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61.
Mohammad M. Fares Adeeb S. El-faqeeh Hasan Ghanem Mohammad E. Osman Elfatih A. Hassan 《Journal of Thermal Analysis and Calorimetry》2010,99(2):659-666
The synthesis, characterization, and hydrogel properties of starch-g-(tert-butylacrylate) and starch-g-(n-butylacrylate) copolymers were studied. The optimum conditions for the grafting process of tert-butylacrylate into 1.0 g of starch were as follows: [tert-butylacrylate] = 0.04 mol/L, [CAN] = 9.0 × 10−4 mol/L, temperature = 20 °C in 100 mL solution, whereas the results using n-butylacrylate monomer were as follows: [n-butylacrylate] = 0.04 mol/L, [CAN] = 4.0 × 10−3 mol/L, temperature = 30 °C in 100 mL solution. The grafting evidences of monomers into starch were done through TG and its
derivative DTG for thermal changes and mass losses, scanning electron microscope (SEM) for morphological changes, powder X-ray
for crystallinity measurements and FTIR for functional group changes. Acid hydrolysis method was used efficiently to allow
the calculations of the viscosity average molecular weight (M
v) of the grafted chains on starch and consequently the real percent of grafting efficiency (i.e. %GY). The capability of starch-g-(n-BAC) hydrogel to absorb water were found 10 times more than starch-g-(tert-BAC) hydrogel, which were clarified through the X-ray and SEM results. 相似文献
62.
A direct liquid chromatographic enantioselective separation of a set of β-blocker enantiomers on the new immobilized and conventional coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) was studied using methanol as mobile phase and ethanolamine as an organic modifier (100:0.1, v/v). The separation, retention and elution order of the enantiomers on both columns under the same conditions were compared. The effect of the immobilization of the amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase on silica (Chiralpak IA) on the chiral recognition ability was noted when compared to the coated phase (Chiralpak AD) which possesses a higher resolving power than the immobilized one (Chiralpak IA). A few racemates, which were not or poorly resolved on the immobilized Chiralpak IA were most efficiently resolved on the coated Chiralpak AD. However, the immobilized phase withstand solvents like dichloromethane when used as an eluent or as a dissolving agent for the analyte. The versatility of the immobilized Chiralpak IA in monitoring reactions performed in dichloromethane using direct analysis techniques without further purification, workup or removal of dichloromethane was studied on a representative example consisting of the lipase-catalyzed irreversible transesterification of a β-blocker using either vinylacetate or isopropenyl acetate as acyl donor in dichloromethane as organic solvent. 相似文献
63.
The problem of grating coupling of a focused incident beam under non-normal incidence into a slab waveguide is given a complete three-dimensional (3D) solution. The diffracted field is expressed as the Fourier integral of a regular part and of a singular part resulting from the existence of the coupled guided mode. A suitable expression of the field in the neighborhood of the pole and a rigorous definition of the modal field lead to a generalized coupled mode equation relating the incident field and the two-dimensional (2D) modal field propagating in the plane of the slab waveguide. The phenomenological parameters involved in the coupled wave equation: the propagation constant, the radiation coefficient as well as the modal field shape are derived from the exact treatment of plane wave diffraction in the same structure. The solution of the complete coupling problem is given in the particular case of a Gaussian incident beam, and of a high index step-index waveguide. 相似文献
64.
A. Ghanem P. Meurisse F. Laupreatre C. Noëulz 《Molecular Crystals and Liquid Crystals》2013,570(1):339-352
PCILO conformational calculations have been carried out on several model compounds of thermotropic liquid crystalline polyesters [—OC—φ—φ—φ—CO—Os—R—O—] where R = (—CH2—)2; (—CHCH3—)2; (—CHCH3—CH2—). Several conformations corresponding to the trans and gauche states of the C-C single bonds are preferred, the TGT form being of lower energy than the TTT form. The replacement of—CH2—group by—CH(CH3) group results in a decrease of the number of the energy minima, an increase in the energy of the molecule in all the preferred conformations, compared to that of the TGT form, a sharpening of the potential energy wells and an increase in the energy barriers. The presence of a methyl group also shifts the aliphatic chain away from the ideal trans and gauche positions. 相似文献
65.
The kinetics of oxidation of pindolol by peroxodisulfate (PDS) in sulfuric acid and 40%(v/v) methanol + water solvent has
been investigated. The pH profile of the rate constant was also investigated. It has been found that the reaction proceeds
only in the pH range 0 to 4. A mechanism was proposed for the oxidation reaction; the reaction starts by the attack of peroxodisulfate
(PDS) to form an indoleninic species that can rearrange into an indoxyl species. Once the indoxyl intermediate is formed,
it can follow different paths leading to different products, depending on the acidity and PDS concentration. At low acid concentration,
oxipindolol is formed whereas at high acid concentration dioxipindolol forms instead. Dioxipindolol can dimerize to form the
indigo form of pindolol. A polar mechanism was proposed for the oxidation reaction, and the thermodynamic parameters were
determined. 相似文献
66.
Rodrigo Lima de Miranda Jan Kruse Klaus Rätzke Franz Faupel Detlev Fritsch Volker Abetz Peter M. Budd James D. Selbie Neil B. McKeown Bader S. Ghanem 《固体物理学:研究快报》2007,1(5):190-192
The performance of polymeric membranes for gas separation is mainly determined by the free volume. Polymers of intrinsic microporosity are interesting due to the high abundance of accessible free volume. We performed measurements of the temperature dependence of the positron lifetime, generally accepted for investigation of free volume, in two polymers of intrinsic microporosity (PIM‐1 and PIM‐7) in the range from 143 to 523 K. The mean value of the free volume calculated from the ortho‐positronium lifetime is in the range of typical values for high free volume polymers. However, the temperature dependence of the local free volume is non‐monotonous in contrast to the macroscopic thermal expansion. The explanation is linked to the spirocenters in the polymer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
Films of low-density polyethylene grafted with various amounts of polyacrylic acid were prepared by the direct irradiation method, using a 10 MeV linear electron accelerator. Aqueous solutions of acrylic acid were used with FeSO4 · 7H2O as a redox system. The best graft/homopolymer ratios were obtained at radiation doses between 2 and 3 Mrad, at acrylic acid concentrations of 40–60% and at FeSO4 · 7H2O concentrations of 0.25-0.5% by weight. The grafted films were tested for reverse osmosis properties. A membrane with 60% polyacrylic acid content gave 87% salt rejection and a water flux of 0.75 × 10?5 gm/cm2 per sec. 相似文献
68.
Ghanem A 《Journal of separation science》2007,30(7):1019-1028
Chiralpak IB, a new chiral stationary phase (CSP) containing cellulose tris(3,5-dimethylphenylcarabamate) immobilized onto silica gel, is investigated for the direct enantioselective separation of a set of racemic N-alkylated barbiturates and analogs of thalidomide alkylated in position 3 of the piperidin-2,6-dione ring using different nonstandard solvents such as dichloromethane (DCM), ethyl acetate, THF, methyl tert-butyl ether as an eluent and diluent, respectively, in HPLC. The separation, resolution, and elution order of the investigated compounds were compared on both immobilized and coated cellulose tris(3,5-dimethylphenylcarbamate) CSPs (Chiralpak IB and Chiralcel OD, respectively) using a mixture of n-hexane/2-propanol (90:10 v/v) as mobile phase with different flow-rates and fixed UV detection at 254 nm. The effect of the immobilization of the cellulose tris-(3,5-dimethylphenylcarbamate) CSP on silica (Chiralpak IB) on the chiral recognition ability was noted as the coated phase (Chiralcel OD) possesses a higher resolving power in some cases than the immobilized one (Chiralpak IB). However, a few racemates, which were not or poorly resolved on the immobilized Chiralpak IB or the coated Chiralcel OD when using standard solvents were most efficiently resolved on the immobilized Chiralpak IB upon using nonstandard solvents. Furthermore, the immobilized phase withstands the nonstandard (prohibited) HPLC solvents mentioned previously when used as eluents or as a dissolving agent for the analyte itself. An example of inversion or apparent inversion of elution order on Chiralpak IB is reported. The direct analysis of a spiked plasma sample extracted using DCM on Chiralpak IB is also shown. 相似文献
69.
70.
Liquid crystals (LCs) are soft materials that combine the fluidity of disordered liquids and the long-range orientational or positional order of crystalline solids, along one or two directions of space. A search for better stationary phases, including highly selective ones, is an important trend in chromatography development. Among the stationary phases under investigation are LC stationary phases that have been recently generated much interest. A variety of isomeric molecules were separated with high accuracy. Successfully, X-ray scattering is widely used to investigate and characterise the microscopic structure of most LCs. In this paper, a new liquid crystalline material that can be used potentially as stationary phase in gas chromatography was synthesised and characterised by means of nuclear magnetic resonance (NMR), infrared (IR) spectra, elemental analysis and X-ray diffraction. 相似文献