Página 1 dos resultados de 4804 itens digitais encontrados em 0.015 segundos

Estudo espectrofotométrico do sistema cobalto(II)/tiocianato e seu aproveitamento analítico ; Spectrophotometric study of cobalt(II)/thiocyanate system and its analytical use

Sader, Ana Paula de Oliveira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/12/2002 PT
Relevância na Pesquisa
37.08%
Estudos sobre a formação dos complexos de metais, seus equilíbrios e, também, o aproveitamento analítico desses diferentes sistemas constituem uma tradicional linha de pesquisa em Química. Mais especificamente, as espécies formadas entre os vários pseudo-haletos e outros ligantes, com muitos cátions dos metais de transição, vêm sendo sistematicamente investigadas em nossos laboratórios de Química Analítica. Nesta linha, o emprego do íon tiocianato como ligante tem se destacado dentre os métodos analíticos para a determinação de cobalto, cuja procura tem sido crescente à medida que o homem, ao longo de sua evolução, descobre e produz novos materiais contendo esse metal. Desta forma, tendo em vista algumas características típicas do sistema Co(II)/SCN-, tal como sua intensa coloração, objetivou-se, nesta oportunidade, explorá-lo espectrofotometricamente com maior profundidade. Conseqüentemente, diversos parâmetros envolvidos na complexação dos íons cobalto (II) pelo tiocianato, tais como: a acidez do meio, a concentração disponível de ligante e a presença de solventes orgânicos no sistema, tiveram seus efeitos avaliados individualmente. Com os resultados destes estudos, estabeleceram-se as condições experimentais otimizadas para a montagem do método analítico...

Estudo da deposição química de cobalto em superfícies de silício pré-ativadas por paládio.; Study of chemical deposition of cobalt on a surface of silicon pre-activated by palladium.

Hashimoto, Alexandre Ichiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/06/2008 PT
Relevância na Pesquisa
37.06%
Neste trabalho investigamos a deposição química de filmes finos de cobalto sobre superfícies de lâminas de silício, tipo P (100), previamente ativadas com paládio e estudamos alguns mecanismos químicos envolvidos no processo de deposição química de filmes finos de cobalto. Os filmes de cobalto foram caracterizados quanto sua morfologia utilizando técnicas de Microscopia de Força Atômica (AFM) e Espectrometria de Retroespalhamento de Rutherford (RBS).Estudamos dois tipos de banho para deposição química: Receita 1 (2,0M NH4Cl, 0,005M CoCl2.6H2O, 0,15M NaH2PO2 H2O) e Receita 2 (0,14M Na3C6H5O7, 0,65M (NH4)2SO4, 0,19M CoSO4.7 H2O, 0,28M NaH2PO2 H2O) onde o pH dos banhos foi variado na faixa de 3,7 a 10 através da adição de hidróxido de amônio e a temperatura, na faixa de 65°C a 90°C. Nesta investigação sobre a deposição de cobalto sobre silício tipo P inicialmente foi observado que os sítios de paládio ficam esparsamente distribuídos sobre toda a superfície da lâmina de silício. A receita 1 não permitiu realizar deposição química sobre silício (100) tipo P em amplas faixas de pH e temperatura, com ou sem ativação das superfícies por paládio. Tal fato foi atribuído ao NH4Cl que teve o duplo papel de agente complexante e agente tamponante ...

A existência de onda catalítica no sistema cobalto (II) azeteto/ácido azotídrico; Polarographic cataltytic process in azide/hydrazoic buffer in the presence of cobalt (II)

Tokoro, Roberto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/09/1974 PT
Relevância na Pesquisa
37.03%
Os primeiros estudos sobre a utilização do azoteto de sódio, NaN3, como eletrólito de suporte em polarografia, revelaram a existência de onda catalítica quando o meio era acidulado, contendo HN3, na presença de íons de cobalto(II). O presente trabalho procurou esclarecer a natureza da onda catalítica com os íons de cobalto(II). Para isto foram estudados diversos fatores como ânions indiferentes, a presença de íons de hidrogênio, a influência do oxigênio, composição da solução em relação à concentração de azoteto, de cobalto(II) e papel da substância tensoativa. Os resultados experimentais levaram à conclusão de que se tratava de onda catalítica com evolução de hidrogênio, cujo mecanismo se assemelha muito ao observado no sistema CO(II)/CN-. Há evidências de participação de fenômenos de adsorção de complexos de cobalto(II) com azoteto, passando intermediariamente ao estado de oxidação (I) e reoxidação a hidreto complexo de cobalto(III). Este por ação catalítica de espécie neutra Co(N3)2 se decompõe liberando hidrogênio molecular e regenerando o complexo de cobalto(II). Verificou-se também corrente catalítica no sistema HN3N-3 na presença de níquel(II).; Previous studies about sodium azide as suporting electrolyte in polarography showed existence of a catalytic wave in acidic media...

Contribuição ao estudo da estrutura de complexos de fosfinóxidos com cobalto (II); Crystal structure of cobalt (II) bis-tribenzylphosphinoxide chloride

Santos, Regina Helena de Almeida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/05/1979 PT
Relevância na Pesquisa
37.08%
Foram determinadas as estruturas cristalinas e moleculares, por método de difração de raios-X de monocristais, da série de quatro complexos de cloreto de Cobalto (II) com tri-benzilfosfinóxido, dibenzilfenilfosfinóxido, benzildifenilfosfinóxido e trifenilfosfinóxido. Os dados cristalinos sao: Dicloro bis(tribenzilfosfinóxido) Cobalto(II), CoCl2.2tbpo, COCl2‌(C7H7)3PO‌ 2; sistema cristalino: ortorrômbico; grupo espacial: P212121; a = 15,133(1), b = 15,905(1), c = 16,493(1)Å, V = 3954 ޵ dc = 1,289(2) g.cm-3; do = 1,29(1) g.cm-3. Dicloro bis(dibenzilfosfinóxido) Cobalto(II), CoCl2.2dbfpo, CoCl2 ‌(C7H7)2(C6H5)PO‌ 2; sistema cristalino: monoclínico; grupo espacial: c2/c; a = 18,187(9), b = 10,998(7), c = 18,954(3) Å, β = 96,12#176(4), V = 3769޵ dc = 1,314 (3) g.cm-3, do = 1,33(1) g.cm-3. Dicloro bis(benzilfosfinóxido) Cobalto(II), CoCl2.2dbfpo, CoCl2 ‌(C7H7)2(C6H5)PO‌ 2; sistema cristalino: monoclínico; grupo espacial: p21/c; a = 10,217(2), b = 16,776(2), c = 21,920(3)Å, = 112,15°(3), V = 3494 ޵ dc = 1,364(3) g.cm-3; do = 1,37(1) g.cm-3. Dicloro bis(trifenilfosfinóxido) Cobalto(II), CoCl2.2tbpo, CoCl2‌(C6H5)3PO‌ 2; sistema cristalino: ortorrômbico; grupo espacial: Fdd2; a = 20...

Effect of the balance between Co(II) and Co(0) oxidation states on the catalytic activity of cobalt catalysts for Ethanol Steam Reforming

Passos, Aline R.; Martins, Leandro; Pulcinelli, Sandra H.; Santilli, Celso V.; Briois, Valerie
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 88-94
ENG
Relevância na Pesquisa
36.99%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Changes of the oxidation state of cobalt species during activation under H-2 gas and ethanol steam reforming reaction on Co/Al2O3 were investigated using time-resolved operando Quick-XAS analysis. Prior to activation and reaction, the catalysts were calcined at two different temperatures: 450 and 600 degrees C, the cobalt species of the as-calcined catalysts are slightly different depending on the temperature of calcination. At the end of activation the same amount of metallic cobalt (similar to 63%) was detected for both catalysts calcined at different temperatures. The cobalt species interacted more strongly with the support in the catalyst calcined at 600 degrees C, what resulted in the formation of more cobalt aluminate species and lower amount of Co2+. A relationship between the catalytic performance of catalyst and the molar ratio of Co2+/Co-0 was established: deactivation of catalysts mainly occurred by carbon deposition, however the control of Co-2+/Co-0 ratio helped to equilibrate the steps of ethanol activation and carbon oxidation...

Studies of the electrodeposition of cobalt on a vitreous carbon electrode

Bertazzoli,Rodnei; Sousa,Maria de Fátima Pinto
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1997 EN
Relevância na Pesquisa
36.99%
Experiments of cobalt deposition on a vitreous carbon electrode were carried out using cyclic voltammetry and potential steps techniques, in a sulfate medium. Cyclic voltammetry showed two stripping peaks that were attnbuted to the dissolution of two phases: a hydrogen nch cobalt phase and a bulk cobalt phase. Kinetic analysis of I-E response on the reverse scan for a 0.37 M of Co(II), pH 6, presented a value of -0.58 V vs. SCE for the equilibrium potential of the Co/Co(II) couple. The exchange current density was estimated as Io = 4.8 x 10-6 A cm-2 in this solution. Potential step experiments showed that the cobalt deposit on vitreous carbon is formed by a mechanism of progressive nucleation followed by 3-D growth. Both techniques confirmed that cobalt deposition takes place in two single electron steps.

Enhancing cobalt dispersion in supported Fischer-Tropsch catalysts via controlled decomposition of cobalt precursors

Khodakov,Andrei Y.
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2009 EN
Relevância na Pesquisa
37.12%
Fischer-Tropsch synthesis is a part of Gas-to Liquids (GTL), Biomass-to-Liquids (BTL) and Coal to Liquids (CTL) technologies, which produce alternatives clean fuels from natural gas, biomass and coal. The catalytic performance of cobalt catalysts in Fischer-Tropsch synthesis strongly depends on the size of cobalt particles in nanoscale range (6-30 nm). Cobalt catalysts are usually prepared via incipient wetness impregnation using cobalt salts (cobalt precursors). Catalyst preparation involves several important steps. The paper shows that decomposition of cobalt precursors is often a crucial step in the catalyst design; slower rate of decomposition of cobalt precursors favors smaller size of cobalt particles, higher cobalt dispersion and enhances catalytic performance in Fischer-Tropsch synthesis.

Cobalt and vitamin B12 in diets for commercial laying hens on the second cycle of production

Kato,RK; Bertechini,AG; Fassani,EJ; Santos,CD; Dionizio,MA; Fialho,ET
Fonte: Fundação APINCO de Ciência e Tecnologia Avícolas Publicador: Fundação APINCO de Ciência e Tecnologia Avícolas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2003 EN
Relevância na Pesquisa
37.03%
The supplementation of cobalt and vitamin B12 in diets for commercial laying hens on the second production cycle was studied. Four hundred and eighty light commercial laying hens, Lohmann LSL, were used at initial phase of forced molting laying period. The trial was conducted in a randomized design. The plots were the treatments which were constituted by combination of five cobalt levels (0.00; 0.30; 0.60; 0.90 and 1.20ppm) and two vitamin B12 levels (without and with 10µ/kg), and the split-plots were four periods (21, 42, 63 and 84 days) during the second period of production, with 4 repetitions and 12 hens per experimental unit. Food and water were provided ad libitum and eggs were collected twice daily. Performance and egg quality parameters were evaluated. At the end of experimental period, two layers from each treatment were slaughtered, and liver and blood samples were taken for analysis. Performance and egg quality were not different (p>0.05) among cobalt supplementation levels, although egg damage data were different (p<0.05). Supplementation with vitamin B12 decreased egg weight. No influence of cobalt or vitamin B12 supplementation was seen on the concentration of cobalt in the liver and yolk as well as on blood analysis (hematrocrit...

Synthesis and reactivity of low-coordinate cobalt complexes and iron(I) alkyl complexes supported by β-diketiminate ligand

Ding, Keying (1980 - ); Holland, Patrick L.
Fonte: University of Rochester. Publicador: University of Rochester.
Tipo: Tese de Doutorado Formato: Number of Pages:xix, 145 leaves
ENG
Relevância na Pesquisa
37.15%
Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2009.; The strategy of using exposed metal centers to efficiently perform chemical transformations is shared by enzymes, metal surfaces and synthetic homogeneous catalysts. Three-coordinate complexes of the transition metals are rare, because it is difficult with only three ligand donors to reach preferred configurations with 16 or 18 electrons in the metal bonding and nonbonding orbitals. By using extremely bulky β-diketiminate ligands, chemists have been able to stabilize three-coordinate iron centers. However, there has been much less attention to the area of diketiminate cobalt chemistry, which promised to be equally exciting. This thesis mainly describes the synthesis and reactivity of low-coordinate cobalt dinitrogen, hydride, fluoride complexes supported by β-diketiminate ligand LtBu. The final chapter discusses the synthesis of unusual iron(I) alkyl complexes of LtBu and their catalytic suitability for aryl-alkyl cross coupling reactions. In Chapter II, three low-coordinate cobalt dinitrogen complexes were synthesized, structurally characterized and compared to their iron analogues. Despite the identical ligand environment, there are significant differences between the cores of the two LtBuMNNMLtBu (M = Fe...

Síntese e caracterização de compósitos mesoporosos de sílica-óxido de cobalto e avaliação catalítica na reação de redução de no com CO; Synthesis and characterization of mesoporous silica composite cobalt oxide and catalytic evaluation in the reduction reaction with CO

SANTOS, Gustavo Amorim
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Química; Educação em Química Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Química; Educação em Química
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
37.19%
In this work, a methodology for the synthesis of silica-cobalt oxide-based composites was developed by modifying the well known Stöber sol-gel method. The main novelty of the procedure was the use of colloidal suspensions of cobalt oxide or cobalt hydroxide nanoparticles (Co3O4,Co(OH)2), which were previously prepared from the precipitation of Co2+ ions in alkaline medium. The silica-cobalt composites having cobalt contents (w/w) around 8.4 to 11% were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG/DTA), temperature programmed reduction (TPR) and adsorption /desorption of nitrogen. The characteristics of the composites which were prepared by employing the colloidal suspensions were compared to those exhibited by other composites which were obtained from cobalt nitrate solution. The influence of cerium nitrate and citric acid was also evaluated. The methodology employed in the synthesis of nanoparticles and composites were reproducible and the prepared materials showed surface areas (300 to 567 cm3/g) and pore diameters (3.8 to 8.1 nm) values which were considered appropriate to use them as catalysts. The calcined composites which were prepared using colloidal suspensions of Co3O4 nanoparticles showed TPR curves with maximum picks at relatively low temperatures...

Complexes pinceurs de cobalt et de nickel : synthèse, caratérisation, réactivité

Lefèvre, Xavier
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
Relevância na Pesquisa
37.06%
Plusieurs nouveaux complexes pinceurs de cobalt et de nickel ont été préparés avec le ligand pinceur de type POCOP : 2,6-(i-Pr2PO)2C6H4. Dans le cas du cobalt, une nouvelle voie de synthèse a été développée. Contrairement au cas du nickel, il s’agit ici de cobalt au degré d’oxydation +III. Les composés obtenus sont paramagnétiques. En outre, le dérivé bromé est instable à la lumière et se décompose en perdant un brome pour former le complexe pinceur de Co(II). La réactivité de ces complexes a été étudiée. Pour ce qui est du nickel, la catalyse de l’hydroamination a été élargie aux dérivés de l’acrylonitrile et aux amines aromatiques. En outre, la réaction d’hydroaryloxylation a été étudiée dans les mêmes conditions. Enfin, avec le 4-cyanostyrène et le cinnamonitrile, la formation d’amidines a été observée. Un complexe pinceur portant cette amidine a été isolé. Enfin, le cation réagit avec des anions fortement coordonnants tels le cyanure ou l’isocyanate. En outre, l’anion triflate peut être déplacé par l’eau, l’acrylonitrile et ses dérivés. Enfin, une réactivité particulière a été observée avec la morpholine, l’acétone et un mélange 1:1 aniline/triéthylamine.; A large variety of new POCOP pincer type complexes of cobalt and nickel have been prepared. All those complexes are based on the following POCOP pincer type ligand: 2...

Biologic effects of cobalt chrome in cell and animal models

Howie, D.; Rogers, S.; McGee, M.; Haynes, D.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Artigo de Revista Científica
Publicado em //1996 EN
Relevância na Pesquisa
37.03%
The literature on animal and cellular models used to study the response to cobalt chrome alloy implants and wear and corrosion products is reviewed. Animal studies show that in solid form cobalt chrome alloy is relatively well tolerated. Injections of large numbers of particles in a single bolus lead to acute inflammation and necrosis, followed by a chronic inflammatory response. Macrophages are the predominant cell type and may persist in the tissues for years. Long term studies have failed to confirm the induction of tumors. In vitro studies confirm the toxic effects of cobalt chrome alloy corrosion products and wear particles, especially cobalt, and show that intracellular corrosion is an important mechanism for early release of cobalt ions. In vitro studies show that cobalt chrome alloy particles induce the release of inflammatory mediators from macrophages before causing cell death. These mediators have significant effects on osteoblastlike cells, as well as inducing bone resorption. Variations in the cell types, implantation site, and characteristics of the particles used in experimental models make interpretation of the results difficult. Standardized methods to control for size, shape, and number of particles for testing are proposed. It is important that in vitro and in vivo findings not be taken in isolation...

Cobalt(II) Catalysts - Their Use in the Enantioselective Ring-opening of 1,2-Dioxines

Jenkins, Natalie Faye
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado Formato: 1474935 bytes; 157217 bytes; application/pdf; application/pdf
Publicado em //2003 EN
Relevância na Pesquisa
37.03%
A series of new cobalt(II) beta-keto iminato complexes and cobalt(II) salens have been made and the effect of chirality in the northern, southern and peripheral quadrants of these catalysts, with respect to induced enantiomeric excess, during the ring-opening of 1,2-dioxines has been determined. Synthesis of a series of cobalt beta-keto iminato complexes was achieved after modification of literature procedures used for the synthesis of manganese beta-keto iminato complexes and this procedure was applied to generate ligands with ethyl, t-butyl, (-)-bornyl, (+)-menthyl and (-)-menthyl esters and a methyl side chain. Synthesis of the cobalt salens was also achieved using a modified literature procedure, in respect to the more complex aldehydes made. It was ascertained that chirality in the northern quadrant of these catalysts, obtained by the use of optically pure diamines, was of greatest importance in introducing enantiomeric excess into the products of ring-opening of 1,2-dioxines; namely gamma-hydroxy enones, and chirality in the southern and peripheral quadrants was of lesser, although still significant, importance. The reaction conditions were optimised and the conditions under which the highest enantiomeric excess was introduced were determined. The ideal solvent for the ring-opening was found to be THF with a catalyst concentration between 5 and 10 mol% at a temperature of -15oC. These conditions were found to be applicable to all catalysts and 1...

Characterization of Graphite-Supported Palladium-Cobalt Catalysts by Temperature-Programmed Reduction and Magnetic Measurements

Noronha, Fábio Bellot; Schmal, Martin; Nicot, C.; Moraweck, B.; Fréty, R.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
37.03%
Journal of catalysis, 168(1): 42-50, Maio 1997.; Graphite-supported cobalt, palladium, and cobalt-palladium systems were prepared by a simple impregnation technique and submitted to hydrogen reduction in a temperature-programmed mode. Using X-ray diffraction to define the structure of the calcined precursors, magnetic measurements to determine the amount of metallic cobalt formed after reduction, and analysis of the gaseous medium during the reduction, a general model for the reduction of the graphite supported catalysts has been suggested. At room temperature, both pure Pd~ and Pd~ associated with C0304 are reduced to the metallic state. In the case of bimetallic systems, a fraction of C0304 in close proximity or interfaced with Pd~ can be reduced to the metallic state and to CoO species, demonstrating a strong catalytic effect of palladium on the reduction of cobalt oxides. At temperatures between 298 and 500 K, depending on the catalyst formulation, the presence of metallic palladium promotes the reduction of a large fraction of oxidized cobalt. At higher reduction temperature, at least two competitive phenomena were detected: direct reduction of the residual oxidized cobalt by the graphite, leading to carbon monoxide and dioxide formation...

Determination of cobalt species in niobia supported catalysts

Schmal, Martin; Noronha, Fábio Bellot; Fréty, R.; Perez, C. A. C.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
37.06%
Physical Chemistry Chemical Physics, 1(11): 2861-2867 Jun 1, 1999.; Niobia-supported cobalt catalysts were prepared by incipient wetness impregnation and were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reductioon (TPR) and magnetic measurements. At least two different types of cobalt species were present on the calcined catalysts: Co3O4 particles and Co2+ surface species. At high cobalt content, Co3O4 particles are the main species whereas the percentage of Co2+ species linked to the support increases as the cobalt loading is decreased. XPS results revealed that the Co2+ species could be better represented by a mixture of Co2Nb5O14 and CoNb2O6. TPR analyses allowed one to quantify the percentage of Co3O4 particles on the niobia-supported Co catalyst. However, due to partial reduction of niobia, TPR alone did not permit the quantification of the reduction degree of cobalt in these catalysts. Magnetic measurements linked to a TPR technique is a possible way to measure the reduction degree of cobalt in Co/Nb2O5 catalysts. After reduction at high temperature, the mixture of cobalt niobates was reduced and NbO2 produced led to the strong metal-support interaction (SMSI) effect.

Synthesis of 2-(nitromethyl)ornithine from ornithine mediated by cobalt(III).

Butler, Philip; Crane, Christopher; Golding, Bernard; Hammershoi, Anders; Hockless, David; Petersen, Tue; Sargeson, Alan; Ward, Stephen A
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.12%
Rac.-p-(tris(2-aminoethyl)amine-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d) was obtained by a simple three-step procedure from ornithine using cobalt template chemistry. p-(Tris(2-aminoethyl)amine-ornithine)cobalt(III) trichloride (2a) was obtained from tris(2-aminoethyl)amine (tren) and (S)-ornithine in the presence of cobalt(II), which was oxidised to cobalt(III) during the reaction. Complex 2a was selectively oxidised with thionyl chloride-dimethyl formamide to p-(tris(2-aminoethyl)amine-dehydro-ornithine)cobalt(III) trichloride 2b. Complex 2c, in which reaction of thionyl chloride-dimethyl formamide has also occurred at the δ-amine of ornithine, was obtained at longer reaction times. Complex 2b reacted with nitromethane anion to give rac.-p-(tris(2-aminoethyl)amino-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d). The amino acid rac.-2-(nitromethyl)ornithine (1b) was released by reducing complex 2d with aqueous ammonium sulfide. Complex 2d was expected to release 2-(nitromethyl)ornithine (1b) in hypoxic cells, where the amino acid could act as an inhibitor of ornithine decarboxylase. Preliminary data indicated that complex 2d was weakly cytotoxic in one cell type studied.

Cobalt exposure: toxicological aspects; Exposição ocupacional ao cobalto: aspectos toxicológicos

Alves, Atecla Nunciata Lopes; Della Rosa, Henrique Vicente
Fonte: Universidade de São Paulo. Faculdade de Ciências Farmacêuticas Publicador: Universidade de São Paulo. Faculdade de Ciências Farmacêuticas
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Artigo Avaliado pelos Pares Formato: application/pdf
Publicado em 01/06/2003 POR
Relevância na Pesquisa
37.03%
Cobalt is a chemical element that, besides its essentiality as a vitamin B12 component, has its main use in metallurgy to produce steel with special features of hardness and resistance. Oxides have been used as catalists for chemical and oil industry, in salts forms, as pigments in ceramics plants. This work has the purpose of a toxicocinetic and toxicodinamic review of exposure to cobalt in metal, salt and oxide forms. The toxic effects observed in exposure to different cobalt compounds are more pronunciated in pulmonary level, in bronchial and fibrotic forms. The toxic effects observed in the exposure to different cobalt compounds, the dose-effect relationship and dose-response, and the reference values in health and non-exposed population, have brought ACGIH (American Conference of Governmental and Industrial Hygienists) of the United States to propose since 1995 a BEI (Biological Exposure Indice) to this kind of exposure. Although Brazil has not included cobalt in the PCMSO (Programa de Controle Médico de Saúde Ocupacional), the toxicological studies can lead to the use of a biological indicator to cobalt and respective compound exposure.; O cobalto é um elemento químico, além de ser essencial, presente na vitamina B12, tem sua utilização principal na indústria metalúrgica para produção de aços com características especiais de dureza e resistência. Na forma de óxidos é utilizado como catalisador na indústria química e de óleos. Na forma de sais...

Spontaneously resolving chiral cis-[dinitrobis(ethylenediamine)cobalt]X complexes (X = Cl, Br) from the Alfred Werner collection of original samples at the University of Zurich - Alfred Werner's missed opportunity to become the 'Louis Pasteur' of coordination compounds

Blacque,Olivier; Berke,Heinz
Fonte: Universidad Nacional Autónoma de México, Facultad de Química Publicador: Universidad Nacional Autónoma de México, Facultad de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
Relevância na Pesquisa
37.13%
17 original crystals of [Λ-dinitrobis(ethylenediamine)cobalt]X complexes from the Alfred Werner collection of original samples of the University of Zurich were studied by single crystal X-ray diffraction revealing that the complexes with X = Cl, Br can undergo spontaneous chiral resolution upon crystallization. The main focus of this article was the chiral [Λ- and Δ-dinitrobis(ethylenediamine)cobalt]Cl complexes, which crystallize from racemic solution in the space group P 21 mainly as synthetical twins enriched in one enantiomer, but to a small extent also as pure enantiomorphs. The twinning effect was recognized and correctly described by PhD student Richard Hessen of the Alfred Werner group (PhD thesis 1914). Richard Hessen eventually resolved the [Δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complex by the conglomerate salt resolution method. Based on the availability of the pure [Δ- or Λ-dinitrobis(ethylenediamine)cobalt]Cl complex, he carried out seeding experiments, which proved that the [Δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complexes can be enriched to a great extent in one enantiomer by spontaneous chiral resolution. Already in the period of time from 1900 to 1904, various PhD students of Alfred Werner's group (Adolf Grün...

Comparing the extent of the dissolution of copper-cobalt ores from the DRC Region

Stuurman,S.; Ndlovu,S.; Sibanda,V.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2014 EN
Relevância na Pesquisa
37.03%
Inorganic acids such as sulphuric acid have found use together with certain reducing agents in leaching of copper-cobalt oxide ores. These reagents are not ideal due to the adverse effect the inorganic acids generally have on the environment and the high costs of the reducing agents. In this study a copper-cobalt oxide ore from the Central African Copperbelt was leached in two different environments; sulphuric acid in conjunction with hydrogen peroxide as a reducing agent and tartaric acid. The effects of acid concentration, reducing agent concentration, and temperature were independently determined for both leaching environments. The sulphuric acid concentration was varied between 0.4 M and 1.2 M and the concentration of hydrogen peroxide between 4.0 M and 6.5 M, while the tartaric acid concentration was varied between 0.15 M and 0.35 M. The temperature was varied between 20°C and 50°C. The results showed that the extraction of both copper and cobalt increased with sulphuric acid concentration, reaching a peak at approximately 0.8 M and then decreasing at higher acid concentrations. A similar increase and decrease in metal extraction was observed when the reducing agent was increased. In leaching with tartaric acid, the extraction of cobalt was much higher than that of copper...

Evaluation of different adsorbents for copper removal from cobalt electrolyte

Yahorava,V.; Kotze,M.; Auerswald,D.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2014 EN
Relevância na Pesquisa
37.06%
Ion exchange is considered to be an effective technology for the removal of various impurities from cobalt advance electrolytes. With the correct choice of resin, ion exchange can consistently remove the required impurities to the levels for the production of high-grade cobalt metal. Although ion exchange was in the past used primarily for nickel removal, more recently it has been also considered for the removal of copper, zinc, and cadmium. Generally, granular ion exchange products are used, but Mintek is currently evaluating ion exchange fibres for a number of applications, including the removal of copper from cobalt advance electrolytes. Fibrous ion exchangers have major advantages compared to granular resins in that they have significantly higher reaction rates, and wash water volumes could be limited. Granular and fibrous ion exchangers were evaluated and compared for the removal of copper from cobalt advance electrolyte. A synthetic electrolyte containing 50 g/L cobalt and 50 mg/L copper was used for the test work. Equilibrium isotherms, mini-column tests, and split elution tests were done. The results were used to size a full-scale operation to treat 100 m³/h of electrolyte. The potential cobalt losses or recycle requirements were estimated...