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21.
Mokhtar Benziane Kamel Khimeche Abdellah Dahmani Sawsen Nezar Djalal Trache 《Journal of Thermal Analysis and Calorimetry》2013,112(1):229-235
Solid–liquid equilibria for three binary mixtures of {n-eicosane (1) + methyl palmitate (2)}, {n-tetracosane (1) + methyl stearate (2)} and {n-octacosane (1) + methyl stearate (2)} were measured using differential scanning calorimeter. Simple eutectic behaviours for these systems were observed. The experimental results were correlated by means of the modified UNIFAC (Larsen and Gmehling versions), UNIQUAC and ideal models. The root-mean-square deviations of the solubility temperatures for all measured data vary from 0.21 K (for UNIQUAC model) to 1.07 K (for Ideal model) and depend on the particular model used. The best solubility correlation was obtained with UNIQUAC model. 相似文献
22.
A novel proaporphine-tryptamine dimer alkaloid, named phoebegrandine C 1, was isolated from the leaves of Phoebe grandis (Nees) Merr. Its structural elucidation was carried out using spectroscopic techniques, notably 2D NMR. 相似文献
23.
Kee CH Ariffin A Awang K Takeya K Morita H Hussain SI Chan KM Wood PJ Threadgill MD Lim CG Ng S Weber JF Thomas NF 《Organic & biomolecular chemistry》2010,8(24):5646-5660
The syntheses of fourteen unusual o-carboxamido stilbenes by the Heck protocol revealed surprising complexity related to intriguing substituent effects with mechanistic implications. The unexpected cytotoxic and chemopreventive properties also seem to be substituent dependent. For example, although stilbene 15d (with a 4-methoxy substituent) showed cytotoxicity on HT29 colon cancer cells with an IC(50) of 4.9 μM, the 3,4-dimethoxy derivative (15c) is inactive. It is interesting to observe that the 3,5-dimethoxy derivative (15e) showed remarkable chemopreventive activity in WRL-68 fetal hepatocytes, surpassing the gold standard, resveratrol. The resveratrol concentration needed to be 5 times higher than that of 15e to produce comparable elevation of NQO1. 相似文献
24.
Alaa Eldin Mokhtar Abdel-Hady Rabie S. Farag Ahmad S. Abu-Khadra 《Transition Metal Chemistry》2010,35(5):571-576
The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H2O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H2O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed. 相似文献
25.
A series of dealuminated mordenites treated under various conditions of acid leaching was impregnated in an aqueous solution of ammonium heptamolybdate to achieve a loading of 12 wt% Mo. These samples were characterized by XRD, UV-DRS, N(2) adsorption, TGA, and FTIR techniques. Special attention was given to the far-IR measurements and IR study of surface hydroxyl groups before and after dealumination. A polymolybdate species was recognized by the appearance of bands at 344, 319, and 236 (229) cm(-1) due to the vibrational modes of delta(Mo-O) and delta(Mo-O-Mo), respectively. The disappearance of the 236 cm(-1) band as well as that at 344 cm(-1) in favor of the 319 cm(-1) band, with the dealumination, was related to the high dispersion of Mo species in the produced mesopore surface assessed by the N(2) adsorption at 77 K. No bands due to bulk MoO(3) were detected from the IR and XRD results. A strong interaction between Mo species and dealuminated mordenite surfaces (OH groups) was recognized by a decrease in intensity and a marked shift of the band at 3745 to 3727 cm(-1) as well as the appearance of a new band at 3668 cm(-1). The latter band was produced by the interaction of the framework Al-OH with Mo species. The BET surface areas of Mo-dealuminated mordenite samples were higher than the corresponding Mo-free ones. The diffuse reflectance measurements suggested that Mo cations are predominantly present as an octahedrally coordinated Mo(6+), along with some tetrahedral Mo(6+). New spectral features as a consequence of dealumination events in the far-IR range were evaluated and discussed. 相似文献
26.
Brahim Lakhrissi Mohamed Massoui El Mokhtar Essassi Vincent Lequart Nicolas Joly Patrick Martin Grard Goethals 《Journal of heterocyclic chemistry》2004,41(6):1011-1014
Reaction of 1,5‐benzodiazepin‐2,4‐dione with 3‐O‐substituted‐5,6‐anhydro‐1,2‐isopropylidene‐α‐D‐glucofuranose gave the unexpected N,N'‐di‐glucofuranosyl benzimidazol‐2‐one by a novel rearrangement and ring closure reaction. A mechanism is proposed. 相似文献
27.
Khalil Al Mamari Hamid Ennajih Hafid Zouihri Rachid Bouhfid Seik Weng Ng El Mokhtar Essassi 《Tetrahedron letters》2012,53(18):2328-2331
The 1,3-dipolar cycloaddition of 1-allyl-5-haloisatin derivatives as dipolarophiles with the azomethine ylides generated in situ from N-allylisatin and l-proline to furnish novel dispiro-oxindoles has been investigated. The structures and relative stereochemistry of both types of cycloadducts were confirmed by single crystal X-ray diffraction, 1H and 13C NMR spectroscopy and mass spectrometry. 相似文献
28.
Why Is the Spontaneous Deprotonation of [Cu(uracil)2]2+ Complexes Accompanied by Enolization of the System? 下载免费PDF全文
Oriana Brea Prof. Manuel Yáñez Prof. Otilia Mó Dr. Al Mokhtar Lamsabhi 《Chemphyschem》2015,16(11):2375-2382
The reaction‐force formalism is applied to carry out a detailed analysis of the mechanisms behind the enolization processes undergone by the complexes formed on interaction of uracil dimers with Cu2+ ions after spontaneous deprotonation of the resulting complexes. These enolization processes apparently involve a single proton transfer (PT) from an NH group to a carbonyl group of the same uracil moiety, which should involve a rather high activation barrier that prevents the process occurring. However, the reaction‐force, chemical‐potential, and electronic‐flux profiles unambiguously indicate that the actual mechanism involves three low‐barrier elementary steps, and this explains why enolization of the [Cu(uracil?H)(uracil)]+ complexes is a highly facile, assisted PT process. All of the observed PT processes show a typical profile for both the chemical potential and the electronic flux associated with the bond‐breaking and the bond‐formation processes. 相似文献
29.
Trujillo C Lamsabhi AM Mó O Yáñez M Salpin JY 《Organic & biomolecular chemistry》2008,6(20):3695-3702
The structures and relative stabilities of the complexes formed by uracil and its sulfur derivatives, namely, 2-thio-, 4-thio, and 2,4-dithio-uracil when interacting with Ca(2+) in the gas phase have been analyzed by means of density functional theory (DFT) calculations carried out at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) level. For uracil and 2,4-dithiouracil, where the two basic sites are the same, Ca(2+) attachment to the heteroatom at position 4 is preferred. However, for the systems where both types of basic centers, a carbonyl or a thiocarbonyl group, are present, Ca(2+)-oxygen association is favored. The most stable complexes correspond to structures with Ca(2+) bridging between the heteroatom at position 2 of the 4-enol (or the 4-enethiol) tautomer and the dehydrogenated ring nitrogen, N3. The enhanced stability of these enolic forms is two-fold, on the one hand Ca(2+) interacts with two basic sites and on the other triggers a significant aromatization of the ring. Besides, Ca(2+) association has a clear catalytic effect on the tautomerization processes which connect the oxo-thione forms with the enol-enethiol tautomers. Hence, although the enol-enethiol tautomers of uracil and its thio derivatives should not be observed in the gas phase, the corresponding Ca(2+) complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Ca(2+) binding energies. 相似文献
30.