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201.
202.
Mohamed MM 《Journal of colloid and interface science》2003,265(1):106-114
Two series of dealuminated Na-mordenite zeolites (DML and DMH) were impregnated, in comparison with the parent nondealuminated NaMSP, in aqueous nitrate solutions of Cu and Ni to achieve varying loadings for both of the cations. These samples were characterized by N(2) adsorption, XRD, DSC of ammonia desorption, ammonia volumetric sorption, IR of ammonia adsorption, and FTIR-photoacoustic (FTIR-PAS) techniques. The FTIR-PAS spectrum of CuNi-loaded NaMSP shows a band at 935 cm(-1) ascribed to O(3)Siz.sbnd;Oz.sbnd;SiO(3) linkages produced as a result of dealumination caused by the synergistic effect of Cu and Ni cations under the preparation conditions. As a confirmation, this band was intensified upon acid dealumination (DML) where, at the extent of dealumination (DMH), collapsing of the zeolite structure was obtained subsequent to cation modification. In addition, the dealumination effect was markedly enhanced upon increasing the load of Cu in proportion to Ni. A total erosion of OH group characteristics of Siz.sbnd;(OH)z.sbnd;Al at 3610 cm(-1) was depicted when the Ni content exceed that of Cu where it did not show any change when the Cu content surpasses that of Ni. The amount of adsorbed ammonia measured volumetrically was enlarged after dealumination as well as after increasing the contents of the modificating cations. The IR study of ammonia adsorption revealed a band at 1428 cm(-1), in either nondealuminated or dealuminated-modified samples, assigned to stronger Bronsted acid sites than those at 1455 cm(-1). The band at 1428 cm(-1) was markedly enhanced in the latter samples than in the former. This was due in part to the replacement of the protons by cations, producing sufficiently mobile protons. In conformity, DeltaH values obtained for DSC effects via ammonia desorption were enhanced after dealumination. Other correlations with XRD and surface texturing on one hand and the structural variations following cations incorporation on the other hand are evaluated and discussed. 相似文献
203.
A procedure was developed and validated for measuring chlorpheniramine maleate and tincture ipecac (as emetine hydrochloride) by reversed-phase liquid chromatography with methanol-10 mM sodium heptanesulfonate (20 + 30) as the mobile phase; the pH was adjusted to 4 with acetic acid, and the flow rate was at 1.5 mL/min, with ultraviolet detection at 254 nm. Propyl paraben was used as the internal standard. The standard curves were linear (r = 0.998 and 0.9998) for both chlorpheniramine maleate and emetine hydrochloride over the ranges of 5-100 and 0.1-40 microg/mL, respectively. The mean recoveries +/- standard deviation were 101.37 +/- 2.77% for chlorpheniramine maleate and 98.8 +/- 1.47% for emetine hydrochloride. The proposed method was applied to the determination of chlorpheniramine maleate alone in tablet and syrup dosage forms. The method also was applied to the determination of the emetine content of ipecac liquid extract and tincture ipecac; the results were compared with those of the method of the British Pharmacopoeia. The proposed method was applied successfully to the simultaneous determination of chlorpheniramine maleate and tincture ipecac, as emetine hydrochloride, in syrup dosage form. Both drugs and the internal standard were separated from all interfering components in < 5 min. The proposed method is simple, specific, and economical, when compared with other published methods that determine each component alone. 相似文献
204.
Mohamed Amari Mokhtar Fodili Bellara Nedjar‐Kolli Algrie Pascal Hoffmann Jacques Pri 《Journal of heterocyclic chemistry》2002,39(4):811-816
Reaction of pyrone 1a or tetronic acid 1b with o‐phenylenediamine derivatives gave enaminone compounds 2 . When reacting with different electrophiles, these intermediates allowed versatile access to different heterocyclic structures: when DMA derivatives or triphosgene was used, cyclization occurred through nitrogen, leading to benzimidazoles 3 and benzimidazolones 4 , respectively, while reaction with benzaldehyde yielded benzodiazepines 5 . 相似文献
205.
The purpose of this paper is to study the existence, the uniqueness and the limit in , as of solutions of general initial-boundary-value problems of the form and in a bounded domain with dynamical boundary conditions of the form
Received: 5 December 2000 / Revised version: 20 November 2001 / Published online: 4 April 2002 相似文献
206.
207.
This paper recommends some procedures for the selection of step sizes in the context of subgradient optimization. The first of these procedures is developed in detail in this study and is a theoretically convergent scheme. This method has two phases, the first phase is designed to accelerate the solution procedure towards an optimal solution, while the second phase helps to close in on an optimal solution. A second technique recommended is a simple-minded scheme which, although not theoretically convergent, seems to be computationally very efficient. These two methods are shown to compare favorably with Held, Wolfe and Crowder's scheme for prescribing step sizes. We also suggest some modifications of the latter scheme to make it computationally more efficient. 相似文献
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210.
Microdifferential thermal analysis (μ-DTA), X-ray diffraction (XRD) and infrared (IR) spectroscopy were used for the first time to investigate the liquidus and solidus relations in the KPO3–Y(PO3)3 system. The only compound observed within the system was KY(PO3)4 melting incongruently at 1033 K. An eutectic appears at 13.5 mol% Y(PO3)3 at 935 K, the peritectic occurs at 1033 K and the phase transition for potassium polyphosphate KPO3 was observed at 725 K. Three monoclinic allotropic phases of the single crystals were obtained. KY(PO3)4 polyphosphate has the P21 space group with lattice parameters: a=7.183(4) Å, b=8.351(6) Å, c=7.983(3) Å, β=91.75(3)° and Z=2 is isostructural with KNd(PO3)4. The second allotropic form of KY(PO3)4 belongs to the P21/n space group with lattice parameters: a=10.835(3) Å, b=9.003(2) Å, c=10.314(1) Å, β=106.09(7)° and Z=4 and is isostructural with TlNd(PO3)4. The IR absorption spectra of the two forms show a chain polyphosphates structure. The last modification of KYP4O12 crystallizes in the C2/c space group with lattice parameters: a=7.825(3) Å, b=12.537(4) Å, c=10.584(2) Å, β=110.22(7)° and Z=4 is isostructural with RbNdP4O12 and contains cyclic anions. The methods of chemical preparations, the determination of crystallographic data and IR spectra for these compounds are reported. 相似文献