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Exposição ocupacional à sílica no Brasil no ano de 2001

Ribeiro,Fátima Sueli Neto; Camargo,Esther Archer de; Algranti,Eduardo; Wünsch Filho,Victor
Fonte: Associação Brasileira de Saúde Coletiva Publicador: Associação Brasileira de Saúde Coletiva
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2008 PT
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OBJETIVO: Estimar o número de trabalhadores brasileiros expostos à sílica no ano de 2001. MÉTODO: Informações sobre ocupações e setores econômicos foram reunidas em uma matriz de exposição ocupacional (MEO) com 347 categorias ocupacionais por 25 subsetores econômicos. Informações sobre o número de trabalhadores por ocupação foram extraídas da base de dados Relatório Anual de Informações Sociais (RAIS) do Ministério do Trabalho e Emprego. A exposição à sílica foi avaliada e classificada por dois peritos em quatro categorias, de acordo com a freqüência semanal de exposição no ambiente de trabalho. RESULTADOS: Foram considerados não expostos 31.451.594 trabalhadores (85,7%), possivelmente expostos 976.939 (2,65%), provavelmente expostos 2.404.955 (6,52%) e definitivamente expostos à sílica 2.065.929 (5,6%). Os setores com a maior prevalência de exposição foram: construção civil 65%, extração de pedras 59%, indústria de mineral não metálico 55% e indústria metalúrgica 24%. No setor de serviços de terceiros, a prevalência foi de 2%. CONCLUSÃO: A prevalência de trabalhadores brasileiros definitivamente expostos à sílica é mais alta do que aquela observada em países europeus, onde estudos semelhantes foram conduzidos.

Rice hull-derived silica: applications in Portland cement and mullite whiskers

Souza,M.F. de; Batista,P.S.; Regiani,I.; Liborio,J.B.L.; Souza,D.P.F. de
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2000 EN
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Silica was extracted from rice hulls by three processing routes, starting with acid treatment followed by burning and milling. The amorphous white silica powder showed a surface area of 260 to 480 m²/g, purity above 99% and average particle size of 2.0 to 0.6 mm. This silica is suitable for the preparation of mullite whiskers employing the rare earth aluminosilicate glass technique. Due to its highly pozzolanic reaction, this prepared silica is used as an additive in high performance concrete.

Effect of silica nanoparticles and BTCA on physical properties of cotton fabrics

Nallathambi,Gobi; Ramachandran,Thangavelu; Rajendran,Venkatachalam; Palanivelu,Rajagoundar
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 EN
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Silica nanoparticles particles were synthesized from rice hulls and characterized. The particles were found to be amorphous in nature, ranging in size from 50 to 100 nm. The concentration of silica nanoparticles, pH and curing time were taken as independent variables to design the experiment. Box-Behnken method has been used to derive the experimental plan and fifteen experiments were conducted. Regression equations have been formed with the dependent and independent variables and the results of all possible combinations have been derived. The combination of optimized concentration of BTCA and SHP were used as crosslinking agent and catalyst respectively and silica nano particles were used to enhance the physical properties of the cotton fabric. The effect of pH and curing time on physical properties were analysed by FTIR studies. By ranking method the best combination of process parameters were identified. From this study, it was observed that higher concentration of silica nanoparticles with BTCA improve the crease recovery angle and tensile strength. FTIR studies revealed that the increase of pH and curing time increases the ester carbonyl band intensity ratio.

Comparative study of the characteristics of nano silica - , silica fume - and fly ash - incorporated cement mortars

Biricik,Hasan; Sarier,Nihal
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
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The structural characteristics of cement mortars, impregnated with nano silica (NS), silica fume (SF) and fly ash (FA), were comparatively studied using Fourier transform infrared spectrometer (FTIR), thermogravimeter-differential thermogravimeter (TG-DTG) and scanning electron microscope (SEM). The mechanical strengths of the specimens were determined at early (7th day) and standard (28th day) curing ages. The compressive strengths and flexural strengths developed in the mortar specimens containing NS particles were found considerably higher than those of the corresponding specimens of SF and FA over and above the control at both ages. FTIR, TG-DTG and SEM analyses results were consistent with the remarkable increase in the mechanical strength of the mortars with NS. These increases in the strengths of the mortars with NS are attributable to the nano sized particles and extensive surface area of NS. The nano sized particles, as nucleating agents, promoted the hydration of C3S and C2S and the formation of C - S - H phase. Plenty of active sites on the surface of NS particles induced their pozzolanic reactivity and the extent of bond formation between NS particles and free CH.

Prediction of energy absorption capability in fiber reinforced self-compacting concrete containing nano-silica particles using artificial neural network

Tavakoli,Hamid Reza; Omran,Omid Lotfi; Kutanaei,Saman Soleimani; shiade,Masoud Falahtabar
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/11/2014 EN
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The main objective of the present work is to utilize feedforward multi-layer perceptron (MLP) type of artificial neural networks (ANN) to find the combined effect of nano-silica and different fibers (steel, polypropylene, glass) on the toughness, flexural strength and fracture energy of concrete is evaluated.For this purpose, 40 mix plot including 4 series A and B and C and D, which contain, respectively, 0, 2, 4 and 6% weight of cement, nano-silica particles were used as a substitute for cement. Each of series includes three types of fibers (metal: 0.2, 0.3 and 0.5% volume and polypropylene: 0.1, 0.15 and 0.2 % volume and glass 0.15 and 0.2 and 0.3% by volume) were tested. The obtained results from the experimental data are used to train the MLP type artificial neural network. The Results of this study show that fibers conjugate presence and optimal percent of nano-silica improved toughness, flexural strength and fracture energy of concrete of Self-compacting concrete (SCC). Results of this study show that fibers conjugate presence and optimal per-cent of nano-silica improved toughness, toughness, fracture ener-gy and flexural strength of SCC.

Síntese de novas matrizes de sílica contendo grupos éteres coroa

Marques da Silva Leoterio, Dilmo; Alves Junior, Severino (Orientador)
Fonte: Universidade Federal de Pernambuco Publicador: Universidade Federal de Pernambuco
Tipo: Outros
PT_BR
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Este trabalho reporta a síntese e caracterização de novos materiais de sílica contendo éteres coroa tendo como fonte de sílica o precursor tetraetilortosilicato (TEOS). Os materiais foram sintetizados pelo método tradicional e por rotas alternativas como forno mufla e microndas. Os materiais foram caracterizados por um conjunto de técnicas como análise elementar, ressonância magnética nuclear de 13C e 29Si, espectroscopia de absorção na região do infravermelho, termogravimétrica, e microscopia eletrônica de varredura. Os novos materiais sintetizados apresentam uma alternativa versátil para o desenvolvimento de ionóforo covalentemente ligado à rede de sílica. Todos os compostos mostraram um efeito sinérgico do ponto de vista termodinâmico, uma vez que o composto análogo, o éter (15-coroa-5) apresenta uma baixa temperatura de decomposição. O aumento da proporção do precursor de sílica (TEOS) proporcionou uma melhoria das propriedades mecânicas e térmicas do material, bem como o aumento da robustez da rede inorgânica, devido ao aumento do número de unidades de siloxano. Os materiais sintetizados apresentar uma variedade de aplicações, principalmente na composição de sensores e catalisadores

Silica carcinogenesis and the possibility to assess the carcinogenesis by micronucleus formation in alveolar macrophaes ex vivo

Wang, He; Peng, X. D.; Lawson, G.
Fonte: Australian Institute of Environmental Health Publicador: Australian Institute of Environmental Health
Tipo: Artigo de Revista Científica
Publicado em //2006 EN
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Silica is well known to induce inflammatory and fibrotic reactions. During these processes, various substances such as reactive oxygen species and cytokines can be produced. Silica itself, and its induced reactants, may cause genetic damage of lung cells and hyperplasia of pneumocyte leading to the development of silica-induced lung cancer. Micronucleus incidence in alveolar macrophages has been used as an index of potentially genotoxic inhalable agents, which may or may not be inflammation inducing. Since alveolar macrophages physically exist in the surface of alveolar epithelial cells and they will have the same in vivo exposure as the epithelial cells. Therefore, alveolar macrophages may be useful in testing potentially genotoxic agents which induce pulmonary inflammation since these cells are easily obtainable in large numbers as well as being long-lived and proliferative. One of the advantages of this method is that it can test not only the toxicity of silica itself but also its induced reactants.; He Wang, Xuedong Peng and Graeme Lawson; © Australian Institute of Environmental Health

Poly-L-lysine functionalized large pore cubic mesostructured silica nanoparticles as biocompatible carriers for gene delivery

Hartono, S.; Gu, W.; Kleitz, F.; Liu, J.; He, L.; Middelberg, A.; Yu, C.; Lu, G.; Qiao, S.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
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Large pore mesoporous silica nanoparticles (LP-MSNs) functionalized with poly-L-lysine (PLL) were designed as a new carrier material for gene delivery applications. The synthesized LP-MSNs are 100-200 nm in diameter and are composed of cage-like pores organized in a cubic mesostructure. The size of the cavities is about 28 nm with an entrance size of 13.4 nm. Successful grafting of PLL onto the silica surface through covalent immobilization was confirmed by X-ray photoelectron spectroscopy, solid-state (13)C magic-angle spinning nuclear magnetic resonance, Fourier transformed infrared, and thermogravimetric analysis. As a result of the particle modification with PLL, a significant increase of the nanoparticle binding capacity for oligo-DNAs was observed compared to the native unmodified silica particles. Consequently, PLL-functionalized nanoparticles exhibited a strong ability to deliver oligo DNA-Cy3 (a model for siRNA) to Hela cells. Furthermore, PLL-functionalized nanoparticles were proven to be superior as gene carriers compared to amino-functionalized nanoparticles and the native nanoparticles. The system was tested to deliver functional siRNA against minibrain-related kinase and polo-like kinase 1 in osteosarcoma cancer cells. Here...

A study of silica gel adsorption desalination system.

Wu, Jun Wei
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2013
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Rising water scarcity due to climate change and over-exploitation of traditional water resources is of increasing concern around the World, both because of its economic implications as well as the continued habitability of long-standing communities. One solution to this issue is desalination of saline or brackish water, which has long been used in regions that have traditionally faced water shortage such as the Middle East. There are several ways in which desalination is carried out, including multi-effect desalination, multi-stage flash desalination, and membrane-based reverse osmosis (RO), which are all widely exploited commercially. The high energy demands and large ‘carbon footprint’ of these various current commercial technologies have spurned interest in several potential alternative technologies. One of these alternatives is adsorption-based desalination (AD). This approach uses low-grade heat such as waste heat from a process or solar energy to generate potable water and, depending on the cycle details, cooling as well. The low-grade heat is used to form water vapour from the saline or brackish source. The vapour is then passed through a bed of silica into which it adsorbs until the silica is saturated. Once saturated, the bed of silica is heated using further low-grade heat to drive off the now desalinated water before being re-condensed in a receiving vessel. Adsorption-based desalination has a range of advantages...

Multifunctional Silica Particles as Contrast Agents for Optical and Magnetic Resonance Imaging; Multifunktionale Silica-Partikel als Kontrastmittel für Optische Bildgebung und Magnetresonanztomographie

Feldmann, Verena
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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The development of magnetic resonance imaging (MRI) towards one of the most powerful techniques in clinical diagnosis is accompanied by progress in the design of paramagnetic contrast agents (CAs) to enhance imaging sensitivity. Most of the currently applied CAs for enhanced T1-contrast are based on gadolinium(III)-chelate-complexes and are mainly extracellular agents which only distribute non-specifically throughout the circulatory system and interstitial space. Since those agents are excreted easily and quite fast from the body, they are not suitable for targeting or long-term tracking applications. Therefore, nano-sized materials were developed and they are gaining increasing importance in medical diagnosis and treatments. Silica nanoparticles can serve as a matrix not only for Gd(III)-chelate-complexes, but also for vector- and sensor-biomolecules for targeting applications. Spherical, non-porous and monodisperse silica nanoparticles with diameters of 50 - 100 nm were synthesised by means of the Stöber process. The surface of the bare particles was functionalised with carboxylic acid and amino groups, respectively, thus allowing to build peptide bonds with Gd(III)-chelate-complex systems and/or biomolecules. Lysine was introduced as bifunctional linker. The materials were fully characterised after each synthetic step by DLS...

Preliminary Report on High-Silica Sand in Indiana

Murray, Haydn H.; Patton, John B.
Fonte: Indiana Department of Conservation Publicador: Indiana Department of Conservation
Tipo: Relatório
EN_US
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In the past few years, largely because of increased freight rates, a keen interest in finding sources of high-silica sand has developed. The Geological Survey has received many inquiries about possible sources of high-silica sand in the state. Although published information on the geology of the formations that may contain high-silica sand has been available, economic information, such as quality, distribution, extent, and accessibility, has not been available.

Efeitos da alteração do limite de exposição ocupacional à sílica cristalina no processo de seleção de respiradores; An update in the threshold limit value for crystalline silica and its effects on respirator selection

Beltrame, André Lomonaco; Eston, Sérgio Médici de; Iramina, Wilson Siguemasa; Chieregati, Ana Carolina; Tachibana, Ivan Koh
Fonte: Escola de Minas Publicador: Escola de Minas
Tipo: Artigo de Revista Científica
POR
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O objetivo desse trabalho foi investigar o processo de seleção de equipamentos de proteção respiratória e verificar a existência de mudanças nesse processo quando o limite de exposição ocupacional de uma substância é alterado. Utilizaram-se, como base de dados, dois estudos anteriormente realizados em empresas mineradoras da região metropolitana da cidade de São Paulo, selecionando-se, como contaminante, a sílica cristalina devido à sua abrangência e à gravidade das doenças relacionadas à sua exposição. Os fatores de proteção atribuídos aos equipamentos fornecidos pelas empresas estudadas foram comparados com os requeridos pelas atividades e com a metodologia do programa de proteção respiratória da FUNDACENTRO. Os resultados mostraram que, até 2005, algumas empresas estavam fornecendo equipamentos inadequados e que, a partir de 2006, ano em que foi alterado o limite de exposição, todas as empresas estudadas forneciam proteção insuficiente. Concluiu-se ser oportuna a criação de um portal na internet onde a seleção dos EPIs possa ser feita, de maneira atualizada, a partir das informações fornecidas pelas empresas.; The purpose of this study was to investigate the respiratory protective device selection process and to identify changes in this process when an exposure limit value is updated. Two previous studies conducted in mining industries in the metropolitan area of São Paulo were put through the respiratory protective device selection process. The protection factors of the equipment provided by the companies were compared with the required protection factors and with the FUNDACENTRO's respiratory protection program. The results showed that until 2005...

Fabricação de tijolos modulares de solo-cimento por prensagem manual com e sem adição de sílica ativa; Production of soil-cement modular bricks by manual pressing with and without silica fume addition

Grande, Fernando Mazzeo
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 10/02/2003 PT
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Neste trabalho, por meio de uma metodologia experimental foram analisados vários aspectos de tijolos modulares compostos por misturas binárias e ternárias de solo-cimento e solo cimento-sílica produzidos em prensa manual modelo SAHARA, com a finalidade de se obter parâmetros e diretrizes que visam um melhor desempenho do material. Realizaram-se ensaios em corpos-de-prova cilíndricos de maneira acessória no decorrer do trabalho, o que resultou no suporte para fundamentação de diversas avaliações sobre as composições de traços utilizados na fabricação dos tijolos. Foram executados painéis de parede com o objetivo de verificar o comportamento da alvenaria em relação à resistência à compressão e à deformabilidade das paredes, possibilitando correlações com os resultados dos ensaios de prismas, tijolos e argamassa de assentamento. As contribuições da pesquisa permitem relacionar a tecnologia da fabricação de tijolos de solo-cimento com o contexto de construção sustentável e o aproveitamento de resíduos industriais, além de sistematizar informações para a elaboração de um projeto tecnológico com os tijolos modulares; In this work, several aspects of modular bricks composed by binary and ternary mixtures of soil-cement and soil-cement-silica...

Desenvolvimento de um metodo de produção de silica de porosidade controlada e sua utilização na imobilização de proteinas

Henrique Celso Trevisan
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em //1993 PT
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Essa dissertação apresenta os resultados com o objetivo de se produzir suportes silicicos de porosidade controlada para a imobilização de enzimas. Inicialmente, sílicas de três procedências, uma preparada em laboratório e duas disponíveis comercialmente, foram submetidas a tratamento hidrotérmico em cinco temperaturas, os produtos resultantes caracterizados por porosimetria de intrusão de mercúrio e suas capacidades de imobilização da enzima amiloglicosidase avaliadas. Os resultados sugeriram uma relação linear entre a pressão do tratamento hidrotermico e o diâmetro de poro médio resultante, mostrando também que a sílica preparada em laboratório era mais adequada para imobilização da enzima. Partindo-se dos dados anteriores, começou-se a otimizar o método de preparação da sílica, como o objetivo de melhorar a capacidade de imobilização do material, avaliando-se a qualidade dos produtos pela medida do volume de intrusão de água, porosimetria de mercúrio e imobilização de amiloglicosidase. Os suportes foram considerados adequados quando se conseguiu imobilizar uma quantidade de enzima equivalente aos melhores dados encontrados na literatura. Para suportes tratados a 150-270'GRAUS'C, obteve-se diâmetros médios de poro de 100-790A e conseguiu-se estabelecer uma relação simples entre a temperatura e o tamanho de poro resultante. Esses suportes foram caracterizados por porosimetria de mercúrio e microscopia eletrônica de varredura e utilizados na imobilização de "horsehadish" peroxidase...

Catalisadores de paladio-cobre suportados sobre silica e niobia

Marivone Nunho Sousa de Camargo Roma
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/12/1999 PT
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Catalisadores monometálicos de paládio, cobre e paládio-cobre suportados sobre silica e nióbia foram preparados com teores de 0,5% ou 3% de Pd e 3% de Cu (% em massa). O método de impregnação ou coimpregnação seca foi empregado, utilizando-se como precursores: cloreto de paládio e sulfato de cobre. Os sólidos foram secados e submetidos a tratamentos térmicos distintos, a 300°C, sendo eles: calcinação sob ar sintético, redução sob hidrogênio ou uma associação desses. Estes catalisadores foram submetidos a análise química elementar, quimissorção de hidrogênio, titulação hidrogênio-oxigênio, microscopia eletrônica de transmissão, espectrometria dispersiva de energia acoplada ao microscópio eletrônico de varredura, redução à temperatura programada e EXAFS. Testes catalíticos foram realizados com a reação de desidrogenação do cicloexano, e uma avaliação destes catalisadores foi realizada na reação de oxidação parcial do benzeno a fenol. Os catalisadores monometálicos com 0,5% de paládio suportado apresentaram dispersões metálicas em tomo de 20%, enquanto aqueles com 3% de Pd apresentaram valores menores, em tomo de 7%, independentemente dos suportes utilizados ou dos tratamentos térmicos a que foram submetidos. Tais dispersões foram determinadas pelas técnicas de adsorção de gases. A análise de catalisadores suportados sobre silica por microscopia eletrônica de transmissão confirmou tais resultados. Os catalisadores calcinados e reduzidos foram submetidos a análise por redução à temperatura programada...

Study of the morphology and mechanical properties of polypropylene composites with silica or rice-husk

Yazdani-Pedram Zobeiri, Mehrdad; Murillo, O.; Quijada Abarca, Raúl; Toro, P.
Fonte: JOHN WILEY & SONS LTD Publicador: JOHN WILEY & SONS LTD
Tipo: Artículo de revista
EN
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The mechanical, morphological behavior and water absorption characteristics of polypropylene (PP) and silica, or PP and rice-husk, composites have been studied. The silica used in this study as filler was a commercial type produced from soluble glass or rice husks. The compatibilizing effect of PP grafted with monomethyl itaconate (PP-g-MMI) and/or with vinyltriethoxysilane (PP-g-VTES) as polar monomers on the mechanical properties and water absorption was also investigated. In general, a high loading of the studied fillers in the polymer matrix increases the stiffness and the water absorption capacity. This effect is more noticeable in the tensile modulus of the PP/silica composite with PP-g-VTES as compatibilizer. However, the increase of the rice-husk charge as a natural filler in the PP matrix decreases the stiffness, and in the presence of PP-g-MMI as compatibilizer in PP/rice-husk, the tensile modulus and water absorption of the composite were improved. The better adhesion and phase continuity in the PP/silica and PP/rice-husk composites with different compatibilizers was confirmed by the morphological study.

Porous silica derived from chitosan-containing hybrid composites

Yazdani-Pedram Zobeiri, Mehrdad; Quijada Abarca, Raúl; Arias, V.; Retuert de la Torre, Pedro Jaime
Fonte: MATERIALS RESEARCH SOCIETY Publicador: MATERIALS RESEARCH SOCIETY
Tipo: Artículo de revista
EN
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In this paper, we report the preparation by the sol-gel technique of organic-inorganic hybrid composites containing the biopolymer chitosan incorporated in a siloxane-based inorganic network. The hybrid xerogels were transformed into porous silica particles by elimination of the organic phase. Surface characteristics of the silica samples can be easily tailored. In this way Brunauer-Emmett-Teller areas, pore volume, and pore diameter of the prepared silica can be predetermined within a wide range. Morphology of the particles at longer length scales can be designed to obtain either irregularly shaped particles with layered morphology or spherical particles. The results are explained on the basis of the cationic polyelectrolytic properties of chitosan, which allows easy association with siloxane oligomers, the precursors of silica in forming hybrid nanocomposites.

Morphogenesis of Self-Assembled Nanocrystalline Materials of Barium Carbonate and Silica

García Ruiz, Juan Manuel; Melero García, Emilio; Hyde, Stephen T.
Fonte: American Association for the Advancement of Science Publicador: American Association for the Advancement of Science
Tipo: Artículo Formato: 205 bytes; text/plain
ENG
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4 pages, 3 figures.-- Supporting information (Suppl. materials and methods, references and movies S1-S9) available at: http://www.sciencemag.org/cgi/content/full/323/5912/362/DC1; The precipitation of barium or strontium carbonates in alkaline silica-rich environments leads to crystalline aggregates that have been named silica/carbonate biomorphs because their morphology resembles that of primitive organisms. These aggregates are self-assembled materials of purely inorganic origin, with an amorphous phase of silica intimately intertwined with a carbonate nanocrystalline phase. We propose a mechanism that explains all the morphologies described for biomorphs. Chemically coupled coprecipitation of carbonate and silica leads to fibrillation of the growing front and to laminar structures that experience curling at their growing rim. These curls propagate in a surflike way along the rim of the laminae. We show that all observed morphologies with smoothly varying positive or negative Gaussian curvatures can be explained by the combined growth of counterpropagating curls and growing laminae.; This work was supported by the Spanish Ministry of Education and Science (project MAT2006-11701) and is part of the Consolider-Ingenio 2010 project Factoría Española de Cristalización. E.M.-G. acknowledges financial support from the program Juan de la Cierva (Ministerio de Innovación y Ciencia). S.T.H. acknowledges the Australian Research Council for a Federation Fellowship.; Peer reviewed

Influence of activation on the multipoint immobilization of penicilline G acylase on macroporous silica

Cardias, H. C. T.; Grininger, C. C.; Trevisan, Henrique Celso; Guisán, José Manuel; Giordano, R. L. C.
Fonte: Associação Brasileira de Engenharia Química Publicador: Associação Brasileira de Engenharia Química
Tipo: Artículo
ENG
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Penicillin G acylase is the second most important enzyme used by industry in an immobilized form. Penicillin hydrolysis is its main application. This reaction is used to produce 6-aminopenicillanic acid (6-APA), an intermediate in the synthesis of semisynthetic antibiotics. This work aims to compare catalytic properties of different penicillin G acylase (PGA) derivatives obtained by multipoint immobilization of the enzyme on macroporous silica. Enzyme amino groups react with different aldehyde groups produced in the support using either glutaraldehyde or glyoxyl activation. In the former method, silica reacts with g-aminopropyltriethoxysilane (g-APTS) and glutaraldehyde; in the latter, a reaction with glycidoxypropyltrimethoxysilane (GPTMS) is followed by acid hydrolysis and oxidation using sodium periodate. This work determines the influence of degree of activation, using glutaraldehyde, on immobilization parameters. PGA was immobilized on these two different supports. Maximum enzyme load, immobilized enzyme activity (derivative activity), rate of immobilization and thermal stability were checked for both cases. For glutaraldehyde activation, the results showed that 0.5% of the g-APTS is sufficient for all the hydroxyl groups in the silica to react. They also showed that degree of activation only affects immobilization yield and reaction velocity and that reduction of the glutaraldehyde derivatives with sodium borohydride does not affect their thermal stability. In comparing the derivatives obtained using glyoxyl and glutaraldehyde activation...

The Use of silica and alumina to catalyze the addition of hydrogen chloride to alkenes

Liu, Ying
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
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The use of pre-heated silica gel and alumina along with a chlorinating agent, generates HC1 in situ, which has been found to add to norbornadiene ( IX ). Treated in this fashion, norbornadiene readily results in the formation of two isomers, exo-5- chloronorbornene ( XI ) and 3-chloronotricyclene ( XII ) at room temperature in methylene chloride, with ejco-5-chloronorbornene being the predominant product ( 70% 1% ). In promoting the hydrohalogenation reaction, silica gel was found to be less efficient compared to alumina, but undesired diadducts appeared to be less prominent when silica gel rather than alumina was used. Deuterated alumina and thionyl chloride in methylene chloride solution was found to result in the addition of DC1 to norbornadiene. Three deuterated products: 29% exo,ejco-6-chlorobicyclo[2.2.1]hept-2-ene-5-d ( XVII ), 14% ea,5>7i-5-chlorobicyclo[2.2.1]hept-2-ene-7-d ( XVTIa ) and 19% 5- chlorotricyclo[2.2.1.02'6]heptane-3-d ( XV111 ), as well as the two undeuterated products, 27% ejco-5-chloronorbornene ( XI ) and 11% 3-chloronotricyclene ( XII ), were detected by GC/MS analysis. A higher ratio of XVU/XVlla for the catalyzed DC1 addition over the uncatalyzed addition suggests that the surface of the alumina somewhat slowed Wagner-Meerwein rearrangement during this reaction. *See document for exact formulas