An examination of oxidation products of the pterin cofactor in the formate dehydrogenase of Methanobacterium formicicum revealed that the cofactor is a 6-substituted pterin similar to the molybdopterin of xanthine oxidase. In contrast to the molybdopterin from xanthine oxidase the formate dehydrogenase cofactor was unable to complement the cofactor-deficient nitrate reductase of Neurospora crassa mutant nit-1 and possessed two phosphate groups. Incubation of oxidized formate dehydrogenase with cyanide resulted in an irreversible loss of enzyme activity which could not be restored by treatment with sulfide. Equimolar amounts of thiocyanate were released from cyanide-treated formate dehydrogenase suggesting the loss of one terminal sulfur ligand to molybdenum. These results along with electron paramagnetic resonance spectroscopy of the cyanide-inactivated formate dehydrogenase suggest that the the molybdenum ligands of the enzyme are similar to those of xanthine oxidase. The concentration of molybdenum and the level of formate dehydrogenase activity in extracts of hydrogen-grown Methanobacterium formicicum decreased by at least 10- fold when the organism was grown for several transfers in molybdenum-deficient media or with added tungstate. Immunochemical analysis showed that both subunits of the formate dehydrogenase were produced regardless of the growth condition. However the amount of formate dehydrogenase protein decreased more than 10-fold when the amount of molybdenum in the cell was low. The pterin cofactor was present in the inactive enzyme from tungstategrown cells; however the protein contained less than 0.05 molecules of molybdenum or tungsten per formate dehydrogenase. Messenger RNA specific for fdh gene was detected in high amount in cells grown without added molybdenum and in low amount in cells that contained high amounts of molybdenum. These results suggest that molybdenum is required for the synthesis of a stable formate dehydrogenase and that a molybdenum-dependent repressor may be required for the termination of fdh transcription. / Ph. D.

No description available.

Binuclear mixed biscarbene complexes of bithiophene were synthesized via the classical Fischer method of synthesis. The metal carbonyls, Mo(CO)6, Cr(CO)6, W(CO)6 and Mn(MeCp)(CO)3 were reacted with dilithiated bithiophene to afford complexes of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(OEt})M'(CO)5] (in case of manganese, M(CO)5 is replaced with MMeCp(CO)2), where [M] and [M'] are the metal carbonyls in different combinations. Quenching was achieved with triethyl oxonium tetrafluoroborate. In all the reactions the products included monocarbene complexes, biscarbene complexes and the decomposition products. C-C coupling reactions produced unexpected biscarbene complexes of Cr, W, and Mo having extended bithiophene spacers. The complexes were of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(R)-C(R)C4H2S-C4H2SC(OEt})M'(CO)5] (R = O, OH or OEt). These complexes were characterized with NMR, infrared spectroscopy and some with mass spectrometry. Furthermore, three biscarbene complexes of the metal combinations Mo(CO)6 and Cr(CO)6, W(CO)6 and Cr(CO)6, and Mn(MeCp)(CO)3 and Cr(CO)6 were all reacted with 3-hexyne. The result was the benzannulation or the Dötz products. / Chemistry / M. Sc. (Chemistry)

Conducting polymers that contain metals are remarkable materials, because they have the properties of both organic backbones and metals. Depending on the position of the metal relative to the conjugated backbone, i.e. attached to or directly in the backbone, these two can couple resulting in advancement of the functionality and therefore potential applications of these types of materials. Complexes of tridentate ligands with donor atoms such as phosphorus, nitrogen, and sulfur also have a wide variety of applications. In addition, complexes of tridentate ligands have advantages of stability and control of electron density by variation of donor atoms. Therefore, conjugated polymers with tridentate ligand units will have promise for various applications and advantages in their designs. Complexes of PNP ligand with molybdenum and carbonyl ancillary ligands were synthesized and characterized. Isomerization and conversion reactions between them were investigated as well as the coordination modes. Many types of PNP ligands have been studied in the literature because the hemilabile property of the nitrogen atom promotes some catalytic reactions and gives different coordination geometries. Conducting polymers can be used as redox-active ligands and they can be used to control electron density on the metal attached to them. Synthesis and characterization of a novel polymerizable ligand 3,5-bis-EDOT-N,N-bis[2-diphenylphosphinoethyl]aniline was achieved. Related molybdenum complexes with ancillary ligands as carbonyls were also synthesized and characterized. Monomer complexes and the free ligand were electropolymerized and studied. Tris(bipyridine)ruthenium(II) chloride and analogous complexes have been studied extensively in the literature due to their luminescent and photochemical properties, and excited state lifetimes. Conducting polymers with similar ruthenium groups have been investigated for various applications. Synthesis of four ruthenium complexes with the polymerizable ligand 2,6-Bis[4-[2-(3,4-diethylenedioxy)thiophene]pyrazol-1-yl]pyridine and four different bidentate ligands were reproduced; electropolymerizations of the complexes were achieved; electrochemical, UV-Vis and luminescence studies were performed and discussed. Various complexes of copper, silver, platinum, and palladium with nitrogen and phosphorus donors have been reported for their luminescence behavior as well as their interesting structures. Model complexes of these metals with N,N-bis[2-(diphenylphosphino)ethyl]phenyl-amine (a PNP ligand) have been synthesized and characterized. Absorption and luminescence behaviors as well as the coordination modes were investigated. / text

Thesis (Ph.D. (Engineering mechanics)) --University of Limpopo, 2004 / This thesis explores the important issues associated with the insertion of Mg2+ and Li+ into the solid materials: molybdenum sulphide and titanium disulphide. This process, which is also known as intercalation, is driven by charge transfer and is the basic cell reaction of advanced batteries. We perform a systematic computational investigation of the new Chevrel phase, MgxMo6S8 for 0 ≤ x ≤ 2, a candidate for high energy density cathode in prototype rechargeable magnesium (Mg) battery systems. Mg2+ intercalation property of the Mo6S8 Chevrel phase compound and accompanied structural changes were evaluated. We conduct our study within the framework of both the local-density functional theory and the generalised gradient approximation techniques. Analysis of the calculated energetics for different magnesium positions and composition suggest a triclinic structure of MgxMo6S8 (x = 1 and 2). The results compare favourably with experimental data. Band-structure calculations imply the existence of an energy gap located ~1 eV above the Fermi level, which is a characteristic feature of the electronic structure of the Chevrel compounds. Calculations of electronic charge density suggest a charge transfer from Mg to the Mo6S8 cluster, which has a significant effect on the Mo-Mo bond length. There is relatively no theoretical work, in particular ab initio pseudopotential calculations, reported in literature on structural stability, cations "site energy" calculations, and pressure work. Structures obtained on the basis from experimental studies of other ternary molybdenum sulphides are examined with respect to pressure-induced structural transformation. We report the first bulk and linear moduli of the new Chevrel phase structures. This thesis also studies the reaction between lithium and titanium disulfide, which is the perfect intercalation reaction, with the product having the same structure over the range of reaction 0  x  1 in LixTiS2. Calculated lattice parameters, bulk moduli, linear moduli, elastic constants, density of states, and Mulliken populations are reported. Our calculations confirm that there is a single phase present with an expansion of the crystalline lattice as is typical for a solid solution, about 10% perpendicular to the basal plane layers. A slight expansion of the lattice in the basal plane is also observed due to the electron density increasing on the sulfur ions. Details on the correlation between the electronic structure and the energetic (i.e. the thermodynamics) of intercalation are obtained by establishing the connection between the charge transfer and lithium intercalation into TiS2. The theoretical determination of the densities of states for the pure TiS2 and Li1TiS2 confirms a charge transfer. Lithium charge is donated to the S (3p) and Ti (3d) orbitals. Comparison with experiment shows that the calculated optical properties for energies below 12 eV agrees well with reflectivity spectra. The structural and electronic properties of the intercalation compound LixTiS2, for x = 1/4, 3/4, and 1, are also investigated. This study indicates that the following physical changes in LixTiS2 are induced by intercalation: (1) the crystal expands uniaxially in the c-direction, (2) no staging is observed. We also focus on the intercalation voltage where the variation of the cell potential with the degree of discharge for LiTiS2 is calculated. Our results show that it can be predicted with these well-developed total energy methods. The detailed understanding of the electronic structure of the intercalation compounds provided by this method gives an approach to the interpretation of the voltage composition profiles of electrode materials, and may now clearly be used routinely to determine the contributions of the anode and cathode processes to the cell voltage. Hence becoming an important tool in the selection and design of new systems. Keywords Magnesium rechargeable battery; Chevrel, Lithium batteries; Li and Mg-ion insertion; TiS2; Mo6S8; Charge transfer; reflectivity, intercalation, elastic constants, voltage, EOS, Moduli. / the National Research Foundation, the Royal Society(U.K),the Council for Scientific and Industrial Research,and Eskom

Molybdenum chalcohalide nanowires are systems, which structural, electronic and optical properties have been analyzed in detail. However, their potential as building blocks for electronic devices has not been investigated so far. This question is raised in Dissertation, focusing on unique electronic transport properties of these systems, and comparing them with those of the popular carbon nanotubes.

Silanethiolate salts of K(18-crown-6)+, N(CH3)4 +, Cs+, K+ were synthesized and characterized by vibrational and NMR spectroscopy. The [N(CH3)4][SSi(CH3)3] salt was used to prepare the new [N(CH3)4][WSF5] salt directly from WF6. Alternatively, [N(CH3)4][WSF5] was prepared by the reaction of WSF4 with [N(CH3)4][F]. Pure WSF4 was prepared via a facile new route and was fully characterized by Raman, infrared, and 19F NMR spectroscopy, and an improved crystal structure. The Lewis-acid properties of WSF4 were studied in reactions with pyridine, yielding the new WSF4·C5H5N adduct, which was studied by Raman and 19F NMR spectroscopy. A 2:1 stoichiometry of WSF4 and [N(CH3)4][F] yielded W2S2F9 - in solution. The novel W2SOF9 - anion was characterized in solution by 19F NMR spectroscopy. Molybdenum sulfide tetrafluoride was synthesized and unambiguously characterized by Raman, infrared, and 19F NMR spectroscopy and single-crystal X-ray diffraction. The experimental characterization of WSF4, MoSF4, WSF5 -, and SSi(CH3)3 - was supplemented by density functional theory calculations. / xv, 131 leaves : ill. ; 29 cm.

Access to abstract permanently restricted to Ball State community only / Construction of experimental setup -- Synthesis of MoS₂ and WS₂ fullerene like structures -- Synthesis of MoS₂ and WS₂ nanotube like structures -- Infrared spectroscopy of acetonitrile adsorption on synthesized MoS₂ materials. / Access to thesis permanently restricted to Ball State community only / Department of Chemistry

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2315" Vikas Behrani. 12/19/2004. Report is also available in paper and microfiche from NTIS.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 161-169). Also available on the World Wide Web.