Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11800
Navegar
11 resultados
Resultados da Pesquisa
Item Avaliação de bis(4-metilfenilditiocarbimato)zincato(II) de tetrabutilamônio como acelerador em composições de borracha natural(Polímeros, 2008) Mariano, Roberta M.; Visconte, Leila L. Y.; Oliveira, Marcelo R. L.; Rubinger, Mayura M. M.Neste trabalho a substância ZNIBU [bis(4-metilfenilditiocarbimato)zincato(II) de tetrabutilamônio] foi usada em formulações de borracha natural (NR) e o seu efeito como acelerador de vulcanização foi investigado. As composições, vulcanizadas com a substância em questão, foram submetidas a testes mecânicos e os resultados comparados com os de outras composições vulcanizadas com os aceleradores comerciais CBS (N-ciclohexil-2-benzotiazol-2-sulfenamida), TMTD (dissulfeto de tetrametiltiuram) e MBTS (dissulfeto de benzotiazol). Propriedades como dureza, resiliência e densidade foram avaliadas em presença ou não da carga negro de fumo.Item Determinação da relação siringila/guaiacila da lignina em madeiras de eucalipto por pirólise acoplada à cromatografia gasosa e espectrometria de massas ( PI - CG/ EM)(Química Nova, 2008) Barbosa, Luiz C. A.; Maltha, Célia R. A.; Silva, Vanessa Lopes; Colodette, Jorge LuizThe use of analytical pyrolysis combined with gas chromatography/mass spectrometry (Py-GC/MS) to determine the syringyl/guaiacyl ratio (S/G) in lignins from Eucalyptus spp woods was investigated. Sample of E. grandis and "E. urograndis" wood, with and without extractives, were subjected to pyrolysis from 300 ºC to 600 ºC. The products that results from pyrolysis were identified by mass spectrometry and the S/G ratio was determined based on the areas of the peaks corresponding to the guaiacyl and syringyl derivatives. The best S/G estimation is achieved when pyrolysis is carried out at 550 ºC. Extractives and carbohydrate present in the woods do not interfere with the results.Item Atividade antiinflamatória de carboidrato produzido por fermentação aquosa de grãos de quefir(Química Nova, 2008) Moreira, Maria E. C.; Santos, Marcelo H.; Pereira, Ivan O.; Ferraz, Vany; Barbosa, Luiz C. A.; Schneedorf, José M.Kefir, a symbiont microorganism suspension, presents benefic effects to health. Some kefir grains were cultivated in brown sugar, allowing to isolate a substance named CSQ. This was evaluated on a biologic essay of mouse foot edema, presenting an inhibitory activity of 30+4 % against carrageenan after the stimulus. It was observed that a cultivation mean containing sucrose, and not the milky mean, lead to the production of different sugar polymeric chains of kefir. The results in vivo suggest that the CSQ exerted an anti-inflammatory activity.Item Triacylglycerol molecular species variation in stored coffee beans determined by reverse-high-performance liquid chromatography/refractive index detector(Journal of Stored Products Research, 2008) Jham, Gulab N.; Muller, Helcio Vidigal; Cecon, PauloSamples of three types of coffee beans (immature, random mixture and cherry) were each divided into roughly two halves and dried by two widely known procedures (conventional dryer and open air cement floor patio) to attain about 14% moisture. All samples were stored on wood shelves without temperature or moisture control. After 4, 7, 10, 13, 16 and 19 months, portions of all samples were withdrawn and the relative percentages of the nine triacylglycerol (TAG) molecular species determined by reverse-high-performance liquid chromatography with a refractive index detector. The experiment consisted of 36 treatments (combinations of bean types, drying procedures and storage times) in a randomized block design with three repetitions. Nine TAG molecular species were identified in all the coffee samples. While apparently random variation was observed in TAG composition in a few cases, no significant effects of storage time, storage type or coffee type on TAG composition were observed.Item Investigation on the esterification of fatty acids catalyzed by the H3PW12O40 heteropolyacid(Journal of the American Oil Chemists' Society, 2008-03-26) Cardoso, Abiney L.; Augusti, Rodinei; Silva, Márcio J. DaIn this work, the H3PW12O40 heteropolyacid (HPW) was employed as a homogeneous catalyst to promote the efficient esterification (ethanolysis) of a number of saturated and unsaturated fatty acids (myristic, palmitic, stearic, oleic, and linoleic) under mild reaction conditions. HPW showed a similar activity to those observed for p-toluene sulfonic acid (PTSA) and sulfuric acid (H2SO4), the other acidic catalysts we compared them with in this study. In the HPW-catalyzed esterification of stearic acid, the addition of water caused a remarkable decrease in the ethyl stearate yields. On the other hand, the increase in the HPW concentration (up to a maximum value) promoted a proportional improvement in the oleic acid to ethyl oleate conversion. Kinetic measurements using oleic acid as a prototype substrate revealed that the esterification reactions catalyzed by HPW, H2SO4, and PTSA are of first-order in relation to the fatty acid concentration. Finally, the catalytic activity of HPW remained unaltered even after several recovery/reutilization cycles whereas the tungsten content in the final product (biodiesel produced by the HPW-catalyzed esterification of oleic acid) was found to be at an acceptably low level (0.0095 mg of W per g of biodiesel).Item Estórias do Harry Potter: um catalisador para o estudo da alquimia(Revista Ponto de Vista, 2008-01) Carvalho, Regina Simplício; Silva, Amanda Cristina SantiagoCom o intuito de estimular a curiosidade com relação a alquimia, os livros da coletânea de Harry Potter foram utilizados como um recurso catalisador, pois estes revelam vários aspectos alquímicos. Algumas características da alquimia são mostradas e discutidas ao longo das estórias, assim como alguns alquimistas. Dos livros estudados, os que abordaram de forma mais contundente a alquimia foram: Harry Potter e a Pedra Filosofal e Harry Potter e o Cálice de Fogo. A alquimia pode ser considerada como precursora da química, pois foi através desta que se conceberam os primeiros materiais e métodos, utilizados ainda nos dias de hoje, em práticas laboratoriais.Item Composition and antifungal activity of the essential oil of the Brazilian Chenopodium ambrosioides L.(Journal of Chemical Ecology, 2008-08-05) Jardim, Carolina Marangon; Jham, Gulab Newandram; Dhingra, Onkar Dev; Freire, Marcelo MoreiraThe antifungal activity of essential oil (EO) from the Brazilian epazote (Chenopodium ambrosioides L.) was evaluated by the poison food assay at concentrations of 0.3%, 0.1%, and 0.05% with eight postharvest deteriorating fungi (Aspergillus flavus, Aspergillus glaucus, Aspergillus niger, Aspergillus ochraceous, Colletotrichum gloesporioides, Colletotrichum musae, Fusarium oxysporum, and Fusarium semitectum). EO components were tentatively identified by Kováts retention indices (RIs) using gas chromatography and gas chromatography combined with mass spectrometry (GC-MS). Growth of all fungi was completely inhibited at 0.3% concentration, and by 90% to 100% at 0.1% concentration. The following 13 tentatively identified compounds (relative percent) accounted for 90.4% of the total volatile oil: α-terpinene (0.9), p-cymene (2.0), benzyl alcohol (0.3), p-cresol (0.3), p-mentha-1,3,8-triene (0.2), p-cimen-8-ol (0.6), α-terpineol (0.5), (Z)-ascaridole (61.4), piperitone (0.9), carvacrol (3.9), (E)-ascaridole (18.6), (E)-piperitol acetate (0.5), and (Z)-carvyl acetate (0.3). Autobiographic thin layer chromatography of the EO to separate the principal fungitoxic fraction yielded only one fraction that completely inhibited the growth of all test fungi at a concentration of 0.1%. This fraction was characterized by RIs and GC-MS presenting a composition (%) of p-cymene (25.4), (Z)-ascaridole (44.4), and (E)-ascaridole (30.2). The results suggest ascaridoles were the principal fungitoxic components of the EO.Item Mercury fractionation in stream sediments from the Quadrilátero Ferrífero gold mining region, Minas Gerais State, Brazil(Environmental Monitoring and Assessment, 2008-09-11) Varejão, Eduardo V. V.; Bellato, Carlos R.; Fontes, Maurício P. F.The Iron Quadrangle (IQ) region, located in the state of Minas Gerais, has been the most important gold producing area in Brazil since the end of seventeenth century. The use of mercury for gold amalgamation in small scale mines has been responsible for large release of Hg to aquatic and terrestrial environments during 300 years of mining. The present work sought to evaluate the fractionation of Hg in stream sediments is the southern region of the IQ by utilizing sequential extraction. Since mobility and availability of Hg are related to its distribution among sediment partitions, fractionation methods provide detailed information on the ecotoxicological impact and risks associated to the presence of Hg in sediments. The total Hg concentration varied from 179.3 to 690.1 μg kg − 1 and Hg0 accounted for the majority at all sample sites, ranging from 42% to 56% of the total.Item Low-temperature clean-up method for the determination of pyrethroids in milk using gas chromatography with electron capture detection(Talanta, 2008-02-08) Goulart, Simone Machado; Queiroz, Maria Eliana L.R. de; Neves, Antônio Augusto; Queiroz, José Humberto deThis paper describes a new gas-chrormatography with electron capture detection (GC-ECD) method for determination of some pyrethroids in milk samples. The extraction of the pyrethroids was carried out by liquid–liquid extraction with clean-up by precipitation at low temperature, without additional stages for removal of fat interferences. The method was efficient with recoveries of 93.0 ± 0.1% for cipermethrin and 84.0 ± 0.3% for deltamethrin. The quantification limits were 0.75 μg L−1 for both pyrethroids. The method was simple, of easy execution, and used only small quantities of organic solvent. After optimization and validation, the method was used for the determination of residues of the pyrethroids cipermethrin and deltamethrin in milk and in lactea drink commercialized in Viçosa (MG, Brazil). Some samples presented contamination with deltamethrin at levels below the maximum contamination limits established by the FAO.Item Antioxidant activity of Maytenus imbricata Mart., Celastraceae(Revista Brasileira de Farmacognosia, 2008-11-29) Barbosa, Luiz C. A.; Ribeiro, Sonia M. R.; Queiroz, José H.; Oliveira, Márcio L. R.; Silva, Grácia D. F.; Silva, Silvia R. S.; Duarte, Lucienir P.; Vieira Filho, Sidney A.The free radical scavenging activity (FRS) using 2,2-diphenyl-1-picrylhydrazyl (DPPH), the reducer power and the total phenolic concentration of extracts and compounds isolated from leaves, branches and roots of Maytenus imbricata Mart. (Celastraceae) were evaluated. Some extracts, a mixture of phenolic compounds (MPC) and epicatechin showed higher RP and FRS (DPPH) activities in comparison with the standard butylhydroxyanisole (BHA) and galic acid (GA) used in assays. The ethyl acetate extract from leaves showed higher total phenolic content and also higher RP and FRS (DPPH) than the other extracts. These facts indicate that there are some relations between phenolic concentration in the extract and the antioxidant activity and the reducer power. The solvent used in the extraction process influences the chemical composition of the extracts and consequently its antioxidant and reducer power activities.