Addition Of Tungstate Research Articles

Characterization of the ModABC Molybdate Transport System of Pseudomonas putida in Nicotine Degradation.

Pseudomonas putida J5 is an efficient nicotine-degrading bacterial strain that catabolizes nicotine through the pyrrolidine pathway. In our previous study, we used Tn5 transposon mutagenesis to investigate nicotine metabolism-associated genes, and 18 nicotine degradation-deficient mutants were isolated from 16,324 Tn5-transformants. Three of the mutants were Tn5 inserts into the modABC gene cluster that encoded an ABC-type, high-affinity, molybdate transporter. In-frame deletion of the modABC genes abolished the nicotine-degrading ability of strain J5, and complementation with modABC either from P. putida or Arthrobacter oxidans restored the degrading activity of the mutant to wild-type level. Nicotine degradation of J5 was inhibited markedly by addition of tungstate, a specific antagonist of molybdate. Molybdate at a non-physiologically high concentration (100 μM) fully restored nicotine-degrading activity and recovered growth of the modABC mutant in a nicotine minimal medium. Transcriptional analysis revealed that the expression of modABC was up-regulated at low molybdate concentrations and down-regulated at high moybdate concentrations, which indicated that at least one other system was able to transport molybdate, but with lower affinity. These results suggested that the molybdate transport system was essential to nicotine metabolism in P. putida J5.

The effect of tungsten doping on the catalytic activity of α-MnO2 nanomaterial for ozone decomposition under humid condition

Ozone is a universal air pollutant and its stable decomposition under humid condition is still a challenge. In this work, the effect of tungsten doping on the activity of α-MnO2 for ozone decomposition was first investigated. Tungsten was doped into MnO2 with addition of tungstate in a hydrothermal reaction solution. The as-synthesized catalysts were characterized by XRD, SEM, TEM, BET, XPS, ICP-AES, Raman, H2-TPR, O2-TPD, NH3-TPD and EPR. The results indicated that doping of tungsten made the morphology change from nanorods to nanoparticles with great increase of specific surface area. In addition, more oxygen vacancies were formed, and the surface acidity was greatly enhanced, accordingly the tungsten-doped MnO2 exhibited enhanced activity and stability at room temperature under dry and particularly under humid condition (RH = 65%). It indicates that the doping with a high valence metal such as W6+ into MnO2 is a promising method to obtain efficient ozone-decomposition catalyst.

Synthesis of sol–gel derived calcium silicate with calcium tungstate addition

Synthesis of sol–gel derived calcium silicate with calcium tungstate addition

Electrochemical Dissolution of Tungsten Carbide in NaCl-KCl-Na2WO4 Molten Salt

Tungsten carbide was utilized as anode to extract tungsten in a NaCl-KCl-Na2WO4 molten salt, and the electrochemical dissolution was investigated. Although the molten salt electrochemical method is a short process method of tungsten extraction from tungsten carbide in one step, the dissolution efficiency and current efficiency are quite low. In order to improve the dissolution rate and current efficiency, the sodium tungstate was added as the active substance. The dissolution rate, the anode current efficiency, and the cathode current efficiency were calculated with different contents of sodium tungstate addition. The anodes prior to and following the reaction, as well as the product, were analyzed through X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The results demonstrated that the sodium tungstate could improve the dissolution rate and the current efficiency, due to the addition of sodium tungstate decreasing the charge transfer resistance in the electrolysis system. Due to the fact that the addition of sodium tungstate could remove the carbon during electrolysis, pure tungsten powders with 100 nm diameter were obtained when the content of sodium tungstate was 1.0 pct.

Plasma electrolytic oxidation of AZ31 magnesium alloy in aluminate-tungstate electrolytes and the coating formation mechanism

Plasma electrolytic oxidation (PEO) of AZ31 magnesium alloy under pulsed bipolar regimes has been carried out in an aluminate electrolyte with the addition of 0–25 g l−1 Na2WO4·2H2O. Black coatings are formed with the addition of tungstate. Sequential anodizing has also been adopted to investigate the coating formation mechanisms by tracing the elemental distribution of W and Al in the coatings. The coatings develop an outer layer, inner layer and a barrier layer after a certain period of PEO. At the later stage of the PEO, the coating grows inwardly, which was accompanied by the strong penetrating discharges. The penetrating discharges have caused significant anion deposition, and the electrolyte species, such as W and Al, can be transported to the coating/substrate interface instantly. The anodic current density within the penetrating discharge channels is estimated to be ∼104 A cm−2, which is high enough to melt the coating materials beneath the pancake structure and cause the direct thermal decomposition of water and hence the anomalous gas evolution reported for PEO. X-ray photoelectron spectroscopy (XPS) denies that free state W exists in PEO coatings.

Effects of pulsed current on plasma electrolytic oxidation

In this paper, the effects of different current pulse parameters on the resulting PEO layers are described. The properties of the layers were assessed optically, with a scanning electron microscope, and the corrosion resistance has been measured. It is shown that the polarity and the frequency of the applied current has a high influence on the properties of the resulting layers. Unipolar pulses with low frequencies produce rougher layers with reduced corrosion protection. Different additives were added to the electrolyte in order to improve corrosion resistance of the resulting layers. Some of the additives, especially if based on tungstate and molybdate resulted in a colouring effect of the layer. This colouring effect is most pronounced when low frequencies and unipolar pulses are used. Higher frequencies and bipolar pulses create smoother and denser layers with higher corrosion resistance. The highest corrosion resistance was obtained by combining addition of tungstate and high frequency bipolar pulses.

Improving Corrosion Resistance of AA2014 Welds with Micro Arc Oxidation

Autogenous single pass full penetration welds of 2.8 mm thick AA 2014 plates were produced by un-pulsed and pulsed gas tungsten arc welding (GTAW) process. In pulsed current mode, two levels of pulsing viz., 3 and 6 Hz were employed. In order to improve the corrosion resistance of weld metals, micro arc oxidation (MAO) treatment was given in aqueous silicate solution containing either borax or tungstate. The MAO treatment was carried out for 10, 20 and 30 minutes. Irrespective of the electrolyte composition, surface roughness increased with increasing treatment duration. However, the effect was observed to be significant with borax addition. X-ray diffraction studies showed that γ-Al2O3 content in the coating continued to increase up to 20 minutes and for the coating produced with 30 minutes duration the α-Al2O3 content was found to be more than γ-Al2O3. The coating treated for 30 minutes exhibited relatively poorer corrosion resistance than the other coated specimens. The better corrosion resistance offered by the coating obtained after 20 minutes, compared with the other coatings, could be attributed to the nature of the oxide and its content. Even though tungstate addition improved hardness of the coating, borax addition was found to enhance the corrosion resistance.

Effect of halides ions on H2 production during aluminum corrosion in formic acid and using some inorganic inhibitors to control hydrogen evolution

This study reports on the systematic assessment of H2 production by corrosion of aluminum in formic acid solution in the absence and presence of halide ions and some inorganic inhibitors using hydrogen evolution measurements and complemented by scan electron microscope (SEM) and energy dispersive X-ray (EDX). It is shown that the rate of H2 production and in turn the dissolution of aluminum increases with increasing acid concentration and solution temperature. Addition of halides ions enhances the active dissolution of aluminum and tends to breakdown the passive film and increases H2 production. The addition of tungstate, molybdate and nitrite anions to (1.0 M formic acid + 0.2 M Cl−) solution retard the rate of H2 production, where the H2 production process decreases in the following in the order: tungstate > molybdate > nitrite.

Alternative Nitrogenases in Anabaena variabilis: The Role of Molybdate and Vanadate in Nitrogenase Gene

Anabaena variabilis ATCC 29413 has two distinct nitrogenases that function in heterocysts, a conventional Mo-nitrogenase and an alternative V-nitrogenase. Synthesis of these two enzymes was repressed in cells growing with a source of fixed nitrogen, such as ammonium; however, the V-nitrogenase was also repressed by Mo. Expression of the V-nitrogenase which was not affected by V and expression of the Mo-nitrogenase was not affected by the presence or absence of either Mo or V. In the absence of both Mo and V in an environment lacking fixed nitrogen, cells became starved for both metals; however, low levels of nitrogen fixation and slow growth persisted. A mutant lacking the V-nitrogenase was still able to grow very slowly in Mo-and V-free medium; however, loss of the Mo-nitrogenase in a nifDK1 mutant abolished the residual growth, suggesting that only the Mo-nitrogenase functioned under these conditions to support slow growth. The addition of vanadate, molybdate, or tungstate, which is transported by the molybdate transporter, to cells starved for these metals resulted in an increase in nitrogenase activity within two hours after the addition of the metal and this increase required new protein synthesis. While tungstate functioned about as well as vanadate in supporting acetylene reduction, the cells were not able to grow any better with tungstate than with no added metal. A mutant lacking the V-nitrogenase showed no increase in nitrogenase activity upon addition of tungstate, suggesting that the V-nitrogenase was able to incorporate tungstate. Tungstate was able to substitute for molybdate in repressing transcription of a Mo-transport gene, but it did not repress transcription of the vnfH gene, which was repressed by Mo. The availability of Mo and V plays an important role in controlling whether the Mo-or the V-nitrogenase is used for nitrogen fixation.

Connecting ruthenium substituted Keggin-type tungstophosphates by oxotungstic bridges: Evidence for the steric effect of {RuL3}2+ (L3 = η6-arene, (DMSO)3) fragments

Abstract The intrinsic reactivity of the organoruthenium-grafted tungstophosphates [α-PW11O39{Ru(η6-arene)(H2O)}]5− and [α-PW11O39{Ru(DM S O)3(H2O)}]5− has been studied as a prerequisite for later catalytic studies. Upon reflux in aqueous solution, they partially transform into [{PW11O39Ru(η6-arene)}2{WO2}]8− (when arene = benzene, toluene…) and [α-PW11O39{Ru(DM S O)}]5−, respectively. In the former case, the conversion is markedly increased by deliberate addition of tungstate: through a solution NMR study, we show that [{PW11O39Ru(η6-p-cymene)}2{WO2}]8− is quantitatively obtained by refluxing a 2:1:2 mixture of [α-PW11O39]7−, [Ru(η6-p-cymene)Cl2]2 and [WO4]2− at pH 3. In contrast, a different type of complex, [{PW11O39Ru(DM S O)3}2{(WO2(H2O))2O}]8−, is formed by reaction of [α-PW11O39{Ru(DM S O)3(H2O)}]5− with tungstate; it has been characterized by single crystal X-ray diffraction analysis of an acidic potassium salt, and by 183W solution NMR. The more sterically demanding {Ru(DM S O)3}2+ fragment probably does not allow the formation of [{PW11O39Ru(DM S O)3}2{WO2}]8−, while connection of {PW11O39Ru(DMSO)3}5− subunits is possible through the larger {(WO2(H2O))2O}2+ bridge.

Oxidation of tungstate‐containing green rust (Cl–) in aqueous solution

AbstractThe influence of tungstate on the oxidation of green rust [GR(Cl–)], which contains both Fe(II) and Fe(III), was investigated by synthesizing suspensions of GR(Cl–) containing tungstate and oxidizing them via injection of N2 gas containing O2. XRD and TEM analyses were used for characterizing the solid particles formed during synthesis and oxidation. The results showed that the formation of fine α‐FeOOH was enhanced by the addition of tungstate to the GR(Cl–) suspensions, while GR(Cl–) without tungstate was transformed primarily into γ‐FeOOH. The pH, oxidation‐reduction potential (ORP), and dissolved oxygen (DO) values of the aqueous solution were measured during oxidation of GR(Cl–) with and without tungstate. The results showed that whereas the pH value of the solution was decreased and the ORP value was increased monotonically by oxidation of GR(Cl–), the pH and ORP values during oxidation the GR(Cl–) suspension containing tungstate revealed characteristic changes with time. XAS was also used for characterizing the chemical state and local structure of tungstate in the oxidized particles. The results indicated that the local structure of WO was essentially retained in the particles precipitated from GR(Cl–) suspensions.

Enhanced Eu3+ Emission in Aqueous Phosphotungstate Colloidal Systems: Stabilization of Polyoxometalate Nanostructures

Luminescent Eu(3+)-containing polyphosphate-tungstate aqueous colloidal systems were prepared and studied as a function of the relative polyphosphate-tungstate content. In polyphosphate-rich solutions, Eu(3+) ions occupy cagelike sites composed of phosphate groups from the metaphosphate chains. In these sites, an average number of 0.5 water molecule coordinates to an Eu(3+) ion and the (5)D(0) emission quantum efficiency is 0.22. Tungstate addition leads to important modifications in neighboring Eu(3+) leading to coordination sites in the aqueous medium where metal ions are completely hidden from interactions with solvent molecules. Transmission electron microscopy results clearly show W-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstate relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu(3+) in polyoxometalate (POM)-like sites by comparison with the well-known decatungstoeuropate [EuW(10)O(36)](9-) structure. These new aqueous colloids display surprisingly high (5)D(0) emission quantum efficiencies of ca 80% because of the strong ligand field provided by tungstate POM ligands and the complete absence of water molecules from the Eu(3+) first coordination shell.

Involvement of nitrate reduction in the tolerance of tomato (Solanum lycopersicum L.) plants to prolonged root hypoxia

The putative role of nitrate and nitrate reductase in the tolerance to prolonged hypoxia was investigated in tomato plants. Nitrogen nutrition has been modified either by deprivation of nitrate or by addition of tungstate—an inhibitor of nitrate reductase (NR)—in the culture medium. In the absence of nitrate as well as in the presence of tungstate, plant growth was significantly disturbed. In the presence of nitrate, the growth of hypoxic plants maintained, nitrate absorption and NR activity increased and a significant release of nitrite into the medium was observed. This mechanism of nitrate reduction, called nitrate respiration, could be an alternative pathway to oxygen-dependent respiration during root hypoxia and a transient adaptation of tomato roots to hypoxic conditions.

Sodium tungstate (Na2WO4) exposure increases apoptosis in human peripheral blood lymphocytes

The potential for adverse health effects of using tungsten and its alloys in military munitions are an important concern to both civilians and the US military. The toxicological implications of exposure to tungsten, its alloys, and the soluble tungstate (Na2WO4) are currently under investigation. To examine tungstate toxicity, a series of experiments to determine its in vitro effects on cells of the immune system were performed. We identified alterations in isolated human peripheral blood lymphocytes (PBL) treated in vitro with sodium tungstate (0.01, 0.1, 1.0, and 10 mM). Analyses of apoptosis with annexin V and propidium iodide revealed a dose- and time-dependent increase in the quantity of cells in early apoptosis after tungstate exposure. Reductions in the number of cells entering into the cell cycle were also noted. Exposure of PBL to tungstate (1 mM) and Concanavalin A (ConA) for 72 h reduced the number of cells in S and G2/M phases of the cell cycle. There were alterations in the numbers of cells in G0/G1, S, and G2/M phases of the cell cycle in long-term THP-1 (acute leukemic monocytes) cultures treated with tungstate (0.01, 0.1, 1.0, and 10 mM). Gel electrophoresis, silver staining, and LC-MS/MS showed the cytoplasmic presence of histone H1b and H1d after 72 h of tungstate exposure. The addition of tungstate to cultures resulted in significant reductions in the quantity of interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α), and IL-6 produced by stimulated [CD3/CD28, ConA, or lipopolysaccharide (LPS)] and tungstate-treated lymphocytes. Taken together, these data indicate that tungstate increases apoptosis of PBL, alters cell cycle progression, reduces cytokine production, and therefore warrants further investigation.

Unexpected chemoreceptors mediate energy taxis towards electron acceptors in Shewanella oneidensis

Shewanella oneidensis uses a wide range of terminal electron acceptors for respiration. In this study, we show that the chemotactic response of S. oneidensis to anaerobic electron acceptors requires functional electron transport systems. Deletion of the genes encoding dimethyl sulphoxide and trimethylamine N-oxide reductases, or inactivation of these molybdoenzymes as well as nitrate reductase by addition of tungstate, abolished electron acceptor taxis. Moreover, addition of nigericin prevented taxis towards trimethylamine N-oxide, dimethyl sulphoxide, nitrite, nitrate and fumarate, showing that this process depends on the DeltapH component of the proton motive force. These data, together with those concerning response to metals (Bencharit and Ward, 2005), support the idea that, in S. oneidensis, taxis towards electron acceptors is governed by an energy taxis mechanism. Surprisingly, energy taxis in S. oneidensis is not mediated by the PAS-containing chemoreceptors but rather by a chemoreceptor (SO2240) containing a Cache domain. Four other chemoreceptors also play a minor role in this process. These results indicate that energy taxis can be mediated by new types of chemoreceptors.

Physicochemical Properties of Micelles of Poly(styrene-b-[3-(methacryloylamino)propyl]trimethylammonium chloride-b-ethylene oxide) in Aqueous Solutions

Polymeric micelles from a new triblock copolymer, polystyrene-block-poly[(3-(methacryloylamino)propyl)trimethylammonium chloride]-block-poly(ethylene oxide) (PS-b-PMAPTAC-b-PEO), were prepared in aqueous solutions and characterized by various techniques including dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. The micelle consists of a PS core, PMAPTAC shell, and PEO corona. It was revealed by SEM and DLS measurements that the micelles have a spherical structure with a hydrodynamic diameter about 75 nm. The addition of tungstate to the micellar solution caused a morphological change in the micelles from extended to shrunken spheres, which can be attributed to the fact that electrostatic repulsion among the cationic PMAPTAC blocks is canceled by the negative charge of the bound tungstate ions. Effective incorporation of tungstate ions into the micelles were confirmed by TEM and zeta-potential measurements.

Tungstate as complex‐forming reagent facilitating separation of selected polyphenols by capillary electrophoresis and its comparison with borate

A novel electrophoretic BGE containing tungstate as complex-forming reagent is suitable for the separation of polyphenols. Similar to molybdate-containing BGE reported earlier (cf. M. Polásek, et al.., Talanta 2006, 69, 192) addition of tungstate to BGE affects significantly migration of compounds/ligands with vicinal -OH groups due to the formation of negatively charged complexes involving W(VI) as central ion. Baseline separation of mixtures of flavonoids (apigenin, luteolin, hyperoside, quercetin, and rutin) and phenolic acids (chlorogenic and p-coumaric acid) was achieved within 15 min with optimized BGE of pH 7.4 containing 50 mM N-(2-hydroxyethyl)piperazine-2'-(2-ethanesulfonic acid) (HEPES), 2.2 mM tungstate, and 25% v/v of methanol. The separation was performed in a 75 cm (effective length 42 cm)x 75 microm id uncoated fused-silica capillary at 30 kV with spectrophotometric detection at 275 nm. The calibration curves were rectilinear for 25-175 microg/mL of all analytes (cinnamic acid as the internal standard). The LODs ranged from 1.8 to 6 microg/mL for all analytes except for chlorogenic acid. Intraday precision (n = 6) of migration times (RSD < or = 1.2%) and peak areas (RSD < or = 5.6%) was evaluated. The tungstate-based BGEs can be alternatively utilized for the analysis of polyphenols at considerably lower pH than with conventional alkaline borate-based BGEs.

Involvement of carbon monoxide produced by heme oxygenase in ABA-induced stomatal closure in Vicia faba and its proposed signal transduction pathway

Carbon monoxide (CO) has recently proven to be an important bioactive or signaling molecule in mammalian cells. Its effects are mainly mediated by nitric oxide (NO) and cyclic GMP (cGMP). In Vicia faba leaves, CO production and heme oxygenase (HO) activity, an important CO synthetic enzyme, are first reported to increase in response to ABA treatment, which could result in stomatal closure. Interestingly, ABA-induced stomatal closure in V. faba guard cells is partially blocked when the synthetic CO inhibitor ZnPP, or the CO/NO scavenger Hb is added. Furthermore, we show that, exogenously applied CO donor, hematin, and CO aqueous solution not only result in the enhancement of CO release, but also time-dependently induce stomatal closure, and the latter is mimicked by the application of an NO donor SNP. The above-mentioned stomatal closure effects are differentially reversed by the addition of tungstate, a potent inhibitor of NO synthetic enzyme nitrate reductase (NR), the specific NO scavenger cPTIO, ZnPP, or Hb. During treatment for 4 h, SNP, 0.01% CO aqueous solution or hematin significantly triggers NO synthesis, whereas cPTIO, or tungstate approximately fully inhibits NO fluorescence. Additionally, application of the GC inhibitor ODQ blocks CO-induced stomatal closure. This inhibition could be reversed when 8-Br-cGMP is added. Thus, the above results suggest that CO produced by HO is involved in ABA-induced stomatal closure, and NO and cGMP may function as downstream intermediates in the CO signaling responsible for stomatal closure.

Genetic and Biochemical Evidence for the Involvement of a Molybdenum-Dependent Enzyme in One of the Selenite Reduction Pathways ofRhodobacter sphaeroidesf. sp.denitrificansIL106

Selenite reduction in Rhodobacter sphaeroides f. sp. denitrificans was observed under photosynthetic conditions, following a 100-h lag period. This adaptation period was suppressed if the medium was inoculated with a culture previously grown in the presence of selenite, suggesting that selenite reduction involves an inducible enzymatic pathway. A transposon library was screened to isolate mutants affected in selenite reduction. Of the eight mutants isolated, two were affected in molybdenum cofactor synthesis. These moaA and mogA mutants showed an increased duration of the lag phase and a decreased rate of selenite reduction. When grown in the presence of tungstate, a well-known molybdenum-dependent enzyme (molybdoenzyme) inhibitor, the wild-type strain displayed the same phenotype. The addition of tungstate in the medium or the inactivation of the molybdocofactor synthesis induced a decrease of 40% in the rate of selenite reduction. These results suggest that several pathways are involved and that one of them involves a molybdoenzyme. Although addition of nitrate or dimethyl sulfoxide (DMSO) to the medium increased the selenite reduction activity of the culture, neither the periplasmic nitrate reductase NAP nor the DMSO reductase is the implicated molybdoenzyme, since the napA and dmsA mutants, with expression of nitrate reductase and DMSO reductase, respectively, eliminated, were not affected by selenite reduction. A role for the biotine sulfoxide reductase, another characterized molybdoenzyme, is unlikely, since its overexpression in a defective strain did not restore the selenite reduction activity.

Tungstate Treatment Improves Leydig Cell Function in Streptozotocin‐Diabetic Rats

Oral administration of sodium tungstate to adult male streptozotocin-diabetic rats for 3 months normalized serum levels of glucose, insulin, luteinizing hormone, and follicle-stimulating hormone. These effects were accompanied by an increase in reproductive performance, which was related to a strong improvement in Leydig cell function markers, such as the recovery of the number of Leydig cells and serum testosterone levels. Moreover, this in vivo recovery was related to a concomitant increase in the cell expression of insulin receptors. Tungstate treatment did not modify Leydig cell function in healthy rats. Furthermore, the addition of tungstate or insulin to the mTLC-1 cell line from Leydig cell origin increased the phosphorylation states of MAP-kinase and glycogen synthase kinase-3. Our results indicate that tungstate treatment in diabetic rats leads to a recovery of reproductive performance by increasing the number of Leydig cells. This increase contributes to the recovery of their functionality, thereby improving the overall function of these cells. We propose that this improvement is caused by the combined effect of the tungstate-induced normalization of insulin glucose and luteinizing hormone serum levels and a direct action of the effector on Leydig cells through modulation of at least MAP-kinase and glycogen synthase kinase-3 activities.