Estudo de catalisadores derivados do WC16 em reações de metátese do hexeno-1

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Homopolimerização de etileno utilizando-se catalisadores zirconocênicos ativados por metilaluminoxana

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Homopolimerização de etileno utilizando-se catalisadores zirconocênicos ativados por metilaluminoxana

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Polimerização de etileno em presença de (nBuCp)2ZrCl2 imobilizado sobre sílica

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Polimerização de etileno em presença de (nBuCp)2ZrCl2 imobilizado sobre sílica

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Optimization of a silica supported bis(butylcyclopentadienyl)-zirconium dichloride catalyst for ethylene polymerization

A series of heterogeneous α-olefin polymerization catalysts were prepared by the immobilization of bis(butylcyclopentadienyl)zirconium dichloride, (nBuCp)2ZrCl2, on a commercial silica support (Grace 948) using different procedures. The preparation parameters, namely, silica activation temperature, grafting temperature, grafting time, and solvent, were evaluated in terms of metal content on silica and ethylene homopolymerization activity. Metal contents were determined by Rutherford back-scattering spectrometry (RBS). In the temperature activation range between 373 and 723 K, silica surface saturation in Zr was found to be around 0.34 wt.-% Zr/SiO2. However, polymer polydispersity is shown to decrease with increasing support activation temperature. A better control in the generation of the active surface species was achieved with thermal pretreatment temperatures close to 723 K. The grafting reaction was seen to be immediate. Longer grafting times or higher temperatures bore deactivated species. Practically all the systems were active in ethylene polymerization in the presence of MAO, but the highest yield was obtained after grafting at 353 K for 1 h in toluene solution, employing silica pretreated at 723 K

Metabolomic Study of Urine from Workers Exposed to Low Concentrations of Benzene by UHPLC-ESI-QToF-MS Reveals Potential Biomarkers Associated with Oxidative Stress and Genotoxicity

Benzene is a human carcinogen whose exposure to concentrations below 1 ppm (3.19 mg·m−3) is associated with myelotoxic effects. The determination of biomarkers such as trans-trans muconic acid (AttM) and S-phenylmercapturic acid (SPMA) show exposure without reflecting the toxic effects of benzene. For this reason, in this study, the urinary metabolome of individuals exposed to low concentrations of benzene was investigated, with the aim of understanding the biological response to exposure to this xenobiotic and identifying metabolites correlated with the toxic effects induced by it. Ultra-efficient liquid chromatography coupled to a quadrupole-time-of-flight mass spectrometer (UHPLC-ESI-Q-ToF-MS) was used to identify metabolites in the urine of environmentally (n = 28) and occupationally exposed (n = 32) to benzene (mean of 22.1 μg·m−3 and 31.8 μg·m−3, respectively). Non-targeted metabolomics analysis by PLS-DA revealed nine urinary metabolites discriminating between groups and statistically correlated with oxidative damage (MDA, thiol) and genetic material (chromosomal aberrations) induced by the hydrocarbon. The analysis of metabolic pathways revealed important alterations in lipid metabolism. These results point to the involvement of alterations in lipid metabolism in the mechanisms of cytotoxic and genotoxic action of benzene. Furthermore, this study proves the potential of metabolomics to provide relevant information to understand the biological response to exposure to xenobiotics and identify early effect biomarkers

Cloning and expression of meta-cleavage enzyme (CarB) of carbazole degradation pathway from Pseudomonas stutzeri

In this work, the 1082bp PCR product corresponding to carBaBb genes that encode the heterotetrameric enzyme 2'-aminobiphenyl-2,3-diol 1,2-dioxygenase (CarB), involved in the Pseudomonas stutzeri ATCC 31258 carbazole degradation pathway, was cloned using the site-specific recombination system. Recombinant clones were confirmed by PCR, restriction enzyme digestion and sequencing. CarB dioxygenase was expressed in high levels and in active form in Escherichia coli BL21-SI using the His-tagged expression vector pDEST TM17 and salt induction for 4h.<br>Carbazol e seus derivados são compostos nitrogenados aromáticos, presentes comumente em petróleo e potencialmente poluentes. A rota de biodegradação de carbazol a ácido antranílico em Pseudomonas sp. é composta por três enzimas responsáveis, respectivamente, pelas reações de dioxigenação angular, meta-clivagem e hidrólise. A segunda enzima da rota, 2'-aminobifenil-2,3-diol 1,2-dioxigenase (CarB), codificada por dois genes (carBa e carBb), é um heterotetrâmero com atividade catalítica na quebra do anel catecol do susbtrato na posição meta. Neste trabalho, foi clonado o produto de PCR de 1082pb correspondente aos genes carBaBb da bactéria degradadora de carbazol Pseudomonas stutzeri ATCC 31258. A estratégia de clonagem empregada foi a de recombinação sítio-específica e a construção dos plasmídeos foi confirmada por PCR, digestão com enzima de restrição e seqüenciamento. A enzima ativa foi expressa em altas concentrações em vetor pDEST TM17 com cauda de histidina e promotor T7 em Escherichia coli BL21-SI com indução por NaCl durante 4h