Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Tungsten Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources
PubMed1986

The influence of tunichrome and other reducing compounds on tunic and fin formation in embryonic Ascidia callosa Stimpson.

Tunic in 46-hr-old Ascidia callosa larvae reared from dechorionated neurulae is either markedly reduced in thickness or absent altogether. The epidermis is fragile and cuticular fins fail to develop. Dechorionated neurulae treated with tunichrome and other reducing compounds (e.g., glutathione, ascorbate) show an enhancement in tunic formation and rudimentary fin development. UV absorbance spectra of extracts from unfertilized eggs, late tail-bud embryos, and tadpole larvae indicate that tunichrome may be present in all developmental stages. Experiments with neurulae in which the chorion was punctured with tungsten needles but not removed signify that the test cells are the most likely source of tunichrome. Results are consistent with the hypothesis that tunichrome is involved in the natural processes of tunic morphogenesis in ascidian embryos.

Animals↗
PubMed1991

Activation of rabbit liver high affinity cAMP (type IV) phosphodiesterase by a vanadyl-glutathione complex. Characterization of the role of the sulfhydryl.

Activation of rabbit liver microsomal high affinity cAMP phosphodiesterase (Type IV PDE) by vanadyl-glutathione complexes was studied as a possible model of insulin stimulation of the enzyme in a cell-free system. The effect of VO.2GSH activation of PDE was a 21-fold decrease in the IC50 value for cGMP inhibition and a 2.6-fold increase in the Vmax of the higher affinity cAMP catalytic site. Cyclic AMP and cGMP substrate affinities and cGMP hydrolysis were unaffected by VO.2GSH activation. Selective Type IV PDE inhibitors and cGMP analogs indicated that VO.2GSH complexes activated the cGMP-inhibitable form of the Type IV PDE activities which co-localized in hepatic microsomes. The Type IV PDE activating complex appears to consist minimally of vanadyl ion and 2 oxidized electron donor compounds. The components of the electron donor required to achieve an enzyme activation complex are: 1) a free -SH group as the electron donor for vanadate reduction and 2) a minimum structure of cysteamine (NH2-CH2-CH2-SH). Maximal activation of the enzyme required near 2:1 molar ratios of either glutathione or cysteamine mixed with sodium orthovanadate. Active vanadyl-cysteamine complexes were isolated by reverse- phase high performance liquid chromatography. Tungsten, niobium, and tantalum, but not manganese, chromium, or molybdenum, substituted for vanadium to form enzyme-activating complexes with glutathione. VO.RSH complex activation occurred rapidly upon addition to microsomes and was reversible. We conclude from these studies that VO.RSH complexes and insulin activate the same form of Type IV PDE in rabbit liver microsomes; our findings are discussed with respect to the involvement of a possible electron transfer enzyme oxidation in the activation mechanism.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2003

Depth of cure and microleakage with high-intensity and ramped resin-based composite curing lights.

BACKGROUND: The authors conducted a study to determine whether high-intensity curing lights in high and ramped intensity modes affect microleakage of resin-based composite restorations and whether different types of resin-based composites meet American National Standards Institute/American Dental Association Specification no. 27 (1993): 7.7 for depth of cure when polymerized using these lights. METHODS: The authors compared five high-intensity lights, three plasma arc lights and two quartz-tungsten-halogen lights in their regular and ramped intensity modes with a quartz-tungsten-halogen 40-second light. The parameters tested were microleakage one month after bonding and curing depth for different resin-based composite types. The authors measured curing depth using a scratch test. RESULTS: Light curing with Optilux 501 (Kerr/Demetron, Orange, Calif.) for 10 seconds and ADT Power PAC (American Dental Technologies, Corpus Christi, Texas) for 10 seconds resulted in higher microleakage values than light curing with other lights (P < .05). The microhybrid resin-based composite was the only material that met the specification when light cured with all of the lights tested. The flowable resin-based composite did not meet the specification when light cured with all lights tested. Microhybrid resin-based composite had the greatest depth of cure, and flowable resin-based composite had the least depth of cure. CONCLUSIONS: Microhybrid resin-based composite microleakage is affected by some light-curing modes. Different categories of resin-based composites are cured to different depths using high-intensity lights. CLINICAL IMPLICATIONS: Light curing with some high-intensity lights compared with halogen lights may result in higher microleakage values. Use caution when light curing flowable resin-based composite with the high-intensity lights. Place increments less than 2 millimeters in depth when using this material.

Analysis of Variance↗
PubMed2004

Continuous monitoring of alkali metals in gas flows using direct-current plasma excited atomic spectroscopy.

A measuring instrument employing direct current (dc) plasma excited atomic line spectroscopy was developed for continuous measurement of alkali in combustion flue gases. Alkali compounds are dissociated by mixing sampled flue gas with a nitrogen plasma jet generated with a non-transferred dc plasma torch. The instrument can be used in two operating modes. The molar fraction is determined either by measuring the transmittance of the gas jet or by monitoring the emission. A tungsten halogen lamp and scanning monochromator are used for the measurement of the optical signals. Measurement of sodium and potassium has been demonstrated. The detection limits of the instrument are 50-70 ppb in the absorption mode. The detection limits are 2-3 ppb at 0.1 MPa pressure and 0.1-0.2 ppb at 1.0 MPa in the emission mode. The instrument is designed to withstand corrosive, particle laden, and pressurized flue gases at temperatures up to 1373 K.

Journal Article↗
PubMed1985

Formate dehydrogenase molybdenum and tungsten sites--observation by EXAFS of structural differences.

Preliminary EXAFS data has been collected on the molybdenum (K-edge) in C. pasteurianum formate dehydrogenase and the tungsten (LIII-edge) in C. thermoaceticum formate dehydrogenase. In the presence of dithionite, the tungsten enzyme was devoid of W = O bonds, and exhibited average W-(O, N) and W-S bond lengths of 2.13 +/- 0.03 A and 2.39 +/- 0.03 A, respectively. In sharp contrast, the C. pasteurianum molybdenum site has three Mo = O bonds with an average bond length of 1.74 +/- 0.03 A. It is also the first molybdenum enzyme found lacking Mo-S bonds, and does not appear to be redox active in the presence of formate or dithionite. Model compounds WO2(8-hydroxyquinoline)2 = WO2(ox)2, and WO2(8 mercaptoquinoline)2 = WO2(tox)2, were also examined. Respective predicted bond lengths for WO2(ox)2 and WO2(tox)2 were W = O of 1.71, 1.73 A; W-N of 2.31, 2.29 A; W-O or W-S of 1.92 or 2.40 A, with estimated uncertainties of +/- 0.03 A.

Aldehyde Oxidoreductases↗
PubMed2006

Papaya (Carica papaya L.).

Transgenic papaya plants were initially obtained using particle bombardment, a method having poor efficiency in producing intact, single-copy insertion of transgenes. Single-copy gene insertion was improved using Agrobacterium tumefaciens. With progress being made in genome sequencing and gene discovery, there is a need for more efficient methods of transformation in order to study the function of these genes. We describe a protocol for Agrobacterium-mediated transformation using carborundum-wounded papaya embryogenic calli. This method should lead to high-throughput transformation, which on average produced at least one plant that was positive in polymerase chain reaction (PCR), histochemical staining, or by Southern blot hybridization from 10 to 20% of the callus clusters that had been co-cultivated with Agrobacterium. Plants regenerated from the callus clusters in 9 to 13 mo.

Agrobacterium tumefaciens↗
PubMed2003

Cation-directed synthesis of tungstosilicates. 1. Syntheses and structures of K10A-alpha-[SiW9O34].24H2O, of the sandwich-type complex K10.75[Co(H2O)6]0.5[Co(H2O)4Cl]0.25A-alpha-[K2(Co(H2O)2)3(SiW9O34)2].32H2O and of Cs15[K(SiW11O39)2].39H2O.

The influence of the nature of alkali metal cations on the structure of the species obtained from the trivacant precursor A-alpha-[SiW(9)O(34)](10-) has been studied. Starting from the potassium salt 1, K(10)A-alpha-[SiW(9)O(34)].24H(2)O, the sandwich-type complex 2, K(10.75)[Co(H(2)O)(6)](0.5)[Co(H(2)O)(4)Cl](0.25)A-alpha-[K(2)(Co(H(2)O)(2))(3)(SiW(9)O(34) )(2)].32H(2)O, has been obtained. The crystal structures of these two compounds consist of two A-alpha-[SiW(9)O(34)](10-) anions linked by a set of potassium (1) or cobalt plus potassium cations (2), and the relative orientation of the two half-anions is the same. Attempts to link two A-alpha-[SiW(9)O(34)](10-) anions by tungsten atoms instead of cobalt failed whatever the alkali metal cation. Moreover, the nondisordered structure of Cs(15)[K(SiW(11)O(39))(2)].39H(2)O is described. Two [SiW(11)O(39)](8-) anions are linked through a potassium cation with a "trans-oid" conformation, and the potassium occupies a cubic coordination site.

Journal Article↗
PubMed2004

Determination of phosphorous and sulfur in environmental samples by electrothermal vaporization inductively coupled plasma atomic emission spectrometry.

From the viewpoint of selective introduction of the analyte from its solvent and matrices, electrothermal vaporization (ETV) is useful for the sample introduction into the inductively coupled plasma (ICP). By using a tungsten boat furnace (TBF) vaporizer system, the loss of analyte phosphorus, which normally occurs during the drying and ashing stages, is suppressed. The phosphate ion is reacted with the tungsten supplied from the surface of the TBF to form stable tungsten phosphate species. Regarding the determination of sulfur, additional chemical modifiers such as copper(II), lead(II), etc., are necessary to retain the analyte on the TBF. The furnace-fusion (FF) method or wet-digestion technique on the TBF is applied to unify the chemical forms of the analytes. Various oxidative and reductive inorganic compounds as well as organic compounds of phosphorus and sulfur show the same sensitivities after the FF digestion with hydrogen peroxide. The detection limits are 1.5 ng and 0.12 ng for phosphorous and sulfur, respectively. The repeatabilities in terms of the relative standard deviations of 10 replicate measurements of phosphorus and sulfur are 4.2% and 2.0%, respectively. Finally, the established method is applied to the determination of several environmental waters.

Electrochemistry↗
PubMed2002

Molybdenum and tungsten complexes of sulfene (thioformaldehyde S,S-dioxide).

Propionitrile complexes fac-[M(CO)(3)(P-P)(NCEt)] (M = Mo (3), W (4); P-P = Ph(2)PCH(2)PPh(2) (a), Ph(2)PC(2)H(4)PPh(2) (b), Ph(2)PC(3)H(6)PPh(2) (c), (S,S)-Ph(2)PCHMeCHMePPh(2) (d), Fe(C(5)H(4)PPh(2))(2) (e)) were synthesized from [M(CO)(3)(NCEt)(3)] and the corresponding diphosphine. Reactions of 3 and 4 with sulfur dioxide initially gave complexes fac-[M(CO)(3)(P-P)(eta(2)-SO(2))] (M = Mo (5), W (6)), which slowly isomerized to mer-[M(CO)(3)(P-P)(eta(1)-SO(2))] (M = Mo (7), W (8)). The structures of 7b and 8b were determined by X-ray crystallography. Both compounds are isostructural (monoclinic, space group P2(1)/n (No. 14)) with almost identical unit cell dimensions (7b, a = 14.511(5) A, b = 12.797(2) A, c = 16.476(6) A, beta = 115.92(2); 8b, a = 14.478(8) A, b = 12.794(3) A, c = 16.442(9) A, beta = 116.01(2)) and molecular geometries. Treatment of either fac-[M(CO)(3)(P-P)(eta(2)-SO(2))] or mer-[M(CO)(3)(P-P)(eta(1)-SO(2))] with diazomethane yielded the sulfene complexes mer-[M(CO)(3)(P-P)(eta(2)-CH(2)SO(2))] (M = Mo (9), W (10)). The structure of 10a was determined crystallographically: monoclinic, space group P2(1)/n (No. 14), a = 11.719(2) A, b = 17.392(4) A, c = 13.441(3) A, beta = 95.58(2). The tungsten atom resides in the center of a distorted pentagonal bipyramid. The sulfene ligand occupies two adjacent equatorial sites with the bond distances W-C, 2.322(13) A, W-S, 2.353(3) A, and S-C, 1.721(12) A. The latter equals the S-C single bond distance in thiirane S,S-dioxide, indicating a high degree of charge density transfer into the LUMO of the sulfene ligand.

Journal Article↗
PubMed2001

Electrochemical synthesis, X-ray single crystal, IR spectroscopic, and quantum chemical investigation of molybdenum and tungsten hexamethoxides.

The anodic oxidation of molybdenum metal in MeOH at both low anodic and cathodic current density (0.025 A/cm2) and electrolyte temperatures kept below 20 degrees C provides an efficient approach to Mo(OMe)6 (I). W(OMe)6 (II) can be obtained from the electrolytes, prepared via anodic dissolution of tungsten, by fractional crystallization. The symmetrically independent units in the structures of I and II, being isomorphous, follow the C1 (slightly distorted D2d) symmetry. Theoretical calculations performed for a free molecule of I indicate that this low symmetry may be the result of the packing of the molecules in the crystal structure and also an inherent property imposed by the bonding in this compound. Crystal data for I: Mo(OMe)6 at 22 degrees C, a = 7.0976(13), b = 6.6103(12), and c = 12.286(2) A, beta = 90.068(3) degrees, V = 576.41(18) A3, monoclinic P2/n, Z = 2. Crystal data for II: W(OMe)6 at 22 degrees C, a = 7.1164(19), b = 6.6414(18), and c = 12.304(3) A, beta = 90.047(5) degrees, V = 581.5(3) A3, monoclinic P2/n, Z = 2.

Journal Article↗
PubMed2003

A facile synthesis of enantiopure tricyclic furanyl and pyranyl derivatives via tungsten-mediated cycloalkenation and Diels-Alder reaction.

We report the synthesis of chiral furanyl and pyranyl dienes 1 and 2 based on cycloalkenation of chiral tungsten alkynol complexes. These two dienes bear a chiral 1,3-dioxolane group to control diastereoselective Diels-Alder reactions with electron-deficient olefins. The chiral 1,3-dioxolane substituents of the cycloadducts were degraded into hydrogen atoms to make these molecules possess common furan and pyran rings. Dienes 1 and 2 are good building blocks for enantiopure forms of tricyclic oxygen compounds.

Journal Article↗
PubMed2002

Intermolecular recognition and crystal packing in molybdenum and tungsten coordination polymers as deduced from powder X-ray diffraction data.

The molecular conformations and packing of [(tBuCO2)3M2(mu-X)M2(O2CtBu)3], where M = Mo and W, and X = oxalate and perfluoroterephthalate, determined in the solid-state from powder X-ray diffraction analysis, reveal one-dimensional coordination polymers involving pivalate-oxygen to metal interactions (X = perfluoroterephthalate), and oxalate--as well as pivalate-oxygen to metal bonds (X = oxalate), and allows explanation of the unusual state-dependent chromic properties of these compounds.

Journal Article↗
PubMed2001

Neoplastic transformation of human osteoblast cells to the tumorigenic phenotype by heavy metal-tungsten alloy particles: induction of genotoxic effects.

Heavy metal-tungsten alloys (HMTAs) are dense heavy metal composite materials used primarily in military applications. HMTAs are composed of a mixture of tungsten (91-93%), nickel (3-5%) and either cobalt (2-4%) or iron (2-4%) particles. Like the heavy metal depleted uranium (DU), the use of HMTAs in military munitions could result in their internalization in humans. Limited data exist, however, regarding the long-term health effects of internalized HMTAs in humans. We used an immortalized, non-tumorigenic, human osteoblast-like cell line (HOS) to study the tumorigenic transforming potential of reconstituted mixtures of tungsten, nickel and cobalt (rWNiCo) and tungsten, nickel and iron (rWNiFe). We report the ability of rWNiCo and rWNiFe to transform immortalized HOS cells to the tumorigenic phenotype. These HMTA transformants are characterized by anchorage-independent growth, tumor formation in nude mice and high level expression of the K-ras oncogene. Cellular exposure to rWNiCo and rWNiFe resulted in 8.90 +/- 0.93- and 9.50 +/- 0.91-fold increases in transformation frequency, respectively, compared with the frequency in untreated cells. In comparison, an equivalent dose of crystalline NiS resulted in a 7.7 +/- 0.73-fold increase in transformation frequency. The inert metal tantalum oxide did not enhance HOS transformation frequency above untreated levels. The mechanism by which rWNiCo and rWNiFe induce cell transformation in vitro appears to involve, at least partially, direct damage to the genetic material, manifested as increased DNA breakage or chromosomal aberrations (i.e. micronuclei). This is the first report showing that HMTA mixtures of W, Ni and Co or Fe cause human cell transformation to the neoplastic phenotype. While additional studies are needed to determine if protracted HMTA exposure produces tumors in vivo, the implication from these in vitro results is that the risk of cancer induction from internalized HMTAs exposure may be comparable with the risk from other biologically reactive and insoluble carcinogenic heavy metal compounds (e.g. nickel subsulfide and nickel oxide).

Alloys↗
PubMed1975

Silicomolybdate and silicotungstate mediated dichlorophenyldimethylurea-insensitive photosystem II reaction: electron flow, chlorophyll a fluorescence and delayed light emission changes.

We have investigated the possible role of silicomolybdate and silicotungstate as acceptors of electrons in chloroplasts directly from Q, the primary electron acceptor of Photosystem II. Our data show: 1. Either of these compounds can accept electrons directly from Q in a 3-(3', 4'-dichlorophenyl)-1, 1-dimethylurea (DCMU)-insensitive electron transport; however, the DCMU insensitivity is only short-lived, so initial rates must be used exclusively. 2. High concentrations of these silico compounds act as direct chemical quenchers of chlorophyll a fluorescence, but lower concentrations which also mediate O2 evolution affect only the variable component of fluorescence in a manner suggestive of their electron-accepting capabilities. 3. Measurements of delayed light emission confirm the conclusions made from the fluorescence data. Also, they show the role of Q in delayed light emission as hydroxylamine data of other investigations have shown the role of Z, the electron donor of Photosystem II. 4. Silico compounds appear to be acting as electron acceptors and not as simple membrane modifiers allowing other acceptors to support a DCMU-insensitive electron transport.

Chlorophyll↗
PubMed2006

Structural characterization of mono-ruthenium substituted Keggin-type silicotungstates.

We have synthesized the mono-ruthenium substituted Keggin-type silicotungstate [SiW(11)O(39)Ru(III)(H(2)O)](5-) (1a) by reaction of the mono-lacunary silicotungstate precursor [SiW(11)O(39)](8-) with Ru(acac)(3) under hydrothermal conditions and isolated as the caesium salt Cs(5)[SiW(11)O(39)Ru(III)(H(2)O)] (1). The DMSO-coordinated complex [SiW(11)O(39)Ru(III)(DMSO)](5-) (2a) was prepared by reaction of 1a with DMSO in aqueous solution at 353 K and isolated as the caesium-potassium mixed salt Cs(4.9)K(0.1)[SiW(11)O(39)Ru(III)(DMSO)] (2). Both compounds 1 and 2 were characterized by single-crystal X-ray structure analysis, powder X-ray structure analysis, UV-Vis spectroscopy, cyclic voltammetry, IR-spectroscopy and elemental analysis. 1 crystallized in the tetragonal space group P4(2)/ncm with a = 20.9299(4), c = 10.3603(4) Angstrom, Z = 4. The ruthenium atom in the Keggin unit could not be distinguished from the tungsten due to disorder. The structural analysis of 2 (monoclinic, P2(1)/c, a = 13.5850(4), b = 20.2764(7), c = 18.1326(4) Angstrom, beta = 90.8730(10) degrees , Z = 4) successfully revealed that the incorporated ruthenium atom is coordinated by DMSO through a Ru-S bond. Polyanion 2a represents the first mono-substituted Keggin ion in which the ruthenium center is not crystallographically disordered. UV-Vis spectroscopy combined with controlled potential electrolysis confirmed that the incorporated rutheniums in 1 and 2 have a valence state of +3. The IR spectra of both 1 and 2 were very similar. All these data indicate that 1 synthesized by reaction of the mono-lacunary silicotungstate K(8)[SiW(11)O(39)] with Ru(acac)(3) under hydrothermal conditions is truly the mono-ruthenium substituted Keggin-type silicotungstate.

Journal Article↗
PubMed1992

Synthesis, characterization, and anti-human immunodeficiency virus activity of water-soluble salts of polyoxotungstate anions with covalently attached organic groups.

The cesium and tetramethylammonium (TMA) salts of polyoxotungstate anions with covalently attached organosilyl groups of formula [(RSi)2O]SiW11O39(4-), where R = CH2CH2COCH3, (CH2)3CN, and CH==CH2 (1-R, cesium salt, unless otherwise noted) have been prepared, purified, and spectroscopically characterized. The water solubility (25 degrees C) of these 10 new compounds ranges from 0.14 mM to 2.16 mM. All appear to be stable in aqueous media over a period of several hours as assessed by 1H NMR. The activities (EC50) of the new compounds against human immunodeficiency virus in primary human lymphocytes range from 3.3 microM to 39.0 microM. Their toxicities (IC50) are all greater than 100 microM. The inhibition constants of the new compounds against purified virion-derived HIV-1 reverse transcriptase are in the 1-10 microM range.

Anions↗
PubMed1999

Synthesis, Structure, and Properties of Molybdenum and Tungsten Cyano Complexes with Cuboidal M(4)(&mgr;(3)-E)(4) (M = Mo, W; E = S, Se, Te) Cores.

Four new tungsten and molybdenum cyano complexes of formula KCs(5)[W(4)S(4)(CN)(12)].CH(3)OH.2H(2)O (1), K(6)[W(4)Se(4)(CN)(12)].6H(2)O (2), K(6)[W(4)Te(4)(CN)(12)].5H(2)O (3), and K(7)[Mo(4)Te(4)(CN)(12)].12H(2)O (5) have been prepared by high-temperature 430-450 degrees C reaction of the polymeric chain compounds {W(3)S(7)Br(4)}(x)(), {W(3)Se(7)Br(4)}(x)(), {Mo(3)Te(7)I(4)}(x)() and solid-state WTe(2) with KCN, and crystallization from aqueous solutions. In addition Cs(6)[Mo(4)Te(4)(CN)(12)].2H(2)O (4) has been prepared by oxidation of 5 with bromine water. The molecular structures have been investigated by X-ray crystallography. Mixed-valence (3.5) compounds 1-4 are diamagnetic. Mixed-valence (3.25) compound 5 is paramagnetic (&mgr; = 2.03 &mgr;(B) at 77 K). In addition to the structural data for these complexes IR and UV-vis spectroscopy have been used to characterize the complexes. Cyclic-voltammetry data have shown that M(4)E(4)(n)()(+) (M = Mo, W; E = S, Se, Te) cubes are capable of existing in three oxidation states ranging from the most oxidized (n = 6; 10 electrons) to the most reduced electron-precise (n = 4; 12 electrons). The (77)Se, (125)Te, and (183)W NMR spectra of the cubes (1-3) demonstrate unambiguously the unaltered environments of the W and E atoms in aqueous solution.

Journal Article↗