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排序方式: 共有187条查询结果,搜索用时 312 毫秒
171.
Mercury (II) ion-selective PVC membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate (EBPCA) as a novel nitrogen containing sensing material is successfully developed. The sensor exhibits good linear response of 30 mV per decade within the concentration range 10(-6)-10(-3) mol l(-1) Hg(II). The sensor shows good selectivity for mercury (II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The EBPCA-based sensor is suitable for use with aqueous solutions of pH 2.0-4.5 and exhibits minimal interference by Ag(I) and Fe(III), which are known to interfere with other previously suggested sensors. The nature and composition of the sensing material and its mercury complex are examined using Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques. The proposed sensor is applied as a sensor for the determination of Hg(II) content in some amalgam alloys. The results show good correlation with data obtained by atomic absorption spectrometric method. 相似文献
172.
Ibrahim El-Sayed El-Kholy Morcos Michael Mishrikey Mohamed Gaber Marei 《Journal of heterocyclic chemistry》1982,19(6):1421-1424
Thermal cyclization of 1,5-diarylpent-1-yne-3,5-diones led to the formation of 2-benzyliden-5-aryl-3(2H) furanones as well as 2,6-diaryl-4H-pyran-4-ones as minor products. The structure of the furanones was established from their ir, 1H nmr and mass spectral data. Their reaction with hydrazine hydrate gave pyrazole derivatives. 相似文献
173.
Mohamed Gaber Marei Morcos Michael Mishrikey Ibrahim El-Sayed El-Kholy 《Journal of heterocyclic chemistry》1986,23(6):1849-1852
3-Iodo-4H-pyran-4-ones have been synthesised in excellent yield by the reaction of acetylenic β-diketones with iodine monochloride and were converted into the corresponding 4H-pyran-4-thiones. The iodopyrones and thiopyrones gave with methylamine the respective N-methylpyridones and thiopyridones. The structure of the above compounds was confirmed from their spectral characteristics. 相似文献
174.
Gaber M. Abu El-Reash Magdy M. Bekheit Kamal M. Ibrahim 《Transition Metal Chemistry》1990,15(5):357-360
Summary The synthesis and characterization of CrII, MnII, FeII, CoII, NiII, PdII, CuII, ZnII, CdII and UO
2
2+
complexes of 1-meotinoyl-4-phenyl-3-thiosemicarbazide (H2NTS) are reported. I.r. spectral data show that the ligand behaves in a bidentate and/or tetradentate manner. An octahedral structure is proposed for the CrII, FeII and NiII complexes; a tetrahedral structure for the MnII, CoII and Cu(NTS)·2H2O complexes; and a square planar structure for the PdII and Cu(HNTS)Cl·H2O complexes. The i.r. data suggest that the FeII complex contains a hydroxo bridge. 相似文献
175.
The kinetics of oxidation of N,N-dimethyl- and N,N,N,N-tetramethyl-p-phenylenediamines, to the corresponding semiquinonediimine radical and the quinonediimine, with a macrocyclic copper(II)-complex were studied at pH7. Under pseudo-first order conditions, the reaction rate for the N,N,N,N-tetramethyl derivative was much faster than for N,N-dimethyl-p-phenylenediamine, due to the increased probability of electron transfer. The reaction rate decreases with increasing acidity of the medium as a result of protonation of the amine nitrogen atoms. The rate constants and activation parameters were evaluated and the reaction was found to be enthalpy controlled. Furthermore, kinetic measurements revealed a remarkable superadditive effect when CuCl2 solution was added, even at concentrations lower than that of the copper complex. This observation was used for the kinetic determination of copper ions at concentrations <10–5M. 相似文献
176.
Adsorptive cathodic stripping voltammetry was used for the determination of furazolidone (FZ) and furaltadone (FD) in borax
and phosphate buffers, respectively, using HMDE as working electrode. The influence of different factors upon the peak current
response such as accumulation potential, scan rate, preconcentration time, pH and other variables was studied.
Furazolidone and furaltadone showed an adsorption character on HMDE in presence of borax and phosphate buffers, respectively.
A single cathodic peak at −0.36 V in borax (pH = 9.5) was observed for FZ, while FD gave a cathodic peak at −0.32 V in phosphate
buffer (pH = 8.5).
The calibration graph showed a linear behavior over the range 3×10−9–9×10−8 mol dm−3 for furazolidone. In the case of FD, concentrations from 3×10−9 to 2×10−7 mol dm−3 gave a linear relationship with the peak current. A detection limit of 2×10−9 mol dm−3 and 1×10−9 mol dm−3 was obtained for furazolidone and furaltadone, respectively. This method was applied to determine these drugs in pharmaceutical
formulations, urine and serum samples.
Received December 15, 1998. Revision February 4, 2000. 相似文献
177.
We propose, implement, and test experimentally long Josephson 0-pi junctions fabricated using conventional Nb-AlOx-Nb technology. We show that by using a pair of current injectors one can create an arbitrary discontinuity of the Josephson phase and, in particular, a pi discontinuity, just as in d-wave/s-wave or in d-wave/d-wave junctions, and study fractional Josephson vortices which spontaneously appear. Moreover, using such junctions, we can investigate the dynamics of the fractional vortices-a domain which is not yet available for natural 0-pi junctions due to their inherently high damping. We observe half-integer zero-field steps which appear on the current-voltage characteristics due to the hopping of semifluxons. 相似文献
178.
Ahmed M. Donia Asaiid A. Amer Rafaat M. Issa Mohamed Gaber 《Transition Metal Chemistry》1990,15(6):465-467
Summary The thermal stabilities of the [(di--oxo)Mn2] cores of bi- and tetranuclear MnIV complexes have been studied. The stabilities are discussed in terms of structural and conformational factors. The energies of activation (Ea) of the decomposition reactions were determined. The nature of interaction of the solvent of crystallization is also discussed. 相似文献
179.
T. Gaber K. Buckenmaier D. Koelle R. Kleiner E. Goldobin 《Applied Physics A: Materials Science & Processing》2007,88(3):587-592
Photon-induced band bending changes and subsequent relaxation at the buried insulator/semiconductor interface of BaF2/Si(001) have been investigated. This is achieved by creating free charge carriers through absorption of a visible pump laser
pulse (λ=532 nm, E=2.33 eV) in the silicon, followed by time resolved photoelectron spectroscopy using vacuum-ultraviolet
synchrotron radiation (E=18 eV) as a probe of the BaF2 valence band (VB). Since the excitation takes place in the semiconductor and the probe photoemission signal originates from
the BaF2, the relaxation at the interface has been probed.
PACS 41.60.Ap; 33.60.Cv; 79.60.Jv; 73.40.Qv 相似文献
180.
Ukmar T Godec A Planinšek O Kaučič V Mali G Gaberšček M 《Physical chemistry chemical physics : PCCP》2011,13(35):16046-16054
Compounds embedded into mesoporous or even microporous matrices are interesting for many emerging applications, such as novel catalysts, sensors, batteries, hydrogen storage materials or modern drug delivery devices. We report on two unexpected phenomena regarding the structural and dynamic properties of a model drug substance (indomethacin) when confined in mesoscopic matrices. Firstly, we show that the confinement directs the crystallization of the drug into a stable polymorph that is not otherwise formed at all; its relative amount depends on the pore size. This phenomenon is also explained theoretically using a modified classical heterogeneous nucleation theory. Secondly, we demonstrate that--even at relatively low volume fractions--the confined drug forms a condensed phase in a way that obstructs the passage of the pore channels. This may have far-reaching consequences for understanding the mechanisms of drug release from porous matrices. 相似文献