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51.
Redouane Chebout Didier Tichit Géraldine Layrac Akila Barama Bernard Coq Iuliana Cota Eliana Ramirez Rangel Francisco Medina 《Solid State Sciences》2010,12(6):1013-1017
A new route for the preparation of basic mixed oxides using nanocomposite precursors obtained from layered double hydroxides (LDH) was investigated. These nanocomposites have been prepared by intercalation of negatively charged guest entities containing Ca2+, Sr2+, Ba2+ or La3+ cations in the interlayer space of host Mg/Al LDH by anionic exchange. The guest entities have been previously prepared by complexation of the required cations in the presence of edta or citrate chelating anions. Intercalation of [Mn+(edta)](4?n)? or [La(cit)OH]? complexes is proved by elemental analysis, XRD analysis and FT-IR spectroscopy. However, in order to satisfy the charge equilibrium in the materials, (edta)4? and (citrate)3? species are also co-intercalated in the nanocomposites. The basic properties of the mixed oxides obtained after thermal decomposition of the nanocomposites precursors were evaluated in the disproportionation of 2-methyl-3-butyn-2-ol (MBOH) and the transesterification of 1-phenylethanol with diethylcarbonate (DEC). The Sr- and Ba-containing mixed oxides exhibit basicity close to the one of MgO and Mg(La)O mixed oxides. A comparative study of the reactivity of La-containing mixed oxides obtained following different preparation routes, i.e. coprecipitation or anionic exchange, allows to conclude that the nanocomposite route led to the most active samples. 相似文献
52.
M. Milagros Delgado‐Zamarreño Myriam Bustamante‐Rangel Sergio Sierra‐Manzano Marcela Verdugo‐Jara Rita Carabias‐Martínez 《Journal of separation science》2009,32(9):1430-1436
Tocopherols and tocotrienols have been simultaneously determined in food samples using a rapid and simple analytical method including pressurized liquid extraction (PLE) and LC with electrochemical detection. Separation was carried out on a Phenomenex Synergi 4 μm Hydro‐RP 80A column, using a solution of 2.5 mM acetic acid/sodium acetate in methanol/water (99:1, v/v) as mobile phase at a flow rate of 1.0 mL/min. Column temperature was maintained at 30°C. Detection was performed by coulometric detection at 500 mV except for (β+γ)‐tocotrienol, in wheat and rye samples, which was at +350 mV. A palm oil containing a relatively large amount of γ‐tocotrienol and lower concentrations of α‐ and δ‐tocotrienols and α‐ and γ‐tocopherols was used to provide reference retention times for the tocotrienols. Analyte quantification was performed using the external standard method. The calibration equations of tocopherols were used to quantify both tocopherols and their corresponding tocotrienols. The extraction recoveries obtained using the optimized PLE conditions were in the 80–114% range, with RSDs lower than 15%. The method was successfully applied to the determination of tocotrienols and tocopherols in cereal (wheat, rye, barley, maize and oat) and palm oil samples. 相似文献
53.
Sansón J Corchado JC Rangel C Espinosa-García J 《The journal of physical chemistry. A》2006,110(31):9568-9574
The effects of the methane torsional (nu(2)), umbrella (nu(4)), and the combination nu(2)+nu(4) bending mode excitations on the reactivity and dynamics of the gas-phase Cl + CH(4) --> HCl + CH(3) reaction were analyzed. Quasi-classical trajectory (QCT) calculations, including corrections to avoid zero-point energy leakage along the trajectories, were used on an analytical potential energy surface previously developed by our group. With respect to the reactivity, we found that excitation of either bending mode independently gave similar increases in the reactivity, while the increase observed upon excitation of both modes was larger than the sum of the effect of exciting them independently. Both results agree with recent experimental measures. With respect to the dynamics (rotovibrational and angular distributions of the products), the two bending modes and their combination gave very similar pictures, reproducing the experimental behavior. The satisfactory agreement obtained with a great variety of experimental data (always qualitatively acceptable and sometimes even quantitatively) of the present QCT study lends confidence to the potential energy surface constructed by our group. 相似文献
54.
Braga GU Rangel DE Flint SD Anderson AJ Roberts DW 《Photochemistry and photobiology》2006,82(2):418-422
The importance of conidial pigmentation to solar UV radiation tolerance in the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, was estimated by comparing the effects of exposure to simulated solar UV radiation on the wild-type parent strain U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) Collection of Entomopathogenic Fungal Cultures (ARSEF) 23, which has dark green conidia, and three groups of color mutants with yellow, purple and white conidia. The comparisons included inactivation levels and the kinetics of germination of conidia exposed or not exposed to simulated solar UV radiation. In addition to significantly inactivating the conidia of different mutants, exposure to radiation delayed for several hours the germination of surviving conidia of the wild type and all mutants. In general, mutants with white conidia were more sensitive to simulated solar UV radiation than mutants with purple conidia, which were more sensitive than mutants with yellow conidia, which in turn were more sensitive than the green wild strain. A significant variation in tolerance to simulated solar radiation was observed among mutants within each color group, particularly among mutants with yellow conidia. Revertants with green conidia, DWR 179 and DWR 176, were obtained from the very sensitive UV mutants DWR 148 (yellow conidia) and DWR 149 (purple conidia), respectively. These revertants had levels of tolerance to simulated solar UV radiation similar to those of the wild-type ARSEF 23. This observation is strong evidence of the importance of green conidial pigmentation for tolerance to simulated solar UV radiation, a factor that could be manipulated to produce M. anisopliae strains with more tolerance to solar UV radiation. 相似文献
55.
A new compound was elucidated as 9-acetyl-6-caryophyllen-15-ol. Iridoid glucosides including catalpol, methyl catalpol, 7-deoxy-8-epiloganic
acid, and aucubin, were isolated from leaves of Buddleia parviflora, while the known compounds were identified as dehydrobuddledin A and buddledin C. The structures was elucidated by extensive
1D-2D-NMR spectroscopy.
Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 29–31, January–February, 2008. 相似文献
56.
Kinetic studies of the oxidation of the bis[1-hydroxy-2-(salicylideneamino)ethane]manganese(II) complex by hydrogen peroxide in acetonitrile solutions, at (30.0±0.2)°C, are described. A first-order dependence on the total manganese and the peroxide concentrations was verified, leading to the rapid formation of a Mn(III) intermediate, monitored by stopped-flow measurements, at 394 nm, with a rate constant kf=(1.15±0.03)×105 mol−1 dm3 s−1. The participation of hydroxyl radicals in the process was detected by spin-trapping EPR spectra. The final product was monitored both by EPR spectra, and spectrophotometrically by the slow decay of the intermediary Mn(III) species, with a rate constant kd=(2.60±0.09) s−1. It was identified as the corresponding mononuclear Mn(IV) complex, and characterized by different spectroscopic techniques. Comparative results of the reactivity of the starting complex versus molecular oxygen, leading to the same final product, were also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 889–897, 1998 相似文献
57.
A straightforward test of the quality of potential energy surfaces in polyatomic systems is proposed based on obtaining thermochemical
properties, in this case, standard enthalpies of formation, from kinetics results. Agreement with experiment lends confidence
to the PESs, and the disagreement serves to help improve them. 相似文献
58.
Transition Metal Chemistry - 相似文献
59.
L. H.C. Andrade P. G. Freitas B. G. Mantovani M. S. Figueiredo R. A. Lima S. M. Lima M. A.S. Rangel R. M. Mussury 《The European physical journal. Special topics》2008,153(1):539-541
In this work the Photoacoustic Infrared
Spectroscopy from 4000 to 400 cm-1 was applied, by the first time to
our knowledge, to diagnostic the soy bean rust or Asian rust contamination
on soy leafs caused by the fungi Phakopsora pachyrhizi. The obtained results shown that a
premature, fast and precise diagnosis can be achieved using this technique
before it can be detect by the conventional visual method. The early
identification of the fungi infection avoid massive lost in the soy
production and decrease the intense use of fungicide whose is necessary when
the infection is in advanced stagy. 相似文献
60.
Herein we present the synthesis and characterization of new phosphonate‐, bisphosphonate‐ and hydroxybisphosphonatebenzimidazole derivatives substituted at the N‐1 position and new regioisomers phosphonate‐, bisphosphonate‐, and hydroxybisphosphonatebenzotriazole derivatives substituted at N‐1 or N‐2 positions. The compounds were characterized by NMR and IR spectroscopies, and mass spectrometry (low and high resolution) allowing the assignment of their structure, including the identification of regioisomers. These new azole monomers will be precursors for a mesoporous silica host to produce novel membrane materials with high proton conductivity for intermediate temperature proton exchange membrane fuel cells. 相似文献