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排序方式: 共有2314条查询结果,搜索用时 31 毫秒
961.
Mohammed Ibrahim Walash Mohie Khalid Sharaf‐El‐Din Mohammed El‐Sayed Metwally Mostafa Reda Shabana 《中国化学会会志》2004,51(3):523-530
Two spectrophotometric methods were developed for the determination of ranitidine. The first method was a kinetic spectrophotometric method based on the catalytic effect of ranitidine on the reaction between sodium azide and iodine in an aqueous solution. The calibration graph was linear from 4–24 μg/mL. The drug was determined by measuring the decrease in the absorbance of iodine at 348 nm using a fixed time method. The decrease in the absorbance after 1 minute from the initiation of the reaction was related to the concentration of drug. The detection limit of the procedure was 0.76 μg/mL. The proposed procedure was successfully utilized in the determination of the drug in pharmaceutical preparations with mean recovery in the range of 99.83 ? 101.16%. The second method is a colorimetric method, which depends on the measurement of absorbances of tris (o‐phenanthroline) iron(II) [method 2A] and tris (bipyridyl) iron(II) [method 2B] complexes at 512 nm. The complexes obeyed Beer's law over the concentration range of 2–16 μg/mL and 4–40 μg/mL for methods 2A and 2B, respectively. The developed method has been successfully applied for the determination of ranitidine in bulk drugs and pharmaceutical formulations. The common excipients and additives did not interfere in its determination. 相似文献
962.
The morphology and thermal properties of liquid natural rubber (LNR)-compatibilized 60/40 NR/LLDPE blends 总被引:1,自引:0,他引:1
The effects of LNR as a compatibilizer in binary blends of 60/40 NR/LLDPE have been investigated by means of differential scanning calorimetry, dynamic mechanical analysis and scanning electron microscopy. Special emphasis was given to the role of LNR in inducing interactions between NR and LLDPE. It has been observed that increasing LNR content decreases Tm and ΔHf which are indicators of the crystalline part of the blends. The decrease reflects a reduction in the degree of crystallinity which is due to the interference in the form of NR dissolution into the LLDPE phase. The phenomenon leads to a shift in Tg of the amorphous part of LLDPE to higher temperatures as observed by DMA thermograms. The dissolution effect creates better interactions between the phases leading to improvements in the compatibility of the blends. Further confirmation was obtained through SEM examination. 相似文献
963.
Gibson SE Ibrahim H Pasquier C Peplow MA Rushton JM Steed JW Sur S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(1):269-276
Metal isocyanides have been used and studied by organometallic chemists for many years and, as a result, they have a rich and interesting chemistry. The nature of metal-free isocyanides and the methods of making isocyanide complexes, however, has resulted in the vast majority of studies to date being performed with structurally simple isocyanides. We report here a new approach to the synthesis of isocyanide ligands that involves the reaction of a metal carbonyl ligand with the anion of a phosphoramidate. As phosphoramidates can be synthesised in one step from amines, our method means that the structural diversity of readily available amines, particularly chiral amines, can now be incorporated into isocyanide ligands. 相似文献
964.
Johann Mulzer Peter De Lasalle Alexander Chucholowski Ursula Blaschek Gisela Brüntrup Ibrahim Jibril Gottfried Huttner 《Tetrahedron》1984,40(12):2211-2218
New stereoselective syntheses are reported for racemic 4-epi-blastmycinone (6) and δ-multistriatine (13) utilizing the anti-configurated γ, β-unsaturated β-hydroxy-carboxylic acids 2a/b. A diastereo- and enantioselective aldoltype addition of phenylacetic acid dianion to benzaldehyde has been achieved by employing optically active alkoxide amide bases. Finally, highly stereocontrolled additions to the novel β-lactone substituted ester enolates 22 are described. 相似文献
965.
Anwar Usman Ibrahim Abdul Razak Suchada Chantrapromma Hoong‐Kun Fun A. Sreekanth S. Sivakumar M. R. Prathapachandra Kurup 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):m461-m463
One half of the molecule of the title complex, [Mn(C14H13N4S)2], is related to the other half by a twofold axis passing through the Mn atom. This high‐spin Mn atom is six‐coordinated, in an octahedral geometry, by the azomethine N, the pyridyl N and the thiolate S atom of two planar 1‐(pyridin‐2‐yl)ethanone N(4)‐phenylthiosemicarbazone ligands. In the crystal, the molecules are interconnected by N—H?S and C—H?N interactions, forming a three‐dimensional network. 相似文献
966.
For the first time sequential injection analysis (SIA) technique has been employed for titrimetry. A new SI titrimetric spectrophotometric method for the assay of vitamin C in drug formulations was explored. The method is based on the oxidation reaction of vitamin C with cerium(IV) in sulfuric acid media using a spectrophotometer as a detector with the wavelength monitored at 410 nm. A 2(3) factorial design chemometric approach was employed to study the interaction effect of the chemical and system variables, mainly cerium(IV), sulfuric acid concentrations and the flow rate. The results of the chemometric optimization revealed that the optimum operating conditions for the SI titrimetric analysis of vitamin C were 7.0 x 10(-3) M cerium(IV), 0.455 M sulfuric acid and 28.9 microL s-1 flow rate. A linear calibration plot for the determination of vitamin C was obtained in the concentration range between 30 to 200 ppm. The method was applied to the determination of vitamin C in pharmaceutical preparations and no excipient was found to pose any interference, thus rendering the method suitable for the determination of the drug in pharmaceutical preparations. The SIA method is found to be accurate when the results were statistically compared with the results obtained by the BP standard method. The SIA method is superior when compared to the conventional titration method, the BP standard method and previous methods with respect to precision and automation in solution handling. 相似文献
967.
Nadia Sobhy Ibrahim Fathy Mohamed Abdelrazek Suzan Ibrahim Aziz Mohamed Hilmy Elnagdi 《Monatshefte für Chemie / Chemical Monthly》1985,116(4):551-556
The reaction of trichloroacetonitrile with active methylene reagents such as acetylacetone, benzoylacetone, cyanoacetamide and cyanoacethydrazide is reported. A new simple route for the synthesis of polysubstituted phenols, pyrazoles and pyrroles is also described.
Nitrile bei organischen Synthesen: Die Reaktion von Trichloracetonitril mit aktiven Methylen-Reagentien
Zusammenfassung Es wird über die Reaktionen von Trichloracetonitril mit aktiven Methylen-Reagentien wie Acetylaceton, Benzoylaceton, Cyanacetamid und Cyanacethydrazid berichtet. Ein neuer einfacher Weg für die Synthese polysubstituierter Phenole, Pyrazole und Pyrrole wird beschrieben.相似文献
968.
Anwar Usman Ibrahim Abdul Razak Hoong‐Kun Fun Suchada Chantrapromma Yan Zhang Jian‐Hua Xu 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):o477-o479
In the title compounds, C24H17NO3, (I), and C43H27NO5, (II), the dioxine ring is not planar and tends toward a boat conformation. The oxazoline ring adopts a twisted conformation in molecule (I) but is essentially planar in molecule (II). The configuration of the dioxine–oxazoline system is determined by the sp3 state of the two shared atoms. The phenanthrene moiety is nearly coplanar with the dioxine ring, while the phenyl ring is perpendicular to the attached oxazole ring. The triclinic unit cell of (II) contains two crystallographically independent molecules related by a pseudo‐inversion centre. 相似文献
969.
Ibrahim H. Mutlu Maharram Z. Zarbaliyev Ferhat Aslan 《Journal of Sol-Gel Science and Technology》2007,43(2):223-226
Preparation and characterization of In–Se compound thin films prepared by sol–gel methods on glass substrate have been studied.
X-ray diffraction analyses and optical transmission spectrum of In–Se compound thin film samples show that the fabricated
sol–gel In–Se thin films features formed mainly as an In2Se3 crystal structure. From transmission spectra of In–Se thin films band gap energy were estimated approximately as ∼1.24 eV. 相似文献
970.
S. S. E. H. Elnashaie G. Ibrahim S. S. Elshishini 《Applied biochemistry and biotechnology》1984,9(5-6):455-474
The present investigation concentrates on the study of the complex phenomenon of multiplicity in membranes carrying substrate-inhibited,
hydrogen ion-sensitive enzyme. The investigation takes into consideration both symmetrical and asymmetrical steady states.
The number of steady states (symmetrical and asymmetrical) found in this case is quite large, giving rise to multiple hysteresis
loops and multiple “isolas.” 相似文献