the hydrothermal fluid associated with chloritization: the progress of chloritization results in gradual increase of silicon, potassium, and chlorine and gradual decrease of calcium and sodium in the hydrothermal fluid with temperature decrease. The biotite chloritization involves two essential formation mechanisms: chlorite formation (CF) mechanism 1, small volume decrease from biotite to chlorite and large inflow of metallic ions such as Al3+, Fe2+, Mn2+, and Mg2+ from the hydrothermal fluid, and CF mechanism 2, large volume decrease and large outflow of the metallic ions into hydrothermal fluid. Chlorite produced with CF mechanism 1 dominates over that of CF mechanism 2, resulting in the gradual decrease of the metallic components in the hydrothermal fluid with chloritization progress. The chloritization reactions also give the temporal variations in physicochemical parameter of the hydrothermal fluid: a gradual decrease of pH and a gradual increase of redox potential in the hydrothermal fluid as chloritization proceeds. The combination of continuous reactions based on compositional variations in chlorite together with corresponding continuous AlIV variations gives an indication of the temporal variations in rates of decreasing and increasing concentration of chemical components in the hydrothermal fluid associated with chloritization. The biotite chloritization and resultant temporal variations of chemical and physicochemical characteristics in hydrothermal fluid act as a trigger for the successive dissolution–precipitation process of a granitic rock.

Out of the dark: transitional subsurface-to-surface microbial diversity in a terrestrial serpentinizing seep (Manleluag, Pangasinan, the Philippines).

In the Zambales ophiolite range, terrestrial serpentinizing fluid seeps host diverse microbial assemblages. The fluids fall within the profile of Ca2+-OH−-type waters, indicative of active serpentinization, and are low in dissolved inorganic carbon (DIC) (<0.5 ppm). Influx of atmospheric carbon dioxide (CO2) affects the solubility of calcium carbonate as distance from the source increases, triggering the formation of meter-scale travertine terraces. Samples were collected at the source and along the outflow channel to determine subsurface microbial community response to surface exposure. DNA was extracted and submitted for high-throughput 16S rRNA gene sequencing on the Illumina MiSeq platform. Taxonomic assignment of the sequence data indicates that 8.1% of the total sequence reads at the source of the seep affiliate with the genus Methanobacterium. Other major classes detected at the source include anaerobic taxa such as Bacteroidetes (40.7% of total sequence reads) and Firmicutes (19.1% of total reads). Hydrogenophaga spp. increase in relative abundance as redox potential increases. At the carbonate terrace, 45% of sequence reads affiliate with Meiothermus spp. Taxonomic observations and geochemical data suggest that several putative metabolisms may be favorable, including hydrogen oxidation, H2-associated sulfur cycling, methanogenesis, methanotrophy, nitrogen fixation, ammonia oxidation, denitrification, nitrate respiration, methylotrophy, carbon monoxide respiration, and ferrous iron oxidation, based on capabilities of nearest known neighbors. Scanning electron microscopy and energy dispersive X-ray spectroscopy suggest that microbial activity produces chemical and physical traces in the precipitated carbonates forming downstream of the seep's source. These data provide context for future serpentinizing seep ecosystem studies, particularly with regards to tropical biomes.

Electrochemical synthesis of polyaniline in reverse microemulsion

The electro-polymerization behavior of aniline in reverse (W/O) microemulsion was investigated. The experiment results show that the cyclic voltammetry polymerization behavior of aniline in W/O microemulsion is different from that in aqueous solution remarkably. With the increase of scan cycle, the oxidation potential shifts positively and the reduction potential shifts negatively, i.e., the redox potential difference increases. H+ apparent concentration affects the aniline polymerization evidently. When H+ concentration is lower than 0.08 mol/L, the electro-polymerization of aniline is difficult. With the increase of H+ concentration, the polymerization current of aniline increases gradually. Only when H+ concentration is high enough (0.5 mol/L), aniline can be well electro-polymerized. Moreover, under the same condition, the aniline polymerization current in W/O microemulsion is higher than that in aqueous solution. The scanning electron microscopy image shows that the deposited polyaniline (PANI) has uniform fiber morphology with diameter of about 100 nm. Further study result suggests that the electrochemical activity of the PANI in HCl is similar to that of the PANI prepared in aqueous solution.

Characteristics of Chromium Coprecipitation Mediated by Acidithiobacillus ferrooxidans DC

Removal of hexavalent chromium by precipitation from wastewater has received increasing interest in recent years. This study described the behavior of chromium and iron coprecipitation mediated by Acidithiobacillus ferrooxidans DC in an artificial simulated acid environment. In four parallel groups with the different concentrations of chromium(VI) (30, 60, 90, 120 mg/L), the precipitation efficiencies of chromium were enhanced uniformly by A. ferrooxidans DC. But chromium coprecipitation efficiency reduced as the initial chromium concentration increasing at the early stage. Especially in the 30 and 60 mg/L chromium groups, the maximum precipitation efficiency of chromium was improved from 56.22, 55.01 to 75.72, 74.37 % on the fourth day. Additionally, the characteristics of the precipitates were analyzed by x-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). Results showed that the precipitates were mainly present as jarosites and A. ferrooxidans was conducive to producing precipitates with good crystalline form and uniform dispersion with pH decrease, redox potential (ORP) increase, and iron oxidation. It can be concluded that the chromium could be incorporated into the jarosites through a certain biochemical reaction such as structural substitution, which shows a potential to remove chromium from wastewater by the bio-coprecipitation.

ANTIBACTERIAL EFFECT OF CATIONS ON HEAVY METALS

Objective: to study bactericidal properties of metal cations against Staphylococcus aureus and Pseudomonas aeruginosa . Material and methods. Minimum inhibitory and minimum bactericidal concentrations of metal salts were determined by the method of broth dilution. The kinetics of growth and dying of S.aureus and P.aeruginosa was studied in broth culture medium in the presence of metal cations in concentrations four times exceeding the minimum bactericidal concentrations. Results. The cations of silver and copper proved to possess a marked bactericidal effect. It was showed that an increase of oxidation-reduction potential leads to an increase of the antibacterial efficiency of the metal cations. Conclusion. A relation of the oxidizing activity of the metal cations and their bactericidal action was revealed.

Self-Discharge Phenomena in LiCoPO4 Electrodes

Polyanion-type materials, like lithium iron phosphate, are one of the recent great success in the research field of applied electrochemistry. Within this family, LiFePO4 (LFP) is a now mature material and its properties have been largely optimized thus opening the door to its commercial exploitation as cathode material in lithium-ion cells for power tools. In recent years the attention of the scientific community is focusing the great advantage of the substitution in the LFP lattice of Fe with Mn, Co or Ni. In fact the Mn3+/Mn2+, Co3+/Co2+ and Ni3+/Ni2+ couples show increasing redox potentials, all higher than the Fe3+/Fe2+, thus opening the door to large improvements in the energy performances. Among them LiCoPO4(LCP) is the best compromise: it shows in lithium cells an higher working potential compared to LFP, still within the working limits of the carbonate-based liquid electrolytes. However many fundamental aspects of the LCP properties and reaction mechanisms in lithium cells are not completely understood. Owing to this, large room for improvements in the performances in Li-cells of LCP is expected by assessing the synthesis route, the coatings, the doping/substitution and the electrolyte additives.The aim of this communication is to present our recent results concerning the study of one of the most detrimental phenomenon observed in the use of LCP in lithium-ion cells: self-discharge.Upon charge in lithium cells LCP undergoes to the following reversible two step oxidation:LiCoPO4 → Li0.7CoPO4+0.3Li++0.3e- → CoPO4+ Li+ + e- At the end of charge, in absence of flowing current, the self-relaxation of the charged LCP electrode is accompanied by a change in the OCV very similar to the discharge curve at constant current. Apparently prolonged OCV relaxation leads to the re-incorporation of lithium ions into the electrode that can be newly electrochemically charged. Self-discharge is a spontaneous phenomenon and has big technological consequences as it limits the use of LCP in commercial electrodes.Here we discuss the results of our study of LCP self-discharged electrodes by ex-situ synchrotron powder diffraction, synchrotron infrared spectroscopy and transmission electron microscopy. Self-discharge apparently occurs by the following spontaneous reactions in OCV conditions:CoPO4 + 0.7 Li++electrolyte (reduced form) → Li0.7CoPO4 + electrolyte (oxidized form)Li0.7CoPO4 + 0.3 Li++electrolyte (reduced form) → LiCoPO4 + electrolyte (oxidized form)The two self-discharge steps are accompained by accumulation of electrolyte decomposition by-products on the electrode surfaces.

Characterization of apoplast phenolics: In vitro oxidation of acetosyringone results in a rapid and prolonged increase in the redox potential

Previous work demonstrated that when tobacco cell suspensions were inoculated with certain bacterial strains, the redox potential of the suspensions would increase (oxidative), as much as 100 mV, and in some cases last more than an hour. To discover possible contributors to this prolonged redox potential burst, we examined the oxidation of various plant phenolics that were similar to those found in the cell suspensions. Acetosyringone, one of the major extracellular phenolics in tobacco cell suspensions, was unique in causing a prolonged increase in redox potential of more than 100 mV when incubated with H2O2 and peroxidase. The increase in potential appears to be due to a relatively stable radical intermediate. The length of time that the redox potential increased was dependent on the ratio of H2O2 and acetosyringone. The most favorable was a 1:1 ratio. In vitro characterization showed that production of this intermediate is favored by relatively low pH (around 6) and cooler temperatures possibly due to slower kinetics. Phosphate buffer was substituted for MES buffer, which had been used initially but was found to interfere with the oxidation. The results of this study demonstrate that apoplastic phenolics, in addition to often playing a role as antioxidants that reduce H2O2, can also cause rapid transient periods of extreme redox potential creating a local environment hostile to pathogen ingress.

Structural and redox properties of the small laccase Ssl1 from Streptomyces sviceus

Laccases (EC 1.10.3.2) are members of the multicopper oxidase family. They oxidize diverse electron-rich substrates through electron abstraction by the type 1 copper ion in the enzyme active site. Abstracted electrons are transferred to the trinuclear copper cluster, where molecular oxygen serves as final acceptor and is reduced to water. Laccase activity is assumed to depend on the redox potential of its type 1 copper ion. Whereas numerous studies have been undertaken to elucidate the determinants of the redox potential of type 1 copper ions in one-domain cupredoxins and in three-domain laccases, such experimental investigations are lacking for recently described, small, two-domain laccases. In this work, the crystal structure of the small laccase Ssl1 from Streptomyces sviceus was solved, and the positions that might influence the redox potential of Ssl1 were depicted. On the basis of this knowledge, several Ssl1 variants were constructed with an increase in redox potential of 16-81 mV, from 375 mV to 391-456 mV. Mutation of residues in close proximity to the type 1 copper center resulted in a predicted increase in the redox potential of the copper center; however, there was a reduced specific activity for the oxidation of 2,6-dimethoxyphenol, which has a relatively low redox potential. Mutations more distant to the type 1 copper also led to an increased redox potential of the copper center, and resulted in variants able to oxidize the high redox potential substrates 1,2-dihydroxyanthraquinone-3-sulfonic acid (Alizarin Red S) and indigo carmine more efficiently than wild-type Ssl1. The atomic coordinates of the structure of Ssl1 laccase from Streptomyces sviceus and structure factors have been deposited in the RCSB Protein Data Bank (4M3H) STRUCTURED DIGITAL ABSTRACT: •Ssl1 and Ssl1 bind by x-ray crystallography (View interaction).

Effect of redox potential on heavy metals and As behavior in dredged sediments

The effect of redox changes with respect to mobility of Cr, Cu, Pb, Zn, and As in five dredged sediments originating from disposal sites in the Netherlands was studied in the paper. An extraction procedure with a neutral unbuffered salt solution (0.01M CaCl2) was used to investigate the behavior of heavy metals and As in laboratory-based batch experiments conducted under oxidized and reduced redox conditions and carried out for 21 d. An increase in the redox potential (above +400 mV up to +503 mV) resulted in a rise of solubility of heavy metals in all sediments. However, at low redox potentials, an increase in As concentration was observed in the highly As-contaminated sediment. Mass balances were performed to follow the use of oxygen and the production of CO2, NO3-, SO42- and PO43-. An increase in redox potential has a large effect (40–80%) on the oxidation of reduced sulfur compounds to SO42-. Such increase in redox potential led to a solubilization of only about 1% of Cr, Cu, Pb, and Zn. Still, such low solubilization of these heavy metals leads to an increase of significance of the issue concerning ground and surface water quality.

Synthesis of mesoporous polymeric carbon nitride exhibiting enhanced and durable visible light photocatalytic performance

A thiourea precursor was employed to synthesize mesoporous carbon nitride (C3N4) by a thermal polycondensation process with high surface area SiO2 and nanosphere SiO2 as two types of hard templates. The resultant mesoporous C3N4 samples have high surface areas (105–112 m2/g) and mesopores with narrow sizes distribution (9.3 nm). Photocatalytic performance was evaluated by removal of NO in air under visible light irradiation. The results showed that mesoporous C3N4 samples exhibited significantly improved photocatalytic activity in comparison with bulk C3N4, which also exceeded that of N-doped TiO2 and C-doped TiO2. The activity enhancement can be ascribed to the synergistic effects of large surface area and pore volume, enhanced light-harvesting ability, increased redox potential, and reduced recombination of charge carriers. In addition to the high activity, the mesoporous C3N4 samples also showed high photochemical stability. The mesoporous C3N4 photocatalysts with enhanced and durable activity could provide a new efficient material for environmental pollution control.

Ascorbylperoxide from parenteral nutrition induces an increase of redox potential of glutathione and loss of alveoli in newborn guinea pig lungs

BackgroundBronchopulmonary dysplasia is one of the main complications associated with extreme prematurity. Oxidative stress is suspected to be a trigger event of this lung disease, which is characterized by impaired alveolar development. Peroxides, mainly ascorbylperoxide and H2O2, are known contaminant of parenteral nutrition. We hypothesize that these oxidant molecules induce bronchopulmonary dysplasia development. The aim was to determine if the infusion of ascorbylperoxide, whether in presence or absence of H2O2, is associated with oxidative stress, apoptosis and loss of alveoli in the lungs of newborn guinea pigs. MethodThree-day-old guinea pigs received parenteral solutions containing 0, 20, 60 or 180 µM ascorbylperoxide in the presence or not of 350 µM H2O2 (concentrations similar to those measured in parenteral nutrition). After 4 days, the lungs were collected for determination of glutathione's redox potential, caspase-3 activation (an apoptosis marker), alveolarization index (by histology), activation of Nrf2 and NFκB (biological markers of oxidative stress), and IL-6 and PGJ2 levels (markers of NFκB activation). Groups were compared by ANOVA, p < 0.05. ResultsLoss of alveoli was associated with ascorbylperoxide in a dose-dependent manner, without an influence of H2O2. The dose-dependent activation of caspase-3 by ascorbylperoxide was lower in the presence of H2O2. Ascorbylperoxide induced an increase of redox potential in a dose-dependent manner, which reached a plateau in presence of H2O2. Nrf2 and NFκB were activated by H2O2 but not by ascorbylperoxide. ConclusionResults suggest that ascorbylperoxide, generated in parenteral nutrition, is involved in the development of bronchopulmonary dysplasia, independently of the increase of the redox potential. This study underlines the importance of developing a safer formulation of parenteral nutrition.

The sustainable restoration of lakes—towards the challenges of the Water Framework Directive

Most in-lake restoration projects use deeply intrusive methods. They include the removal of bottom sediments and the use of high doses of precipitants. They are very radical, causing extinction of many organisms, and are very expensive. Alternative methods described in this paper are inexpensive, easy to use, effective, and sustainable (energy-efficient, not destructive for most of the biota). They have been applied to three lakes located in Poznań and the surrounding area (Western Poland) and their effectiveness has been documented. They include: (i) use of biomanipulation to increase trophic influence of zooplankton on phytoplankton, and small doses of iron sulphate to reduce phosphorus content in the water column, used in Maltański Reservoir, (ii) delivering water rich in nitrates from small tributaries to the deepest part of the lake, thus increasing redox potential and limiting the release of phosphorus from bottom sediments, used in Uzarzewskie Lake, (iii) oxygenation of hypolimnetic waters using wind aerators, iron treatment with small doses of coagulant and biomanipulation, used in Durowskie Lake. Use of limited doses of an innovative solid phosphorus precipitant called Sinobent® is also possible. These methods, in accordance with the intermediate disturbance hypothesis, increased the diversity of flora and fauna in the lakes and contributed to improvements in water quality. Simultaneous application of several methods, which prevented feedback mechanisms, increased the efficiency of lake restoration.

A mesocosm study of the effects of wet–dry cycles on nutrient release from constructed wetlands in agricultural landscapes

Given the projection that wet-dry periods will be more frequent in the US Midwest, a study was conducted to understand the impact of these hydro-climatic alterations on nutrient dynamics in wetlands constructed on former croplands in the region. Soil cores were collected from two constructed wetlands and a wooded riparian area (surface: 0-20 cm; subsurface: 40-60 cm) downslope from an agricultural field. Cores were either kept moist or subjected to a 5-week drying treatment, after which all cores were flooded for 36 days. Initial nitrate flux was significantly (p < 0.001) higher in the dry than in the moist treatment (44.5 vs. 1.9 mg N m(-2) per day), likely due to mineralization of organic matter. The NO3(-) released was rapidly denitrified (N2O flux: 18.9 mg N m(-2) per day), except in the subsurface soil cores in which processing of available N (N2O flux: 0.33 mg N m(-2) per day) was limited by low microbial activity (4 times lower CO2 production rate). The dry treatment also resulted in significantly (p < 0.01) higher inorganic P (Pi) flux (3.1 versus 1 mg P m(-2) per day in moist cores), with water-extractable soil P being the best predictor (r(2): 0.93, p < 0.03) of that flux. Despite a decline in redox potential (as low as -36.4 mv) and progressive increase in pore-water dissolved Fe, no relationship between floodwater Pi and dissolved Fe was observed, suggesting either limited contribution of reductive dissolution to Pi dynamics or rapid adsorption of the Pi released within the cores. Compared to the moist cores, geochemical modeling showed a consistent shift toward greater solubility of the calcium-phosphate minerals controlling pore-water Pi concentration in the dry treatment cores. These results suggest that dissolution of Ca-phosphate minerals could be a key factor controlling Pi mobility in constructed wetlands subjected to wet-dry cycles.

Multifunctional g-C3N4 Nanofibers: A Template-Free Fabrication and Enhanced Optical, Electrochemical, and Photocatalyst Properties

We have developed a facile, scale up, and efficient method for the preparation of graphitic-C3N4 nanofibers (GCNNFs) as electrodes for supercapacitors and photocatalysts. The as-synthesized GCNNFs have 1D structure with higher concentration of nitrogen that is favorable for higher conductivity and electrochemical performance. Secondly, the high surface area of GCNNF provides a large electrode-electrolyte contact area, sufficient light harvesting and mass transfer, as well as increased redox potential. Thus, the GCNNF supercapacitor electrode shows high capacitance of 263.75 F g(-1) and excellent cyclic stability in 0.1 M Na2SO4 aqueous electrolyte with the capacitance retention of 93.6% after 2000 cycles at 1 A g(-1) current density. GCNNFs exhibit high capacitance of 208 F g(-1) even at 10 A g(-1), with the appreciable capacitance retention of 89.5%, which proves its better rate capability. Moreover, the GCNNF shows enhanced photocatalytic activity in the photodegradation of RhB in comparison to the bulk graphitic-C3N4 (GCN). The degradation rate constant of GCNNF photocatalyst is almost 4 times higher than GCN. The enhanced photocatalytic activity of GCNNF is mainly due to the higher surface area, appropriate bandgap, and fewer defects in GCNNF as compared to GCN. As an economical precursor (melamine) and harmless, facile, and template-free synthesis method with excellent performance both in supercapacitors and in photodegradation, GCNNF is a strong candidate for energy storage and environment protection applications.

The influence of pH in metal/bromide catalyzed homogeneous aerobic oxidation. Part 1. Effect on activity and selectivity of p-xylene oxidation

By variation of the pH i.e. the acetate concentration, during oxidation of p-xylene in acetic acid/water mixtures and catalyzed by Co/Mn/Br, a maximum activity and selectivity is observed. The same is observed for the autoxidation of acetic acid by Co(II) acetate. If one operates at a lower or higher than the optimum pH, the rate of the formation of the desired product decreases and the rate of undesirable by-products increases. At sufficiently low pH the autoxidation reaction does not initiate. These observations can be rationalized by noting how the structures of the catalyst metal compounds change resulting in an increase in redox potentials of the metals as the acetate concentration decreases. Thus a thermodynamic balance of the required oxidation and reduction reactions of the metals is required. This explains why metal acetates i.e. basic compounds, are used as the initial catalytic species. Often autoxidation reactions are optimized by changing the catalyst concentration and it should be noted that this changes the pH as well. The pH dependence of the reactions that form undesirable by-products is summarized. The concept of thermodynamic and kinetic balance can also rationalize why metal/bromide catalysts are active while metal/fluoride, chloride, and iodide are either non-active or very weak.

Is copper chelation an effective anti-angiogenic strategy for cancer treatment?

Angiogenesis and the acquisition of an angiogenic phenotype is important for cancer cell proliferation. Copper in an essential trace element that participates in many enzymatic complexes like the cytochrome c, superoxide dismutase and lysyl oxidase and it is involved in processes, like embryogenesis, growth, angiogenesis and carcinogenesis. In particular, its involvement in carcinogenesis was described for the first time in oral submucous fibrosis, where fibroblasts produce large amounts of collagen in the presence of copper. Copper’s action in carcinogenesis is two-fold: (1) it participates in reactions with an increased redox potential that result in the production of oxidative products and oxidative stress. Through this mechanism, copper may cause DNA mutations in the nucleus and mitochondria or alterations to membrane phospholipids, (2) it participates in angiogenesis even in the absence of angiogenic molecules, as it was reported for the first time in rabbit cornea models with copolymer pellets charged with PGE1.Copper chelation regimens like penicillamine and tetrathiomolybdate are being described in the literature as having anti-angiogenic, anti-fibrotic and anti-inflammatory actions. Animal models of brain cancer that evaluated the anti-angiogenic properties of copper, have proven evidence of the reduction of tumor’s microvascular supply, tumor volume and vascular permeability after plasma copper levels reduction. Interestingly, plasma copper levels reduction was shown to suppress micrometastases generation in mice models of breast cancer.We hypothesize that copper chelation therapy: increases oxidative stress in cancer cells to a level that does not allow survival because of the reduction of anti-oxidative enzymes production. It may also result in inhibition of angiogenesis and of the initiation of the angiogenic switch, because copper normally enhances endothelial cell migration and proliferation, improves binding of growth factors to endothelial cells and enhances the expression of angiogenic molecules. Copper chelation may also reduce extracellular matrix degradation and cancer spread, through reduction of MMP-9 production and probably of other collagenases and may inhibit propagation of micrometastases. However, copper chelation therapy may enhance angiogenesis through reduction of thrombospondin-1, that results into an increase in VEGF–VEGFR2 complexes and a high level of active MMP-9.These hypotheses help in understanding of the anti-angiogenic action of copper chelation therapies and of the complex network of interactions between copper and other molecules involved in angiogenesis. It may also stimulate further research regarding differences in copper metabolism, the effects of anti-copper regimens on organs, the development of resistance, and their possible angiogenic action through thrombospondin expression reduction.