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排序方式: 共有342条查询结果,搜索用时 28 毫秒
81.
82.
Federico J. Nores-Pondal M. Pilar Buera Horacio R. Corti 《Journal of power sources》2010,195(19):6389-6397
The thermal properties of phosphoric acid-doped poly[2-2′-(m-phenylene)-5-5′ bi-benzimidazole] (PBI) and poly[2,5-benzimidazole] (ABPBI) membranes, ionomeric materials with promising properties to be used as electrolytes in direct methanol and in high temperature polymer electrolyte membrane (PEM) fuel cells, were studied by means of differential scanning calorimetry (DSC) technique in the temperature range from −145 °C to 200 °C. The DSC scans of samples equilibrated in water at different relative humidities (RH) and in liquid water-methanol mixtures were analyzed in relation to glass transition, water crystallization/melting and solvent desorption in different temperature regions. The thermal relaxation observed in the very low temperature region could be ascribed to the glass transition of the H3PO4-H2O mixture confined in the polymeric matrix. After cooling the samples up to −145 °C, frozen water was detected in PBI and ABPBI at different RH, although at 100% RH less amount of water had crystallized than that observed in Nafion membranes under the same conditions. Even more important is the fact that the freezing degree of water is much lower in ABPBI membranes equilibrated in liquid water-methanol mixtures than that observed for PBI and, in a previous study, for Nafion. Thus, apart from other well known properties, acid-doped ABPBI emerges as an excellent ionomer for applications in direct methanol fuel cells working in cold environments. 相似文献
83.
Nuria Elizabeth Rocha-Guzmán José Alberto Gallegos-Infante Rubén Francisco González-Laredo Rosalía Reynoso-Camacho Minerva Ramos-Gómez Teresa Garcia-Gasca M. Eustolia Rodríguez-Muñoz Salvador Horacio Guzmán-Maldonado Luis Medina-Torres Blanca Azalia Lujan-García 《Food chemistry》2009
Water infusions of mature and fresh Quercus resinosa leaves were evaluated for antioxidant activity and genotoxic effects on HeLa cells. Native Mexicans used to drink Q. resinosa leaves tea as a refreshing beverage. The air dried leaves were pulverised and boiled in water, then their phenolic content and condensed tannins were determined. The chromatographic profile of 15 phenolic components in Quercus leaves infusions was also determined by HPLC. In vitro analysis of antioxidant capacity of leaves infusion extracts were performed by the DPPH method and the deoxyribose assay. The genotoxicity of Q. resinosa leaves extracts was evaluated on HeLa cells as well as its underlying mechanism by the single-cell electrophoresis assay (comet assay). Results show that fresh leaves infusions increase the oxidative process and other damage to DNA in transformed human cells. Fresh leaves from Q. resinosa may serve as a potential source of phenolics with anticancer activity. 相似文献
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85.
Pantano Maria F. Espinosa Horacio D. Pagnotta Leonardo 《Journal of Mechanical Science and Technology》2012,26(2):545-561
A review on the mechanical characterization of materials at small length scale is presented. The focus is on the different micro- and nanoscale testing techniques, the variety of materials investigated by the scientific and industrial communities and the mechanical quantities identified by such methodologies. 相似文献
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88.
Pacheco Henrique P. de Souza Eugenio F. Landi Sandra M. David Marcus V. Tyler Prillaman J. Davis Robert J. Toniolo Fabio S. 《Topics in Catalysis》2019,62(12-16):894-907
Topics in Catalysis - Mg-containing oxides are widely studied as effective catalysts for ethanol upgrading due to their capacity to promote dehydrogenation and coupling reactions. In such systems,... 相似文献
89.
Dr. Evgeniy S. Salnikov Dr. Marta De Zotti Dr. Sara Bobone Dr. Claudia Mazzuca Dr. Jesus Raya Dr. Alvaro S. Siano Prof. Cristina Peggion Prof. Claudio Toniolo Prof. Lorenzo Stella Prof. Burkhard Bechinger 《Chembiochem : a European journal of chemical biology》2019,20(16):2141-2150
Trichogin GA IV is a short peptaibol with antimicrobial activity. This uncharged, but amphipathic, sequence is aligned at the membrane interface and undergoes a transition to an aggregated state that inserts more deeply into the membrane, an assembly that predominates at a peptide-to-lipid ratio (P/L) of 1:20. In this work, the natural trichogin sequence was prepared and reconstituted into oriented lipid bilayers. The 15N NMR chemical shift is indicative of a well-defined alignment of the peptide parallel to the membrane surface at P/Ls of 1:120 and 1:20. When the P/L is increased to 1:8, an additional peptide topology is observed that is indicative of a heterogeneous orientation, with helix alignments ranging from around the magic angle to perfectly in-plane. The topological preference of the trichogin helix for an orientation parallel to the membrane surface was confirmed by attenuated total reflection FTIR spectroscopy. Furthermore, 19F CODEX experiments were performed on a trichogin sequence with 19F-Phe at position 10. The CODEX decay is in agreement with a tetrameric complex, in which the 19F sites are about 9–9.5 Å apart. Thus, a model emerges in which the monomeric peptide aligns along the membrane surface. When the peptide concentration increases, first dimeric and then tetrameric assemblies form, made up from helices oriented predominantly parallel to the membrane surface. The formation of these aggregates correlates with the release of vesicle contents including relatively large molecules. 相似文献
90.
Saúl Gómez-Manzo Jessica Terrón-Hernández Ignacio De la Mora-De la Mora Abigail González-Valdez Jaime Marcial-Quino Itzhel García-Torres America Vanoye-Carlo Gabriel López-Velázquez Gloria Hernández-Alcántara Jesús Oria-Hernández Horacio Reyes-Vivas Sergio Enríquez-Flores 《International journal of molecular sciences》2014,15(11):21179-21201
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme deficiency worldwide, causing a wide spectrum of conditions with severity classified from the mildest (Class IV) to the most severe (Class I). To correlate mutation sites in the G6PD with the resulting phenotypes, we studied four naturally occurring G6PD variants: Yucatan, Nashville, Valladolid and Mexico City. For this purpose, we developed a successful over-expression method that constitutes an easier and more precise method for obtaining and characterizing these enzymes. The kcat (catalytic constant) of all the studied variants was lower than in the wild-type. The structural rigidity might be the cause and the most evident consequence of the mutations is their impact on protein stability and folding, as can be observed from the protein yield, the T50 (temperature where 50% of its original activity is retained) values, and differences on hydrophobic regions. The mutations corresponding to more severe phenotypes are related to the structural NADP+ region. This was clearly observed for the Classes III and II variants, which became more thermostable with increasing NADP+, whereas the Class I variants remained thermolabile. The mutations produce repulsive electric charges that, in the case of the Yucatan variant, promote increased disorder of the C-terminus and consequently affect the binding of NADP+, leading to enzyme instability. 相似文献