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排序方式: 共有137条查询结果,搜索用时 31 毫秒
71.
Francine Novack Victoria Ctia S. Radatz Maraisa Sachini Raquel G. Jacob Gelson Perin Wladimir P. da Silva Eder J. Lenardo 《Tetrahedron letters》2009,50(49):6761-6763
2-Phenylseleno aldehydes and ketones were selectively obtained using solid-supported catalyst (KF/Al2O3) and PEG-400 as clean, recyclable medium in good to excellent yields. The method was applied in the preparation of highly functionalized 2-phenylseleno citronellal and citronellol, potential bactericide agents. The catalytic system KF/Al2O3 and PEG-400 can be re-used for four times without previous treatment. 相似文献
72.
Astrath NG Astrath FB Shen J Zhou J Pedreira PR Malacarne LC Bento AC Baesso ML 《Optics letters》2008,33(13):1464-1466
Thermal lens spectroscopy is a highly sensitive and versatile photothermal technique for material analysis, providing optical and thermal properties. To use less expensive multimode non-Gaussian lasers for quantitative analysis of low-absorption materials, this Letter presents a theoretical model for time-resolved mode-mismatched thermal lens spectroscopy induced by a cw laser with a top-hat profile. The temperature profile in a sample was calculated, and the intensity of the probe beam center at the detector plane was also derived using the Fresnel diffraction theory. Experimental validation was performed with glass samples, and the results were found well consistent with literature values of the thermo-optical properties of the samples. 相似文献
73.
Luppé F Conoir JM Franklin H 《The Journal of the Acoustical Society of America》2002,111(6):2573-2582
In a trabecular bone, considered as a nondissipative porous medium, the scattering of an incident wave by cylindrical pores larger than the wavelength is studied. The goal is to know if scattering alone may cause such a high attenuation as that observed in calcaneus. The porous medium is modelized via Biot's theory and the scattering by a single pore is characterized from the definition of a scattering matrix. An approximation of weakly disordered medium is then discussed to estimate the effective attenuation and dispersion as a function of frequency. These effective properties are shown to be different of those measured on calcaneus, due to the neglect of wave conversions during the scattering process. 相似文献
74.
Pointeau I Piriou B Fedoroff M Barthes MG Marmier N Fromage F 《Journal of colloid and interface science》2001,236(2):252-259
The sorption mechanisms of Eu(3+) on calcium silicate hydrate (CSH) phases of hydrated cement were investigated as a tool for the prediction of the behavior of trivalent radionuclides with aged/degraded cements in radioactive waste repositories. Four techniques were used: site-selective and time-resolved luminescence spectroscopy, XPS, high-resolution SEM coupled with EDX, and XRD. Results showed that europium is not precipitated in the solution despite its low solubility limit. It is strongly retained on CSH, resulting in a more than 99.8% sorption rate. Two main sorption sites were characterized by luminescence spectroscopy. One site, with a long lifetime, can be interpreted as Eu included in the framework of CSH. Another one, with a shorter lifetime, can be interpreted as a site with a hydrated environment that is high but is less than that of europium hydroxide. It corresponds to superficial complexation or precipitation. Copyright 2001 Academic Press. 相似文献
75.
Márcio Lazzarotto Eduardo Ernesto Castellano Francine Furtado Nachtigall 《Journal of chemical crystallography》2007,37(10):699-705
Abstract The structures of the aqua salts of 2,4-dinitrophenolate (2,4-DNP−) with ethylenediammonium (EDA2+) and morpholinium (MP+) have been determined by X-ray diffraction, the first with 2:1 stoichiometry. The EDA2+ salt crystallizes in P21/c space group, with a = 5.887; b = 23.441; c = 7.075, β = 96.61, R1 = 0.0365 for reflections with Fo > 4sig(Fo). MP+ salt crystallizes as P–1 space group; a = 6.655; b = 9.388 c = 11.452; α = 104.82 β = 102.31 γ = 105.24, with R1 = 0.0334. Phenolates and ammonium groups interact through hydrogen bonds and the N+···O distances for MP+ and EDA2+ salts are 2.783 ? and 2.812 ?, respectively. There is one water molecule by asymmetric unit, interacting with phenolate and
ammonium ions. The arrays of hydrogen bonds are cyclic, with six and four members alternated and the position of the units
is dependent on the ability to form hydrogen bonds. The Job’s plot for ethylenediamine and 2,4 dinitrophenol shows the same
2:1 stoichiometry in ethanol for EDA2+-2,4-DNP− salt.
Graphical abstract Structures of the dinitrophenolate aqua salts of morpholinium and ethylenediammonium are described with cyclic networks of
hydrogen bonds between the species.
相似文献
76.
Francine Medjiofack Djeujo Valeria Francesconi Maddalena Gonella Eugenio Ragazzi Michele Tonelli Guglielmina Froldi 《Molecules (Basel, Switzerland)》2022,27(2)
Diabetes mellitus is characterized by chronic hyperglycemia that promotes ROS formation, causing severe oxidative stress. Furthermore, prolonged hyperglycemia leads to glycation reactions with formation of AGEs that contribute to a chronic inflammatory state. This research aims to evaluate the inhibitory activity of α-mangostin and four synthetic xanthenone derivatives against glycation and oxidative processes and on α-glucosidase, an intestinal hydrolase that catalyzes the cleavage of oligosaccharides into glucose molecules, promoting the postprandial glycemic peak. Antiglycation activity was evaluated using the BSA assay, while antioxidant capacity was detected with the ORAC assay. The inhibition of α-glucosidase activity was studied with multispectroscopic methods along with inhibitory kinetic analysis. α-Mangostin and synthetic compounds at 25 µM reduced the production of AGEs, whereas the α-glucosidase activity was inhibited only by the natural compound. α-Mangostin decreased enzymatic activity in a concentration-dependent manner in the micromolar range by a reversible mixed-type antagonism. Circular dichroism revealed a rearrangement of the secondary structure of α-glucosidase with an increase in the contents of α-helix and random coils and a decrease in β-sheet and β-turn components. The data highlighted the anti-α-glucosidase activity of α-mangostin together with its protective effects on protein glycation and oxidation damage. 相似文献
77.
Francine Ziquinatti Roberson G. Hugen César M. Oliveira Luiz A. F. Coelho Sérgio H. Pezzin 《Macromolecular Symposia》2005,229(1):276-280
Summary: Aiming the development of high toughness polymer materials, blends of poly(styrene-co-acrylonitrile) (SAN) and poly(butadiene-co-acrylonitrile) (NBR) rubbers, with contents of acrylonitrile (AN) varying from 21 to 45%, were prepared by casting, coprecipitation and monoscrew extrusion followed by injection molding. SAN/NBR blends, prepared in the compositions (w/w) 90/10, 80/20, 70/30, 60/40, and 50/50, were characterized by differential scanning calorimetry (DSC) and Izod impact tests. DSC analyses showed that blends with 33% AN NBR prepared by casting, and with 39% AN NBR prepared by coprecipitation, are partially miscible at 60/40, 70/30 and 80/20 (SAN/NBR) compositions and immiscible for 50/50 compositions. On the other hand, 90/10 SAN/NBR systems were totally miscible. The blends with 45% AN NBR prepared by coprecipitation showed partial miscibility to 50/50, 60/40, 70/30 and 90/10 compositions and total miscibility to 80/20 composition. The NBR addition results in a significant increase in the impact resistance, strongly dependent on the blend composition and the NBR AN content. The best result of impact resistance — 75.2 ± 8.6 (kJ · m−2) — was obtained for SAN/NBR 50/50, using 45% AN NBR. This value is 15.7 times bigger than that for pure SAN -4.8 ± 0.7 (kJ · m−2). 相似文献
78.
Andr B. Charette Alexandre Gagnon Francine Blanger‐Garipy 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):538-540
The title compound, [Mg2Br2(C14H14NO)2(C4H8O)4]·2C7H8, has been crystallized as a C2‐symmetric dimer and the Mg atom has a distorted octahedral geometry. The metal is chelated by the N atom of the ketiminate and the O atom of the ether moiety, giving a rigid structure. 相似文献
79.
Jéssica Santos Stefano Luiz Otávio Orzari Habdias Araujo Silva-Neto Vanessa Neiva de Ataíde Letícia Francine Mendes Wendell Karlos Tomazelli Coltro Thiago Regis Longo Cesar Paixão Bruno Campos Janegitz 《Current Opinion in Electrochemistry》2022
Electrochemistry combined with economical and sustainable platforms (such as paper) provides portable, affordable, robust, and user-friendly devices. In general, techniques, such as photolithography and sputtering, are excellent alternatives for producing these platforms. However, owing to the requirement of expensive and sophisticated instrumentation, as well as cleanroom facilities, these techniques have limited access. Thus, the search for easy to use and produce approaches have been reported, using consumables, including adhesives, carbon ink, graphite, pencil, office paper, paperboard, among others. In this sense, in this mini-review, we discuss various strategies explored to fabricate low-cost electrochemical sensors, including its main applications. Different manufacturing methods, such as screen and stencil printing, laser-scribing, and pencil drawing, will be discussed here, emphasizing the performance of the obtained devices, in addition to their advantages and disadvantages. 相似文献
80.
The dispersion relation is derived for the coherent waves in fluid or elastic media supporting viscous and thermal effects and containing randomly distributed spherical scatterers. The formula obtained is the generalization of Lloyd and Berry's [Proc. Phys. Soc. London 91, 678-688 (1967)], the latter being limited to fluid host media, and it is the three-dimensional counterpart of that derived by Conoir and Norris [Wave Motion 47, 183-197 (2010)] for cylindrical scatterers in an elastic host medium. 相似文献