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排序方式: 共有88条查询结果,搜索用时 937 毫秒
31.
N. Abidi A. Sivade D. Bourret A. Larbot B. Boutevin F. Guida-Pietrasanta A. Ratsimihety 《Journal of membrane science》2006,270(1-2):101-107
The potential of hybrid organic–inorganic membranes for separating organic molecules from air, based on solubility selective mechanism, was evaluated. Alumina and titana membranes with average pore size near 4 nm were surface modified using trimethoxysilane fluorinated coupling reagent. The permeabilities to helium, nitrogen, methane, ethane, propane, butane and carbon dioxide were evaluated at feed pressures lying between (1.5 × 105 and 3.5 × 105 Pa) 1.5 and 3.5 bar and permeate outlet near 1 × 105 Pa (1 bar). The permeabilities of the grafted membranes generally decreased by about two to three orders of magnitude compared with the untreated membranes. The CO2/N2 permselectivity increased significantly in the case of the TiO2 grafted membrane. The membranes performances were compared and the TiO2 grafted membrane exhibits higher permselectivity and permeability, so that, it is a good candidate for CO2 to N2 separation and CO2 to hydrocarbon separation. 相似文献
32.
S. L. Abidi 《Journal of heterocyclic chemistry》1987,24(3):845-852
Optical resolution of selected rotenoids containing 1-3 asymmetric centers in dihydrobenzopyranofuroben-zopyranone and dihydrobisbenzopyranopyranone series has been achieved on two chiral high-performance liquid chromatographic (hplc) stationary phases. In most cases, the absolute stereochemistry at the cis-B/C ring junction of the rotenoidal antipodes can be related to their elution order. Generally, the 6aα,12aα-enantiomers were more strongly retained by the chiral substrate than their corresponding optical antipodes. The elution-configuration relationship provides potential utility for predicting the absolute configuration of related rotenoidal compounds. Chiral phase hplc on amino-acid-bonded-silica yielded results explicable in terms of Pirkle's bonding schemes for chiral recognition. Resolution data for 12a-hydroxy-, 12a-methoxy-, and 12-hydroxyiminorotenoids further corroborate the mechanistic rationale, and demonstrate that nonpolar π-π interactions appeared to be important for enantiomeric separation on helic poly-triphenylmethylacryl-ate-silica (CPOT). In the latter system, steric effects and conformational factors in association with the modification of E-ring structures might play significant roles in the chiral separation process in view of the reversal to the elution order observed for all methoxylated rotenoids and elliptone derivatives including the parent deguelin. The unique separability (α = 1.44) of 12a-hydroxyelliptone on CPOT was suggestive of structural effects of the 5′-side chain on the resolution of the rotenoids having a five-membered-E-ring. The results obtained with two different types of chiral phases are complementary and useful for optical resolution of a wide variety of natural and synthetic rotenoidal compounds. 相似文献
33.
Chromatographic analysis of tocol-derived lipid antioxidants 总被引:7,自引:0,他引:7
Abidi SL 《Journal of chromatography. A》2000,881(1-2):197-216
This paper provides a comprehensive overview of existing chromatographic methods for the analysis of tocol-derived lipid antioxidants in various sample matrices. After a brief introductory discussion on biological and nutritional aspects of the vitamin E active compounds, the review focuses on various techniques for the isolation, purification, chromatographic separation, and detection of tocopherols and tocotrienols. Compiled published normal-phase (NP) and reversed-phase (RP) high-performance liquid chromatographic (HPLC) methods demonstrate general trends and analytical variability and versatility of HPLC methodology. The relative merits of the two HPLC methods are assessed. NP and RP elution characteristics are delineated to aid in the identification of antioxidant components. Technical novelty of certain analytical procedures for non-food samples warrants their inclusion in this review in light of the potential applicability in food assays. 相似文献
34.
Both the consequences of 1,3-cyclization of calix[4]arenes by diamide formation, and the effect of 2- and 2,4-alkoxycarbonylmethylation of two 1,3-bridged calix[4]azacrowns on their metal ion-binding capacities have been studied by synthesis of the derivatives in their cone conformation and measurement of the stability constants for their complexation in a range of alkaline earth and transition metal cations. In these two cases, the conformation of the ligand in the solid state has been defined in detail by a crystal structure determination. In the first case, a tubular architecture performing methanol channels is displayed, however, in the second case a zigzag architecture generated by a chloroform network connecting calixarene molecules is present. Speciation in solution appears to be limited to the formation of 1:2 and/or 1:1 and/or 2:1 (M-L) complexes, depending on the system, with values of the stability constants determined by absorption spectroscopy in acetonitrile, lying in the ranges log β12 ca. 10, log β11 ca. 2-5, and log β21 ca. 7-9. There is evidence for selectivity toward Cu(II) and for some unexpected anion effects. None of these ligands appear to be an efficient extractant for the metals as their picrate. 相似文献
35.
Faycal Abidi Mekki Ayadi Khaled Omrani 《Journal of Applied Mathematics and Computing》2008,27(1-2):293-305
A finite difference scheme is derived for the initial-boundary problem for the nonlinear equation system $$\frac{\partial u}{\partial t}=A\frac{\partial^{2}u}{\partial x^{2}}+f(u),$$ where A is a complex diagonal matrix, f is a complex vector function. The stability and convergence in discrete L ∞-norm of proposed Crank-Nicolson type finite difference schemes is proved. No restrictions on the ratio of time and space grid steps are assumed. Some numerical experiments have been conducted in order to validate the theoretical results. 相似文献
36.
Inside Back Cover: Piling Up Pillar[5]arenes To Self‐Assemble Nanotubes (Chem. Eur. J. 18/2016) 下载免费PDF全文
37.
38.
Thermal decomposition of cellulose has been widely studied for the past several years. It has been reported that the source of cellulose and its composition greatly affect its pyrolysis. One of the most widely used analytical tools for the study of cellulose pyrolysis is thermogravimetric (TG) analysis. Several model-fitting methods have been employed to study cellulose pyrolysis kinetics. An alternative to the model-fitting approach is the so-called model-free method developed by Vyazovkin. This isoconversional technique calculates the activation energy as a function of the degree of the conversion. In this article, the pyrolysis of cellulose in cotton fibers compared to microcrystalline cellulose (Avicel, PH 105) was investigated. TG curves were acquired as a function of the heating rates (4, 5, 8, 10, and 16 °C min?1) and the model-free method was used to analyze the data. Activation energies of cotton fibers and Avicel were obtained, and compared to the data reported in the literature. In addition, models for isothermal decomposition were calculated and compared with experimental data at the same temperature. 相似文献
39.
Tlili Kadri Noomen Khiari Faycal Abidi Khaled Omrani 《Numerical Methods for Partial Differential Equations》2008,24(6):1501-1516
L∞‐error estimates for finite element for Galerkin solutions for the Benjamin‐Bona‐Mahony‐Burgers (BBMB) equation are considered. A priori bound and the semidiscrete Galerkin scheme are studied using appropriate projections. For fully discrete Galerkin schemes, we consider the backward Euler method and analyze the corresponding error estimates. For a second order accuracy in time, we propose a three‐level backward method. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008 相似文献
40.
Lassaad Baklouti Najah Cheriaa Mouna Mahouachi Rym Abidi Jong Seung Kim Yang Kim Jacques Vicens 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(1-2):1-7
This timely review focuses on the synthesis of dendrimers from calix[4]arenes and thiacalix[4]arenes. Some interesting features
of these calix-dendrimers are given. 相似文献