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41.
Meriam Jebari Nabil Bouazizi Radhouane Bargougui Farhat Rezgui Jacques Maddaluno Franck Le Derf Julien Vieillard Julien Legros 《Tetrahedron letters》2018,59(45):4044-4046
Several iron oxides nanoparticles (Fe2O3@Fe2O3, Fe°@Fe2O3, GO@Fe2O3 and calcinated Fe2O3) have been assessed as catalysts in the 1,4-addition of a cyclic β-ketoester onto methyl vinyl ketone under neat conditions. It appeared that calcinated Fe2O3NP are efficient catalysts at 1?mol% loading for the Michael addition of 1,3-dicarbonyl compounds onto various enones. 相似文献
42.
Quantitative Prediction of Rate Constants for Aqueous Racemization To Avoid Pointless Stereoselective Syntheses 下载免费PDF全文
Dr. Andrew Ballard Dr. Hiwa O. Ahmad Dr. Stefania Narduolo Lucy Rosa Nikki Chand Dr. David A. Cosgrove Dr. Peter Varkonyi Dr. Nabil Asaad Dr. Simone Tomasi Dr. Niklaas J. Buurma Dr. Andrew G. Leach 《Angewandte Chemie (International ed. in English)》2018,57(4):982-985
Racemization has a large impact upon the biological properties of molecules but the chemical scope of compounds with known rate constants for racemization in aqueous conditions was hitherto limited. To address this remarkable blind spot, we have measured the kinetics for racemization of 28 compounds using circular dichroism and 1H NMR spectroscopy. We show that rate constants for racemization (measured by ourselves and others) correlate well with deprotonation energies from quantum mechanical (QM) and group contribution calculations. Such calculations thus provide predictions of the second‐order rate constants for general‐base‐catalyzed racemization that are usefully accurate. When applied to recent publications describing the stereoselective synthesis of compounds of purported biological value, the calculations reveal that racemization would be sufficiently fast to render these expensive syntheses pointless. 相似文献
43.
A series of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines were prepared via oxidative cyclization of aldehyde N-(1,3-diphenylpyrazolo[3,4-d]pyrimidin-4-yl)hydrazones. Dimroth rearrangement of such a series yielded pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines. 相似文献
44.
Mamdouh Nabil Samy Ashraf Nageeb El-Sayed Hamed Sachiko Sugimoto Hideaki Otsuka Mohamed Salah Kamel 《Natural product research》2016,30(8):967-972
A new lignan glucoside, officinalioside (1), was isolated from n-BuOH fraction of the aerial parts of Borago officinalis L., together with four known compounds: actinidioionoside (2), roseoside (3), crotalionoside C (4) and kaempferol 3-O-β-D-galactopyranoside (5). The structure of the new compound was established by means of spectroscopic and chemical analyses. Compounds 1 and 2 showed a moderate DPPH radical scavenging activity (IC50: 52.6 ± 1.70 and 41.3 ± 0.25 μM, respectively) comparable with that of the standard trolox (16.6 ± 2.2 μM) without any significant cytotoxicity towards human cell line A549 (IC50 > 100 μM). 相似文献
45.
46.
A new acousto-optic diffraction configuration is described. At a liquid-solid interface, a light beam is incident from the solid side of higher refractive index. The maximum acousto-optic diffraction of the Raman-Nath type occurs in the liquid with light incident at the critical angle. The angular dependence of the diffraction efficiency indicates accurate optical alignment requirement. Application to acoustic imaging is briefly discussed. 相似文献
47.
A high average power (≈150 mW) subpicosecond (0.5 ps) passively double mode-locked dye laser is described. Two synchronized cw pulse trains are generated which are independently tunable over broad wavelength ranges (≈600 Å). 相似文献
48.
M. Nabil Yasin M. M. Sherif S. M. Abd El-Halim M. A. Jilany 《Journal of Experimental and Theoretical Physics》1997,84(4):635-640
Projectile multifragment breakup of 16O, 2C and 7Li at energies 3.0–4.5 A-GeV is studied by means of the Weizsäcker-Williams method. The fragmentation channels of the 16O projectile at 4.5 A-GeV are investigated and compared with that of 16O at 200 A-GeV. The events characterized by N h=0 and the events due to both Coulomb and diffraction dissociation have been selected and analyzed as a function of impact parameter. Also, the dependence of the electromagnetic dissociation cross-section on incident energy and the charge of projectile and target is found. 相似文献
49.
The diffusion of rhodamine-6G dye in ethanol is observed to be inhibited by optical pumping by a cadmium laser. The diffusion process is observed as a function of the solution temperature. The relative difference in diffusion coefficients with and without optical pumping is calculated. The effect is interpreted as being due to a stronger solvent-dye interaction in the first excited singlet state of rhodamine-6G. 相似文献
50.
The properties of the solid solution VSe2?xSx 0 ? xnom ? 2 have been investigated for secondary battery application. The phase VSe2 is observed for 0 ? xnom ? 1.2 and the phase V5S8 is found using RX analysis for xnom >1.2. The amount of lithium chemically incorporated in this structure by reaction with n-butyllithium is 2 Li/vanadium for 0 ? xnom ? 0.8 and 1.4 Li/vanadium for V5S8. An electrochemical technique (galvanostatic) indicates that the amount of lithium incorporated depends on the xnom values, the grain size and the discharge rate. The best results are obtained for 0.2 ? xnom ? 0.6 (capacity = 164?172 Ah kg?1 and energy density = 385?465 Wh kg?1). 相似文献