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11.
Vera L. P. Soares L. N. Batista Rosane A. S. San Gil 《Journal of Thermal Analysis and Calorimetry》2007,87(3):805-809
MgO was
incorporated into montmorillonite (MMT) though the controlled formation of
Mg(OH)2 followed by calcination. The evidence for Mg2+
in MMT before calcination was concluded from TG curves where two different
temperature ranges for Mg(OH)2 dehydroxylation suggested that the location
of Mg2+ at its internal and external surfaces.
FTIR by diffuse reflectance technique of calcined sample showed a typical
MgO band. XRD indicated a decrease in structural order and no collapse of
clay structure. The organic compounds adsorption to MMT modified with MgO
as suggested by increased degradation temperatures occurred at internal and
external clay surfaces besides in an area formed probably by MgO and MMT layers. 相似文献
12.
Ion-exchange resins have been often used as catalysts especially those based on styrene-divinylbenzene copolymers with sulfonic acid groups in the aromatic rings of polymer chains. That is due to the advantages of heterogenous catalysis over the homogeneous acid catalysis. Moreover, resin catalysts can often lead to high selectivity in organic reactions due to the matrix effects. Therefore, the study of copolymers synthesis conditions to determine the type of polymer structure produced as well as the characterization of sulfonic resins obtained thereof are of great interest. The current paper describes the synthesis, characterization and evaluation as catalysts of sulfonic resins derived from polymer supports synthesized by aqueous suspension polymerization of styrene and divinylbenzene. The reaction conditions were varied and polymer supports with different physical properties and morphological characteristics were obtained. The polymer supports were chemically modified by sulfonation. The resultant sulfonic resins had their catalyst activity evaluated in the esterification of acetic acid with n-butanol. 相似文献
13.
Let \(\Omega \) be a bounded domain in a n-dimensional Euclidean space \(\mathbb {R}^{n}\). We study eigenvalues of an eigenvalue problem of a system of elliptic equations of the drifting Laplacian Estimates for eigenvalues of the above eigenvalue problem are obtained. Furthermore, a universal inequality for lower order eigenvalues of the problem is also derived. Finally, we prove an universal inequality type Ashbaugh and Benguria for the drifting Laplacian on Riemannian manifold immersed in an unit sphere or a projective space.
相似文献
$$\begin{aligned} \left\{ \begin{array}{ll} \mathbb {L_{\phi }}\mathbf{{u}} + \alpha (\nabla (\mathrm {div}{} \mathbf{{u}}) - \nabla \phi \mathrm {div}{} \mathbf{{u}})= -\bar{\sigma }\mathbf{{u}}, &{} \hbox {in} \,\Omega ; \\ \mathbf{{u}}|_{\,\partial \Omega }=0. \end{array} \right. \end{aligned}$$
14.
Optical inclinometer based on a single long-period fiber grating combined with a fused taper 总被引:1,自引:0,他引:1
A new concept to measure rotation angles based on a fiber-optic modal Mach-Zehnder interferometer is demonstrated by using a nonadiabatic taper cascaded with a long-period fiber grating. Information about the magnitude of the rotation angle can be obtained from the measurement of the interference pattern visibility, and under certain conditions it is also possible to obtain the sign of the rotation angle from the induced phase variation in the fiber interferometer. 相似文献
15.
Laerte C. Azeredo Maria Aparecida A. Azeredo Rosane N. Castro Marcelo Francisco C. Saldanha Daniel V. Perez 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12)
A new method is described for the separation of molybdenum based on its chelation in a column packed with quercetin, immobilized on silica gel in a slightly acidic medium (pH 5.0). Recovery ranged from 95% (NIST 1515 apple leaves) to 99% (deionized, distilled water; DDW) with an absolute blank of 27.5±1.6 pg obtained for the analysis of DDW. Detection limits, absolute and relative, based on a 5.0-ml sample volume were 4.8 pg and 1 ng l−1, respectively. Results are presented for molybdenum determination in two standard reference materials, NIST 1515 and NIST 1547 peach leaves, using simple calibration curves for quantification. α-Benzoinoxime was used as the eluent. 相似文献
16.
Rosane Aguiar da Silva San Gil Magaly Giro Albuquerque Ricardo Bicca de Alencastro Angelo da Cunha Pinto Fabiano do Espírito Santo Gomes Tereza Neuma de Castro Dantas Maria Aparecida Medeiros Maciel 《Journal of Molecular Structure》2008,885(1-3):82-88
Solid-state 13C nuclear magnetic resonance (13C NMR) with magic-angle spinning (MAS) and with cross-polarization and magic-angle spinning (CP/MAS) spectra, and differential scanning calorimetry (DSC) techniques were used to obtain structural data from a sample of acetyl aleuritolic acid (AAA) extracted from the stem bark of Croton cajucara Benth. (Euphorbiaceae) and recrystallized from acetone. Since solid-state 13C NMR results suggested the presence of more than one molecule in the unitary cell for the AAA, DSC analysis and molecular modeling calculations were used to access this possibility. The absence of phase transition peaks in the DSC spectra and the dimeric models of AAA simulated using the semi-empirical PM3 method are in agreement with that proposal. 相似文献
17.
Fidelis QC Castro RN Guilhon GM Rodrigues ST de Salles CM de Salles JB de Carvalho MG 《Molecules (Basel, Switzerland)》2012,17(7):7989-8000
The chemical study of the extracts from leaves and stems of Ouratea ferruginea allowed the identification of a new isoflavone, 5-hydroxy-7,3'4'5'-tetramethoxyisoflavone, and twenty two known compounds, including friedelin, 3β-friedelinol, lupeone, a mixture of sitosterol, stigmasterol and campesterol, sitosteryl- and stigmasteryl-3-O-b-D-glucopyranosides, 5,4'-dihydroxy-7,5',3'-trimethoxyisoflavone, 5,4'-dihydroxy-7,3'-di-methoxyisoflavone (7,3'-di-O-methylorobol), 5,7,4'-trihydroxy-3',5'-dimethoxyisoflavone (piscigenin), 2R,3R-epicatechin, syringic acid, 2,6-dimethoxybenzoquinone, 2,6-dimethoxyhydroquinone, syringic and ferulic aldehyde, a mixture of vanillic acid, 1-hydroxy-2-methoxy-4-(1E-3-hydroxy-1-propenyl)-benzene and 3,5-dimethoxy-4-hydroxy-dihydrocinamaldehyde, besides amenthoflavone and 7-O-methylamenthoflavone (sequoiaflavone) which are considered as chemotaxonomic markers of Ouratea. The structures were identified by IR, (1)H- and (13)C-NMR and GC-MS, HPLC-MS, besides comparison with literature data. The inhibitory effects of 5,4'-dihydroxy-7,5',3'-trimethoxyisoflavone, 7,3'-di-O-methylorobol, piscigenin and 7-O-methylamenthoflavone on cytochrome P450-dependent 7-ethoxycoumarin O-deethylase (ECOD) and glutathione S-transferase (GST) were evaluated in vitro. The 5,4'-dihydroxy-7,5',3'-trimethoxy-isoflavone was the best inhibitor, inhibiting almost 75% of GST activity. Sequoiaflavone was the most potent inhibitor, inhibiting ECOD assay in 75%. These activities allow us to consider both these flavonoids as potential anticancer and chemopreventive agents. 相似文献
18.
19.
Paulo R. R. Costa ClÁUdio C. Lopes Rosacaronngela S. C. Lopes Maria F. G. Marinho Rosane N. Castro 《合成通讯》2013,43(14):1723-1730
Phthalides have bcen employed as useful intcriucdiates in tic sqrnthcsis of my condcnscld aromatic carbocyclic and heterocyclic compounds, including several natural products In this paper we report two alternative synthetic pathways for the preparation of phthalides as shown for the synthesis of the isomeric pairs of compounds 5a-d and 7a-d. 相似文献
20.
Rosane Catarina dos SantosNalva Vivian da Silva Faleiro Leandra Franciscato CampoMaria Lúcia Scroferneker Valeriano Antonio CorbelliniFabiano Severo Rodembusch Valter Stefani 《Tetrahedron letters》2011,52(23):3048-3053
New fluorescent succinimidyl benzazole derivatives were synthesised and successfully used to stain Candida albicans ATCC 10231 cells. The dyes were characterised by means of infrared, 13C and 1H NMR spectroscopies and elemental analysis. UV-Vis and steady-state fluorescence in solution were also applied to characterise their photophysical behaviour. The novel dyes were fluorescent in the yellow-green region by a phototautomerism in the excited state (ESIPT) with a large Stokes shift (9065-10962 cm−1). Dual fluorescence could also be observed depending on the solvent polarity. The present dyes were used as new probes by means of culture methodology or direct staining to study the micromorphology of Candida albicans. 相似文献