Showing papers on "Cobalt published in 1979"

Homogeneous catalysis of the photoreduction of water by visible light. Mediation by a tris(2,2'-bipyridine)ruthenium(II)-cobalt(II) macrocycle system

Abstract: The approach of researchers at Brookhaven National Laboratory to the homogeneous generation of hydrogen is to convert the luminescent excited state of tris(2,2'-bipyridine)-ruthenium(II) (*Ru(bpy)/sub 3//sup 2 +/) to the more strongly reducing (and longer lived) ion Ru(bpy)/sub 3//sup +/. The Ru(bpy)/sub 3//sup +/ reduces a metal complex which reacts with H/sub 3/O/sup +/ or H/sub 2/O to form an unstable hydride. The hydride in turn decomposes to yield hydrogen. The blue cobalt(I) bipyridine complexes produced by Na(Hg) or electrochemical reduction of cobalt(II) bipyridine complexes are very powerful reducing agents and are not likely to form stable hydrides in solution. Cobalt(I) bipyridine complexes are thus excellent candidates for mediating the homogeneous formation of hydrogen. This expectation has been confirmed: visible-light irradiation of solutions containing Ru(bpy)/sub 3//sup 2 +/, ascorbate, Co/sup 2 +/, and bpy or phen derivatives produces hydrogen with a quantum yield of up to 0.13 mol einstein/sup -1/. Low yields of H/sub 2/ are also produced in the absence of Co/sup 2 +/.

Some first row transition metal complexes of nicotinamide and nicotinic acid

Abstract: Some complexes of the chlorides and bromides of manganese(II), iron(II), cobalt(II), nickel(II) and copper(II) with nicotinamide and nicotinic acid have been prepared. These complexes have stoichiometryML 2X2 whereM is a metal ion,L is an organic ligand andX is a halide ion. Spectral and magnetic properties indicate that these compounds have octahedral polymeric structures. The decomposition of the complexes was studied by thermogravimetry and differential thermal analysis. In only one instance was a decomposition product of the formulaMLX2 obtained. Its structure was also octahedral.

Site-specific substituted cobalt(II) horse liver alcohol dehydrogenases. Preparation and characterization in solution, crystalline and immobilized state.

Abstract: The specific substitution, using highly selective techniques, of catalytic and/or noncatalytic zinc ions by cobaltous ions in horse liver alcohol dehydrogenase (EC 1.1.1.1) has been studied with dissolved, crystalline and agarose-immobilised enzyme, in order to examine the effect of protein structure on the specificity of the metal exchange. The different binding sites can be clearly distinguished by the absorption spectra of their cobalt derivatives. In solution an anaerobic column chromatographic method made it possible to exchange half of the zinc in the enzyme by cobalt ions in a much shorter time than previous procedures. By raising the temperature in the exchange step, even the slowly exchanging zinc ions were substituted by cobalt, yielding products similar to cobalt alcohol dehydrogenases described earlier. Treatment of crystal suspensions of the enzyme with chelating agents (preferentially dipicolinic acid) gave an inactive protein with two zinc ions remaining bound. The enzyme could be reactivated by treatment of the crystalline protein with 5 mM zinc or cobaltous ions or by dialysis of dissolved inactive protein against 20 microM zinc or 1 mM cobaltous ions. Higher metal concentrations led to denaturation but the inactive protein could be crystallized from solution and then reactivated completely at higher metal concentrations. The preparation and absorption spectrum show that cobalt is bound specifically at the catalytic sites. Since metal substitution at these sites critically depends on the maintenance of the correct tertiary and quaternary structure, these must be preserved in the crystal lattice and partially altered in solution when the catalytic zinc ions are removed (or when excess of metal ions is applied), thus demonstrating the structure-stabilizing role of the catalytic metal ions. The enzyme immobilised on agarose, with unchanged content of active sites [Schneider-Bernlohr et al. (1978) Eur. J. Biochem. 41, 475--484], was treated like the crystal suspensions. Although half of the zinc was removed, some activity remained. After reactivation with cobaltous ions, a loss of about 30% active sites was measured. Thus the apparently homogenous bound enzyme was rather heterogeneous in the properties of its catalytic metal binding sites. These results are taken as further proof for the dependence of the metal substitution on the proper tertiary and quaternary structure which is strained by multiple interactions in the covalently immobilised enzyme.

Cobalt-catalyzed one-step synthesis of annulated pyridines

Abstract: A method of synthesizing fused ring pyridines (annulated) by co-oligomerization of α,ω-diynes with about molar equivalents of nitriles using a Co+1 catalyst preferably cyclopentadienyl cobalt dicarbonyl. Additionally, new compounds of tricyclic quinolizine-4-ones were produced where excess cyanoacetic ester starting materials were utilized (about 2:1 equivalent nitriles:diyne). The results with the catalyst employed indicated a stepwise mechanism in which cobalt(I) catalyst first forms a metallocycle intermediate derived from the bisacetylene. This cobalt(III) intermediate reacts preferentially with nitriles to give the product annulated pyridines in good yield. Generally, preferred conditions indicated roughly molar equivalents of reactants with no substantial excess of either reactant for the bicyclic compounds. Preferred conditions include a moderate temperature (solvent reflux temperature) and a preferred solvent such as BTX-type solvent (xylene) or an alkane (N-octane) under an inert blanket (nitrogen) for a multi-day period.

Mutagenicity of metal cations in cultured cells from Chinese hamster.

Abstract: The mutations at the hypoxanthine—guanine phosphoribosyl transferase (HGPRTase) locus in Chinese hamster V79 cells induced by metal cations were examined by the development of resistance to 8-azaguanine (8AG). The spontaneous frequency of 8AG resistance was 5.8 per 10 6 cells, and the frequency was enhanced to 2–6 times that of the control by treatment of cells with the chlorides of beryllium and manganese. About 75% of 8AG-resistant colonies were sensitive to amethopterin, and 86% of the resistant colonies showed less than 3% of the HGPRTase activity of the wild-type cells. The mutant frequency in cultures treated with cobalt and nickel chlorides were slightly increased, and mutation induction was only detectable at very low rates of cell survival.

Phase transformations and vacancy formation energies of transition metals by positron annihilation

Abstract: The technique of the coincidence count rate at the peak of the angular correlation curve (CCR) in positron annihilation has been applied to the investigation of vacancy formation energies in thermal equilibrium in nickel, cobalt, and iron. The monovacancy formation energyE1v/F has been determined to (1.55±0.05) eV and (1.34±0.07) eV for nickel and cobalt, and (1.60±0.10) eV for α-iron, and (1.40±0.15) eV for γ-iron, respectively. The structural phase transformations in cobalt (693 K) and iron (1183 K, 1663 K) are exhibited by discontinuities of the CCR. In the case of cobalt the CCR follows exactly the change of the thermal expansion at the transition temperature. The temperature dependence of the CCR in the prevacancy region is found to be proportional to the thermal expansion for all metals investigated.

Polymer-anchored cobalt tetraarylporphyrin catalysts for the conversion of quadricyclane to norbornadiene

Abstract: Methods are described for the preparation of carboxamide- and sulfonamide-linked polystyrene-anchored cobalt (II) tetraarylporphyrins containing 0.28 to 0.44% cobalt, which are highly active catalysts for the conversion of quadricyclane to norbornadiene. These cobalt catalysts gradually lose some of their activity upon repeated recycling. This loss in catalytic activity apparently arises from partial oxidation, since the loss of catalytic activity can be partially restored by treatment with a strong reducing agent such as titanium(III). The apparent activities of these catalysts are increased if the catalyst is finely powdered, thereby suggesting diffusion limitation of the catalytic activity. Applications are discussed of these catalysts in a proposed solar energy storage system based on the reversible valence isomerization of norbornadiene to quadricyclane. 1 figure, 5 tables.

Complex boride particle containing alloys

Abstract: Boron-containing transition metal alloys based on one or more of iron, cobalt and nickel, and containing at least two metal components, are characterized by being composed of ultrafine grains of a primary solid-solution phase randomly interspersed with particles of complex borides which are predominantly located at the junctions of at least three grains of the primary solid-solution phase. These alloys are obtained by devitrification of the solid, amorphous state under specific heat-treatment conditions. These alloys can be consolidated into three-dimensional bodies.

Electrocatalytic behavior of metal porphyrins in the reduction of carbon dioxide

Abstract: The catalytic activity of metal porphyrins for the electroreduction of carbon dioxide was investigated by the measurements of current-potential curves on the Hg(Pt) electrode in aqueous electrolytic solutions. Metal-free, cobalt, iron and copper porphyrins(mesotetracarboxyphenylporphyrins, tetraphenylporphinesulfonate) were examined. Cobalt complexes were active but other metal porphyrins showed no activity. The reduction product was confirmed to be formic acid by the resorcinol test.