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Unveiling the Interaction of Vanadium Compounds with Human Serum Albumin by Using 1H STD NMR and Computational Docking Studies

Dias, David M.; Rodrigues, João P. G. L. M.; Domingues, Neuza S.; Bonvin, Alexandre M. J. J.; Castro, M. M. C. A.
Fonte: Wiley-VCH Verlag Publicador: Wiley-VCH Verlag
Tipo: Artigo de Revista Científica
ENG
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The binding of the VV oxidation products of two vanadium( IV) compounds, [VO(dmpp)2] and [VO(maltolato)2], which have shown promising anti-diabetic properties, to human serum albumin (HSA) in aqueous aerobic solution has been studied by 1H saturation transfer difference (STD) NMR spectroscopy and computational docking studies. Group epitope mapping and docking simulations indicate a preference of HSA binding to the 1:1 [VO2(dmpp)(OH)(H2O)]– and 1:2 [VO2(maltol)2]– vanadium(V) species. By using known HSA binders, competition NMR experiments revealed that both complexes preferentially bind to drug site I. Docking simulations carried out with HADDOCK together with restraints derived from the STD results led to three-dimensional models that are in agreement with the NMR spectroscopic data, providing useful information on molecular interaction modes. These results indicate that the combination of STD NMR and data-driven docking is a good tool for elucidating the interactions in protein–vanadium compounds and thus for clarifying the mechanism of drug delivery as vanadium compounds have shown potential therapeutic properties.; Financial support by the Portuguese Fundação para a Ciência e Tecnologia (FCT) within the Programa Nacional de Reequipamento Científico Varian (contract number REDE/1517/ RMN/2005) as part of the Portuguese-NMR network (Rede Nacional de RMN) is acknowledged. D. M. D. thanks the The European NMR Large Scale Facility Utrecht for the contact with SONNMRLSF (project number BIO-NMR-00041). A. M. J. J. B. and J. R. acknowledge funding from the Dutch Foundation for Scientific Research (NWO) (VICI grant number 700.56.442) and Utrecht University (Focus and Massa grant).

Vanadium, rubidium and potassium in Octopus vulgaris (Mollusca: Cephalopoda)

Seixas, Sónia; Pierce, Graham J.
Fonte: Universidade Aberta de Portugal Publicador: Universidade Aberta de Portugal
Tipo: Artigo de Revista Científica
Publicado em //2005 ENG
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The levels of vanadium, rubidium and potassium were determined in Octopus vulgaris caught during commercial fishing activities at three locations (Cascais, Santa Luzia and Viana do Castelo) in Portugal in autumn and spring. We determined the concentration of these elements in digestive gland, branchial heart, gills, mantle and arms in males and females. At least five males and five females were assessed for each season/location combination. Elemental concentrations were determined by Particle Induced X-ray Emission (PIXE). Vanadium was detectable only in digestive gland and branchial heart samples. Its concentration was not correlated with total weight, total length or mantle length. There were no differences in concentrations of V, Rb and K between sexes. There were significant differences in vanadium concentrations in branchial hearts in autumn between samples from Viana do Castelo and those from the other two sites. We found a significant positive relationship between the concentration of vanadium and those of potassium and rubidium in branchial hearts. Branchial hearts appear to play an important role in decontamination of V.; Se determinaron los niveles de vanadio, rubidio y potasio en Octopus vulgaris capturado durante las actividades pesqueras en tres localidades de Portugal (Cascais...

Obtenção, caracterização e estudos das propriedades de compósitos formados por xerogel de pentóxido de vanádio e óxido de silício; Synthesis, characterization and properties of xerogel composite obtained by vanadium pentoxide and silicon oxide.

Barbosa, Glauciane do Nascimento
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 27/03/2007 PT
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A síntese, caracterização e propriedades de um novo compósito xerogel formado por óxido de vanádio e óxido de silício, com alta concentração de vanádio foi o objetivo deste trabalho. O compósito xerogel foi obtido mediante a formação de uma rede complexa envolvendo a condensação de polioxovanadato em meio aquoso com concomitante hidrólise e condensação de um alcóxido de silício. Conseqüentemente, este método possibilitou a obtenção de um material multicomponente homogêneo, no qual a rede Si O Si está interpenetrada com as cadeias poliméricas V-O- V e V-OH-V, promovendo uma solubilidade mútua, devido a formação de ligações cruzadas. Além disso, resultados experimentais apontam que, mesmo após a imobilização em matriz de sílica, a estrutura bi-dimensional, bem como as propriedades eletroquímicas do xerogel de pentóxido de vanádio são preservadas. A atividade catalítica do material obtido também foi avaliada na oxidação do cicloocteno e do estireno na fase líquida. O compósito xerogel V2O5/SiO2 obtido com tetraetiltrietóxisilano (TEOS), mediante catálise básica, o qual apresentou área superficial elevada (324 m2/g), e apresentou atividade catalítica em reações de oxidação do estireno e do cicloocteno na presença de PhIO como doador de oxigênio. Contudo...

Síntese de nanopartículas de óxido de vanádio obtidas pela decomposição de peróxido; Synthesis of Vanadium Oxide Nanoparticles obtained by the decomposition of peroxide

Avansi Junior, Waldir
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 29/09/2010 PT
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A utilização de novas rotas de síntese de materiais nanoestruturados tem levado à obtenção de materiais apresentando novas propriedades e aplicações. O presente trabalho teve como principal objetivo realizar a síntese e a caracterização de nanopartículas de óxido de vanádio obtidas pelo método da decomposição de peróxido utilizando o tratamento hidrotermal. Por meio do controle do tempo e da temperatura de síntese, foi possível obter nanoestruturas de pentóxido de vanádio com diferentes fases cristalinas e morfologias. Os resultados de espectroscopia Raman e difração de raios X (DRX) mostraram que o tratamento hidrotermal da solução em temperaturas de até 180oC, durante 2 horas, leva à formação da fase V2O5nH2O monoclínica, apresentando uma orientação preferencial na direção 00l. A partir desta temperatura, o material obtido passou a ter a fase ortorrômbica perdendo sua orientação preferencial. Através das medidas de termogravimetria (TG) foi observado que, dependendo da condição de síntese, as amostras apresentam diferentes quantidades de moléculas de água (H2O) intercaladas em sua estrutura. Imagens de microscopia eletrônica mostraram que as nanoestruturas obtidas podem possuir a forma de fitas...

Caracterização eletroquímica de filmes nanoestruturados de óxido de manganês e de vanádio em líquidos iônicos: aplicação em baterias de lítio e supercapacitores; Electrochemical characterization of nanostructured films of manganese and vanadium oxide in ionic liquids: lithium batteries and supercapacitors application.

Benedetti, Tânia Machado
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 20/05/2011 PT
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Este trabalho apresenta a preparação de filmes nanoestruturados de óxido de manganês e de vanádio por diferentes técnicas e a sua caracterização eletroquímica utilizando diferentes líquidos iônicos como eletrólito. Os filmes de óxido de manganês foram preparados por automontagem camada-por-camada e por eletrodeposição assistida por molde de nanoesferas de poliestireno. Os filmes de óxido de vanádio foram preparados também por automontagem camada-por-camada e por deposição eletroforética. Diversos aspectos relacionados ao uso dos líquidos iônicos como eletrólitos foram discutidos: os resultados obtidos para os filmes de óxido de manganês por automontagem camada-por-camada mostraram que os íons do líquido iônico participam do processo de compensação de carga superficialmente e que o cátion do líquido iônico, apesar de mais volumoso, apresenta coeficiente de difusão maior que o Li+, formando uma barreira à intercalação dos mesmos na estrutura do material. A partir dos resultados obtidos para os filmes de óxido de manganês por eletrodeposição assistida por nanoesferas de poliestireno, foi possível verificar que o desempenho do sistema depende da natureza do líquido iônico utilizado, sendo possível obter desempenho superior aos solventes orgânicos convencionais com um dos líquidos iônicos utilizados do ponto de vista da ciclabilidade. Desempenho superior aos eletrólitos convencionais também foi observado para os filmes de óxido de vanádio obtidos por automontagem camada-por-camada. Por fim...

Síntese, caracterização e estudos das propriedades catalíticas de compostos formados por óxido de tungstênio e pentóxido de vanádio; Synthesis, Characterization and Study of Catalytic Properties of Compounds Formed by Tungsten Oxide and Vanadium Oxide.

Bolsoni, Aline Turini
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 11/11/2011 PT
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Métodos de síntese que viabilizam a obtenção de compósitos contendo xerogéis de óxido de tungstênio e de pentóxido de vanádio pelo método sol-gel foram investigados, bem como a caracterização e propriedades catalíticas nas reações de epoxidação destes materiais. Brometo de cetiltrimetilamina e hexadecilamina foram intercalados nos xerogéis de óxidos vanádio e de tungstênio formando compostos híbridos orgânico-inorgânico ternários. Estas moléculas foram usadas com o objetivo de aumentar a distância interlamelar e conferir caráter hidrofóbico nos compostos híbridos para que facilitasse o acesso dos substratos orgânicos quando utilizados como catalisadores nas reações de epoxidação. Os parâmetros de difração de raios X comprovam a intercalação, com aumento da distância interplanar. Observa-se uma variação na posição da banda M=O para maiores valores de energia devido à interação eletrostática entre as cargas positivas das espécies convidadas com densidade de carga negativa das ligações M=O. O xerogel de óxido de tungstênio e o compósito com xerogel de óxido de vanádio com óxido tungstênio foram dispersos em matrizes de óxido hidróxido de alumínio e de xerogel de óxido de silício. Foi observado que os modos vibracionais no infravermelho não sofreram variações significativas...

Desenvolvimento de procedimentos analíticos empregando multicomutação em sistemas de análises em fluxo para determinação fotométrica de vanádio em águas e estanho em alimentos; Development of analytical procedures employing multicommutation flow analysis systems for the photometric determination of vanadium in water and tin in foods

Dias, Tuanne dos Reis
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 06/11/2014 PT
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Esta tese tem como foco o desenvolvimento de procedimentos analíticos automáticos, visando as determinações fotométricas de vanádio e de estanho em águas e em alimentos empregando o processo de multicomutação em fluxo. Um microcontrolador da família PIC e um programa escrito em linguagem Visual Basic 6.0 foram empregados para controle dos dispositivos e aquisição de dados. A unidade de detecção foi construída empregando LED de alto brilho e celas de fluxo com longo caminho óptico (50-200 mm) para ganho em sensibilidade. O módulo de análises, empregando bombas solenoide como propulsores de fluido e o fotômetro foram integrados, formando uma unidade compacta. A determinação de vanádio em águas, mineral e de rio, foi baseada na redução do V(V) à V(IV) com ácido ascórbico e posterior complexação com Eriocromo Cianina R (ECR). Empregando uma cela de 150 mm, o sistema apresentou resposta linear de 0,02 a 1,00 mg L-1, limite de detecção estimado em 13 ?g L-1, coeficiente de variação de 0,87% (n=10) e frequência analítica de 47 determinações por hora. Recuperações entre 89 e 109% foram obtidas para adição de V(V) nas amostras de águas. O procedimento para a determinação de estanho em alimentos foi desenvolvido empregando bomba de multi-seringa como unidade de propulsão de fluidos...

Methods for vanadium determination in fuel oil by GF AAS with microemulsification and acid digestion sampling

Amorim, Fábio A.C.; Lima, Daniel de Castro; Amaro, Joana Angélica de Azerêdo; Vale, Maria Goreti Rodrigues; Ferreira, Sérgio Luis Costa
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
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Dois métodos para determinação de vanádio em óleo combustível são propostos utilizando GF AAS. O primeiro é baseado na preparação de uma microemulsão da amostra que é diretamente injetada no tubo de grafite. As temperaturas de pirólise e atomização, 1500 e 2700 °C, respectivamente, foram otimizadas a partir das curvas de temperatura. Para este procedimento obteve-se um limite de detecção de 0,10 μg g-1 e uma massa característica de 87 pg. O outro método utiliza digestão da amostra com ácido sulfúrico, ácido nítrico e peróxido de hidrogênio. As temperaturas de pirólise e atomização, otimizadas, foram 1000 e 2700 °C, respectivamente. Para este procedimento, obteve-se um limite de detecção de 0,25 μg g-1 e uma massa característica de 63 pg. A exatidão de ambos os métodos foi confirmada pela análise do material de referência certificado NIST SRM 1634c-trace metals in fuel oil.; Two methods for vanadium determination in fuel oil are proposed using GF AAS. The first is based on the preparation of a microemulsion followed by direct injection into the graphite tube. The pyrolysis and atomization temperatures, 1500 and 2700 °C, respectively, were chosen from the temperature curves. This procedure allows determination of vanadium with a detection limit of 0.10 μg g-1 and characteristic mass of 87 pg. The other method uses total acid digestion of the sample with sulfuric acid...

Vanadium pentoxide effects on stress responses in wine Saccharomyces cerevisiae strain UE-ME3

Rosado, T; Conim, A; Alves-Pereira, I; Ferreira, R
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
POR
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Vanadium pentoxide mainly used as catalyst in sulphuric acid, maleic anhydride and ceramics industry, is a pollutant watering redistributed around the environment. Research on biological influence of vanadium pentoxide has gained major importance because it exerts toxic effects on a wide variety of biological systems. In this work we intent to evaluate the effects of vanadium pentoxide ranging from 0 to 2 mM in culture media on a wine wild-type Saccharomyces cerevisiae from Alentejo region of Portugal. Our results show that 2.0 mM vanadium pentoxide in culture medium induced a significant increase of malonaldehyde level and Glutathione peroxidase activity, a slightly increase of Catalase A activity as well as a decrease of wet weight and mitochondrial NADH cit c reductase of S. cerevisiae UE-ME3. Also our results show that cycloheximide prevent cell death when cells grows 30 min in presence of 1.5 mMof vanadium pentoxide.

Spectrometric and electrochemical investigation of vanadium(V) and vanadium(IV) tartrate complexes in solution

Khan,Ahmad R.; Crans,Debbie C.; Pauliukaite,Rasa; Norkus,Eugenijus
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2006 EN
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Spectroscopic and electrochemical studies were carried out to characterize the vanadium(IV) and (V) complexes that form in solution and their interconversions. 51V NMR spectroscopy coupled with ¹H NMR, 13C NMR and EPR spectroscopy were used to characterize the vanadium(V)-tartrate complexes that form in the vanadium-tartrate system. The major complex that forms over most of the pH range is a 1:1 complex. In addition a minor 1:2 complex forms. The 1:2 complex formed from enantiomerically pure tartaric acid was less stable than complex formed from racemic tartaric acid. These complexes are different than the 2:2 complex that is the major contributor in the vanadium(IV)-tartrate system. The polarographic and cyclic voltammetic investigations of the electrochemical behavior of V(V) in the presence of tartrate demonstrated a complex formation. The diffusion coefficient values of free vanadium ions and vanadium-tartrate complexes were determined. The minimum average values for the diffusion coefficient for the vanadium(IV)-tartrate 2:2 complexes were determined to range from 3 ´ 10-6 cm² s-1 to 17 ´ 10-6 cm² s-1 depending on pH.

THE INFLUENCE OF NIOBIUM ON THE ACIDITY AND STRUCTURE OF GAMMA-ALUMINA-SUPPORTED VANADIUM OXIDES

Sathler,M.N.B.; Eon,J.G.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1998 EN
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Gamma-alumina-supported niobium oxide was used as a support for vanadium oxides. The influence of the addition of niobium oxide was studied by looking for changes in the structure and acid-base character of superficial species. Vanadium oxide was deposited using the continuous adsorption method; niobium oxide was impregnated using the incipient wetness method. The catalysts were characterized by XPS, UV-visible and IR spectroscopy. Catalytic tests were performed using propane oxidation reaction at 400oC. For coverage below the monolayer, both vanadium and niobium oxides were observed in slightly condensed superficial species. The presence of vanadium oxide on the support was found to increase the Lewis acidity and create some Bronsted acidity. Higher catalytic activity and selectivity for propene were associated with vanadium oxides. The presence of niobium did not contribute to the modification of the chemical properties of superficial vanadium but did decrease the adsorption of vanadium on the alumina.

The influence of calcium, magnesium, phosphorus and silica on vanadium precipitation in acidic sulfate solutions

Martins,A. H.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2000 EN
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The experimental research work was carried out in accordance with the Factorial Design Statistical Method to evaluate and analyze the influence of calcium, magnesium, silica and phosphorus on the precipitation of vanadates. Precipitation was performed by neutralization with H2SO4 of alkaline aqueous solutions containing vanadium pentoxide (V2O5) at 60± 2ºC. The experimental responses measured were percent of vanadium recovery and vanadium pentoxide content in the precipitate. These impurities are considered representative of those present in a leach liquor from the ore obtained at Campo Alegre de Lourdes (Brazil). The operational variables in this work were used under optimum conditions as determined by the statistical approach. Among the impurities under study, phosphorus exhibited the highest negative influence on the experimental responses. Phosphorus diminished the percent of vanadium recovered from 98.9 to 34.5 and the vanadium oxide content in the precipitate from 91.2 % to 39.3 %.

Reaktionsverhalten von Vanadium-(chlorimid)-trichlorid; Reactions of Vanadium-(chlorimid)-trichloride

Binder, Anja
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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Ziel dieser Arbeit ist die Untersuchung des Reaktionsverhaltens des Chlorimidokomplexes Cl3VNCl gegenüber Lewissäuren bzw. -basen und der Eignung als nitridübertragendes Reagenz. Im ersten Teil wird auf die Umsetzung von K.-P. Lörcher eingegangen, der mit Vanadium-(chlorimid)-trichlorid und Triphenylphosphan die Verbindung Cl3(PPh3)VNCl erhalten hatte. Er konnte diese Verbindung lediglich mittels Pulvediffraktometrie identifizieren. Daher wurde Cl3VNCl in dieser Arbeit in einer Festkörperreaktion mit PPh3 umgesetzt, um Kristalle zu erhalten. Bei den Umsetzungen mit PPh3 wurden hier die Verbindungen [VCl4][(PPh3)2N] und VNCl2(OPPh3)2 isoliert. Nach den Umsetzungen mit PPh3 sollte ein weniger basischer Ligand benutzt werden. Es wurden Umsetzungen von Vanadium-(chlorimid)-trichlorid mit Dimethylphenylphosphan vorgenommen. Bei den Umsetzungen konnten drei Produkte isoliert und untersucht werden. Die Reaktion von Cl3VNCl mit PMe2Ph in der Ampulle ergab [VCl4(PMe2Ph)2][HPMe2Ph]. Weiterhin wurde PMe2Ph mit Cl3VNCl ohne thermische Einwirkung umgesetzt. Dabei wurde die ionische Verbindung HPMe2PhCl synthetisiert. Auf demselben Weg konnte VCl3[(PMe2Ph)2(OPMe2Ph)] isoliert werden. In weiteren Umsetzungen sollte der Einfluss von Pyridin und komplexierenden Lösungsmitteln auf das Vanadium-(chlorimid)-trichlorid untersucht werden. Bei der Umsetzung konnte das Produkt V(µ-N)Cl2(py)2 isoliert werden. Bei der Umsetzung von Cl3VNCl mit PPh3 in dem komplexierenden Lösungsmittel Tetrahydrofuran konnte die Verbindung [VCl4(THF)2][PPh3O] isoliert werden. Weiterhin sollte die Umsetzung des Cl3VNCl mit Lewissäuren...

Lettuce cationic nutrition and yield, and soil chemical characteristics as affected by vanadium application to leaves or soils

Álvarez, Carlos Enrique; Amin, M.; Reyes, C. M.; Fernández, M.
Fonte: Inderscience Publishers Publicador: Inderscience Publishers
Tipo: Artículo Formato: 2373 bytes; 3225301 bytes; text/plain; application/pdf
ENG
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9 pages, 7 tables.; Lettuce plants (Lactuca sativa, L., cv. 'trocadero') were grown in pots filled with an Alfisol Udalf or an Andisol Udand soil, under greenhouse conditions. Treatments consisted of adding vanadium to soils (0, 100, 250, 500 and 1000 mg kg-1 or as foliar sprays (0, 10, 25, 50, and 100 mg l-1. Soil chemical characteristics, the cationic nutrition of lettuce and their yields were assessed. No relation was found among vanadium treatments and soil pH, organic matter, or available Ca, Mg, and K. Vanadium added to soils increased available vanadium in the soil, but foliar sprays did not. Treatments did not influence foliar K, Ca, Mg, Cu, Mn and Zn concentrations, and only foliar iron levels showed a correlation with available vanadium in the soils treated with this heavy metal. Higher concentrations of vanadium added to soil or in foliar sprays significantly increased the vanadium content of the lettuces, but they did not affect the yields of either fresh or dry matter.; We acknowledge the Consejería de Educación, Cultura y Deportes of the Canary Government for the grant that made this work possible.

Isolation and Purification of Vanadium Haloperoxidase Mutants for Characterization by 51V Solid-state NMR Spectroscopy

Nuzzio, Kristin
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
EN
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Tatyana Polenova; Vanadium containing compounds have shown excellent potential in the treatment of diabetes, particularly as insulin enhancing compounds, as well as in the treatment of some forms of cancer. However, in order for these compounds to be useful in biomedical applications, the structures of their vanadium active sites and the mechanisms of their biochemical activity need to be determined. Vanadium haloperoxidases (VHPO) are a specific class of vanadium containing enzymes commonly found in marine algae, lichens and terrestrial fungi. These enzymes are the most efficient halide oxidants known to date. The focus of this project is to understand the catalytic mechanism of VHPO and their active site mutants by utilizing 51V solid-state NMR spectroscopy as a site-specific probe of the diamagnetic ???spectroscopically silent??? vanadium active sites. This knowledge is expected to be important in designing artificial vanadium enzymes with tuned halogenating activities. In this thesis, two VCPO active site mutants as well as the wild type protein have been successfully isolated and purified, and 51V solid-state NMR spectra have been acquired.; Chemistry

Electron paramagnetic resonance and electron spin echo study of supported and unsupported vanadium oxides

Luca, Vittorio; MacLachlan, Dugald; Bramley, Richard
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
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Electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies have been used to characterize paramagnetic centers in crystalline and gel forms of vanadium pentoxide as well as vanadia supported on silica, titania, and magnesia. A number of different paramagnetic centers are observed in the bulk and supported vanadia phases that are characterized by their spin Hamiltonian parameters. ESEEM data for all the bulk vanadium oxide samples show intense modulation at the51V Larmor frequency. This modulation originates from interlayer VO2+ species in gel samples and from V4+ centers in crystalline oxides. The intensity of the51V modulation varies considerably from sample to sample depending on the specific nature of the paramagnetic center. For the supported vanadia samples, complex EPR spectra are obtained that show two classes of signals. Signals with narrow linewidths and resolved hyperfine structure are observed suggesting magnetically isolated V4+ in addition to dipolar exchange broadened signals. ESEEM spectroscopy reveals that the spectra observed for vanadia supported on silica are from surface bound vanadyl species that interact with predominantly diamagnetic surface vanadia clusters. In contrast...

Determination of vanadium accumulation in onion root cells (Allium cep a L.) and its correlation with toxicity

Marcano,Letty; Carruyo,Ingrid; Fernández,Yusmary; Montiel,Xiomara; Torrealba,Zaida
Fonte: Biocell Publicador: Biocell
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2006 EN
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The vanadium is a metal that presents great interest from the toxicological point of view, because of the numerous alterations that can take place in different biological systems. This work evaluated the capacity of vanadium accumulation and its correlation with genotoxic effects in root cells of Allium cepa L. The bulbs were cultivated in renovated filtered water each 24 h, at a temperature of 25 ± 0.5 ° C, in darkness and constant aeration. Treatments were carried out under the same experimental conditions, using water solutions of vanadium of 25, 50, 75 and 100 µ g/g for 0, 12, 24, 48 and 72 h. A control was carried out where metal solution was substituted by distilled water. After the treatment, the meristems were fixed with alcohol - acetic acid (3:1) and stained according to the technique of Feulgen. The capacity of accumulation was determined by GFAAS. The analysis of the results revealed an accumulation of the metal for all times and concentrations. No correlation was presented among vanadium accumulation, growth and mitotic index; however, positive correlation was given with the induction of chromosomic aberrations. In conclusion, vanadium is able to induce cytotoxic effect in the exposed roots, but only genotoxic effect was correlated with metal accumulation.

Oxidative dehydrogenation of propane and n-butane over aluminia supported vanadium catalysts

Murgia,V.; Sham,E.; Gottifredi,J. C.; Farfan Torres,E. M.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2004 EN
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Structural properties of vanadium dispersed species on g-A1203 are investigated with the scope to detect changes related with V loading in the oxidative dehydrogenation (ODH) of propane and nbutane. XPS, FTIR, and FTIR of absorbed pyridine were used to study the nature of vanadium supported species. Tetrahedral V5+ and probably V4+ species were detected. For vanadium loadings higher than 4.3 % wt octahedral species were also observed. In the n-butane ODH reaction, the selectivity to ODH products decreases when vanadium content increases. However, for propane ODH, the selectivity seems to be independent of vanadium loadings. Low oxygen/alkane feeding ratios favor selectivity to olefins. It is also shown that low V loading catalysts reach selectivities as good as best reported V-Mg-O catalyst.

Influence of Vanadium Oxidation States on the Performance of V-Mg-Al Mixed-Oxide Catalysts for the Oxidative Dehydrogenation of Propane

Schacht,Leticia; Navarrete,Juan; Schacht,Persi; Ramírez,Marco A.
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 EN
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374.0915%
V-Mg-Al mixed-oxide catalysts for oxidative dehydrogenation of propane were prepared by thermal decomposition of Mg-Al-layered double hydroxides with vanadium interlayer doping. The obtained catalysts were tested for the oxidative dehydrogenation of propane, obtaining good results in catalytic activity (conversion 16.55 % and selectivity 99.97 %). Results indicated that catalytic performance of these materials depends on how vanadium is integrated in the layered structure, which is determined by the Mg/Al ratio. Vanadium interlayer doping modifies the oxidation state of vanadium and consequently catalytic properties. Surface properties were studied by X-ray photoelectron spectroscopic and diffuse reflectance, UV-visible spectroscopy, and temperature programmed reduction (TPR). The analyses provided information about the oxidation state, before and after the reaction. From these results, it is suggested that selectivity to propylene and catalytic activity depend mainly on vanadium oxidation state.

Determination of Leachable Vanadium (V) in sediment

Mampuru,Lekgala A.; Panichev,Nikolay A.; Ngobeni,Prince; Mandiwana,Khakhathi L.; Kalumba,Makonga M.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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377.49363%
A method for speciation of vanadium in solid samples was developed for quantification of vanadium( + 5) in solid samples of sediment Certified Reference Materials (CRM) PACS-2 and MESS-3 (Trace Elements in Sediments) of known total vanadium content. The method relies on a classical analytical chemistry procedure based on leaching water-insoluble vanadium( + 5) compounds from the solid state into solution using Na2CO3 followed by electrothermal atomic absorption spectrometry (ET-AAS) detection. The total amount content of vanadium was determined after complete digestion of the CRMs and found to be 132 ± 5 and 245 ±12 μg g-1 in PACS-2 and MESS-3, respectively, in good agreement with the certified values of 133±6 μg g-1 and 243 ± 12 μg g-1. The concentrations of vanadium(+5) were determined to be 25 ± 3 μg g-1 and 13 ± 2 μg g-1 in PACS-2 and MESS-3, respectively. These results were verified by the method of standard additions for which quantitative recoveries (100±2 and 97 ± 3 %, one standard deviation, n = 3) were obtained for spikes added to PACS-2 and MESS-3, respectively. Approximately 18.8 % of the total vanadium content of PACS-2 and 5.3 % in MESS-3 is in the form of vanadium(+5) species.