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PubMed2006

Tungsten effects on survival, growth, and reproduction in the earthworm, Eisenia fetida.

To provide basic toxicity data for formulating risk characterization benchmarks, the effects of tungsten on survival, growth, and reproduction were investigated in the earthworm Eisenia fetida. Parallel studies with lead as a reference toxicant also were conducted. Although sodium tungstate (Na2WO4) was less acutely toxic than lead nitrate (Pb(NO3)2) in 14-d spiked field soil acute toxicity assays (lethal concentrations for 50% of organisms: W, 6,250 mg/kg; Pb, 2,490 mg/kg), tungstate completely inhibited reproduction in 28- and 56-d assays at all tested tungsten concentrations (> or = 704 mg/kg). By comparison, cocoon production was not significantly reduced for lead concentrations until concentrations reached 766 mg/kg, and cocoon production was still observed at the highest concentration tested (1,650 mg/kg). These data indicate that tungsten is a reproductive toxicant for earthworms and that, by comparison, its sublethal toxicity is greater than that of lead. Toxicity data for other soil invertebrate species are required to fully establish benchmark levels/ecological soil screening levels for tungsten.

Animals↗
PubMed2000

Stimulation of nitrate reductase activity of the salt-tolerant yeast Rhodotorula glutinis by tungsten in the presence of molybdenum.

Tungsten in the presence of molybdenum stimulates nitrate reductase activity and growth of the salt-tolerant yeast Rhodotorula glutinis on medium with nitrates. Tungsten is not incorporated in proteins possessing nitrate reductase activity. A significant increase in molybdenum cofactor in cells grown on medium with equimolar amounts of molybdenum and tungsten may relate to the stimulatory action of tungsten.

Enzyme Stability↗
PubMed2002

Potential late health effects of depleted uranium and tungsten used in armor-piercing munitions: comparison of neoplastic transformation and genotoxicity with the known carcinogen nickel.

Limited data exist to permit an accurate assessment of risks for carcinogenesis and mutagenesis from embedded fragments or inhaled particulates of depleted uranium (DU). Ongoing studies have been designed to provide information about the carcinogenic potential of DU using in vitro and in vivo assessments of morphological transformation as well as cytogenetic, mutagenic, and oncogenic effects. For comparison, we also examined tungsten alloys used in military projectiles and the known carcinogen nickel. Quantitative and qualitative in vitro transformation studies were done to assess the carcinogenic potential of radiation and chemical hazards. Using a human osteosarcoma cell model, we demonstrated that soluble and insoluble DU compounds can transform cells to the tumorigenic phenotype, as characterized by morphological, biochemical, and oncogenic changes consistent with tumor cell behavior. Tungsten alloys and nickel were also shown to be neoplastic transforming agents, although at a frequency less than that of DU. Sister chromatid exchange, micronuclei, and alkaline filter elution assays showed DU and tungsten alloys were genotoxic. Exposure to a nontoxic, nontransforming dose of DU induced a small but statistically significant increase in the number of dicentrics formed in cells. These results suggest that long-term exposure to DU or tungsten alloys could be critical to the development of neoplastic disease in humans and that additional studies are needed.

Carcinogens↗
PubMed1993

[Risks attributable to the occurrence of tin, silver and tungsten in the air of the workplace environment--methods of determination].

Tin, silver and tungsten constitute serious threat to the health of the employees of Polish industry. As no standard methods for determination of those metals in the atmospheres of workplaces were available, measurements of their concentrations in the workplace atmospheres were not performed, and, therefore, determination of the resultant risks to the health of the people exposed to those metals was not possible. A spectrophotometric method of determination has been developed for tin, which is based on the formation of coloured Sn(IV)--pyrocatechine complexes in the dilute sulfuric and citric acid medium in the presence of cetyltrimethylammonium bromide (absorbance determined at lambda = 600 nm). The detectability of the method is 0.5 mg/m3. To ensure the selectivity of the method in the presence of foreign cations and acid anions. Sn should be pre-separated from the disturbing ions by the extraction method. For silver determination, a method using atomic absorption spectrometry with air-C2H2 flame has been developed. The detectability of the method is 0.005 mg/m3. The presence of cations of other metals or of acid anions does not affect the results obtained with this method. The new-developed method of tungsten determination involves reaction with calcium thiocyanate in HCl medium in the presence of stannous chloride, followed by assessing the tungsten complex, pre-extracted with izoamyl, alcohol, by spectrophotometry at lambda = 405 nm. This method enables determination of 1 mg/m3 tungsten. The results are affected only by the presence of Mo in quantities exceeding 4 mg/m3 and Al in quantities exceeding 2 mg/m3.

Air Pollutants, Occupational↗
PubMed1997

The nature of thrombosis induced by platinum and tungsten coils in saccular aneurysms.

PURPOSE: To compare the efficacy and biocompatability of electrolytic and mechanically detachable embolization coils of two metal types. METHODS: Experimental saccular aneurysms in pigs were used to assess embolization induced by platinum or tungsten coils. Longitudinal angiographic and histologic studies were performed on treated and untreated (control) aneurysms to compare thrombosis and cellular responses after embolization with electrolytically detachable platinum coils and with mechanically detached tungsten coils. RESULTS: Fewer tungsten than platinum coils were needed to induce thrombosis. The inflammatory response within the aneurysmal lumen was more florid in embolized aneurysms than in control aneurysms. No difference was found in the timing or extent of accumulation of eosinophils, lymphocytes, or polymorphs between the two coils used. Giant cell responses were more marked in treated aneurysms; tungsten coils more than platinum coils. The amount of collagen and fibrosis present increased over the study period and was similar in treated and control aneurysms. CONCLUSION: The coil type influenced the initial cellular response but had little effect on the rate or degree to which blood clot within the aneurysm was replaced by fibrous tissue.

Animals↗
PubMed1997

Tungsten determination in biological fluids, hair and nails by plasma emission spectrometry in a case of severe acute intoxication in man.

A healthy 19-year-old recruit in a French artillery regiment drank 250 mL of a mixture of beer and wine that had rinsed in a hot 155-mm gun-barrel. Fifteen minutes later, he complained of nausea followed by seizures. He was comatose for 24 h, presenting signs of encephalopathy. A moderate renal failure was noted initially and worsened to an extensive tubular necrosis with anuria on the day after the incident. The first toxicological investigations only showed a 0.31 g/L blood ethanol. Then inductively-coupled plasma (ICP) emission-spectrometry revealed very high concentrations of tungsten in the "beverage" as well as in gastric content, blood and urine (1540 mg/L, 8 mg/L, 5 mg/L, and 101 mg/L, respectively). The nature of the metal was confirmed by ICP coupled to mass spectrometry. A simple and reliable ICP quantitative assay of tungsten in biological fluids, hair and nails was then developed. It showed high blood levels (> 0.005 mg/L) until day 13 in spite of six hemodialyses, and in urine until D33. Tungsten was also incorporated in hair and nails. To the best of our knowledge, such an intoxication has never been reported before though this drinking seems to be traditional in the French Artillery. It has probably been favored by the unusually high volume of beverage absorbed and by the new alloy of the gun, containing tungsten. The clinical evolution was satisfactory over weeks and the patient was declared totally cured after five months.

Adult↗
PubMed2006

A simple hydrothermal method for the large-scale synthesis of single-crystal potassium tungsten bronze nanowires.

The large-scale synthesis of single-crystal K(x)WO(3) tungsten bronze nanowires has been successfully realized by a hydrothermal method under mild conditions. Uniform K(0.33)WO(3) nanowires with diameters of 5-25 nm and lengths of up to several micrometers are obtained. It is found that the morphology and crystallographic forms of the final products are strongly dependent on the sulfate and citric acid, which may act as structure-directing and soft-reducing agent, respectively. Some other influential factors on the growth of tungsten bronze nanowires, such as temperature and reaction time, are also discussed. It is worth noting that other alkali metal tungsten bronzes such as (NH(4))(x)WO(3), Rb(x)WO(3), and Cs(x)WO(3) could also be selectively synthesized by a similar route. Thus, this novel and efficient method could provide a potential mild route to selectively synthesize various tungsten bronze on-dimensional nanomaterials.

Journal Article↗
PubMed1998

The Effect of the Simultaneous Addition of Molybdenum and Tungsten to the Culture Medium on the Formate Dehydrogenase Activity from Methylobacterium sp. RXM

Shake flask cultivation of the facultative methylotroph Methylobacterium sp. RXM was carried out by using a statistical experimental design to investigate the role of metal association on the formate dehydrogenase (FDH) levels. The maximal values of FDH activity were obtained for tungsten concentration up to 0.6 µM and for molybdenum concentration between 0.6 and 0.9 µM. The negative polynomial parameter (beta2) for tungsten compared with the positive polynomial parameter (beta1) for molybdenum on the FDH activity suggested that the latter metal exerts a stronger influence on the enzyme stimulation than the tungsten metal. A negative interaction between both metals was found, suggesting that tungsten and molybdenum shared an antagonistic effect on the enzyme activity.

Journal Article↗
PubMedDate not supplied

Combinatorial electrochemical synthesis and characterization of tungsten-based mixed-metal oxides.

Automated systems for electrochemical synthesis and high-throughput screening of photoelectrochemical materials were developed and used to prepare tungsten-based mixed-metal oxides, W(n)O(m)M(x) [M = Ni, Co, Cu, Zn, Pt, Ru, Rh, Pd, and Ag], specifically for hydrogen production by photoelectrolysis of water. Two-dimensional arrays (libraries) of diverse metal oxides were synthesized by automated cathodic electrodeposition of the oxides on Ti foil substrates. Electrolytes for the mixed oxides were prepared from various metal salts added to a solution containing tungsten stabilized as a peroxo complex. Electrodeposition of the peroxo-stabilized cations gave rise to three distinguishable oxide groups: (1) mixed-metal oxides [Ni], (2) metal-doped tungsten oxides [Pt, Ru, Rh, Pd, Ag], and (3) metal-metal oxide composites [Co, Cu, Zn]. The oxides typically showed n-type semiconducting behavior. Automated measurement of photocurrent using a scanning photoelectrochemical cell showed the W-Ni mixed oxide had the largest relative zero bias photocurrent, particularly at a low Ni concentration (5-10 atomic percent Ni). Pt and Ru were also found to increase the photoactivity of bulk tungsten oxide at relatively low concentrations; however, at concentrations above 5 atomic percent, crystallization of WO(3) was inhibited and photoactivity was diminished. Addition of Co, Cu, and Zn to WO(3) was not found to improve the photoelectrochemical activity.

Journal Article↗
PubMed2001

Tungsten fluorides: syntheses and electrochemical characterization in the FLINAK molten salt eutectic.

The following tungsten fluorides have been synthesized by simple addition reactions or by reduction with tungsten metal at elevated temperature: KWF7, K2WF8, MWF6 (M = K, Na, Rb, Cs), K2WF7, M3WF8 (M = K, Na, Rb), and K3WF6. The compounds were characterized by their Raman spectra and by cyclic voltammetry in the molten FLINAK eutectic melt (46.5, 11.5, and 42.0 mol % of LiF, NaF, and KF, respectively) at 475-800 degrees C. X-ray crystal structures are reported for two new compounds K2WF7 and K3WF6. The crystals of K2WF7 were orthorhombic, space group Pnma (No. 62) with a = 9.800(2) A, b = 5.7360(11) A, c = 11.723(2) A, and Z = 4. Crystals of K3WF6 were cubic, space group Fm3 (No. 225) with a = b = c = 8.9160(10) A, Z = 4. Electrodeposition of tungsten metal on Pt from FLINAK, prepared by the addition of WF6 gas and metallic tungsten to the melt, is suggested to result from reduction of an equilibrium mixture of WF8(3-) and WF6(3-).

Journal Article↗
PubMed2004

Adducts of acetylene and dimethylacetylenedicarboxylate at sulfurs in sulfur-bridged incomplete cubane-type tungsten clusters.

Reactions are reported of sulfur-bridged incomplete cubane-type tungsten clusters having W(3)(micro(3)-S)(micro-S)(3) cores with acetylene and its derivative dimethylacetylenedicarboxylate (DMAD). The reaction of the isothiocyanate tungsten cluster [W(3)(micro(3)-S)(micro-S)(3)(NCS)(9)](5)(-) (5) with acetylene in 0.1 M HCl afforded a novel complex having two acetylene molecules in different adduct formation modes, [W(3)(micro(3)-S)(micro(3)-SCH=CHS)(micro-SCH=CH(2))(NCS)(9)](4)(-) (6), and the presence of two kinds of intermediates [W(3)(micro(3)-S)(micro-S)(micro(3)-SCH=CHS)(NCS)(9)](5)(-) (7) and [W(3)(micro(3)-S)(micro-S)(2)(micro-SCH=CH(2))(NCS)(9)](4)(-) (8) was observed. The reaction of the diethyldithiophosphate (dtp) tungsten cluster [W(3)(micro(3)-S)(micro-S)(3)(micro-OAc)(dtp)(3)(CH(3)CN)] (10) with DMAD in acetonitrile containing acetic acid resulted in the formation of another complex having two DMAD molecules of different adduct formation modes, [W(3)(micro(3)-S)(micro-SC(CO(2))=CH(CO(2)CH(3)))(micro(3)-SC(CO(2)CH(3))=C(CO(2)CH(3))S)(micro-OAc)(dtp)(3)] (11), where hydrolysis of one of the four ester groups of the two DMAD groups occurred and the resultant carboxylic group coordinated to tungsten. The conformation of the micro-SCH=CH(2) moiety in 6 is different from that of the corresponding moiety in [W(3)(micro(3)-S)(micro-O)(micro-S)(micro-SCH=CH(2))(NCS)(9)](4)(-) (4). Introduction of the second acetylene molecule to the intermediate [W(3)(micro(3)-S)(micro-S)(2)(micro-SCH=CH(2))(NCS)(9)](4)(-) (8) resulted in the formation of 6. The clusters were characterized by UV-vis spectroscopy, (1)H NMR spectroscopy, and X-ray crystallography (for (Hpy)(4).6.1.33py.0.5H(2)O and 11.CH(3)CN), and the formation of 6 and 11 was examined in detail from a mechanistic point of view.

Journal Article↗
PubMed2003

Magnetic properties of cationic tungsten(IV) half sandwich compounds: experimental and theoretical study of a solvent and ligand stabilized singlet ground state leading to a thermally induced singlet-triplet spin state interconversion.

A series of novel neutral tungsten(III) and cationic tungsten(IV) complexes with disubstituted 4,4'-R,R-2,2'-bipyridyl (R(2)-bpy) ligands of the type [CpW(R(2)-bpy)Cl(2)](n+) (n = 0,1) were prepared and characterized by X-ray crystallography. Susceptibility measurements of the tungsten(IV) complexes revealed an intrinsic paramagnetism of these compounds and evidenced different magnetic properties of the dimethylamino and methyl (R = NMe(2), Me) substituted tungsten(IV) compounds in solution and in the solid state. In dichloromethane solution, singlet ground states with thermally populated triplet states were observed, whereas triplet (R = Me) and singlet ground states (R = NMe(2)) were observed in the solid state. Using both experimental and theoretical techniques (DFT) allowed to establish solvation and ligand effects to account for the different magnetic behavior. Thermodynamic parameters were derived for the spin equlibria in solution by fits of the temperature dependent (1)H NMR shifts to the Van Vleck equation and were found to be in excellent agreement with the DFT calculations.

Journal Article↗
PubMed2003

Vapor phase synthesis of tungsten nanowires.

A concept is presented for synthesizing metal nanowires directly from the vapor phase using chemical vapor transport to temperatures higher than the corresponding metal oxide decomposition temperature. Specifically, this concept is demonstrated with the synthesis of tungsten metal nanowires with sizes ranging from 70 to 40 nm by increasing the condensation temperature. The simultaneous condensation and decomposition of the tungsten oxide species during nucleation and growth is suggested for 1-D growth of metallic tungsten nanowires. This synthesis concept could potentially be extended to the vapor phase synthesis of metal nanowires of several other nonvolatile and refractory metals. The tungsten nanowires could find potential applications in gas sensors and as electron sources in electron microscopes.

Journal Article↗
PubMed2005

Generation and reaction of tungsten-containing carbonyl ylides: [3 + 2]-cycloaddition reaction with electron-rich alkenes.

Novel tungsten-containing carbonyl ylides 7, generated by the reaction of the o-alkynylphenyl carbonyl derivatives 1 with a catalytic amount of W(CO)(5)(thf), reacted with alkenes to give polycyclic compounds 5 through [3 + 2]-cycloaddition reaction followed by intramolecular C-H insertion of the produced nonstabilized carbene complex intermediates 8. In the presence of triethylsilane, these tungsten-containing carbene intermediates 8 were smoothly trapped intermolecularly by triethylsilane to give silicon-containing cycloadducts 17 with regeneration of the W(CO)(5) species. By this procedure, the scope of alkenes employable for this reaction was clarified. The presence of the tungsten-containing carbonyl ylide 7c was confirmed by direct observation of the mixture of o-ethynylphenyl ketone 1c and W(CO)(5)(thf-d(8)). Careful analysis of the intermediate by 2D NMR, along with the observation of the direct coupling with tungsten-183 employing the (13)C-labeled substrate, confirmed the structure of the ylide 7c. Examination using (E)- or (Z)- vinyl ether revealed that the [3 + 2]-cycloaddition reaction proceeded in a concerted manner and that the facial selectivity of the reaction differed considerably depending on the presence or absence of triethylsilane. These results clarified the reversible nature of this [3 + 2]-cycloaddition reaction.

Journal Article↗
PubMed2004

Organic nitriles from acid chlorides: an isovalent N for (O)CL exchange reaction mediated by a tungsten nitride complex.

Nitride NW(N[i-Pr]Ar)3 (1, Ar = 3,5-C6H3Me2) was synthesized in two steps from known NW(O-t-Bu)3 (41% overall yield). Complex 1 is the tungsten congener of NMo(N[i-Pr]Ar)3, a known molecule that has been synthesized using N2 as the nitrido nitrogen source, but which undergoes no reaction with pivaloyl chloride. Compound 1 undergoes metathesis with pivaloyl chloride at 25 degrees C to form the corresponding nitrile in 97% yield. Another substrate examined in this work was the labeled acid chloride 1-Ad13C(O)Cl (Ad = adamantyl). The "(O)Cl" moiety is transferred to tungsten forming an oxo-chloride, (Ar[i-Pr]N)3W(O)Cl (3), as the final tungsten product; both 1 and 3 were characterized structurally by X-ray diffraction. An intermediate observed in the nitrile-forming reaction was characterized spectroscopically to be a tungsten acylimido complex. The latter assignment was substantiated by the synthesis and structural characterization of the compound (Ar[i-Pr]N)3W(NC(O)CF3)(O2CCF3) (2m). In addition, density functional theory calculations performed using ADF lent insight into the thermochemistry of the overall process.

Journal Article↗
PubMed1998

Efficient Synthesis of Bicyclic Lactones via Tungsten-Mediated Intramolecular Cycloalkenation.

A series of tungsten-eta(1)-alkynols tethered with a dimethylacetal, methyl ketone, or trimethoxymethane group are prepared. Treatment of these functionalized tungsten-alkynols with BF(3).Et(2)O leads to intramolecular cycloalkenation, producing bicyclic tungsten-oxacarbeniums in high yields. Air oxidation of these oxacarbenium salts produces unsaturated bicyclic lactones in good yields. The lactone products include delta- and epsilon-lactones fused with five-, six- and seven-membered carbocyclic rings. The preceding bicyclic tungsten-eta(1)-oxacarbeniums are highly reactive toward organocuprates, Grignard reagents, and diazomethane, leading to demetalation to give various derivatives of bicyclic lactones. A short synthesis of (+/-)-mitsugashiwalactone is developed based on this method.

Journal Article↗
PubMed2005

Influence of synthesis methods on tungsten dispersion, structural deformation, and surface acidity in binary WO3-ZrO2 system.

WO3-ZrO2 catalysts were synthesized by precipitating the aqueous solutions of zirconium oxynitrate and ammonium metatungstate with ammonium hydroxide. The white slurry precipitate was treated under three different conditions. In the as-made materials, the amorphous phase was formed in the aged and refluxed samples, while well-crystallized tetragonal and monoclinic phases were obtained in the hydrothermally treated sample. The real amount of tungsten loaded in the samples was similar for the three samples, independently of the treatments; however, the tungsten surface atomic density in the annealed WO3-ZrO2 samples varied between 6 and 9 W atoms/nm2. Two different contrast types of aggregates were determined by scanning electron microscopy, the white particles which are rich in W, and the gray ones which are rich in zirconium; both of them were formed in the calcined solids prepared under aging or reflux condition. A very high dispersion of tungsten species on the zirconia surface was achieved in the hydrothermally treated sample. The degree of the interaction between WO(x) and ZrO2 surface strongly modified the Zr-O bond lengths and bond angles in the structure of tetragonal zirconia as proved by X-ray diffraction analysis and the Rietveld refinement. The catalyst obtained under hydrothermal condition exhibited the highest dispersion of tungsten species in the zirconia, which in turn causes strong structural deformation of the tetragonal ZrO2 phase responsible of the strongest surface acidity and, consequently, the optimum catalytic activity for n-hexane isomerization.

Journal Article↗
PubMed2004

Tungsten isotope evidence that mantle plumes contain no contribution from the Earth's core.

Osmium isotope ratios provide important constraints on the sources of ocean-island basalts, but two very different models have been put forward to explain such data. One model interprets (187)Os-enrichments in terms of a component of recycled oceanic crust within the source material. The other model infers that interaction of the mantle with the Earth's outer core produces the isotope anomalies and, as a result of coupled (186)Os-(187)Os anomalies, put time constraints on inner-core formation. Like osmium, tungsten is a siderophile ('iron-loving') element that preferentially partitioned into the Earth's core during core formation but is also 'incompatible' during mantle melting (it preferentially enters the melt phase), which makes it further depleted in the mantle. Tungsten should therefore be a sensitive tracer of core contributions in the source of mantle melts. Here we present high-precision tungsten isotope data from the same set of Hawaiian rocks used to establish the previously interpreted (186)Os-(187)Os anomalies and on selected South African rocks, which have also been proposed to contain a core contribution. None of the samples that we have analysed have a negative tungsten isotope value, as predicted from the core-contribution model. This rules out a simple core-mantle mixing scenario and suggests that the radiogenic osmium in ocean-island basalts can better be explained by the source of such basalts containing a component of recycled crust.

Journal Article↗