Tungsten Compounds Research Articles

Interaction of fluorinated lipophilic ions with the plasma membrane of mammalian cells studied by electrorotation and dielectrophoresis

Two complementary AC electrokinetic techniques electrorotation (ROT) and dielectrophoresis (DEP) were employed for studying the interaction of the fluorinated tungsten anion [W(CO) 5(SC 6H 4CF 3)] − and a number of its derivatives with the plasma membrane of mouse myeloma cells. The use of microstructured electrodes allowed the measurements to be performed over wide ranges of field frequency and medium conductivity. At micromolar concentrations, most of the fluorinated anions gave rise to dramatic changes in the low-frequency part of both ROT and DEP spectra of cells, indicating that these compounds acted as lipophilic anions capable of introducing large amounts of mobile charges into the plasma membrane. Application of the theoretical models linking the ROT and DEP responses yielded not only the passive electrical properties of the plasma membrane and cytosol but also the ion transport parameters, such as the surface concentration and translocation rate of the lipophilic ions dissolved in the plasma membrane. This study demonstrated that combined ROT and DEP measurements can be employed as a powerful experimental tool for the analysis of the complex relationships between the molecular structure and membrane permeability of charged lipophilic compounds. Due to their strong lipophilicity and fairly low cytotoxicity, the fluorinated tungsten compounds presented here appear to provide a promising new class of field-sensitive molecular probes for membrane structure and transport studies.

Molybdenum and Tungsten Compounds in Sensor Technology

Molybdenum and Tungsten Compounds in Sensor Technology

Structural Characterization of Tungsten Phosphide (WP) Hydrotreating Catalysts by X-ray Absorption Spectroscopy and Nuclear Magnetic Resonance Spectroscopy

This paper presents a detailed discussion of the structure of tungsten phosphide and its relationship to simpler crystalline forms. The structure (space group Pbnm) is based on distorted hexagonal prisms with the phosphorus atoms forming P−P chains. Measurements by 31P magic angle spinning nuclear magnetic resonance show that there is only one type of phosphorus with a Knight shift of 255 ppm from 85% H3PO4, which is located in a highly anisotropic environment. Numerical simulations of extended X-ray absorption fine structure data at the W L3-edge give good agreement with crystallographic data. The W−P distance in WP was found to be 0.246 nm compared to the value of 0.247 nm obtained by X-ray diffraction. The catalytic activity of tungsten phosphide in the hydrotreating of a simulated petroleum feed is reported and compared to those of other tungsten compounds on an areal basis. Bulk (WP) and supported tungsten phosphide (WP/SiO2) are found to be more active in HDS and HDN than tungsten carbide (WC), tung...

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.

The Sensitizing Effects of Undecatungstocobalto(II)silicate on Methicillin-Resistant Staphylococcusaurens to β -Lactams

In a previous study, it was found that Keggin-structural polyoxotungstates such as undecatungsto-silicate ([SiW 1 1 O 3 9 ] 8 - , SiW 1 1 ) greatly sensitizes strains of methicillin-resistant Staphylococcus aureus (MRSA) to β-lactam antibiotics. Of the related tungsten compounds tested, undecatungsto-cobalto(II)silicate ([SiW 1 1 O 3 9 Co] 6 - , SiW 1 1 Co), which is one of the lacunary-substituted molecular species of SiW 1 1 , was found to have the strongest synergism with β-lactams. In this report, the effects of SiW 1 1 Co on the bacterial growth, the expression of penicillin-binding proteins (PBPs) and penicillinase (PCase) activity were studied to confirm the mechanism of action of SiW 1 1 Co. As a result, the suppressive effects of SiW 1 1 Co on the PBPs and PCase were stronger than those of SiW 1 1 , thereby more strongly sensitizing MRSA strains to β-lactams. The most suitable concentration of this compound for experiments appears to be 25-100μM, giving almost maximal synergism without severe growth retardation. Such a tungsten compound may be useful as a tool in laboratory tests for investigating resistant mechanisms.

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

OBJECTIVESTo 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...

Organic Synthesis via Transition Metal Complexes. 112.1 Reactivity Enhancement of Group VI Fischer Carbene Complexes by Copper and Rhodium Catalysts: Experimental Proof of a Carbene Rhodium Complex as an Intermediate

Rhodium(I) compounds were found to efficiently catalyze reactions of Fischer carbene complexes. It was shown that the thermally quite unreactive tungstaoctatetraenes 14a−d were readily transformed into spiro-fused vinylcyclopentadienes 15a−d in the presence of catalytic amounts of RhCl3·3H2O in MeOH or [(COD)RhCl]2. A reactivity enhancement was observed also for the transformation of the tungsten complex 8a into vinylcyclopentadiene 10a. Experimental proof for the intermediacy of carbene rhodium complexes in these reactions was provided by preparation of the rhodaoctatetraene 16c from the reaction of the tungsten compound 14c with a stoichiometric amount of [(COD)RhCl]2. The carbene rhodium compound 16c was transformed into the vinylcyclopentadiene 15c thermally in a smooth reaction and showed a catalytic activity similar to [(COD)RhCl]2. Not only rhodium but also copper compounds were found to be good catalysts for the π-cyclization of tungstaoctatetraenes.

Olefin Epoxidation with Transition Metal η2-Peroxo Complexes: The Control of Reactivity

The activation energies for olefin epoxidation with Mimoun-type η2-peroxo complexes have been calculated using density functional methods. Six degrees of freedom of the complex [MOL(O2)(OER3)] and the olefin CH2CHR′ have been systematically modified. The calculations were based on the assumptions that the reaction follows a concerted oxygen-transfer mechanism suggested by Sharpless and that a peroxo oxygen atom trans to the phosphane oxide ligand is transferred. This was recently proved for the epoxidation of ethylene with the parent complex [MoO(O2)2{OP(CH3)3}]. It has been found that the diperoxotungsten complexes (M = W; L = O2) are more reactive than the diperoxomolybdenum complexes (M = Mo; L = O2). The activation barriers for the monoperoxomolybdenum complexes (M = Mo; L = O) are significantly higher than the barriers for the corresponding diperoxo complexes (M = Mo; L = O2), whereas equal activation energies have been predicted for both tungsten compounds (M = W; L = O2 and O). The influence of the pnicogen oxide OER3 on epoxidation activity is comparably small, while electron-releasing substituents R′ at the C=C bond reduce the activation barrier. The transition states for the epoxidation of alkenes with conjugated double bonds show a large extent of asymmetry, with the C−O bond at the terminal carbon atom being formed first. Additional ligands L′ coordinating to the metal center inhibit oxygen transfer. The results are in agreement with an electrophilic attack of the oxidant on the C=C double bond.

X-ray spectroscopy investigation of hydrogen-containing phases based on the compounds of tungsten with VI group elements

New data on both electronic and atomic structures of hydrogen bronze, H x WO 3, and a compound H x WSe 2 with a layered structure have been obtained using two methods of X-ray absorption spectroscopy — XANES and EXAFS. Information about interatomic interaction, metal–hydrogen bonds and their ionic component has been obtained by means of an investigation of positions and shapes of the L III-absorption edge of tungsten and K-absorption edge of selenium in the nearest absorption region (XANES) in WSe 2, WO 3 and H x WSe 2, H x WO 3 . A possibility of investigation of changes in the atomic-crystalline structure during transformation WO 3⇒H x WO 3 and WSe 2⇒H x WSe 2 was tested, studying changes of the extended fine structure (EXAFS) of the X-ray L III-absorption spectra of tungsten and K-absorption spectra of selenium. The analysis of spectra fine structure indicates a sensibility of the EXAFS-method concerning small atom displacements in the WO 3 and WSe 2 compounds due to hydrogen insertion.

Organic Syntheses via Transition-Metal Complexes. 110.1 A Convenient Regio- and Stereoselective Approach to the Angular Allylation of Bicyclic Cyclopentadienes Generated by the (1-Alkynyl)carbene Complex Route

Reaction of the [2-(1-cyclopentenyl)ethynyl]carbene tungsten compound 1a with secondary allylamines RNHCH2CHCH2 (R = CH2CHCH2, CH2CH2CH3, PhCH2) (2a−c) and pyridine affords (C6a-allyltetrahydropentalen-1-ylidene)amines 3a−c in 72−77% yields. Compounds 3 result from a highly regio- and stereoselective N,C-allyl rearrangement of 1-(allylamino)cyclopentadiene precursors 7, which are generated in a kinetically controlled process from compound 1a. The reaction has been successfully extended to the formation of (C7a-allylpentahydro-3aH-inden-1-ylidene)amines 8a−c from [2-(1-cyclohexenyl)ethynyl]carbene tungsten complex 1b and (C8a-allylhexahydro-3aH-azulenylidene)amines 12a,b from [2-(1-cycloheptenyl)ethynyl]carbene tungsten complex 1c.

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.

Electrodeposition of Tungsten and Related Voltammetric Study in a Basic ZnCl2­NaCl (40-60 mol %) Melt

The electrodeposition of tungsten and voltammetric experiments were performed in basic (40-60 mol %) melts containing various tungsten compounds at 450°C. In constant potential electrolysis, metallic tungsten was obtained from and but not from and Similar to the case of acidic melt (60-40 mol %), the oxide ion or an oxochlorotungsten species may participate in the electrodeposition process. The presence of molecular oxygen does not interfere with the process. © 2000 The Electrochemical Society. All rights reserved.

Triggered switches for high repetition rate commutation of capacitive stores

This paper contains the results of development and testing of a switch used in a high-voltage pulse-frequency generator for use in pilot facilities. The design developed for switches is based on the scheme of three-electrode spark gap switch which involves purging of the interelectrode gaps with intense flow of air for forced removal from the working gap of the plasma and products of electrode erosion which formed as a result of previous discharge. The fairly high values of the switched energy, power and service life are attained by manufacturing the switch electrodes of high-melting materials based on tungsten and copper compounds and by increasing the electrode working surface. The switch is triggered by an overvoltage pulse emerging as a result of transients in the resonance charging circuit of capacitive store. The stability of operation of the switch is accomplished by exposing the interelectrode gaps of the switch to ultraviolet illumination induced by an additional low-power spark gap switch which is likewise controlled by transients in the resonance charging circuit of the capacitive store. The switch is characterized by the following parameters: average switched power, up to 30 kW; switched energy, 1 to 10 J; pulse repetition rate, 0.1 to 3 kHz; peak voltage, up to 25 kV.

Compounds with Unbridged Dative Metal−Metal Bonds of Formula (R3P)2(OC)3OsW(CO)5 and Related Complexes

Complexes of formula (R3P)2(OC)3OsW(CO)5 and similar complexes have been prepared from W(CO)5(THF) and Os(CO)3(PR3)2 in CH2Cl2/hexane at room temperature. The analogous Cr complexes could not be synthesized except for [MeC(CH2O)3P]2(OC)3OsCr(CO)5 and (Me2PCH2CH2PMe2)(OC)3OsCr(CO)5, that is, with sterically undemanding P substituents. Tungsten compounds with P ligands with cone angles greater than ∼125° could also not be prepared. The crystal structures of (Me2PCH2CH2PMe2)(OC)3OsM(CO)5 (M = Cr, W), [MeC(CH2O)3P]2(OC)3OsW(CO)5 (2), (OC)3(Me3P)2OsW(CO)5 (3), [MeC(CH2O)3P](OC)3(Me3P)OsW(CO)5 (4), and [(MeO)3P](OC)3(Me3P)OsW(CO)5 (5) reveal that all have unbridged OsM bonds that are considerably longer than the corresponding OsM bond in (Me3P)(OC)4OsM(CO)5. The P ligands have an axial, radial arrangement except in 3, where the PMe3 ligands have a trans, diradial orientation. In 4 and 5 the phosphite ligands are in the site trans to the OsW bond even though they have smaller cone angles than the PMe3 ligand. Solution NMR data indicates that for 2 and 3 both the ax,rad and dirad isomers are present; for 4 both ax,rad forms are present, whereas for 5 only the solid state form is found. There was no evidence in solution for the dirad forms of 4 and 5. (The 13C NMR spectra of the compounds also indicated that 2JPC becomes zero for PMC angles of about 103°.) The unusual site preference of the P ligands in these molecules is interpreted in terms of steric effects and an electronic preference for a good π-acceptor ligand to adopt the position trans to the dative metal−metal bond. Complexes 2, 3, and 5 react with PPh3 in CH2Cl2 at room temperature over 2 days to give W(CO)5(PPh3) and Os(CO)3(PR3)(PR‘3) in the order 3 > 5 > 2.

Polymerization of tert-butylacetylene by seven-coordinate heterobimetallic tungsten(II) and molybdenum(II) compounds

The reaction of tert-butylacetylene ( t-BA) in the presence of seven-coordinate tungsten(II) and molybdenum(II) compounds [MCl(M′Cl 3)(CO) 3(NCR) 2] (M=Mo, W; M′=Sn, Ge; R=Me, Et) leads to the catalytic coupling of t-BA molecules and the formation of high-molecular-weight ( M̄ n>10 5) soluble polymers. The geometric structure of poly( tert-butylacetylene) (P- t-BA) was determined by means of 1H- and 13C-NMR spectroscopy. The monitoring of the reaction between t-BA and the metal complex by means of 1H-NMR spectroscopy provided further insight into the initiation step of this polymerization process. The reaction of a heterobimetallic compound with a stoichiometric amount of t-BA yields compounds in which CO and/or nitrile ligands have been replaced by a t-BA ligand. The alkyne molybdenum(II) and tungsten(II) complexes formed were characterized structurally by means of IR and NMR spectroscopy. The possible mechanisms for the formation of very reactive intermediate compounds and their role in the catalytic process are discussed.

Synthesis and Spectroscopic Investigations of New Linear Heterobimetallic Clusters [Me4N]3[(TOS3 )2Ag] (T = Mo, W). Crystal Structure of [Me4N]3[(MoOS3 )2Ag

Abstract Red-brown crystals of a new bis(thiomolybdate) complex [Me4N]3[(MoOS3)2Ag] were formed at room temperature through the reaction of a solution of [Me4N]2[MoOS3] in MeCN with solid AgCN. They are monoclinic, space group P21/c with unit cell parameters a = 16.662(9), b = 9.464(3), c = 17.890(8) A, /3 = 101.87(2)°, Z = 4. The crystal structure was determined from single crystal diffractometer data (MoKα-radiation) and refined to R = 0.044 (3614 reflections, 236 variable parameters). The structure is characterized by trinuclear complex anions, [(MoOS3)2Ag]3-. According to Weissenberg investigations the homologous tungsten compound is isostructural. The infrared spectrum of the molybdenum complex (KBr powder) shows absorption bands at 884 (vs) and 871 (w) cm-1 (terminal v(Mo-0)), 483 (vs) cm-1 (terminal v(Mo-S)), 451 (vs), and 435 (w) cm-1 (bridging v(Mo-S)). The tungsten complex showed bands at 901 (vs) cm-1 (terminal v(W-O)), 478 (vs) cm-1 (terminal v(W-S)), and 435 (vs) cm-1 (bridging v(W-S)). The anionic mass spectra shows molecular ion peaks at m/z 524 and 700 for [(MoOS3)2Ag]- and [(WOS3)2Ag]-, respectively, as well as peaks for other fragments.

Tungsten: properties, chemistry, technology of the element, alloys, and chemical compounds

The Element Tungsten: Its Properties. Tungsten History: From Genesis to the 20th Century Products. Important Aspects of Tungsten Chemistry. Tungsten Compounds and Their Application. Industrial Production. Tungsten Alloys. Tungsten and Tungsten Alloy Products. Tungsten in Melting Metallurgy. Tungsten in Hard Metals. Tungsten in Catalysis. Tungsten Scrap Recycling. Ecology. Economy. Tungsten and Living Organisms. Index.

Volatile Liquid Precursors for the Chemical Vapor Deposition (CVD) of Thin Films Containing Tungsten

AbstractA new CVD process is described for depositing conformal layers containing tungsten, tungsten nitride or tungsten oxide. A film of tungsten metal is deposited by vaporizing liquid tungsten(0) pentacarbonyl 1-methylbutylisonitrile and passing the vapors over a surface heated to 400 to 500 °C. This process can be used to form gate electrodes compatible with ultrathin dielectric layers. Tungsten nitride films are deposited by combining ammonia gas with this tungsten-containing vapor and using substrates at temperatures of 250 to 400 °C. Tungsten nitride can act as a barrier to diffusion of copper in microelectronic circuits. Tungsten oxide films are deposited by adding oxygen gas to the tungsten-containing vapor and using substrates at temperatures of 200 to 300 °C. These tungsten oxide films can be used as part of electrochromic windows, mirrors or displays. Physical properties of several related liquid tungsten compounds are described. These low-viscosity liquids are stable to air and water. These new compounds have a number of advantages over tungsten-containing CVD precursors used previously.

Quantitative Analysis of Molybdenum in Tungsten Compounds with a New Approach to the Internal Standard Method Using a Direct-Current/Arc Echelle Spectrometer with CID Detector

Quantitative Analysis of Molybdenum in Tungsten Compounds with a New Approach to the Internal Standard Method Using a Direct-Current/Arc Echelle Spectrometer with CID Detector

Preparation and characterization of chromium, molybdenum and tungsten compounds containing amino acid ester derivatized diimine ligands. Crystal structure of Mo(CO)4(pyca-β-ala-OEt)

Abstract The title compounds were prepared by heating solutions of ester-protected amino acids (H-β-Ala-OEt, H- l -Ala-OEt, H- l -Val-OMe, H- l -Asp(OMe)-OMe, GABA-OMe) and pyridine-2-carboxaldehyde in the presence of M(CO)4(pip)2 (M=Mo,W) or [NEt4][Cr(CO)5I]. The resulting novel complexes, M(CO)4(pyca-xxx-OR) (pyca=pyridinecarbaldehyde imine), contain an η2-N,N′-diimine ligand and were characterized by 1H- and 13C-NMR, IR and UV–vis measurements. The lone band in the visible portion of the electronic spectrum is assigned to a MLCT transition and exhibits solvatochromism. The crystal structure of Mo(CO)4(pyca-β-ala-OEt) (1b), was determined and confirms the presence of the bidentate α-diimine ligand. The metal lies in a pseudo Cs symmetry environment.