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31.
Emanuele Aresu Laura CarrocciaStefania Fioravanti Simona GasbarriLucio Pellacani Fabio Sciubba 《Tetrahedron》2013
Chiral racemic α-diimines, tested in aziridination reactions with NsONHCO2Et, for the first time led to the synthesis of (±)-bidiaziridines, stereoselectively derived from the corresponding meso (E-s-trans-E)-α-diimines. Moreover, a minor bidiaziridine isomer, probably a meso form that was lost under classical work-up conditions, can be obtained by adding water to the crude mixtures at the end of amination reactions. The results definitively prove that the imine aziridination by carbamates is a two-step domino process. The structures of the compounds were determined using 2D NMR on purified bidiaziridines. 相似文献
32.
Laura E. Muresan Adrian I. Cadis Ioana Perhaita Emil Indrea 《Central European Journal of Chemistry》2014,12(10):1023-1031
Yttrium silicate doped with cerium (Y2SiO5:Ce) was obtained from Y-Ce-Si based precursors prepared by the simultaneous addition of reagents (SimAdd) technique. The synthesis of the precursors was done in well controlled conditions using ammonium oxalate, ammonium carbonate or urea as precipitating agents. Results regarding the influence of precipitating agents on the morpho structural and photoluminescent characteristics of Y2SiO5:Ce are reported. The TG analysis in correlation with EGA, FT-IR and XRD investigations reveals the formation of oxalate, hydroxy-carbonate or hydroxy-nitrate based compounds, the same as the conversion of the precursors to well crystallized yttrium silicate. XRD patterns show that the precursors are amorphous except for the sample prepared with ammonium oxalate. Depending on the precipitation conditions, the phosphors phase composition varies from single phase (X2-Y2SiO5) to a mixture of phases (X2-Y2SiO5, X1-Y2SiO5, Y2O3). Under UV excitation, phosphors exhibit the specific blue emission of cerium with an intensity that varies from 175.8% (urea) to 96.0% (ammonium carbonate) and to 78.5% (ammonium oxalate). The emission intensity depends on the phase purity and order degree of the phosphors. PACS Classification codes:78.55 Hx, 81.20Fw 相似文献
33.
Regioselectivity and stereoselectivity of nucleophilic addition to glycal and imino‐glycal vinyl epoxides and their carba analogs: a rationalization based on HSAB theory and MEP 下载免费PDF全文
34.
Laura A. Kranendonk Robert Huber Scott T. Sanders 《Proceedings of the Combustion Institute》2007,31(1):783-790
Using a novel Fourier-domain mode-locking (FDML) laser scanning 1330-1380 nm, we have developed a gas thermometer based on absorption spectroscopy that is appropriate for combustion gases at essentially arbitrary conditions. The path-integrated measurements are particularly useful in homogeneous environments, and here we present measurements in a controlled piston engine and a shock tube. Engine measurements demonstrate a RMS temperature precision of ±3% at 1500 K and 200 kHz bandwidth; the precision is improved dramatically by averaging. Initial shock tube measurements place the absolute accuracy of the thermometer within ∼2% to 1000 K. The sensor performs best when significant H2O vapor is present, but requires only at 300 K, at 1000 K, or at 3000 K for 2% accurate thermometry, assuming a 4 kHz measurement bandwidth (200 kHz scans with 50 averages). The sensor also provides H2O mole fraction and shows potential for monitoring gas pressure based on the broadening of spectral features. To aid in designing other sensors based on high-temperature, high-pressure H2O absorption spectroscopy, a database of measured spectra is included. 相似文献
35.
Kalnina I Klimkane L Kirilova E Toma MM Kizane G Meirovics I 《Journal of fluorescence》2007,17(6):619-625
The fluorescent probe-aminoderivative of benzanthrone, ABM (developed at Riga Technical University, Riga, Latvia) was used
to characterize the membranes of lymphocytes of cancer patients: 46 patients with gastrointestinal diseases, 13 patients having
different primary localizations with massive metastases and intoxication. Patients were divided into three groups: (1) with
decreased fluorescence intensity, (2) normal fluorescence intensity, (3) increased fluorescence intensity. The lymphocytes
distribution among subsets differed between groups, in correspondence to the level of florescence intensity. Surgical treatment
affected the main immunological parameters and elevated the functional activity of lymphocytes. In the advanced tumors group,
fluorescence intensity correlates with the survival rate. Results suggest that determination of lymphocytes functional activity
by ABM can aid evaluation of the immune status in cancer patients. 相似文献
36.
37.
A combined transient and steady state approach for robust lifetime spectroscopy with micrometer resolution 下载免费PDF全文
We present the combination of two complementary micro‐photoluminescence spectroscopic techniques operating in transient and steady state condition, respectively. Introducing the time domain into the well‐established micro‐photoluminescence mapping approach operating under steady state conditions demonstrates a distinct improvement of the robustness and reliability in the determination of charge carrier lifetime measured with micrometer spatial resolution. Lifetimes from 50 ns to above ms are accessible. We elaborate a calibration procedure and apply the combined all‐photoluminescence setup to high‐performance multicrystalline silicon. A lifetime image obtained from the established photoluminescence imaging technique is reconstructed from the microscopic map by considering lateral diffusion and optical blurring, revealing a more detrimental influence of small angle grain boundaries as well as a higher lifetime within grains as may be deduced from the standard imaging technique. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
38.
Antonio Doménech-Carbó Monserrat Lastras Francisco Rodríguez Emilio Cano Juan Piquero-Cilla Laura Osete-Cortina 《Journal of Solid State Electrochemistry》2014,18(2):399-409
A methodology for monitoring washing procedures applied to stabilize archaeological iron is described. It is based on the combination of voltammetry of microparticles (VMP) with electrochemical impedance spectroscopy (EIS). A semi-empirical approach is used where the impedances at low and high frequencies were related with the fraction areas of passive and corrosion layers generated during the stabilizing treatment, the thickness, and the porosity of the corrosion layer. The variation of such parameters with the time of washing was determined from EIS data for four types of desalination procedures using concentrated NaOH and/or Na2SO3 aqueous solutions on archaeological iron artifacts. After 2 months of treatment, EIS data indicate that an essentially identical “stable” state was attained in all cases, as confirmed by the formation of a passive magnetite layer identified in VMP measurements while the rate of variation of corroded surface and porosity at short washing times varied significantly from one stabilization procedure to another. 相似文献
39.
Laura L. Adduci Dr. Matthew P. McLaughlin Trandon A. Bender Dr. Jennifer J. Becker Prof. Dr. Michel R. Gagné 《Angewandte Chemie (International ed. in English)》2014,53(6):1646-1649
The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated C? O bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C6F5)3) is shown to catalyze the metal‐free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products. 相似文献
40.
Laura Hoffmeister Peter Persich Prof. Alois Fürstner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4396-4402
In an attempt to study the ability of the latest generation of alkyne metathesis catalysts to process sterically hindered substrates, two different routes to the bacterial metabolite kendomycin ( 1 ) were explored. Whereas the cyclization of the overcrowded arylalkyne 39 and related substrates turned out to be impractical or even impossible, ring closure of the slightly relaxed diyne 45 was achieved in excellent yield under notably mild conditions with the aid of the molybdenum alkylidyne 2 endowed with triphenylsilanolate ligands. The resulting cycloalkyne 46 was engaged into a gold‐catalyzed hydroalkoxylation, which led to benzofuran 47 that had already previously served as a late‐stage intermediate en route to 1 . 相似文献