969 resultados para RHODIUM-CATALYZED HYDROFORMYLATION


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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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O processo de hidroesterificação (hidrolise seguida de esterificação) se constitui como uma alternativa ao processo convencional de produção de biodiesel, pois permite o uso de matérias-primas de qualquer teor de água e de ácidos graxos. O biodiesel foi gerado a partir da esterificação do óleo de andiroba com alto teor de ácidos graxos sendo utilizado o oxido de nióbio em pó da CBMM (HY-340) como catalisador. Para execução dos experimentos foi utilizado um reator autoclave (batelada). A reação de hidrolise foi conduzida na temperatura de 300°C, ~1200psi e razão molar água/óleo de 20. Nas reações de esterificação foram observados os efeitos da razão molar metanol/acido graxo (1,2; 2,1 e 3,0), da temperatura (150, 175 e 200oC) e da concentração de catalisador (0, 10 e 20% m/m) tendo como resposta a conversão e a taxa inicial da reação. Os dados foram conduzidos segundo um planejamento experimental (fatorial com 23 e adição de 3 pontos centrais) analisado pelo programa Statistica. A conversão das reações de esterificação foi monitorada a partir de medidas titulometricas de acidez das alíquotas, retiradas nos tempos de 5, 10, 15, 20, 25, 30, 45 e 60 min. Nos experimentos de esterificação a maior conversão obtida foi 96,1% com temperatura de 200oC, 20% m/m de catalisador e razão molar metanol/acido igual a 3,0. Eliminando o catalisador e considerando os mesmos niveis para as outras duas variáveis analisadas (temperatura e razão molar), foi obtida uma conversão de 95,3%, porem foi observada uma taxa de conversão menor tendo-se um aumento de 35 minutos no tempo de reação comparando com a reação catalisada.

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ABSTRACT: Methanogenic archaeans are organisms of considerable ecological and biotechnological interest that produce methane through a restricted metabolic pathway, which culminates in the reaction catalyzed by the Methyl-coenzyme M reductase (Mcr) enzyme, and results in the release of methane. Using a metagenomic approach, the gene of the a subunit of mcr (mcrα) was isolated from sediment sample from an anoxic zone, rich in decomposing organic material, obtained from the Tucuruí hydroelectric dam reservoir in eastern Brazilian Amazonia. The partial nucleotide sequences obtained were 83 to 95% similar to those available in databases, indicating a low diversity of archaeans in the reservoir. Two orders were identified -the Methanomicrobiales, and a unique Operational Taxonomic Unit (OTU) forming a clade with the Methanosarcinales according to low bootstrap values. Homology modeling was used to determine the three-dimensional (3D) structures, for this the partial nucleotide sequence of the mcrα were isolated and translated on their partial amino acid sequences. The 3D structures of the archaean mcrα observed in the present study varied little, and presented approximately 70% identity in comparison with the mcrα of Methanopyrus klanderi. The results demonstrated that the community of methanogenic archaeans of the anoxic C1 region of the Tucurui reservoir is relatively homogeneous.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Thermogravimetry (TG), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface and X-ray diffraction (XRD) were used for the study of solid-state reaction on Pt-15%Rh with electrodeposited mercury. The results suggest when heated the mercury film react with the Pt-15%Rh alloy to form intermetallics having different thermal stabilities indicated by three mass loss steps. The first mass loss step occurs between room temperature and 184 degrees C only the bulk Hg is removed and PtHg4, PtHg2 and RhHg2 were characterized by XRD. The second step, between 184 and 271 degrees C, was attributed to PtHg4 decomposition with formation of PtHg2 stabilized by RhHg2. The third step, between 271 and 340 degrees C, was attributed to decomposition of a solid-solution of PtHg2/RhHg2. The fourth step, between 340 and 600 degrees C, was ascribed to: (1) a thermal decomposition of PtHg2, formed by a PtHg eutectoid reaction (similar to 340 degrees C) on the surface and (2) Hg removal from a solid solution of Pt-15%Rh(Hg). (C) 2013 Elsevier B.V. All rights reserved.

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As características estruturais de sonogéis obtidos a partir da hidrólise ácida do TEOS estimulada por ultrasom foram estudadas por espalhamento de raios-x a baixo ângulo (SAXS). O estudo inclui: i) o processo de agregação em diferentes temperaturas; ii) o envelhecimento dos géis úmidos na fase líquida de preparação e depois da troca da fase líquida por álcool e acetona; iii) a secagem dos géis; iv) a estrutural evolução de xerogéis e aerogéis com o tratamento térmico até 1100 oC; e v) um estudo comparativo usando SAXS e adsorção de nitrogênio na caracterização de aerogéis e xerogéis... (Resumo completo, clicar acesso eletrônico abaixo)

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It is believed that epigenetic mechanisms such as DNA methylation are important for the tumorigenesis and maintenance of the altered state of tumor cells. DNA methylation occurs by the addition of a methyl group to carbon 5 of cytosine, catalyzed by the enzyme DNA methyl-transferase, which can change the expression of a gene, including the tumor suppressor genes. In human squamous cell carcinoma, several features have shown the etiological role of genes in tumor development. Among them, FOXE1 gene (forkhead box E1 - thyroid transcription factor) is presented with an important role in susceptibility to disease. Similarly the FOXE1 methylation pattern could alter the expression of this gene in dogs and predisposed to tumor on. Therefore, this study aims to investigate in dogs, the validity of the strategy employed in humans to analyze the FOXE1 methylation status. DNA extraction from fresh frozen tumoral samples was performed by Wizard Genomic® DNA Purification Kit. The methylation status was determined by MSP-PCR (methylation-specific polymerase chain reaction), using 2.0 ng of DNA treated with sodium bisulphate. One hundred micrograms of bisulphite-modified DNA was amplified using primers specific for either methylated or unmethylated DNA (primers sequences are available at http://pathology2.jhu.edu/pancreas/primer.pdf). The analysis of fragments was loaded on to 7% polyacrylamide gels and silver nitrate staining. In this stage of technical approach, 60% were FOXE1 hypermethylated. In conclusion, it was observed that the standard technique for assessing the methylation pattern of gene FOXE1 in humans can be used for the same evaluation in dogs. The correlation of these molecular data with clinical and histopathological parameters may have diagnostic and prognostic value and still be used as a tumor marker for therapeutic decision and surgical approach

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The NbCl5 being a strong electrophile, is a potential candidate to act as a Lewis acid, and therefore it mediates various organic reactions. For this reason, it has received continuous attention by Brazilian researchers, especially in recent decades, since Brazil holds the largest reserves of niobium, besides being the largest producer of this element. The Michael addition reaction is one of the most widely used for forming carbon-carbon bonds and takes place by the addition of nucleophiles to activated olefins. Although this type of reaction is usually catalyzed by base, there are reports in the literature on the use of various Lewis acids in this type of reaction. The synthesis of enamines based acetilenodicarboxilates and amines, aromatic or alkyl, by Michael addition reaction is quite interesting, since these are valuable synthetic intermediates for the synthesis of heterocyclic and they are used in multicomponent reactions. The derivatives of anilino-fumarate also have a great potential for medical application. In this study we investigated the use of niobium pentachloride as Lewis acid to catalyze the Michael additions between the derivatives of aniline and acetilenodicarboxilates the synthesis of enamines