Staining of oligodendroglia with silver ammino tungstate in unembedded and embedded material.
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Animals↗
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Antitumor activity of mono- and dimetallic transition metal carborane complexes of Ta, Fe, Co, Mo, or W.
Complexes containing Ta, Fe, Co, Mo, or W metal centers that are bound to C2B4 or C2B3 small carborane ligands proved to be potent cytotoxic agents in murine and human tissue cultured cells, being more effective in suspended leukemia and lymphomas but surprisingly also effective against the growth of selected solid tumors. These complexes inhibited nucleic acid metabolism, specifically DNA and purine de novo syntheses. Key enzyme activities in nucleic acid metabolism which were inhibited by the complexes were P388 DNA polymerase a, ribonucleotide reductase, dihyrofolate reductase, PRRP-amidotransferase and IMP dehydrogenase. The complexes afforded a moderate amount of DNA-fragmentation in P388 lymhocytic leukemia cells and were moderate inhibitors of human DNA topoisomerase II activity; however, the DNA molecule itself was not a target of the complexes in that there was no evidence that the complexes caused intercalation between base pairs, caused cross-linking of the strands of DNA or alkylated the bases of DNA.
Animals↗
Evaluation of the in vitro direct and indirect genotoxic effects of cobalt compounds using the alkaline comet assay. Influence of interdonor and interexperimental variability.
The mechanisms of cobalt-induced pulmonary interstitial fibrosis and cancer are incompletely understood. DNA damage, either induced by genotoxic (direct or via oxygen radicals) or co-genotoxic (e.g. inhibition of DNA repair) processes may play an important role in the initiation of cancer. The alkaline comet assay provides a sensitive tool to investigate these two processes. Cobalt metal, a mixture of cobalt with tungsten carbide and cobalt chloride, were compared for their DNA-damaging capacity. Concentrations from 0 to 6.0 microg Co-equivalent/ml were tested. All three compounds were able to induce DNA damage in isolated human lymphocytes from three donors, in a dose- and time-dependent way. A relatively large interexperimental and interdonor variability in response was observed. This was ascribed to technical parameters and unidentified individual factors. This confirms the importance of repeating experiments using the same and different donors. The DNA-damaging potential of the cobalt-tungsten carbide mixture was higher than that of cobalt metal and cobalt chloride, which had comparable responses. No significant increase of DNA migration was observed when the DNA of cells treated with cobalt metal, cobalt-tungsten carbide or tungsten carbide were incubated with the oxidative lesion-specific enzyme formamidopyrimidine DNA glycosylase. This suggests that during the short treatment period no substantial oxidative damage to DNA was produced. Cobalt metal was able to inhibit the repair of methylmethanesulphonate-induced DNA damage. This was concluded from simultaneous exposure to cobalt and methyl methanesulphonate, post-incubation and post-treatment with 1.2 microg/ml cobalt of methyl methanesulphonate-treated cells.
Adult↗
Receptor neuron responses to potential sex pheromone components in the caddisfly Rhyacophila nubila (Trichoptera: Rhyacophilidae).
Olfactory single sensillum responses of male and female caddisflies Rhyacophila nubila (Trichoptera: Rhyacophilidae) were examined with the tungsten penetration technique to investigate the presence of receptor neurons tuned to potential sex pheromone components. The compounds tested in the experiment were heptan-2-one, nonan-2-one, (R)-heptan-2-ol, and (R)-nonan-2-ol, which have all been found to be present in female abdominal glands, plus the two antipodes (S)-heptan-2-ol and (S)-nonan-2-ol. Four types of receptor neurons were found in equal proportions in males and females. One type responded primarily to heptan-2-one. A second type responded primarily to (R)-heptan-2-ol and a third type primarily to its enantiomer (S)-heptan-2-ol. The fourth type of receptor neuron responded to nonan-2-one, (R)-nonan-2-one, and (S)-nonan-2-ol, with a bias to nonan-2-one. The receptor neurons responding to the tested compounds made up a great majority of the contacted neurons in both males and females.
Journal Article↗
The lacunary polyoxoanion synthon alpha-P(2)W(15)O(56)(12-): an investigation of the key variables in its synthesis plus multiple control reactions leading to a reliable synthesis.
A reliable way to determine the purity of the kinetically precipitated, noncrystalline lacunary polyoxoanion alpha-P(2)W(15)O(56)(12-) has been developed, namely, the conversion of alpha-P(2)W(15)O(56)(12-) into the tri-Nb(5+)- and V(5+)-containing polyoxoanions P(2)W(15)Nb(3)O(62)(9-) and P(2)W(15)V(3)O(62)(9-), respectively, followed by quantitative analysis of their purity by (31)P-NMR prior to recrystallization. With this previously unappreciated, straightforward alpha-P(2)W(15)O(56)(12-) purity-assessment methodology in hand, the five reported literature syntheses of alpha-P(2)W(15)O(56)(12-) are investigated with an emphasis on understanding the effects of the five differing variables within these syntheses (the amount of Na(2)CO(3) base, the rate of addition of the base, the reaction temperature, the reaction scale, and the product drying method). Two methods of Nb(5+) addition (Nb(6)O(19)(8-) and NbCl(5)) to yield P(2)W(15)Nb(3)O(62)(9-) are also evaluated, as is the issue of whether any purification is provided by the normally optimum strategy of first preparing a water-soluble salt and its crystallization from water (here the (CH(3))(4)N(+) salt of the Nb-O-Nb bridged anhydride, P(4)W(30)Nb(6)O(123)(16-)), followed by its conversion to the organic-solvent soluble, but noncrystalline, (n-C(4)H(9))(4)N(+) salt, [(n-C(4)H(9))(4)N](9)[P(2)W(15)Nb(3)O(62)]. The results yield five previously unavailable and unequivocal insights: (1) Only the amount of added Na(2)CO(3) base affects the purity or yield of the desired alpha-P(2)W(15)O(56)(12-); the amount of added base is key, however. (2) Contant's 1990 Inorganic Syntheses procedure provides the highest-purity alpha-P(2)W(15)O(56)(12-) presently available. (3) All prior syntheses calling for the addition of base to P(2)W(18)O(62)(6-) until pH 9 must be abandoned. (4) The purity of even Contant's alpha-P(2)W(15)O(56)(12-) is only 90%. (5) An identifiable impurity is the 16 tungsten polyoxoanion, alpha-P(2)W(16)()O(59)(12-). Also identified and summarized are multiple compounding errors in the observation of, reporting on, and thinking about the synthesis of alpha-P(2)W(15)O(56)(12-) historically, errors which delayed the most reliable synthesis of alpha-P(2)W(15)O(56)(12-) from being identified for 18 years (from the 1983 discovery of alpha-P(2)W(15)O(56)(12-)). However, these errors yield valuable take-home lessons for anyone interested in working in this demanding area of inorganic synthetic chemistry, where direct structural methods for identifying the products and their purity, such as the lacunary polyoxoanion synthon alpha-P(2)W(15)O(56)(12-), sometimes simply do not exist.
Journal Article↗
Icosahedral quasicrystals of intermetallic compounds are icosahedral twins of cubic crystals of three kinds, consisting of large (about 5000 atoms) icosahedral complexes in either a cubic body-centered or a cubic face-centered arrangement or smaller (about 1350 atoms) icosahedral complexes in the beta-tungsten arrangement.
The twofold-axis electron-diffraction photographs of icosahedral quasicrystals are of three kinds, reflecting three different structures of the cubic crystals that by icosahedral twinning form the quasicrystals. The first kind, represented by Al(13)Cu(4)Fe(3), contains two very large icosahedral complexes, each of about 4680 atoms, in the body-centered arrangement, with six smaller icosahedral complexes (104 atoms each) in the principal interstices. The second kind, represented by Al(5)Mn, contains four of the very large complexes in the face-centered arrangement (cubic close packing), with four of the smaller clusters in the interstices. The third kind, represented by Al(6)CuLi(3), contains eight icosahedral complexes, each of about 1350 atoms, in the beta-W arrangement. The supporting evidence for these cubic structures is discussed as well as other evidence showing that the simple quasicrystal theory, which states that quasicrystals do not involve any translational identity operations, has to be modified.
Journal Article↗
A new HG/LT-GC/ICP-MS multi-element speciation technique for real samples in different matrices.
An improved speciation technique is presented for metal(loid)organic compounds, enabling identification and quantification of species from twelve elements: germanium, arsenic, selenium, molybdenum, tin, antimony, tellurium, iodine, tungsten, mercury, lead and bismuth. At this time it is possible to identify 29 species with boiling points between -88.5 degrees C and 250 C in gaseous, liquid and solid samples in a few minutes. This study shows as an example results from measurements of soil samples from municipal waste deposits. The HG/LT-GC/ICP-MS-(hydride generation/low temperature-gas chromatography/inductively coupled plasma-mass spectrometry) apparatus contains a home-built gas chromatograph that enables satisfactory separation of various species with a boiling point difference of > or = 14 degrees C. The absolute detection limits for the elements mentioned above were below 0.7 pg.
Chromatography, Gas↗
Potent inhibition of respiratory syncytial virus by polyoxometalates of several structural classes.
A series of polyoxometalates (POM) were synthesized and evaluated for anti-respiratory syncytial virus (RSV) activity. POM containing zirconium, tungsten, silicon, platinum, niobium or germanium of a variety of structural types have been evaluated. Sixteen of the compounds had very striking anti-RSV activity against a clinical isolate, Utah 89, with median effective concentration (EC50) values < or = 3 microM and selective indices > 80 as determined by viral cytopathic inhibition effect, neutral red uptake and virus yield reduction assays. The EC50 values for all three assays correlated very well (Pearson correlation coefficients > 0.90). POM containing sodium cations were totally inactive. Germanium-, niobium-, tin- and zirconium-containing compounds were found to be highly potent and selective. The antiviral activity was not cell line-dependent. The median cytotoxic concentration (IC50) values were generally greater than 100 microM. The compounds were also comparably active against a known laboratory RSV strain, A2, as well as other RSV strains. To detect any virus strain-specific inhibitory activity, seven POM were tested against other RSV strains; all were nearly equally inhibitory to the human virus strains, suggesting no strain specificity. Timing studies suggested that these compounds were most inhibitory during virus adsorption and penetration, although RSV was still significantly inhibited when the compound was added 3 h post-infection; which is considered well into the eclipse period. These data suggest that these potent, non-toxic compounds should be further studied as potential chemotherapeutic agents for treating RSV infections.
Animals↗
On the reactions of bisdiolatotungsten(VI) phenoxides. Syntheses, characterizations, and molecular structures of trans-[WCl(2)(Diol)(OAr)(2)].
Coordinated phenoxide groups in [W(eg)(2)(mephe)(2)] (2a) and [W(eg)(2)(prphe)(2)] (2c) (eg = ethanediolate dianion; mephe = OC(6)H(3)Me(2)-2,6; prphe = OC(6)H(3)(i)Pr(2)-2,6) undergo reaction with Br(2), leading to substitution at the para position of the phenyl rings and formation of the complexes [W(eg)(2)(OC(6)H(2)R(2)-2,6-Br-4)(2)] (2b, R = Me; 2d, R = (i)Pr). The reaction of complexes 2a-2d and [W(eg)(2)(buphe)(2)] (2e) (buphe = OC(6)H(3)tBu(2)-2,4) with HCl leads to the displacement of one bidentate diolato ligand from the complex unit and formation of the corresponding trans dichloro diolato bis(phenoxide) tungsten(VI) complex [WCl(2)(eg)(OAr)(2)] (3). The X-ray crystal structure determinations of these compounds confirmed that all complexes 3 have a similar gross structure in which the chloro ligands are arranged at trans positions.
Journal Article↗
Catalytic carbonylation of functionalized diamines: application to the core structure of DMP 323 and DMP 450.
W(CO)(6)-catalyzed carbonylation provides an alternative to phosgene or phosgene derivatives such as 1,1-carbonyldiimidazole (CDI) for the conversion of amines to ureas. As an illustration, the core structure of the HIV protease inhibitors DMP 323 and DMP 450 has been prepared by catalytic carbonylation of diamine intermediates from the original syntheses.
Azepines↗
Developing structure-based models to predict substrate specificity of D-group (Type II) molybdenum enzymes: application to a molybdo-enzyme of unknown function from Archaeoglobus fulgidus.
The AF0174-AF0176 gene cluster in Archaeoglobus fulgidus encodes a putative oxyanion reductase of the D-type (Type II) family of molybdo-enzymes. Sequence analysis reveals that the catalytic subunit AF0176 shares low identity (31-32%) and similarity (41-42%) to both NarG and SerA, the catalytic components of the respiratory nitrate and selenate reductases respectively. Consequently, predicting the oxyanion substrate selectivity of AF0176 has proved difficult based solely on sequence alignments. In the present study, we have modelled both AF0176 and SerA on the recently determined X-ray structure of the NAR (nitrate reductase) from Escherichia coli and have identified a number of key amino acid residues, conserved in all known NAR sequences, including AF0176, that we speculate may enhance selectivity towards trigonal planar (NO(3)(-)) rather than tetrahedral (SeO(4)(2-) and ClO(4)(-)) substrates.
Amino Acid Sequence↗
[Stimulus effect of submaximal trains of impulses on nerves].
Although the occurrence of rate-dependent conduction block upon exposure to supramaximal stimuli is a well-known phenomenon, changes in the stimulus effect of submaximal trains of impulses on nerves remain unknown. To investigate changes in the stimulus effect, we evaluated median nerve action potentials using various frequencies of impulse trains. The subjects were 12 healthy controls and 9 patients with diabetic polyneuropathy. A tungsten microelectrode was inserted into the median nerve trunk at the elbow. Weak stimuli that produced 10 microV compound nerve action potentials were repeated. Each value recorded is the average of 20 trials. Repetition of 1- to 5-Hz stimuli yielded the same average wave, but above 7-Hz, the stimuli produced a diminution in amplitude and slight prolongation of the latency of each peak. This was most prominent with 50-Hz or 100-Hz repeated stimuli. The potentials changed amplitude with a waxing and waning pattern, and gradually stabilized at a lower level. The averaged wave corresponded to the record of reduced stimuli at 0.6 mA, maximally. Paired stimuli at an interval of less than 5 msec were equivalent to a relative refractory period, whereas at an interval of 4-18 msec they were equivalent to a supernormal period, and at 12-90 msec, to a subnormal period. The 'jumping' (unexpected shortening of the latency of a potential in response to increased stimulus intensity) of a single nerve unit was provoked or released corresponding to these periods. No differences were found between healthy individuals and patients with diabetic polyneuropathy. As a consequence of electrogenic Na+/K+ pumping, a three-Na+ ion efflux occurred instead of a two-K+ ion influx. Thus, repeated high-frequency impulses induced membrane hyperpolarization that reduced the stimulus effect on nerves. With trains of impulses at a frequency of 100-Hz, which corresponds to a stimulus every 10 msec, the second response was greater than the first, reflecting the supernormal period, but impulse trains provoked hyperpolarization, as mentioned above, and reduced the amplitude of nerve action potentials. The results of this study show that the stimulus effect on nerves decreased at submaximal stimuli greater than 7-Hz, which reduced the amplitude of compound nerve action potentials. Therefore, averaging should be done at a stimulus frequency below 6-Hz.
Action Potentials↗
Transition from atomic to molecular adsorption of oxygen on tungsten monomer anion.
Using vibrationally resolved ultraviolet photoelectron spectroscopy, we studied oxygen adsorption on W monomer anions. Three oxygen atoms are atomically bound in a WO3- compound, whereas in WO4- the fourth oxygen atom is attached to the oxygen, forming a di-oxygen species, implying that atom to molecule transition of O2 takes place when the number of oxygen atoms attached to a W monomer anion exceeds three. Our results indicate that molecular adsorption of oxygen is preferred on electron-deficient metals, showing that the driving force of the atom to molecule transition for the chemisorption of diatomic molecules can be the variations of electronic structures of metal hosts.
Journal Article↗
Gravitational effects on the weld pool shape and microstructural evolution during gas tungsten arc and laser beam welding of 304 stainless steel and Al-4 wt% Cu alloy.
Effects of gravitational acceleration were investigated on the weld pool shape and microstructural evolution for 304 stainless steel and Al-4wt% Cu alloy. Effects of welding heat source were investigated by using laser beam welding (LBW) and gas tungsten arc welding (GTAW). As the gravitational level was increased from low gravity (LG approximately 1.2 g) to high gravity (HG approximately 1.8 g) using a NASA KC-135 aircraft, the weld pool shape for 304 stainless steel was influenced considerably during GTAW. However, insignificant change in the microstructure and solute distribution was observed at gravitational levels between LG and HG. The GTAW on Al-4 wt% Cu alloy was used to investigate the effect of gravitational orientation on the weld solidification behavior. Gravitational orientation was manipulated by varying the welding direction with respect to gravity vector; that is, by welding upward opposing gravity ( ||-U) and downward with gravity ( ||-D) on a vertical weld piece and welding perpendicular to gravity (perpendicular) on a horizontal weld piece. Under the same welding conditions, a larger primary dendrite spacing in the ||-U weld was observed near the weld pool surface and the fusion boundary than in the case of perpendicular or ||-D welds. The ||-D weld exhibited different solidification morphology and abnormal S shape of solidification rate curve during its growth. For 304 stainless steel GTAW, significant effects of gravitational orientation were observed on the weld pool shape that was associated with weld surface morphology and convection flow. However, the weld pool shape for LBW was mostly constant with respect to the gravitational orientation.
Alloys↗
Dosimetry of a W-188/Re-188 beta line source for endovascular brachytherapy.
PURPOSE: The objective was to determine the dosimetry of a potential endovascular brachytherapy source consisting of a coiled tungsten wire mounted on the distal end of a drive wire and neutron-activated to contain the parent-daughter nuclides tungsten-188 (188W) and rhenium-188 (188Re). METHODS: A coiled tungsten wire 40 mm in length was neutron-activated by double-neutron capture for 78 hours at 1.9 x 10(15) h/cm2/s to contain 925 MBq (25 mCi) of 188W/188Re in equilibrium. The dose-fall off from this source was determined using three independent methods: (a) Thermoluminescence dosimetry with small LiF-100 rods, (b) Gafchromic film dosimetry, and (c) Bang gel dosimetry. In addition, a Monte Carlo simulation was performed to compute the beta-dose. RESULTS: Each of the three measurement methods recorded similar values for the dose fall-off within the distances useful for endovascular brachytherapy. The Monte Carlo calculations closely approximated the measured results in the treatment range between 1 and 3 mm and may thus be useful for evaluating changing geometries in the development of catheters and source setups. A 2 min restenosis treatment delivering 20 Gy at a radius of 2 mm would require a source of 1384.8 MBq/cm (37.4 mCi/cm). CONCLUSIONS: The dose distribution from a 188W/188Re source is similar to that of a 90Y-source. An added advantage of the 188W/188Re source is that it can be used for at least two months and still provides fast treatment times because of the parent isotope's half-life of 69 days. The additional gamma emission from the source is too small to impose a serious radiological hazard. The high atomic number and density of the source material allows direct fluoroscopic imaging without additional markers.
Beta Particles↗
A 1982-1992 surveillance programme on Danish pottery painters. Biological levels and health effects following exposure to soluble or insoluble cobalt compounds in cobalt blue dyes.
This paper provides a short overview of cobalt-related diseases with particular reference to the potential carcinogenicity of cobalt compounds, and a review of a 10-year surveillance programme on plate painters exposed to cobalt in two Danish porcelain factories. Clinical experience and epidemiological studies have demonstrated that cobalt exposure may lead to severely impaired lung function, i.e. hard metal lung disease and occupational cobalt-related asthma, contact dermatitis and cardiovascular effects. However, the evidence for the carcinogenicity of cobalt and cobalt compounds is considered inadequate (IARC, 1991). Most frequently, exposure to cobalt occurs simultaneously with exposure to other elements known to pose a health risk, (e.g. nickel, arsenic, chromium, tungsten). The importance of cobalt as sole causal agent in hard metal lung diseases, cardiomyopathy and cancer are still a matter of controversy. In the two Danish porcelain factories, cobalt blue underglaze dyes have been used since 1888. In contrast to the exposure experience of hard metal factories, the exposure of plate painters occurs with only low trace levels of other potentially harmful compounds such as the carcinogenic metals nickel, arsenic and chromium. Consequently, the nearly-pure cobalt exposure makes the plate painters an attractive group for studies on the health effects of cobalt. During the period 1982-1992 the surveillance programme showed a profound reduction in the urine level of cobalt (Co-U) from 100-fold to 10-fold above the median level of the unexposed control subjects. In the same period, the airborne cobalt exposure declined from 1356 nmol/m3 to 454 nmol/m3, the Danish occupational exposure limit being 845 nmol/m3. In 1982, when the cobalt exposure was above the occupational exposure limit, the plate painters showed a chronic impaired lung function. The obstructive effects may be similar to some of the effects observed in hard metal workers. In 1988, a study on the effect of cobalt exposure at low levels revealed no inhibitory effects on thyroid function, but the ratio between T4 and T3 increased, indicating that low cobalt exposure may have an impact on the metabolism of thyroid hormones. Parallel studies were conducted on the metabolism and excretion of cobalt. The gastrointestinal uptake of soluble CoCl was considerably higher than the uptake of insoluble cobalt(II) oxide. In addition, it was demonstrated that ingestion of controlled amounts of the soluble cobalt compound resulted in significantly higher concentrations of cobalt in urine and blood (Co-B) from females compared with males (P < 0.01). Future studies will involve epidemiology and genotoxicity to evaluate the previous and present cancer risk, and detailed process-related exposure assessment studies to select the methods most reliable for surveillance of low-dose cobalt exposure.
Cobalt↗
The staining of mucopolysaccharides with gallocyanin and metal mordants.
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Animals↗
Polyanion binding to cytochrome c probed by resonance Raman spectroscopy.
The interaction of ferricytochrome c with negatively charged heteropolytungstates was studied by resonance Raman spectroscopy. In analogy to previous findings on ferricytochrome c bound to other types of charged interface (Hildebrandt, P. and Stockburger, M. (1989) Biochemistry 28, 6710-6721, 6722-6728), it was shown that in these complexes the conformational states I and II are stabilized. While in state I, the structure is the same as is in the uncomplexed heme protein, in state II three different coordination configurations coexist, i.e., a six-coordinated low-spin, a five-coordinated high-spin and a six-coordinated high-spin form. These configurations constitute thermal coordination equilibria whose thermodynamic properties were determined. The detailed analysis of the low-frequency resonance Raman spectra reveals that in state II the heme pocket assumes an open structure leading to a significantly higher flexibility of the heme group compared to the native ferricytochrome c. It is concluded that these structural changes are the result of Coulombic attractions between the polyanions and the lysine residues around the exposed heme edge which destabilize the heme crevice. Modifications of these interactions upon variation of the ionic strength, the pH or the type of the polytungstate are sensitively reflected by changes of the coordination equilibria in state II as well as of the conformational equilibrium of state I and state II. The conformational changes in state II significantly differ from those associated with the alkaline transition of ferricytochrome c. However, there are some structural similarities between the acid form of the heme protein stable below pH 2.5 in aqueous solution and the six-coordinated high-spin configuration of the bound ferricytochrome c at neutral pH (state II). This suggests that electrostatic interactions with the heteropolytungstates perturb the ionic equilibria of those amino acid side chains which are involved in the acid-induced transition leading to a significant upshift of the apparent pKa.
Animals↗