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At least 19 recordsLinked to original sources
PubMed2004

Stereoselective synthesis of pentacarbonyl(3-oxa-2-bicyclo[3.1.0]hexylidene)- and pentacarbonyl(cyclopropylmethoxymethylene)tungsten compounds on the route to cyclopropane-gamma-lactones and -carboxylates.

The diastereoselective synthesis of pentacarbonyl-3-oxa-2-bicyclo[3.1.0]hexylidene- and pentacarbonyl(cyclopropylmethoxymethylene)tungsten compounds 4 and 9 by the reaction of lithiated oxazolinyloxiranes 2 and 8 and Fischer carbene tungsten complexes 3 is described. A mechanism for the formation of 4 and 9 is reported as well as their oxidation to cyclopropane-gamma-lactone 13 and -carboxylate 14.

Journal Article↗
PubMed1997

Organometallic Selenolates. 5.(1) Synthesis and Complexing Properties of 2-Propene- and 2-Methyl-2-propeneselenolato Molybdenum and Tungsten Compounds. Crystal Structures of cp(CO)(3)WSeCH(2)C(CH(3))=CH(2), [cp(CO)(2)MoSeCH(2)C(CH(3))=CH(2)](2), [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))W(CO)(5)], [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))Mo(CO)(5)], and [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)].

2-Propene- and 2-methyl-2-propeneselenolato complexes of molybdenum(II) and tungsten(II) have been prepared via insertion of gray selenium into alkali-metal-molybdenum and -tungsten bonds and subsequent reaction with allyl and beta-methallyl chlorides. The complexes are monomeric in the solid state. The (beta-methallyl)molybdenum compound cp(CO)(3)MoSeCH(2)C(CH(3))=CH(2) (2) decomposes slowly in solution with CO loss and formation of the corresponding dimer [cp(CO)(2)MoSeCH(2)C(CH(3))=CH(2)](2) (3), whose crystal structure has been determined (C(22)H(24)Mo(2)O(4)Se(2), monoclinic, P2(1)/c, a = 11.151(2) Å, b = 13.436(3) Å, c = 16.872(3) Å, beta = 102.42(2) degrees, Z = 4). A monomeric structure has been found for cp(CO)(3)WSeCH(2)C(CH(3))=CH(2) (5) (C(12)H(12)O(3)SeW, triclinic, P&onemacr;, a = 7.592(3) Å, b = 7.700(3) Å, c = 12.296(5) Å, alpha = 98.31(4) degrees, beta = 104.24(2) degrees, gamma = 108.49(3) degrees, Z = 2). Additionally, the complexing properties of the selenolato complexes have been investigated. The reactions of the molybdenum complexes cp(CO)(3)MoSeCH(2)CH=CH(2) (1) and (2) with the metal(0)-carbonyl complexes W(CO)(5)(THF), (CH(3)CN)(3)Mo(CO)(3), and (eta(6)-C(7)H(8))Mo(CO)(3) (C(7)H(8) = cycloheptatriene) led to the formation of [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))M(CO)(5)] (M = W (6), Mo (7)) and [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)] (8), respectively. 6 and 7 are isostructural and crystallize in the monoclinic space group P2(1)/n (6, C(17)H(12)MoO(8)SeW, a = 14.708(2) Å, b = 9.837(2) Å, c = 14.958(2) Å, beta = 103.030(10) degrees, Z = 4; 7, C(17)H(12)Mo(2)O(8)Se, a = 14.712(2) Å, b = 9.8670(10) Å, c = 14.982(2) Å, beta = 103.100(10) degrees, Z = 4), whereas [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)] (8) crystallizes in the noncentrosymmetric orthorhombic space group Pna2(1) (C(16)H(10)Mo(2)O(8)Se, a = 18.638(4) Å, b = 9.707(2) Å, c = 11.169(3) Å, Z = 4). Furthermore, (77)Se-NMR spectra displayed chemical shifts consistent with earlier results on related complexes.

Journal Article↗
PubMed2001

Exposure assessment in the hard metal manufacturing industry with special regard to tungsten and its compounds.

OBJECTIVES: To assess the exposure to tungsten, cobalt, and nickel in a plant producing hard metals. The main components of hard metals are tungsten carbide and cobalt metal. According to recent studies, these two components may be responsible for both fibrogenic and carcinogenic effects. METHODS: 87 workers were investigated (86 male, one female) with a median age of 42 (range 22-58) and a mean duration of exposure of 13 years (range 1-27 years). Stationary and personal air sampling, and biological monitoring were carried out. RESULTS: Ambient monitoring yielded maximum tungsten concentrations of 417 microg/m3 in the production of heavy alloys. A maximum cobalt concentration of 343 microg/m3 and a maximum nickel concentration of 30 microg/m3 were found at the sintering workshop. The highest urinary cobalt concentrations were found in the powder processing department. The mean concentration was 28.5 microg/g creatinine and the maximum value was 228 microg/g creatinine. The maximum nickel concentration in urine of 6.3 microg/g creatinine was detected in the department producing heavy alloys. The highest tungsten concentrations excreted in urine were found in grinders and had a mean value of 94.4 microg/g creatinine and a maximum of 169 microg/g creatinine. Due to the different solubility and bioavailability of the substance, there was no correlation between the tungsten concentrations in air and urine on a group basis. CONCLUSIONS: Despite its low solubility, tungsten carbide is bioavailable. The different bioavailability of tungsten metal and tungsten compounds has to be considered in the interpretation of ambient and biological monitoring data in the hard metal producing industry. The bioavailability increases in the order: tungsten metal, tungsten carbide, tungstenate. Only if both monitoring strategies are considered in combination can a valid and effective definition of high risk groups be derived.

Adult↗
PubMed2006

Synthesis and catalytic epoxidation activity with TBHP and H2O2 of dioxo-, oxoperoxo-, and oxodiperoxo molybdenum(VI) and tungsten(VI) compounds containing monodentate or bidentate phosphine oxide ligands: crystal structures of WCl2(O)2(OPMePh2)2, WCl2(O)(O2)(OPMePh2)2, MoCl2(O)2dppmO2.C4H10O, WCl2(O)2dppmO2, Mo(O)(O2)2dppmO2, and W(O)(O2)2dppmO2.

The dioxo tungsten(VI) and molybdenum(VI) complexes WCl2(O)2(OPMePh2)2, WCl2(O)2dppmO2, and MoCl2(O)2dppmO2, the oxoperoxo compounds WCl2(O)(O2)(OPMePh2)2, WCl2(O)(O2)dppmO2, and MoCl2(O)(O2)dppmO2, and the oxodiperoxo complexes, W(O)(O2)2dppmO2 and Mo(O)(O2)2dppmO2 have been prepared and characterized by IR spectroscopy, 31P NMR spectroscopy, elemental analysis, and X-ray crystallography. The structural and X-ray crystallographic data of compounds WCl2(O)2(OPMePh2)2, WCl2(O)(O2)(OPMePh2)2, MoCl2(O)2dppmO2.4H10O, WCl2(O)2dppmO2, Mo(O)(O2)2dppmO2, and W(O)(O2)2dppmO2 are also detailed. All complexes were studied as catalysts for cis-cyclooctene epoxidation in the presence of tert-butyl hydroperoxide (TBHP) or H2O2 as an oxidant. The Mo-based catalysts showed a superior reactivity over W-based catalysts in the TBHP system. On the other hand, in the H2O2 system, the W-based catalysts (accomplishing nearly 100% epoxidation of cyclooctene in 6 h) are more reactive than the Mo catalysts (<45% under some conditions). Various solvent systems have been investigated, and ethanol is the most suitable solvent for the H2O2 system.

Journal Article↗
PubMed2002

[Undecatungstophosphate sensitized strains of methicillin-resistant Staphylococcus aureus to beta-lactams].

Previously, a factor (Factor T) was found in aged mixtures of tungstate and phosphate, which greatly sensitizes strains of methicillin-resistant Staphylococcus aureus to beta-lactams. Factor T was purified and identified as undecatungstophosphate([PW11O39]7-). Undecatungstosilicate([SiW11O39]8-), a compound closely related to undecatungstophosphate, showed a similar enhancing effect. Chemically, these compounds are classified as "polyoxotungstates", and it is expected that these tungsten compounds will be useful as a "tool" in laboratory tests: i.e., in screening media for highly resistant MRSA strains. They may be also useful to investigate the resistant mechanism of the bacterial cells.

Anti-Bacterial Agents↗
PubMed2001

Lacunary-substituted undecatungstosilicates sensitize methicillin-resistant Staphylococcus aureus to beta-lactams.

Some Keggin-structural (hetero)polyoxotungstates with a lacunary hole, such as undecatungstosilicate ([SiW11O39]8-, SiW11), greatly sensitize methicillin-resistant Staphylococcus aureus (MRSA) to beta-lactams. In this study, the effects of lacunary-substituted derivatives of SiW11 were tested to determine if the lacunary hole is required for the sensitizing effect. Initially, it was supposed that the hole functioned as a binding site that interacts with some bacterial components. However, most of the lacunary-substituted species had stronger effects than SiW11, indicating that the hole is not essential for the sensitizing effect. Undecatungsto(ferri)ferrosilicate ([SiW11O39Fe](6/5-)) was the most potent compound tested, but undecatungstocobaltosilicate ([SiW11O39Co]6-) gave better results according to the fractional inhibitory concentration index. Small lipophilic cations enhanced the sensitizing effect, but bulky cations inhibited it. This suggests that a charge interaction between the tungsten compounds and some unknown materials in the culture medium or bacterial cells plays an important role in the sensitizing effect.

Aminoglycosides↗
PubMed1994

Actions of peroxovanadate or tungstate on glucose transport by isolated rat adipocytes.

The effects of peroxovanadate or tungstate on 3-O-methylglucose uptake were characterized using isolated rat adipocytes to elucidate the mechanism(s) of their actions. The stimulatory effect of peroxovanadate was observed from 1 mumol/L and reached the maximum at about 100 mumol/L. The concentration showing the half-maximal effect was approximately 16 mumol/L. The maximal response of peroxovanadate was 1.19 times higher than that of insulin significantly (P < 0.01). On the other hand, the stimulatory effect of tungstate was seen only at the higher concentrations of 10-30 mmol/L. Judging from the experiments using different tungsten compounds, tungstic acid (WO4(2-)) appeared responsible for the effect. The effects of 20 mmol/L tungstate and 20 nmol/L insulin were not additive. The stimulatory effects of 1 mmol/L peroxovanadate, 20 mmol/L tungstate or 20 nmol/L insulin were not seen in the adipocytes deprived of ATP by exposure to 2 mmol/L KCN. The adipocytes which had been stimulated with insulin and further exposed to 2 mmol/L KCN were used to test whether or not peroxovanadate works directly on the function of glucose transporters. In such cells on which GLUT4-rich transporters were rendered immobile, the effect of peroxovanadate was not observed. These results indicate that the effects of peroxovanadate or tungstate are ATP or energy dependent and may be exerted through the mechanism analogous to that of insulin action, and suggest that peroxovanadate does not directly activate the function of GLUT4.

Adipocytes↗
PubMed2003

The effects of tungstophosphate and tungstosilicate on various stress promoters transformed in Escherichia coli.

Although tungsten is an important material in some industrial and chemical processes, the biological and biochemical effects, including the toxicity, of tungsten compounds are not known well. In this study, a reporter gene assay using special strains of Escherichia coli was performed to investigate the mode of action of two polyoxotungstates, i.e. undecatungstophosphate (PW(11)) and undecatungstosilicate (SiW(11)). When the bacterial cells were cultured with PW(11), osmY (a stress promoter gene sensitive to osmotic signals) was induced to some extent, while other stress promoters were expressed only slightly. SiW(11) gave similar results, but clpB (an analogue of human heat shock protein) was more strongly induced. It is possible that PW(11) and SiW(11) can produce an osmotic signal at lower concentrations without increasing ionic strength. Since the constituents of PW(11)/SiW(11) (i.e. HPO(4)(2-), SiO(3)(2-), WO(4)(2-)) showed almost no effect, a chemical feature unique to PW(11)/SiW(11) and originating from neither of their constituents, i.e. a polyanionic characteristic, may play an important role in their biological effects.

Escherichia coli↗
PubMed2005

Effects of tungsten on environmental systems.

Tungsten is a metal with many industrial and military applications, including manufacturing of commercial and military ammunition. Despite its widespread use, the potential environmental effects of tungsten are essentially unknown. This study addresses environmental effects of particulate and soluble forms of tungsten, and to a minor extent certain tungsten alloy components, present in some munitions formulations. Dissolution of tungsten powder significantly acidifies soils. Tungsten powder mixed with soils at rates higher than 1% on a mass basis, trigger changes in soil microbial communities resulting in the death of a substantial portion of the bacterial component and an increase of the fungal biomass. It also induces the death of red worms and plants. These effects appear to be related with the soil acidification occurring during tungsten dissolution. Dissolved tungsten species significantly decrease microbial yields by as much as 38% for a tungsten media concentration of 89 mg l(-1). Soluble tungsten concentrations as low as 10(-5) mg l(-1), cause a decrease in biomass production by 8% which is possibly related to production of stress proteins. Plants and worms take up tungsten ions from soil in significant amounts while an enrichment of tungsten in the plant rhizosphere is observed. These results provide an indication that tungsten compounds may be introduced into the food chain and suggest the possibility of development of phytoremediation-based technologies for the cleanup of tungsten contaminated sites.

Animals↗
PubMed2002

Vanadium and tungsten derivatives as antidiabetic agents: a review of their toxic effects.

Tungstate is an oxyanion that has biological similarities to vanadate. In recent years, a number of studies have shown the antidiabetic effects of oral tungstate in animal models of diabetes. However, because of the tissue accumulation and potential toxicity derived from chronic administration of vanadium and tungsten compounds, the pharmacological use of vanadate or tungstate in the treatment of diabetes is not necessarily exempt from concern. In the context of a potential use in the treatment of human diabetes mellitus, the most relevant toxic effects of vanadium derivatives are reviewed and compared with those reported for tungsten. Hematological and biochemical alterations, loss of body weight, nephrotoxicity, immunotoxicity, reproductive and developmental toxicity, and behavioral toxicity have been reported to occur following exposure to vanadium compounds. Moreover, vanadium also has a mitogenic activity affecting the distribution of chromosomes during mitosis and inducing aneuploidy-related end points. In contrast to vanadate, studies about the toxic effects of tungstate are very scant. Early investigations in cats, rabbits, dogs, mice, and rats showed that tungstate was less toxic than vanadate when given intravenously. Although in vitro investigations showed a direct effect of tungstate on the embryo and fetus of mice at concentrations similar to those causing effects in vivo, information on the potential cellular toxicity of tungstate is particularly scarce. Taking into account the recent interest of tungstate as a new potential oral antidiabetic agent, an exhaustive evaluation of its toxicity in mammals is clearly necessary.

Animals↗
PubMed2003

Reduction pathway of end-on coordinated dinitrogen. 3. Electronic structure and spectroscopic properties of molybdenum/tungsten hydrazidium complexes.

The spectroscopic properties and electronic structure of the hydrazidium complexes [MF(NNH(3))(depe)(2)](BF(4))(2), M = Mo and W, are investigated (depe = 1,2-bis(diethylphosphino)ethane). Vibrational spectroscopic data for both compounds are evaluated with a quantum-chemistry-assisted normal coordinate analysis, giving an N-N force constant of 6.03 mdyn/A and metal-N force constants of 8.01 (Mo-N) and 7.31 mdyn/A (W-N), respectively. On the basis of these results and DFT calculations on a [MoF(NNH(3))(PH(3))(4)](2+) model system, the N-N bond order in these systems is 1 (single sigma bond) and metal-N bonding corresponds to a triple bond. The metal centers are assigned a +IV oxidation state (d(2) configuration) and the NNH(3) ligand is assigned a -1 formal charge which by sigma- and pi-donation to the metal is reduced to +0.48. The two metal-d electrons are located in the nonbonding (n) d(xy)() orbital. This bonding description is supported by the results of optical absorption spectroscopy showing the n --> (metal-ligand)pi transition at 536 nm (not observed in the tungsten compound) and the (metal-ligand)pi --> (metal-ligand)pi transition at 251 nm for the MoNNH(3) and at 237 nm for the WNNH(3) complex. The activation enthalpy for splitting of the N-N bond in these systems to generate NH(4)(+) is estimated to be larger than 40 kcal/mol. Hydrazidium complexes with diphosphine coligands are therefore inert with respect to N-N cleavage and thus represent the ultimate stage of N(2) reduction at six-coordinate d(6) metal centers in the absence of external reductants.

Journal Article↗
PubMedDate not supplied

Chemiluminescent derivatization of adenyl compounds with glyoxal derivatives in the presence of heteropoly acids and its application to the simple and sensitive determination of DNA.

A chemiluminescence (CL) determination of adenyl compounds is described. CL derivatization of adenyl compounds with methylglyoxal dimethyl acetal was performed in the presence of tungstosilicic acid and propan-2-ol. CL from adenyl compounds was produced by hydrogen peroxide and L-cysteine ethyl ester in DMF and water. The proposed method is highly sensitive and specific to compounds containing adenine. Adenine was determined in the range 1.0 x 10(-3)-5.0 x 10(-8) M with the detection limit of 3.0 x 10(-8) M (150 fmol per assay). The method was applied to the determination of DNA and detection limits of a few nanograms of DNA achieved.

Acetone↗
PubMed1997

Inhibition of gibberellin biosynthesis by nitrate in Gibberella fujikuroi.

Gibberellin production in Gibberella fujikuroi starts upon exhaustion of the nitrogen source. To determine the role of nitrate and ammonium in the regulation of gibberellin biosynthesis we have isolated mutants that cannot use nitrate as a nitrogen source. Nitrate inhibited partially the production of gibberellins in mutants devoid of nitrate reductase activity. The inhibition occurred whether nitrate was added before or after the onset of gibberellin production. Addition of tungstate to the wild type mimicked the results with nitrate reductase mutants. We conclude that nitrate inhibits gibberellin biosynthesis by itself, independently of the intracellular signal that conveys nitrogen availability.

Cell Division↗