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PubMed1998

Preparation and Characterization of a Bis(silsesquioxane)tungsten Complex.

By reaction of tungsten(VI) chloride with the trisilanolic silsesquioxane (C(6)H(11))(7)Si(7)O(9)(OH)(3) (1), the bis(silsesquioxane)tungsten [(C(6)H(11))(7)Si(7)O(9)(O)(3)](2)W (3) complex is formed. This is evidenced by proton and carbon NMR and X-ray diffraction. Compound 3 crystallizes in the orthorhombic space group Cmca with a = 19.407(7) Å, b = 25.163(6) Å, c = 22.176(3) Å, V = 10829(5) Å(3), and Z = 4. In addition, the analysis of silsesquioxanes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF), a technique initially developed for the characterization of biomolecules, has been successfully applied.

Journal Article↗
PubMed2004

Formation of dimers that contain unbridged W(IV)/W(IV) double bonds.

A tungsten neopentylidene complex has been found to decompose to yield a heterochiral dimer that contains a W=W double bond and no bridging ligands. Decompositions of related bisalkoxide complexes also yield compounds that contain an "unsupported" W=W double bond, while a sample of [Mo(NAr)(CH2-t-Bu)(OC6F5)]2 has been found to be a homochiral species related to [W(NAr)(CH2-t-Bu)(OC6F5)]2.

Journal Article↗
PubMed1998

Low-Temperature Syntheses and Characterization of Novel Layered Tellurites, A(2)Mo(3)TeO(12) (A = NH(4), Cs), and "Zero-Dimensional" Tellurites, A(4)Mo(6)Te(2)O(24).6H(2)O (A = Rb, K).

Hydrothermal synthetic investigations to prepare new A(2)Mo(3)TeO(12) (A = NH(4), Cs, Rb, K) compounds are described. Novel noncentrosymmetric layered tellurites, (NH(4))(2)Mo(3)TeO(12) (1) and Cs(2)Mo(3)TeO(12) (2), have been synthesized by hydrothermal methods. Their structures contain two-dimensional hexagonal tungsten oxide related (Mo(3)TeO(12))(2)(-) anionic layers interleaved with NH(4)(+)/Cs(+) ions. New "zero-dimensional" tellurites, Rb(4)Mo(6)Te(2)O(24).6H(2)O (3) and K(4)Mo(6)Te(2)O(24).6H(2)O (4), containing discrete centrosymmetric (Mo(6)Te(2)O(24))(4)(-) anionic aggregates and alkali metal ions have been synthesized by simple refluxing of stoichiometric reactants in water. In this hexamolybdoditellurite anion, the Mo(6)O(24) flat hexagonal ring, formed from edge sharing of six MoO(6) octahedra, is capped by tellurium on both sides. The two types of anions have the same empirical formula. Cs(2)Mo(3)TeO(12) (2) could be prepared by a solid state reaction as well. All four new tellurites have been structurally characterized by single-crystal X-ray diffraction studies. Pertinent crystal, data are as follows: for 1, hexagonal space group P6(3), a = 7.332(2) Å, c = 12.028(4) Å, Z = 2; for 2, hexagonal space group P6(3), a = 7.3956(10) Å, c = 12.186(2) Å, Z = 2; for 3, monoclinic space group P2(1)/c, a = 10.0564(14) Å, b = 9.877(8) Å, c = 15.724(3) Å, beta = 109.988(11) degrees, Z = 2; for 4, monoclinic space group P2(1)/c, a = 9.878(3) Å, b = 9.724(4) Å, c = 15.301(3) Å, beta = 108.57(2) degrees, Z = 2. Low-temperature syntheses, structure, and powder X-ray diffraction, spectroscopic, and thermal studies of compounds 1-4 are described.

Journal Article↗
PubMed2002

Synthesis, characterization and antiamoebic activity of benzimidazole derivatives and their vanadium and molybdenum complexes.

Reaction of [MoO(2)(acac)(2)] (where, acac=acetyl acetone) and KVO(3) with 2-(salicylidieneimine) benzimidazole lead to form new complexes [MoO(2)(sal-BMZ)(2)] and K [VO(2)(sal-BMZ)(2)] [where, sal-BMZ=2-(salicylidieneimine) benzimidazole], which showed the monobasic bidentate nature of the ligand in which the phenolic oxygen and the imine nitrogen of the ligand are coordinated to the metal ion. These complexes were characterized along with nine other complexes of oxoperoxovanadium (V), molybdenum (Vl) and tungsten (Vl) with benzimidazole derivatives and screened in vitro by micro dilution technique for their amoebicidal activity with a view to search for a more effective agent against Entamoeba histolytica suggests that compound 2 and 3 might be endowed with important antiamoebic properties since they showed IC(50 )values in a microM range.

Amebicides↗
PubMed2000

Tungsten atomizer--theory of atomization mechanism of some volatile analytes.

Several types of chemical reactions may participate in the evolution of free atoms in a tungsten furnace. Reactions may take place either in the homogeneous or heterogeneous phase. The assumed reactions may be classified into four types according to the phases in which they take place. Reactions occurring in the gaseous phase, i.e. in the inner volume of the furnace, are kinetically more significant. However, for atomization of easily volatile analytes heterogeneous reaction between gaseous compounds and between condensed salts of analytes and the solid surface of the furnace become significant. With regards to the reaction mechanisms during drying, pyrolysis and atomization of nitrates of volatile analytes, three basic types of chemical reactions may be assumed. Free atoms of analytes arise by evaporation of the elementary form of analytes at atomization temperature, where the particular analyte in its elementary form is produced by direct reduction of analyte nitrate by tungsten or by hydrogen at higher temperatures. Precursory reactions of atom formation are reduction reactions which occur between analyte nitrates and tungsten, between analyte nitrates and hydrogen, as well as reactions of thermal dissociation of relevant nitrates. The importance of particular types of precursory reactions for formation of metallic analytes or their oxides is documented by dependence of Gibbs energy values of particular reactions on the temperature.

Journal Article↗
PubMed1993

[Electrophysiological analysis of diabetic polyneuropathy with microneuronography].

We recorded median nerve action potentials in 40 healthy individuals and 40 patients with type II diabetes mellitus by means of microneurography. The latter group included 20 patients complicated by dysesthesia of distal extremities (mean diabetic history: 12.4 years), and another 20 patients without dysesthesia (mean diabetic history; 5.5 years). Mean age of each group was about 60 years old and had no significant difference among three groups. Patients and healthy controls gave an informed consent for participation in this study. A tungsten microelectrode with a tip diameter of about 1 micron was inserted percutaneously into the median nerve trunk at elbow without anesthesia. With supramaximal electric stimulation on the median nerve at wrist, the largest compound nerve action potential was recorded. In healthy controls the median nerve action potential showed a large triphasic wave (positive-negative-positive, 400 microV in average amplitude) followed by small multiphasic waves. In diabetics maximal conduction velocity (NCV) and amplitude of this triphasic wave (Amp) were decreased and multiphasic waves became more prominent. Reproducibility of potentials in the same subject was acceptable. The differences among three groups were most conspicuous in Amp, and the amplitude of the multiphasic wave was increased in diabetic patients with dysesthesia. Thus, the diminution of Amp appeared to be associated with temporal dispersion due to segmental demyelination. In diabetic polyneuropathy NCV and Amp decreased along with the disease progression; in patients with advanced disease and subjective symptoms, small Amp and prominent multiphasic waves became apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2001

"Non-VSEPR" Structures and Bonding in d(0) Systems.

Under certain circumstances, metal complexes with a formal d(0) electronic configuration may exhibit structures that violate the traditional structure models, such as the VSEPR concept or simple ionic pictures. Some examples of such behavior, such as the bent gas-phase structures of some alkaline earth dihalides, or the trigonal prismatic coordination of some early transition metal chalcogenides or pnictides, have been known for a long time. However, the number of molecular examples for "non-VSEPR" structures has increased dramatically during the past decade, in particular in the realm of organometallic chemistry. At the same time, various theoretical models have been discussed, sometimes controversially, to explain the observed, unusual structures. Many d(0) systems are important in homogeneous and heterogeneous catalysis, biocatalysis (e.g. molybdenum or tungsten enzymes), or materials science (e.g. ferroelectric perovskites or zirconia). Moreover, their electronic structure without formally nonbonding d orbitals makes them unique starting points for a general understanding of structure, bonding, and reactivity of transition metal compounds. Here we attempt to provide a comprehensive view, both of the types of deviations of d(0) and related complexes from regular coordination arrangements, and of the theoretical framework that allows their rationalization. Many computational and experimental examples are provided, with an emphasis on homoleptic mononuclear complexes. Then the factors that control the structures are discussed in detail. They are a) metal d orbital participation in sigma bonding, b) polarization of the outermost core shells, c) ligand repulsion, and d) pi bonding. Suggestions are made as to which of the factors are the dominant ones in certain situations. In heteroleptic complexes, the competition of sigma and pi bonding of the various ligands controls the structures in a complicated fashion. Some guidelines are provided that should help to better understand the interrelations. Bent's rule is of only very limited use in these types of systems, because of the paramount influence of pi bonding. Finally, computed and measured structures of multinuclear complexes are discussed, including possible consequences for the properties of bulk solids.

Journal Article↗
PubMed2002

Immediate changes in tuning of inferior colliculus neurons following acute lesions of cat spiral ganglion.

In previous studies, we demonstrated that acute lesions the spiral ganglion (SG), the cells of origin of the auditory nerve (AN), change the frequency organization of the inferior colliculus central nucleus (ICC) and primary auditory cortex (AI). In those studies, we used a map/re-map approach and recorded the tonotopic organization of neurons before and after restricted SG lesions. In the present study, response areas (RAs) of ICC multi-neuronal clusters were recorded to contralateral and ipsilateral tones after inserting and fixing-in-place tungsten microelectrodes. RAs were recorded from most electrodes before, immediately (within 33-78 min) after, and long (several hours) after restricted mechanical lesions of the ganglion. Each SG lesion produced a "notch" in the tone-evoked compound action potential (CAP) audiogram corresponding to a narrow range of lesion frequencies with elevated thresholds. Responses of contralateral IC neurons, which responded to these lesion frequencies, underwent an elevation in threshold to the lesion frequencies with either no change in sensitivity to other frequencies or with dramatic decreases in threshold to lesion-edge frequencies. These changes in sensitivity produced shifts in characteristic frequency (CF) that could be more than an octave. Thresholds at these new CFs matched the prelesion thresholds of neurons tuned to the lesion-edge frequencies. Responses evoked by ipsilateral tones delivered to the intact ear often underwent complementary changes, i.e., decreased thresholds to lesion frequency tones with little or no change in sensitivity to other frequencies. These results indicate that responses of IC neurons are produced by convergence of auditory information across a wide range of AN fibers and that the acute "plastic" changes reported in our previous studies occur within 1 h of an SG lesion.

Acoustic Stimulation↗
PubMed2004

Geometrical control of the active site electronic structure of pyranopterin enzymes by metal-dithiolate folding: aldehyde oxidase.

Density functional calculations on geometry-optimized oxidized (Mo(VI)) and reduced (Mo(IV)) analogues of the isolated active site of aldehyde oxidase (MOP), a member of the xanthine oxidase family of pyranopterindithiolate enzymes, show that fold angle changes of the dithiolate ligand modulate the relative metal and dithiolate contributions to the frontier redox orbitals. Proton abstraction from the equatorial aqua ligand of the oxidized Mo(VI) site also flattens the metal dithiolate fold angle. It is proposed that static and/or dynamic changes in the structure of the protein surrounding the active site can induce changes in the dithiolate fold angle and thereby provide a mechanism for electronic buffering of the redox orbital, for fine-tuning the nucleophilicity of the equatorial aqua/hydroxide ligand, and for modulating the electron-transfer regeneration of the active sites of molybdenum and tungsten enzymes via a "dithiolate folding effect".

Aldehyde Oxidase↗
PubMed2003

Core formation in planetesimals triggered by permeable flow.

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation. But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten. Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (approximately 1,000 degrees C) to trigger segregation of iron alloy by permeable flow within the short timeframe indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of pre-formed cores.

Journal Article↗
PubMed1998

Dinuclear (d(3)-d(3)) Diolate Complexes of Molybdenum and Tungsten. 3.(1) Bridging and Chelating Isomers of M(2)(NMe(2))(2)(O approximately approximately CHMe approximately approximately O)(2), Where O approximately approximately CHMe approximately approximately O Is the Dianion of 2,2'-Ethylidenebis(4,6-di-tert-butylphenol). Kinetic versus Thermodynamic Considerations.

Hydrocarbon solutions of Mo(2)(NMe(2))(6) and 2,2'-ethylidenebis(4,6-di-tert-butylphenol), HO approximately approximately CHMe approximately approximately OH (2 equiv), react to give a mixture of two isomers, A and B, of formula Mo(2)(NMe(2))(2)(O approximately approximately CHMe approximately approximately O)(2). Both A and B are shown to contain the bridging &mgr;-O approximately approximately CHMe approximately approximately O ligands. They are diastereomers differing with respect to the positioning of the CHMe moiety as a result of ring closure with elimination of HNMe(2). Compounds A and B are thermally persistent at 100 degrees C in the solid state and in toluene, but compound A isomerizes in the presence of pyridine to the thermodynamically favored chelate isomer Mo(2)(NMe(2))(2)(eta(2)-O approximately approximately CHMe approximately approximately O)(2), C. Compound C is related to the previously characterized isomer Mo(2)(NMe(2))(2)(eta(2)-O approximately approximately CH(2) approximately approximately O)(2), where the methylene proton that is distal to the Mo-Mo triple bond is replaced by a Me group. Compound B cannot rearrange to this isomer without Mo-O bond dissociation. W(2)(NMe(2))(6) and HO approximately approximately CHMe approximately approximately OH (2 equiv) react to give W(2)(NMe(2))(2)(eta(2)-O approximately approximately CHMe approximately approximately O)(2), D, which is an analogue of C. The three molybdenum isomers A-C and tungsten complex D have been structurally characterized by single crystal X-ray studies. The results of this work are discussed in terms of the earlier work involving the related 2,2'-methylenebis(6-tert-butyl-4-methylphenoxides) and reveal that the initial ring closure reaction determines the stereochemistry of the subsequent substitution by the biphenoxide at the dinuclear center. Crystal data: for A.PhMe at -168 degrees C, a = 16.585(5) Å, b = 19.480(6) Å, c = 10.960(3) Å, alpha = 98.39(2) degrees, beta = 103.19(1) degrees, gamma = 91.44(2) degrees, space group P&onemacr;; for B.2PhH at -168 degrees C, a = 15.167(3) Å, b = 18.210(3) Å, c = 13.964(3) Å, alpha = 92.81(1) degrees, beta = 100.40(1) degrees, gamma = 71.16(1) degrees, space group P&onemacr;; for C.1.5Et(2)O at -168 degrees C, a = 16.483(3) Å, b = 16.817(3) Å, c = 14.305(2) Å, alpha = 106.13(1) degrees, beta = 108.80(1) degrees, gamma = 71.70(1) degrees, space group P&onemacr;; and for D at -168 degrees C, a = 14.638(2) Å, b = 21.188(4) Å, c = 10.273(2) Å, alpha = 94.80(1) degrees, beta = 95.05(1) degrees, gamma = 100.85(1) degrees, space group P&onemacr;.

Journal Article↗
PubMed1995

[Detection of subclinical sensory nerve dysfunction in amyotrophic lateral sclerosis--a microneurographic study].

In amyotrophic lateral sclerosis (ALS) sensory function has been considered to be normal on a clinical basis. There are, however, several pathologic reports indicating that peripheral sensory fibers are involved in ALS. To evaluate changes in sensory nerve function quantitatively, we measured compound nerve action potentials (CNAP) of the median nerve by means of intraneural microneurography (MNG) and compared the results between 16 patients with ALS, age-matched 13 patients with Parkinson disease (PD) and 13 healthy controls. A tungsten microelectrode with a tip diameter of 1 micron was inserted percutaneously into the median nerve trunk at the elbow. With supramaximal electric stimulation on the median nerve at the wrist, the largest CNAP was recorded. The configuration of the CNAP was similar among three groups, consisting of a large triphasic wave followed by small multiphaic waves. In ALS patients the peak to peak amplitude (Amp) of the triphasic wave was 189.0 +/- 49.8 microV (mean +/- SD), which was significantly smaller than 273.1 +/- 90.0 microV in PD patients and 325.4 +/- 81.0 microV in normal controls (p < 0.01). The maximal nerve conduction velocity (NCV) in ALS was also reduced when compared with that in PD patients and in normal controls (p < 0.05). The average reduction in Amp in ALS was 58% of that in normal controls, while decrease in NCV was less apparent than Amp and 96% of normal controls. The Amplitude of nerve action potentials is considered to represent the density of large myelinated fibers more than 7 microns around the microelectrode.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1980

Distribution of 23 elements in the kidney, liver and lungs of workers from a smeltery and refinery in North Sweden exposed to a number of elements and of a control group.

The levels of antimony, arsenic, cadmium, caesium, chromium, cobalt, copper, gold, iron, lanthanum, lead, manganese, mercury, molybdenum, phosphorus, rubidium, scandium, selenium, silver, tellurium, tin, tungsten and zinc in the kidney, liver and lungs of autopsy specimens from exposed workers in North Sweden, as well as from a control group, have been assayed quantitatively. The workers had been exposed to several elements and their compounds, e.g. lead, mercury, arsenic and cadmium, for long periods in arsenic, lead or selenium plants and in a lead or copper smelter. The chemical analysis was by neutron activation analysis and atomic absorption spectrophotometry. Median levels of antimony, arsenic, cadmium, chromium cobalt, lanthanum, lead or selenium in kidney, liver or lungs in the exposed worker group were found to be about 2 to 16 times as great as the corresponding levels for the control group. Long biological half-life values were observed for these elements, especially in lung tissue.

Aged↗
PubMed2002

Relative efficiencies of CpM(CO)(n)CH(3) and CpM(CO)(n)Ph (M = Cr, Mo, W, and Fe) complexes in photoinduced DNA cleavage.

The relative efficiencies of photoinduced DNA cleavage by complexes of the type CpM(CO)(n)()R (M = Cr, Mo, or W, n = 3, R = CH(3) or Ph; M = Fe, n = 2, R = CH(3) or C(6)H(5)) have been investigated using a plasmid relaxation assay. Only the tungsten and iron complexes reproducibly caused single strand scission, in addition to which the iron systems efficiently gave double strand cleavage. The iron complexes gave strand scission at lower concentrations than the corresponding tungsten systems, with the phenyl complexes producing more damage than the methyl systems.

DNA↗
PubMed1988

Cell survival characteristics of a human colon adenocarcinoma cell line after photodynamic treatment: a comparison of Photofrin II and TPPS.

A comparison has been made of the in vitro light-activated drug cytotoxicities of two different porphyrin compounds, Photofrin II and TPPS4. An early passage human colon adenocarcinoma cell line, WiDr, has been exposed to either drug for 24 h, the excess drug washed from the cells and the cells irradiated with light using quartz-tungsten-halogen lamps. Neither light nor drug alone under the experimental conditions employed was toxic to WiDr cells. Together, considerable cytotoxicity could be seen and the shapes of the cell survival curves following exposure to either drug then irradiation with light, were similar. For equal amounts of drug in the medium, Photofrin II was a more efficient photosensitizer of WiDr cells than TPPS4, and differences in cellular uptake could only partly explain this. When the experimental procedure was changed by reducing the temperature of irradiation, a reduction in photosensitizing efficiency could be demonstrated. This was more pronounced for Photofrin II, and was seen as a change in the slope of the final portion of the survival curve; and as a change in the shoulder for TPPS4. Two different batches of the two drugs were compared and shown to give slightly different results for Photofrin II (change in shoulder) but not to differ for TPPS4.

Adenocarcinoma↗
PubMed2005

Long-range electronic coupling of MM quadruple bonds (M = Mo or W) via a 2,6-azulenedicarboxylate bridge.

The preparation of 2,6-azulenedicarboxylic acid (I) from its diester, 2-CO(2)(t)Bu-6-CO(2)-C(10)H(6) (II), is reported together with the crystal and molecular structure of the ester, II. From the reactions between the dicarboxylic acid I and the MM quadruply bonded complexes M(2)(O(2)C(t)Bu)(4), where M = Mo or W, the azulenedicarboxylate bridged complexes [M(2)(O(2)C(t)Bu)(3)](2)(mu-2,6-(CO(2))(2)-C(10)H(6)) have been isolated, III (M = Mo) and IV (M = W). The latter compounds provide examples of electronically coupled M(2) centers via a polar bridge. The compounds show intense electronic absorptions due to metal-to-bridge charge transfer. This occurs in the visible region of the spectrum for III (M = Mo) but in the near-IR for IV (M = W). One electron oxidation with Ag(+)PF(6)(-) in THF generates the radical cations III(+) and IV(+). By both UV-vis-NIR and EPR spectroscopy the molybdenum ion III(+) is shown to be valence trapped or Class II on the Robin and Day classification scheme. Electrochemical, UV-vis-NIR, and EPR spectroscopic data indicate that, in the tungsten complex ion IV(+), the single electron is delocalized over the two W(2) centers that are separated by a distance of ca. 13.6 A. Furthermore, from the hyperfine coupling to (183)W (I = (1)/(2)), the singly occupied highest molecular orbital is seen to be polarized toward one W(2) center in relationship to the other. Electronic structure calculations employing density functional theory indicate that the HOMO in compounds III and IV is an admixture of the two M(2) delta orbitals that is largely centered on the M(2) unit having proximity to the C(5) ring of the azulenedicarboxylate bridge. The energy of the highest occupied orbital of the bridge lies very close in energy to the M(2) delta orbitals. However, this orbital does not participate in electronic coupling by a hole transfer superexchange mechanism, and the electronic coupling in the radical cations of III and IV occurs by electron transfer through the bridge pi system.

Journal Article↗