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PubMed2001

Mechanism of growth inhibition by tungsten in Acidithiobacillus ferrooxidans.

Cell growth of three hundred iron-oxidizing bacteria isolated from natural environments was inhibited strongly by 0.05 mM, and completely by 0.2 mM of sodium tungstate (Na2WO4), respectively. Since no great difference in the level of tungsten inhibition was observed among the 300 strains tested, the mechanism of inhibition by Na2WO4 was studied with Acidithiobacillus ferrooxidans strain AP19-3. When resting cells of AP19-3 were incubated in 0.1 M beta-alanine-SO4(2-) buffer (pH 3.0) with 0.1 mM Na2WO4 for 1 h, the amount of tungsten bound to the cells was 12 microg/mg protein. The optimum pH for tungsten binding to the resting cells was 2 to approximately 3. Approximately 2 times more tungsten bound to the cells at pH 3.0 than at pH 6.0. The tungsten binding was specifically inhibited by sodium molybdenum. However, copper, nickel, cadmium, zinc, manganese, cobalt, and vanadate did not disturb tungsten binding to the resting cells. The iron-oxidizing activity of AP19-3 was inhibited 24, 62, and 77% by 1, 5, and 10 mM of Na2WO4, respectively. Among the components of iron oxidation enzyme system, iron:cytochrome c oxidoreductase activity was not inhibited by 10 mM of Na2WO4. In contrast, the activity of cytochrome c oxidase purified highly from the strain was inhibited 50 and 72%, respectively, by 0.05 and 0.1 mM of Na2WO4. The amounts of tungsten bound to plasma membrane, cytosol fraction, and a purified cytochrome c oxidase were 8, 0.5, and 191 microg/mg protein, respectively. From the results, the growth inhibition by Na2WO4 observed in A. ferrooxidans is explained as follows: tungsten binds to cytochrome c oxidase in plasma membranes and inhibits cytochrome c oxidase activity, and as a results, the generation of energy needed for cell growth from the oxidation of Fe2+ is stopped.

Culture Media↗
PubMed1990

Eleven tungsten atom cluster labels: high-resolution, site-specific probes for electron microscopy.

Two derivatives of a tungstate cluster containing 11 tungsten atoms (W11PO39SiR4-) have been synthesized which enable them to be covalently attached to biomolecules at specific sites. The tungstate cluster is 1.0 nm in diameter, electron dense, and visible in the electron microscope. One derivative is a W11-sulfonyl chloride, reactive with amines and sulfhydryls. The second compound is a W11-thiosulfonate which can be used to label sulfhydryl groups. These new labels are beam resistant and provide significantly higher resolution then most other electron microscopy (EM) markers. Labeling of the protein albumin is described as an example.

Cations↗
PubMed2005

A review of tungsten: from environmental obscurity to scrutiny.

Since its discovery, tungsten, a transition element of Group VIb of the Periodic Table of Elements, and its compounds have been considered environmentally benign. Its presence in biological and drinking water samples in Fallon, Nevada, an acute lymphocytic leukemia cluster struck community has alarmed public health, environmental and regulatory agencies. Tungsten, a metal of extraordinary properties that make it hardly substitutable, is considered an essential commodity with a wide variety of uses stretching from household necessities to highly specialized applications. This work is undertaken in order to explore aspects of environmental behavior of tungsten and its compounds. Occurrence data in terrestrial, atmospheric, aquatic and biotic systems are presented. Various aspects of environmental chemistry, fate transport across environmental interfaces and toxicology are discussed with the objective of identifying knowledge gaps and outlining directions for future research.

Animals↗
PubMed2003

Scratch hardness and chipping of dental ceramics under different environments.

OBJECTIVE: The goal of this program was to identify promising environments that could efficiently minimize machining-induced damage of dental materials. METHODS: Single point abrasion (SPA) scratch testing was used on five materials to determine the scratch hardness and amount of edge chipping as functions of chemical environment, including air, water, saline and glycerol solutions. Limited testing was also done under additional environments expected to promote chemomachining effects via crack growth promotion or debris removal. A conical diamond indenter and a conventional tungsten carbide machining tool were used in the scratch tests. One-way ANOVA analysis was used to determine statistical differences among the variables. RESULTS: There was a consistent trend across materials that the water and saline yielded the lowest values of scratch hardness, air the next lowest, and the tests performed in glycerol yielded the highest hardness values. The measured hardness values using the conical diamond tool in the glycerol environments were about twice the hardness values measured under water and saline solutions. Environmental effects on chipping were minimal, but a linear relationship between load and per cent chipping was determined for the WC tool within the 10-50 N test range. The choice of scratch tool strongly affected scratch hardness and chipping tendency. SIGNIFICANCE: The chemical environment had an effect on machining characteristics, but the effects were more dependent on tool interactions rather than material specific properties. As a result, it may not be possible to utilize a particular single environment to substantially improve the damage response of dental materials to machining operations. Improvements in damage resistance can be environmentally obtained, but only for shallow cuts (finishing operations).

Air↗
PubMed1993

Morphological evidence for migration of particle-laden macrophages through the interalveolar pores of Kohn in the murine lung.

We have investigated the topography of particle-laden macrophages in the pulmonary tissue of CD-1 mice after intratracheal instillation of a suspension of 250 micrograms of calcium tungstate. The mice were sacrificed 1, 3, 7 and 14 days after the particle deposition. Lung fragments were studied by scanning electron microscopy (SEM) coupled with X-ray microanalysis that allowed in situ elemental identification of tungsten in the lungs. Tungsten-positive macrophages were distinctly located in the lungs of mice sacrificed at 1-3 days when compared with samples from mice killed 7-14 days after the calcium tungstate instillation. At 1-3 days, the tungsten-carrying macrophages were accumulated near the terminal bronchioles whereas they were seen predominantly in the alveolar ducts and sacs in the 7- to 14-day groups of mice. This suggests that during pulmonary inflammation there is a redistribution of the particle-containing macrophages throughout the deep lung tissue. In high-magnification SEM views, we observed that the tungsten-positive macrophages presented numerous surface microvilli. Tungsten-laden phagocytes were detected in interalveolar fenestrae, at the so-called Kohn pores. This finding documents that the Kohn pores may be used by inflammatory cells as a pathway for the migration of phagocytes in between adjacent alveolar sacs.

Administration, Inhalation↗
PubMed2003

Investigation of metal-dithiolate fold angle effects: implications for molybdenum and tungsten enzymes.

Gas-phase photoelectron spectroscopy and density functional theory have been used to investigate the interactions between the sulfur pi-orbitals of arene dithiolates and high-valent transition metals as minimum molecular models of the active site features of pyranopterin MoW enzymes. The compounds (Tp*)MoO(bdt) (compound 1), Cp(2)Mo(bdt) (compound 2), and Cp(2)Ti(bdt) (compound 3) [where Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate, bdt is 1,2-benzenedithiolate, and Cp is eta(5)- cyclopentadienyl] provide access to three different electronic configurations of the metal, formally d(1), d(2), and d(0), respectively. The gas-phase photoelectron spectra show that ionizations from occupied metal and sulfur based valence orbitals are more clearly observed in compounds 2 and 3 than in compound 1. The observed ionization energies and characters compare very well with those calculated by density functional theory. A "dithiolate-folding-effect" involving an interaction of the metal in-plane and sulfur-pi orbitals is proposed to be a factor in the electron transfer reactions that regenerate the active sites of molybdenum and tungsten enzymes.

Aldehyde Oxidase↗
PubMed2002

Stereocontrolled synthesis of angularly fused tricyclic ring systems by means of 1-metalla-1,3,5-hexatrienes (M=Cr, W).

An efficient pathway for the stereocontrolled synthesis of functionalized, angularly fused tricyclic ring systems from readily available (1-alkynyl)carbene complexes [(OC)(5)M=C(OEt)C(triple bond)CR] (M=Cr, W; R=Ph, c-C(6)H(9)) is described. The synthesis involves the formation of a 1-metalla-1,3,5-hexatriene from the (1-alkynyl)carbene tungsten complex [(OC)(5)W=C(OEt)C(triple bond)C-c-C(6)H(9)] and a secondary amine, and its thermally induced pi-cyclization to a tetrahydroindene, which undergoes a spontaneous isomerization to another tetrahydroindene. Condensation of these tetrahydroindenes with pyran-2-ylidene complexes derived from (1-alkynyl)carbene complexes [(OC)(5)M=C(OEt)C(triple bond)CPh] (M=Cr, W) proceeds smoothly giving angularly fused tricyclic ring systems, rearrangement of which may generate spiro(cyclopentane-1,1-indanes) as side products. The synthesis is highly versatile and can be applied to the formation of various ring systems, such as steroid-type ring skeletons.

Molecular Structure↗
PubMed1993

Inflammatory response of the lung to tungsten particles: an experimental study in mice submitted to intratracheal instillation of a calcium tungstate powder.

Tungsten has been implicated as a cause of a severe form of pneumoconiosis in humans, the so-called "hard metal" lung disease. We have investigated the effect of intratracheal instillation of a powder of calcium tungstate on the pulmonary tissue of CD-1 mice. The tungsten-induced alterations were studied using 3 microanatomical methods: cytologic study of exudates obtained by bronchoalveolar lavage (BAL); histologic examination of paraffin-embedded sections of the lung; and scanning electron microscopic (SEM) examination of lung samples using x-ray microanalysis to detect tungsten in situ. The animals were sacrificed 1, 3, 7, 14 and 21 days after a single intratracheal instillation of 250 micrograms calcium tungstate particles suspended in 100 microliters of saline. We found that the metal particles induced a marked inflammatory response in the bronchoalveolar space characterized by a biphasic attraction of leukocytes with cellular peaks observed at day 1 and 14. More than 50% of the BAL macrophages showed ingested tungsten. In the lung parenchyma, the inflammatory infiltrates were predominantly located at the periphery of the bronchiolar walls. From 7 days on after the tungsten deposition, large inflammatory exudates were seen invading focal areas of the alveolar domain of the lung. SEM views revealed that the tungsten particles could be inside alveolar macrophages, in cells making up the alveolar wall, or inside periacinar lymphatics. Our data document that tungsten particles cause a marked inflammatory response in the lung tissue and that the leukocyte exudates may invade alveolar areas of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

Quadridentate bridging EO(4)(2-) (E = S, Mo, W) ligands and their role as electronic bridges.

Three compounds containing two quadruply bonded Mo(2)(DAniF)(3) (DAniF = N,N'-di-p-anisylformamidinate) units linked by tetrahedral EO(4)(2-) anions (E = S, Mo, W) have been prepared and characterized by crystallography and NMR. The linkers in these [Mo(2)(DAniF)(3)](2)(mu-EO(4)) compounds hold the Mo(2) units in an approximately perpendicular orientation and mediate strong electrochemical communication between them. Each of the three compounds shows two quasireversible (mu-SO(4)) or fully reversible (mu-MoO(4), mu-WO(4)) features in its cyclic voltammogram corresponding to successive oxidation of each of its Mo(2) units. The DeltaE(1/2) values are the largest thus far measured for Mo(2)-X-Mo(2) bridged complexes and may be sufficiently large to permit isolation of the singly oxidized species.

Crystallography, X-Ray↗
PubMed2007

Isomerization dynamics and control of the eta2/N equilibrium for pyridine complexes.

A series of pyridine complexes are prepared of the general form TpW(NO)(PMe3)(pyr) where pyr is either pyridine or a substituted pyridine. Depending on substitution pattern, the pyridine can be either N- or eta2-coordinated, and the role of the pyridine substituents and metal oxidation state in determining this equilibrium is explored. For eta2-pyridine complexes, the substituent pattern and solubility characteristics also determine the ratio of coordination diastereomers. Rates of both intra- and interfacial linkage isomerizations are explored along with the pyridine rotational barrier. This study is supported by DFT calculations and X-ray data and includes characterization of both eta2-pyridine and eta2-pyridinium complexes.

Crystallography, X-Ray↗
PubMed2004

Synthesis and structure of the incomplete cuboidal clusters [W3Se4H3(dmpe)3]+, [W3Se4H(3-x)(OH)x(dmpe)3]+ and [W3Se4(OH)3(dmpe)3]+, and the mechanism of the acid-assisted substitution of the coordinated hydrides.

The novel incomplete cuboidal cluster [W3Se4H3(dmpe)3](PF6), [1](PF6), has been prepared by reduction of [W3Se4Br3(dmpe)3](PF6) with LiBH4 in THF solution. The trihydroxo complex [W3Se4(OH)3(dmpe)3](PF6), [2](PF6), was obtained by reacting [W3Se4Br3(dmpe)3](PF6) with NaOH in MeCN-H2O solution. The complexes [1](PF6) and [2](PF6) were converted to their BPh4- salts by treatment with NaBPh4. Recrystallisation of [1](BPh4) in the presence of traces of water affords the mixed dihydride hydroxo complex [W3Se4H2(OH)(dmpe)3](BPh4). The crystal structures of [1](BPh4), [2](BPh4) and [W3Se4H2(OH)(dmpe)3](BPh4) have been resolved. Although the [1]+ trihydride does not react with an excess of halide salts, reaction with HX leads to [W3Se4X3(dmpe)3]+ (X = Cl, Br). The kinetics of this reaction has been studied at 25 degrees C in MeCN-H2O solution (1:1, v/v) and found to occur with two consecutive kinetic steps. The first step is independent of the nature and concentration of the X(-) anion but shows a first order dependence on the concentration of acid (k1 = 12.0 mol(-1) dm(3) s(-1)), whereas the second one is independent of the nature and concentration of both the acid and added salts (k2 = 0.024 s(-1)). In contrast, the reaction of [2]+ with acids occurs in a single step with kobs = 0.63 s(-1)(HCl) and 0.17 s(-1)(HBr). These kinetic results are discussed on the basis of the mechanism previously proposed for the reactions of the analogous [W3S4H3(dmpe)3]+ cluster, with special emphasis on the effects caused by the change of S by Se on the rate constants for the different processes involved.

Acids↗
PubMed1998

The molybdenum cofactor of Escherichia coli nitrate reductase A (NarGHI). Effect of a mobAB mutation and interactions with [Fe-S] clusters.

We have studied the effect of a mobAB mutation and tungstate on molybdo-molybdopterin-guanine dinucleotide (Mo-MGD) insertion into Escherichia coli nitrate reductase (NarGHI). Preparation of fluorescent oxidized derivatives of MGD (Form A and Form B) indicates that in a mobAB mutant there is essentially no detectable cofactor present in either the membrane-bound (NarGHI) or purified soluble (NarGH) forms of the enzyme. Electron paramagnetic resonance characterization of membrane-bound cofactor-deficient NarGHI suggests that it has altered electrochemistry with respect to the dithionite reducibility of the [Fe-S] clusters of NarH. Potentiometric titrations of membrane-bound NarGHI indicate that the NarH [Fe-S] clusters have midpoint potentials at pH 8.0 (Em,8.0 values) of +180 mV ([3Fe-4S] cluster), +130, -55, and -420 mV ([4Fe-4S] clusters) in a wild-type background and +180, +80, -35, and -420 mV in a mobAB mutant background. These data support the following conclusions: (i) a model for Mo-MGD biosynthesis and assembly into NarGHI in which both metal chelation and nucleotide addition to molybdopterin precede cofactor insertion; and (ii) the absence of Mo-MGD significantly affects Em,8.0 of the highest potential [4Fe-4S] cluster.

Binding Sites↗