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排序方式: 共有662条查询结果,搜索用时 31 毫秒
631.
632.
Walter A. Szarek Osman Achmatowicz Jan Plenkiewicz Bruno K. Radatus 《Tetrahedron》1978,34(10):1427-1433
The photochemistry of glycosyl azides has been studied. Some of the azides, for example, β-d-glucopyranosyl or α-d-mannopyranosyl azide, were found to afford in good yield, on irradiation with UV light, the corresponding next-lower aldose. In other cases, for example, β-maltosyl or β-d-ribofuranosyl azide, there was observed the formation of an intermediate which, on standing in the dark, reverts back to starting material. A rationalization of the two types of behavior is suggested. 相似文献
633.
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635.
Ahmed Osman 《International Journal of Theoretical Physics》1984,23(1):15-25
A three-body model for the deuteron stripping nuclear reactions is presented. A set of three integral equations is obtained for the wave functions of the three-body problem by introducing a decomposition into angular momentum states into the Lippmann-Schwinger equation. Simple two-particle interactions with separable potentials are used. These separable potentials reduce the three-body problem to the solution of coupled sets of one-dimensional Fredholm integral equations. The angular distributions for28Si(d,p)29Si and40Ca(d, p)41Ca stripping reactions are calculated. From the extracted spectroscopic factors, good agreement with the experimental measurements is obtained. 相似文献
636.
In the present work, five systems of samples have been prepared by the solution casting technique. These are the plasticized
poly(methyl methacrylate) (PMMA-EC) system, the LiCF3SO3 salted-poly(methyl methacrylate) (PMMA-LiCF3SO3) system, the LiBF4 salted-poly(methyl methacrylate) (PMMA-LiBF4) system, the LiCF3SO3 salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiCF3SO3) system, and the LiBF4 salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiBF4) system. The conductivities of the films from each system are characterized by impedance spectroscopy. The room temperature
conductivity in the pure PMMA sample and (PMMA-EC) system is 8.57 × 10−13 and 2.71 × 10−11 S cm−1, respectively. The room conductivity for the highest conducting sample in the (PMMA-LiCF3SO3), (PMMA-LiBF4), ([PMMA-EC]-LiCF3SO3), and ([PMMA-EC]-LiBF4) systems is 3.97 × 10−6, 3.66 × 10−7, 3.40 × 10−5, and 4.07 × 10−7 S cm−1, respectively. The increase in conductivity is due to the increase in number of mobile ions, and decrease in conductivity
is attributed to ion association. The increase and decrease in the number of ions can be implied from the dielectric constant,
ɛr-frequency plots. The conductivity–temperature studies are carried out in the temperature range between 303 and 373 K. The
results show that the conductivity is increased when the temperature is increased and obeys Arrhenius rule. The plots of loss
tangent against temperature at a fixed frequency have showed a peak at 333 K for the ([PMMA-EC]-LiBF4) system and a peak at 363 K for the ([PMM-EC]-LiCF3SO3) system. This peak could be attributed to β-relaxation, as the measurements were not carried out up to glass transition temperature,
T
g. It may be inferred that the plasticizer EC has dissociated more LiCF3SO3 than LiBF4 and shifted the loss tangent peak to a higher temperature.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006 相似文献
637.
Maher I. Nessim Magda M. Osman Dina A. Ismail 《Journal of Dispersion Science and Technology》2018,39(7):1047-1055
Three cationic gemini surface active compounds of the type (1r,4r)-1,4-dialkyl-1,4-dimethy-l-piperazine-1,4-diium bromide (Ia, Ib, and Ic), were synthesized. They were characterized using elemental analysis and 1H-NMR spectra. Their surface-active properties were measured in aqueous solutions with different concentrations at different temperatures (25, 40, and 55°C). Various surface measurements of these gemini surfactants, (compared to the conventional one, 1-Dodecyl-1-methylpiperidinium bromide (a)) were estimated, specifically critical micelle concentration (CMC), effectiveness (πCMC), efficiency (PC20) as well as maximum surface excess (Γmax) and minimum surface area (Amin). The measurements of the gemini compounds gave low CMC, high efficiency in reducing the surface tension, and intense adsorption at air/water interface. These surfactants have lower Krafft points and thus better solubility. Thermodynamic data, free energy, entropy, and enthalpy changes (ΔG°, ΔS°, and ΔH°) for micellization at the air/water interface and also for adsorption in the bulk of surface-active solutions were calculated. 相似文献
638.
Meryem Chemchem Issah Yahaya Burcu Aydıner Nurgül Seferoğlu Osman Doluca Naima Merabet Zeynel Seferoğlu 《Tetrahedron》2018,74(48):6897-6906
A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN? besides other interference anions (F?, AcO? and H2PO4?) in aqueous solution. Moreover, 2 can be used to detect CN? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor. 相似文献
639.
Ahmed Galal Osman Zulfiqar Ali Omer Fantoukh Vijayasankar Raman Ramsay S. T. Kamdem 《Natural product research》2020,34(5):683-691
AbstractFour ursane-type triterpenoid glycosides (1-4), two benzophenone glycosides (5 and 6), and one iridoid glucoside (7) were isolated and characterized from the dried roots of Vangueria agrestis. Compounds 1 (3-O-[α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranosyl]pomolic acid 28-O-β-D-glucopyranosyl ester) and 5 (2-O-[β-D-apiofuranosyl-(1→6)-β-D-glucopyranosyl]-6,4′-dihydroxy-4-methoxy benzophenone) were found to be new metabolites. The identity of all compounds has been accomplished, primarily, based on 1 D and 2 D NMR and HRESMS analysis. Compounds 6 and 2, showed inhibitory effect against Trypanosoma brucei with IC50 22.3 µM for 6 and IC50 11.1 µM, IC90 12.3 µM for 2. 相似文献
640.