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PubMed2007

Synthesis and characterization of cationic tungsten(V) methylidynes.

Cationic tungsten(V) methylidynes [L4W(X)[triple bond]CH]+[B(C6F5)4]- [L = PMe3, 0.5dmpe (dmpe = Me2PCH2CH2PMe2), X = Cl, OSO2CF3] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV) methylidynes L4W(X)[triple bond]CH with [Ph3C]+[B(C6F5)4]-. The ease and reversibility of the one-electron oxidation of L4W(X)[triple bond]CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E1/2 is approximately -0.68 to -0.91 V vs Fc). The paramagnetic d1 (S = 1/2) complexes were characterized in solution by electron spin resonance (g = 2.023-2.048, quintets due to coupling to 31P) and NMR spectroscopy and Evans magnetic susceptibility measurements (mu = 2.0-2.1 muB). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the neutral precursor methylidynes. In addition, the neutral (PMe3)4W(Cl)[triple bond]CH was deprotonated with a strong base at the trimethylphosphine ligand to afford (PMe3)3(Me2PCH2)W[triple bond]CH, a tungsten(IV) methylidyne complex that features a (dimethylphosphino)methyl ligand.

Journal Article↗
PubMed1997

Reduction of Aqueous Na(2)WO(4) by NaBH(4) at Ambient Temperatures To Obtain Lower Valent Tungsten Oxides.

A systematic investigation of the reduction of aqueous Na(2)WO(4) with aqueous NaBH(4) at ambient temperatures reveals the formation of several lower valent tungsten oxides such as the tetragonal (x < 0.38) and cubic (x > 0.43) tungsten bronzes Na(x)()WO(3) and the binary oxides WO(2) and W(24)O(68). The nature of the product formed is influenced both by the (i) reducing power of NaBH(4), which is controlled by the volume and concentration of the borohydride and the reaction pH, and (ii) the degree of condensation of the tungstate ions, which is controlled by the reaction pH. Although the reducing power of NaBH(4) increases with decreasing pH, an increasing degree of condensation of the tungstate tends to lower the degree of reduction in many instances. The as-prepared samples are amorphous as revealed by X-ray diffraction and crystallize around 450 degrees C as revealed by differential scanning calorimerty. The tungsten bronzes undergo interesting crystal-chemical changes with the temperature of heating.

Journal Article↗
PubMed1997

Amino Acid Complexes of Metal Carbonyls: Mechanistic Aspects of the CO-Labilizing Ability of Glycinate Ligands in Zero-Valent Chromium and Tungsten Derivatives.

The amino and phosphino acid derivatives of chromium(0) and tungsten(0), [Et(4)N][Cr(CO)(4)(O(2)CCH(2)NH(2))] (1), [Et(4)N][Cr(CO)(4)(O(2)CCH(2)NHMe)] (2), [Et(4)N][Cr(CO)(4)(O(2)CCH(2)NMe(2))] (3), [Et(4)N][W(CO)(4)(O(2)CCH(C(CH(3))(3))NH(2))] (4), [Et(4)N][W(CO)(4)(O(2)CCH(C(6)H(5))NH(2))], [Et(4)N][W(CO)(4)(O(2)CCH(2)PPh(2))] (5), and [Et(4)N][Cr(CO)(4)(O(2)CCH(2)PPh(2))] have been synthesized from the reaction of the M(CO)(5)THF adduct with the tetraethylammonium salt of the corresponding amino or phosphino acid in THF solution. The complexes have been characterized in solution by (13)C NMR and infrared spectroscopies and in the solid state by X-ray crystallography. The geometry of the metal anion is, in each case, that of a distorted octahedron consisting of four carbonyl ligands and a puckered five-membered glycinate chelate ring, bound through the nitrogen atom and one of its oxygen atoms. Notable about complex 1 is that the crystal obtained exhibited both a different morphology and a different space group than its tungsten analogue. Examination of the packing diagram reveals that this change is due to the different orientation of the chelate ring in 1 relative to the corresponding orientation in the W(CO)(4)(O(2)CCH(2)NH(2))(-) anion. Complexes 1 and 2 exhibit intermolecular hydrogen-bonding interactions between the amine N-H group and the distal oxygen on an adjacent molecule, with N.O distances of 2.828 and 2.821 Å, respectively. Investigations of the lability of the carbonyl ligands have been carried out. The lability is proposed to be due to base-assisted removal of a proton from the amine ligand leading to a substitutionally labile amide transient species. The tungsten analogue of complex 1 was used to obtain evidence in support of this mechanism. The isotope effect (k(H)/k(D)) was measured for W(CO)(4)(O(2)CCH(2)NH(2))(-) using d(5)-glycine and was found to be 2.34. The activation parameters for the intermolecular exchange of CO in the [Et(4)N][W(CO)(4)(O(2)CCH(2)NH(2))] salt were determined and found to be DeltaH() = 15.4 +/- 1.0 kcal/mol and DeltaS() = -23.2 +/- 3.2 eu, values consistent with the proposed mechanism. In addition, the effect of substitution of electron-donating (C(CH(3))(3)) and electron-withdrawing (C(6)H(5)) substituents on the methylene carbon was evaluated. There was little change in the rate of CO exchange observed for W(CO)(4)(O(2)CCH(C(CH(3))(3))NH(2))(-) (5) and W(CO)(4)(O(2)CCH(C(6)H(5))NH(2))(-) vs W(CO)(4)(O(2)CCH(2)NH(2))(-), showing that steric or electronic effects away from the N center are not responsible for the observed CO lability. As anticipated on the basis of the proposed substitutional pathway, the phosphino acid metal carbonyl derivatives did not exhibit facile intermolecular CO exchange.

Journal Article↗
PubMed1999

Coordination Chemistry, Structure, and Reactivity of Thiouracil Derivatives of Tungsten(0) Hexacarbonyl: A Theoretical and Experimental Investigation into the Chelation/Dechelation of Thiouracil via CO Loss and Addition.

The synthesis of 2-thiouracil and 6-methyl-2-uracil derivatives of tungsten carbonyl from the reaction of photogenerated W(CO)(5)(solvent) (solvent = MeOH or THF) and the corresponding [Et(4)N][thiouracilate] is described. The crystal structure of the [Et(4)N][W(CO)(5)(2-thiouracilate)], 1, derivative is reported where the thiouracilate is found to be bound to the tungsten center via the exocyclic sulfur atom. In the solid-state structure of 1 two anions are associated by means of two hydrogen bonds between the metal bound nucleobases. These pentacarbonyl complexes stereoselectively lose cis carbonyl ligands, as is apparent from (13)C-labeling studies, to provide the endocyclic nitrogen N(1)-chelated tungsten tetracarbonyl derivatives, e.g., [Et(4)N][W(CO)(4)(2-thiouracilate)], 3. The kinetics of the loss of CO from the pentacarbonyl anions to afford the metal tetracarbonyls, and the reverse of that process, were monitored by means of in situ infrared spectroscopy in the nu(CO) region as a function of temperature. These studies reveal that the tetracarbonyl anions in CO-saturated acetonitrile ([CO] approximately 6 x 10(-)(3) M) are unstable with respect to the formation of the pentacarbonyl derivatives, i.e., the equilibrium 1 right harpoon over left harpoon 3 + CO lies to the left under an atmosphere of carbon monoxide. From the activation parameters determined for the dissociative CO loss process (DeltaH() = 82.0 +/- 3.6 kJ mol(-)(1) and DeltaS() = -44.9 +/- 9.6 J mol(-)(1) K(-)(1) for complex 1) it is apparent that the sulfur-bound thiouracilate ligand is serving as a pi-donor during CO dissociation, i.e., behaving as a cis-labilizing ligand. Ab initio geometry optimizations carried out for the process 1 right harpoon over left harpoon 3 + CO at the Hartree-Fock and DFT levels support these experimental observations. For example, complex 1 is shown to be more stable than 3 + CO and chelation via the endocyclic N(1) donor is favored over N(3) binding. Finally, the "16-electron" intermediate resulting from CO dissociation in 1 was found to possess a significantly shortened W-S interaction, presumably due to the pi-donating ability of the thiouracilate ligand.

Journal Article↗
PubMed2001

Reactions of halofluorocarbons with group 6 complexes M(C(5)H(5))(2)L (M = Mo, W; L = C(2)H(4), CO). Fluoroalkylation at molybdenum and tungsten, and at cyclopentadienyl or ethylene ligands.

The molybdenum(II) and tungsten(II) complexes [MCp(2)L] (Cp = eta(5)-cyclopentadienyl; L = C(2)H(4), CO) react with perfluoroalkyl iodides to give a variety of products. The Mo(II) complex [MoCp(2)(C(2)H(4))] reacts with perfluoro-n-butyl iodide or perfluorobenzyl iodide with loss of ethylene to give the first examples of fluoroalkyl complexes of Mo(IV), MoCp(2)(CF(2)CF(2)CF(2)CF(3))I (8) and MoCp(2)(CF(2)C(6)F(5))I (9), one of which (8) has been crystallographically characterized. In contrast, the CO analogue [MoCp(2)(CO)] reacts with perfluorobenzyl iodide without loss of CO to give the crystallographically characterized salt, [MoCp(2)(CF(2)C(6)F(5))(CO)](+)I(-) (10), and the W(II) ethylene precursor [WCp(2)(C(2)H(4))] reacts with perfluorobenzyl iodide without loss of ethylene to afford the salt [WCp(2)(CF(2)C(6)F(5))(C(2)H(4))](+)I(-) (11). These observations demonstrate that the metal-carbon bond is formed first. In further contrast the tungsten precursor [WCp(2)(C(2)H(4))] reacts with perfluoro-n-butyl iodide, perfluoro-iso-propyl iodide, and pentafluorophenyl iodide to give fluoroalkyl- and fluorophenyl-substituted cyclopentadienyl complexes WCp(eta(5)-C(5)H(4)R(F))(H)I (12, R(F) = CF(2)CF(2)CF(2)CF(3); 15, R(F) = CF(CF(3))(2); 16, R(F) = C(6)F(5)); the Mo analogue MoCp(eta(5)-C(5)H(4)R(F))(H)I (14, R(F) = CF(CF(3))(2)) is obtained in similar fashion. The tungsten(IV) hydrido compounds react with iodoform to afford the corresponding diiodides WCp(eta(5)-C(5)H(4)R(F))I(2) (13, R(F) = CF(2)CF(2)CF(2)CF(3); 18, R(F) = CF(CF(3))(2); 19, R(F) = C(6)F(5)), two of which (13 and 19) have been crystallographically characterized. The carbonyl precursors [MCp(2)(CO)] each react with perfluoro-iso-propyl iodide without loss of CO, to afford the exo-fluoroalkylated cyclopentadiene M(II) complexes MCp(eta(4)-C(5)H(5)R(F))(CO)I (21, M = Mo; 22, M = W); the exo-stereochemistry for the fluoroalkyl group is confirmed by an X-ray structural study of 22. The ethylene analogues [MCp(2)(C(2)H(4))] react with perfluoro-tert-butyl iodide to yield the products MCp(2)[(CH(2)CH(2)C(CF(3))(3)]I (25, M = Mo; 26, M = W) resulting from fluoroalkylation at the ethylene ligand. Attempts to provide positive evidence for fluoroalkyl radicals as intermediates in reactions of primary and benzylic substrates were unsuccessful, but trapping experiments with CH(3)OD (to give R(F)D, not R(F)H) indicate that fluoroalkyl anions are the intermediates responsible for ring and ethylene fluoroalkylation in the reactions of secondary and tertiary fluoroalkyl substrates.

Journal Article↗
PubMed2005

Growth and assembly of crystalline tungsten oxide nanostructures assisted by bioligation.

Here, we present a systematic study on the influence of the bioligand deferoxamine mesylate on the crystallization and assembly behavior of tungsten oxide in a soft-chemistry process. Without deferoxamine mesylate, this approach yields pseudo-single crystalline tungstite nanoplatelets consisting of a large number of crystallographically almost perfectly aligned primary crystallites. In the presence of a constant amount of deferoxamine, the particle morphology drastically changes with temperature, ranging from wormlike organic-inorganic hybrid nanostructures to single-crystalline tungsten oxide nanowires, highlighting the role of the bioligand in controlling the crystal growth and assembly behavior. The nanowires have a uniform diameter of about 1.3 nm, an aspect ratio of more than 500, and the structural flexibility of tungsten oxide. The presented process is based on the combination of biomimetic construction principles with nonaqueous sol-gel chemistry, thus combining the advantages of both tools, excellent control over particle morphology and high crystallinity at low temperature.

Journal Article↗
PubMed2005

Layered tungsten oxide-based organic-inorganic hybrid materials: an infrared and Raman study.

Tungsten oxide-organic layered hybrid materials have been studied by infrared and Raman spectroscopy and demonstrate a difference in bonding nature as the length of the interlayer organic "spacer" molecule is increased. Ethylenediamine-tungsten oxide clearly displays a lack of terminal -NH3(+) ammonium groups which appear in hybrids with longer organic molecules, thus indicating that the longer chains are bound by electrostatic interactions as well as or in place of the hydrogen bonding that must be present in the shorter chain ethylenediamine hybrids. The presence of organic molecules between the tungsten oxide layers, compared with the layered tungstic acid H2WO4, shows a decrease in the apical W=O bond strength, as might be expected from the aforementioned electrostatic interaction.

Journal Article↗
PubMed2005

Tungsten oxide nanowire growth by chemically induced strain.

We have investigated the formation of tungsten oxide nanowires under different chemical vapor deposition (CVD) conditions. We find that exposure of oxidized tungsten films to hydrogen and methane at 900 degrees C leads to the formation of a dense array of typically 10 nm diameter nanowires. Structural and chemical analysis shows that the wires are crystalline WO3. We propose a chemically driven whisker growth mechanism in which interfacial strain associated with the formation of tungsten carbide stimulates nanowire growth. This might be a general concept, applicable also to other nanowire systems.

Journal Article↗
PubMed2005

Tungsten carbide nanocrystal promoted Pt/C electrocatalysts for oxygen reduction.

Tungsten carbide nanocrystals on carbon (W2C/C) and tungsten carbide nanocrystals and Pt on carbon (Pt-W2C/C) composite electrocatalysts were prepared by the intermittent microwave heating (IMH) method and tested for the electroreduction of oxygen in the acidic media for the first time. The results revealed that the tungsten carbide nanocrystal promoted Pt/C electrocatalyst was very active for ORR with the onset potential of 1.0 V vs SHE at ambient temperature that is over 100 mV more positive compared with that of traditional Pt/C electrocatalyst. The kinetic parameters were determined. The exchange current densities at both high and low overpotential regions are two orders higher for ORR on Pt-W2C/C than that on Pt/C, showing a synergetic effect to improve the activity for ORR. The novel electrocatalysts show a poisoning resistant property toward methanol.

Journal Article↗
PubMed2004

The reduction of tris-dithiolene complexes of molybdenum(VI) and tungsten(VI) by hydroxide ion: kinetics and mechanism.

The kinetic study of the spontaneous reduction of some neutral tris-dithiolene complexes [ML3] of molybdenum(VI) and tungsten(VI), (L = S2C6H4(2-), S2C6H3CH3(2-) and S2C2(CH3)2(2-); M = Mo or W) by tetrabutylammonium hydroxide in tetrahydrofuran-water solutions demonstrates that OH- is an effective reductant. Their reduction is fast, clean and quantitative. Depending upon both the molar ratio in which the reagents are mixed and the amount of water present, one- or two-electron reductions of these tris-dithiolene complexes were observed. If Bu4NOH is present in low concentration or/and at high concentrations of water, the total transformation of the neutral M(VI) complex into the monoanionic M(V) complex is the only observed process. Stopped-flow kinetic data for this reaction are consistent with the rate law: -d[ML3]/dt = d[ML3-]/dt = k[ML3][Bu4NOH]. The proposed mechanism involves nucleophilic attack of OH- to form a mono-anionic seven-coordinate intermediate [ML3OH]-, which interacts with another molecule of [ML3] to generate the monoanionic complex [ML3]- transfering the oxygen from coordinated OH- to water. Hydrogen peroxide was identified as the reaction product. The molybdenum complexes are more difficult to reduce than their corresponding tungsten complexes, and the values of k obtained for the molybdenum and tungsten series of complexes increase as the ene-1,2-dithiolate ligand becomes more electron-withdrawing (S2C6H4(2-) > S2C6H3CH3(2-) > S2C2(CH3)2(2-)). This investigation constitutes the only well-established interaction between hydroxide ion and a tris(dithiolene) complex, and supports a highly covalent bonding interaction between the metal and the hydroxide ion that modulates electron transfer reactions within these complexes.

Journal Article↗
PubMed2004

Appearance of bulk properties in small tungsten oxide clusters.

Contrary to the conventional understanding that atomic clusters usually differ in properties and structure from the bulk constituents of which they are comprised, we show that even a dimer of tungsten oxide (WO(3))(2) possesses bulklike features and the geometry of a small cluster containing only 4 tungsten and 12 oxygen atoms bears the hallmarks of crystalline tungsten oxide, WO(3). This observation, based on a synergistic approach involving mass distributions under quasisteady state conditions, photoelectron spectroscopy, and first principles molecular orbital theory, not only illustrates the existence of a class of strongly covalent or ionic materials whose embryonic forms are tiny clusters but also lends the possibility that a fundamental understanding of complex processes such as catalytic reactions on surfaces may be achieved on an atomic scale with clusters as model systems.

Journal Article↗
PubMed2003

Measurement of positron production efficiency from a tungsten monocrystalline target using 4- and 8-GeV electrons.

Intense positron sources are being widely investigated for the next-generation linear colliders and B factories. A new method utilizing an axially oriented crystal as a positron-production target is one of the bright schemes, since it provides a powerful photon source through channeling and coherent bremsstrahlung processes when high-energy electrons penetrate the target. A series of positron-production experiments with tungsten crystals hit by 4- and 8-GeV single-bunch electron beams were carried out at the KEKB 8-GeV injector linac. Three tungsten crystals with different thicknesses (2.2, 5.3, and 9.0 mm) and those combined with amorphous tungsten plates were tested on a precise goniometer. The positron-production yields were measured with a magnetic spectrometer in the positron momentum (P(e(+))) range from 5 to 20 MeV/c. The angle of the <111> crystal axis with respect to the electron-beam direction was controlled by measuring the relative intensities of the produced positrons as a function of the rotational angle of the goniometer. The results show that the enhancements of the positron yield from crystal targets compared to amorphous targets of the same thickness at P(e(+))=20 MeV/c are from 1.5 to 3.7 and from 1.8 to 5.1, depending upon the target thickness for 4- and 8-GeV electrons, respectively.

Journal Article↗
PubMed1992

Physical trauma and tungsten toxicity reduce the efficiency of biolistic transformation.

A cell suspension culture of tobacco (Nicotiana tabacum L.) was used as a model to study injury to cells during biolistic transformation. Lawns of cells were bombarded with tungsten particles that were coated with a plasmid containing the beta-glucuronidase and the neomycin phosphotransferase II genes. When a gunpowder-driven biolistic device was used, numerous transiently expressing cells were focused around the epicenter of the blast which was manifested by a hole blown in the filter paper supporting the cells. However, transformed cells nearest the blast epicenter were injured and could not be recovered as stable transformants. The injury was primarily caused by physical trauma to the cells from gas blast and acoustic shock generated by the device. Postlaunch baffles or meshes placed in the gunpowder device reduced cell injury and increased the recovery of kanamycin-resistant colonies 3.5- and 2.5-fold, respectively. A newly developed helium-driven device was more gentle to the cells and also increased the number of transformants. Cell injury could be further moderated by using a mesh and a prelaunch baffle in the helium device. Toxicity of the tungsten microprojectiles also contributed to cell injury. Gold microprojectiles were not toxic and resulted in fourfold more kanamycin-resistant colonies than when similar quantities of similarly sized tungsten particles were used.

Journal Article↗
PubMed2001

Phosphate tungsten bronze series: crystallographic and structural properties of low-dimensional conductors.

Phosphate tungsten bronzes have been shown to be conductors of low dimensionality. A review of the crystallographic and structural properties of this huge series of compounds is given here, corresponding to the present knowledge of the different X-ray studies and electron microscopy investigations. Three main families are described, monophosphate tungsten bronzes, Ax(PO2)4(WO3)2m, either with pentagonal tunnels (MPTBp) or with hexagonal tunnels (MPTBh), and diphosphate tungsten bronzes, Ax(P2O4)2(WO3)2m, mainly with hexagonal tunnels (DPTBh). The general aspect of these crystal structures may be described as a building of polyhedra sharing oxygen corners made of regular stacking of WO3-type slabs with a thickness function of m, joined by slices of tetrahedral PO4 phosphate or P2O7 diphosphate groups. The relations of the different slabs with respect to the basic perovskite structure are mentioned. The structural description is focused on the tilt phenomenon of the WO6 octahedra inside a slab of WO3-type. In this respect, a comparison with the different phases of the WO3 crystal structures is established. The various modes of tilting and the different possible connections between two adjacent WO3-type slabs involve a great variety of structures with different symmetries, as well as the existence of numerous twins in MPTBp's. Several phase transitions, with the appearance of diffuse scattering and modulation phenomena, were analysed by X-ray scattering measurements and through the temperature dependence of various physical properties for the MPTBp's. The role of the W displacements within the WO3-type slabs, in two modulated structures (m = 4 and m = 10), already solved, is discussed. Finally, the complexity of the structural aspects of DPTBh's is explained on the basis of the average structures which are the only ones solved.

Journal Article↗
PubMed2002

Extractive spectrophotometric determination of tungsten(VI) in alloy steels using ethopropazine hydrochloride.

Ethopropazine hydrochloride (EPH) has been proposed as a sensitive reagent for the spectrophotometric determination of tungsten(VI). The method is based on the formation of a chloroform-soluble yellow-colored ternary complex by the interaction of EPH and thiocyanate with tungsten(V). The complex exhibits the absorption maximum at 404 nm with Sandell's sensitivity value of 20.03 ng cm-2. The complex obeyed Beer's law in the concentration range of 1-15 micrograms ml-1 with an optimum concentration range of 2.3-12.9 micrograms ml-1. The effects of foreign ions in the determination of tungsten(VI) were investigated. The method has also been successfully applied to the analysis of alloy steels.

Journal Article↗
PubMed2005

Analytical characteristics of a continuum-source tungsten coil atomic absorption spectrometer.

A continuum-source tungsten coil electrothermal atomic absorption spectrometer has been assembled, evaluated, and employed in four different applications. The instrument consists of a xenon arc lamp light source, a tungsten coil atomizer, a Czerny-Turner high resolution monochromator, and a linear photodiode array detector. This instrument provides simultaneous multi-element analyses across a 4 nm spectral window with a resolution of 0.024 nm. Such a device might be useful in many different types of analyses. To demonstrate this broad appeal, four very different applications have been evaluated. First of all, the temperature of the gas phase was measured during the atomization cycle of the tungsten coil, using tin as a thermometric element. Secondly, a summation approach for two absorption lines for aluminum falling within the same spectral window (305.5-309.5 nm) was evaluated. This approach improves the sensitivity without requiring any additional preconcentration steps. The third application describes a background subtraction technique, as it is applied to the analysis of an oil emulsion sample. Finally, interference effects caused by Na on the atomization of Pb were studied. The simultaneous measurements of Pb and Na suggests that negative interference arises at least partially from competition between Pb and Na atoms for H2 in the gas phase.

Journal Article↗
PubMed1991

The novel tungsten-iron-sulfur protein of the hyperthermophilic archaebacterium, Pyrococcus furiosus, is an aldehyde ferredoxin oxidoreductase. Evidence for its participation in a unique glycolytic pathway.

The anaerobic archaebacterium, Pyrococcus furiosus, grows optimally at 100 degrees C by a fermentative-type metabolism in which H2, CO2, and organic acids are end products. The growth of this organism is stimulated by tungsten, and, from it, a novel, red-colored, tungsten-iron-sulfur protein, abbreviated RTP, has been purified (Mukund, S., and Adams, M. W. W. (1990) J. Biol. Chem. 265, 11508-11516). RTP (Mr approximately 85,000) contained approximately 1W, 7Fe, and 5 acid-labile sulfide atoms/molecule and exhibited unique EPR properties. The physiological function of the protein, however, was unknown. We show here that RTP is an inactive form of an aldehyde ferredoxin oxidoreductase (AOR). The active enzyme was obtained by rapid purification under anaerobic conditions using buffers containing dithiothreitol and glycerol. AOR catalyzed the oxidation of a range of aliphatic aldehydes with an optimum temperature for activity above 90 degrees C, but it did not oxidize glucose or glyceraldehyde 3-phosphate, nor reduce NAD(P), and its activity was independent of CoA. The active (AOR) and inactive (RTP) forms of the enzyme were indistinguishable in their contents of metals and acid-labile sulfide and in their EPR properties. The latter are though to originate from two nonidentical and spin-coupled iron-sulfur clusters, whereas the tungsten in this enzyme, which was not detectable by EPR, appears to be present as a novel pterin cofactor. Inhibition and activation studies indicated that AOR contains a catalytically essential W-SH group that is not present in RTP, the inactive form. AOR is a new type of aldehyde-oxidizing enzyme and is the first aldehyde oxidoreductase to be purified from an archaebacterium or a nonactogenic anaerobic bacterium. Its physiological role in P. furiosus is proposed as the oxidation of glyceraldehyde to glycerate in a unique, partially nonphosphorylated, glycolytic pathway that generates acetyl-CoA from glucose without the participation of nicotinamide nucleotides.

Aldehyde Oxidoreductases↗
PubMed1993

Identification of molybdopterin as the organic component of the tungsten cofactor in four enzymes from hyperthermophilic Archaea.

The hyperthermophilic Archaea represent some of the most ancient organisms on earth. A study of enzymatic cofactors in these organisms could provide basic information on the origins of related cofactors in man and other more recently evolved organisms. To this end, the nature of the tungsten cofactor in aldehyde ferredoxin oxidoreductases from Pyrococcus furiosus and ES-4 and in formaldehyde ferredoxin oxidoreductases from P. furiosus and Thermococcus litoralis has been investigated. All four proteins contain molybdopterin, previously characterized as the organic component of the molybdenum cofactor in a large number of molybdoenzymes. Molybdopterin was identified by conversion to the dicarboxamidomethyl derivative by alkylation of the vicinal sulfhydryl groups on the pterin side chain and by conversion to the oxidized fluorescent derivative, Form A. The pterin of the tungsten cofactor in the four enzymes was examined for the presence of appended GMP, CMP, AMP, or IMP previously observed in molybdenum cofactors of some molybdoenzymes. No evidence for the presence of a molybdopterin dinucleotide or other modified form of molybdopterin was obtained. These results further document the essential nature of molybdopterin for the function of molybdenum and tungsten enzymes in diverse life forms.

Aldehyde Oxidoreductases↗