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21.
The composition, overall stability constant and molar absorptivity of the chelate of gallium(III) ion with semimethylthymol blue, SMTB, were determined spectrophotometrically in acetate buffer (pH 4.5–5). A violet Ga(SMTB) chelate was formed with logarithmic overall stability constant of 18.0±0.1 (I=0.1) and molar absorptivity of 4.25×104l mol–1cm–1 (max 580 nm). SMTB is proposed as a new reagent for the spectrophotometric determination of micro-molar amounts of gallium(III). The colour development depends on time, temperature, pH and buffer species. The interference of different cations, anions and organic acids on gallium(III) determination was also investigated. Beer's law was obeyed for 3.5–31.3 gGa(III)/25ml (0.14–1.25 g ml–1). SMTB was used for the spectrophotometric determination of gallium in different grade minerals and ores and the results were of acceptable error and relative standard deviation. Comparison between the two suggested methods and atomic absorption spectrometry for Ga(III) determination was carried out. 相似文献
22.
Ibrahim Y Alsharaeh E Dias K Meot-Ner Mautner M El-Shall MS 《Journal of the American Chemical Society》2004,126(40):12766-12767
We studied the stepwise hydration and solvent-mediated deprotonation of the benzene*+ cation (Bz*+) and found several unusual features. The solvent binding energies DeltaH on-1,n for the reactions Bz*+(H2O)n-1 + H2O --> Bz*+(H2O)n are nearly constant at 9 +/- 1 kcal mol-1 for n = 1 to 8. We observed a remarkable sudden decrease in the entropy of association accompanying the formation of Bz*+(H2O)7 and Bz*+(H2O)8, indicating strong orientational restraint in the hydration shells of these clusters consistent with the formation of cagelike structures. We observed the size-dependent deprotonation of Bz*+ in a cooperative multibody process, where n H2O molecules (n >/= 4) can remove a proton from Bz*+ to form protonated water clusters. We measured, for the first time, the temperature dependence of such a process and found a negative temperature coefficient of a magnitude unprecedented in any chemical reaction, of the form k = AT-67+/- 4, or in an Arrhenius form having an activation energy of -34 +/- 1 kcal mol-1. The temperature effect may be explained by Bz*+ and four H2O molecules needing to be assembled from gas-phase components to form the reactive species. Such large temperature effects may be therefore general in solvent cluster-mediated reactions. 相似文献
23.
The methacrylate monomer, 2-[(5-methylisoxazol-3-yl)amino]-2-oxo-ethyl methacrylate (IAOEMA), was synthesized by reacting 2-chloro-N-(5-methylisoxazol)acetamide dissolved in acetonitrile with sodium methacrylate in the presence of triethylbenzylammoniumchloride (TEBAC). The free-radical-initiated copolymerization of IAOEMA, with styrene (ST) and methyl methacrylate (MMA) was carried out in dimethylsulphoxide (DMSO) solution at 65 °C using 2,2′-azobisisobutyronitrile (AIBN) as an initiator with different monomer-to-monomer ratios in the feed. The monomer (IAOEMA) and copolymers were characterized by FTIR, 1H- and 13C-NMR spectral studies. The copolymer composition was evaluated by nitrogen content in polymers led to the determination of reactivity ratios. The reactivity ratios of the monomers were determined by the application of Fineman-Ross and Kelen-Tüdös methods. The analysis of reactivity ratios revealed that ST and MMA are more reactive than IAOEMA, and copolymers formed are statisticalle in nature. The molecular weights (Mw and Mn) and polydispersity index of the polymers were determined using gel permeation chromagtography. Glass transition temperatures of the copolymers were found to increase with an increase in the mole fraction of IAOEMA in the copolymers. The apparent thermal decomposition activation energies (Ed) were calculated by Ozawa method using the SETARAM Labsys TGA thermobalance. 相似文献
24.
Gehan M. El-Subruiti Kamal H. Halawani Cecil F. Wells Ibrahim M. Sidahmed 《Transition Metal Chemistry》1993,18(3):323-328
Summary The kinetics of the solvolysis of complex ions trans-[Co(Rpy)4Cl2]+, with R = 4-t-Bu, 3-Me and 3-Et, have been investigated in mixtures formed by adding urea to water, which enhances the dielectric constant and decreases solvent structure. Differential effects of the changes in solvent structure on the initial and transition states are found to be important factors controlling changes in the rate constant with solvent composition. The variation of the enthalpy and the entropy of activation with solvent composition are contrasted with their variations found for the solvolysis of [Co(Rpy)4Cl2]+ in mixtures where solvent structure is enhanced by additions of a co-solvent to water. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the Co3+ cation in the transition state is more stable than the Co3+ cation in the initial state in the water + urea mixtures. 相似文献
25.
Aisha I. Ibrahim 《Transition Metal Chemistry》1994,19(6):561-563
Summary By the interaction of anhydrous CoBr2 or CoBr2·2THF with different sodium aryloxides, a new series of complexes of general formula Na2[Co(OAr)4]·nTHF (OAr =o-nitro,o-chloro,o-bromo,m-chloro,p-bromo, 2,4-dichloro, 2,6-dichloro, or 2,4-dimethylphenoxide;n = 1, 3, 4 or 5) were prepared and characterized by physicochemical means. The electronic spectra and magnetic measurements suggest a tetrahedral geometry for cobalt(II). Heating the complexes led to reversible loss of THF with an accompanying colour change. 相似文献
26.
Ibrahim MS 《Fresenius' Journal of Analytical Chemistry》2000,367(2):189-194
The electrochemical behavior of lumazine (LMZ), an important antibacterial agent, has been studied at the hanging mercury drop electrode (HMDE). The nature of the process taking place at the HMDE was clarified. Its adsorption behavior at HMDE has been studied by using a.c and cyclic voltammetry (CV). Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Controlled adsorptive accumulation of LMZ on the HMDE provides the basis for the direct stripping measurement of that compound in the subnanomolar concentration level. Experimental and instrumental parameters for the quantitative determination were optimized. Phase-selective a.c voltammetry provided the best signal and gave a detection limit of 0.15 microg L(-1) (9.0 x 10(-10) mol/L) LMZ in aqueous solution. Molecules or ions which may interfere were studied. 相似文献
27.
Mustafa R. Ibrahim Zacharia A. Fataftah Paul von Ragu Schleyer Peter D. Stout 《Journal of computational chemistry》1987,8(8):1131-1138
Sets of hydrogen molecule equivalents have been developed which permit the calculation of hydrogenation of different types of carbon-carbon bonds from ab initio total energies (3-21G and 6-31G* basis sets, and, to a more limited extent, for MP2/6-31G* data) of reactants and products. The calculated enthalpies of hydrogenation are in good agreement with experiment for unstrained molecules, with average errors on the order of 2 kcal/mol. The 6-31G* equivalents allow the enthalpies for strained molecules to be calculated accurately, but the 3-21G equivalents do not. The equivalents for both basis sets have been tested by calculating the enthalpies of hydrogenation of carbon-carbon bonds in nitrogen- and oxygen-containing organic molecules, free radicals, and classical carbocations. The results are in good agreement with experiment in most cases. 相似文献
28.
We report experimentally measured cross sections for pressure broadening of ammonia inversion transitions by J=0, ortho-D2 at temperatures of 18-40 K. These measurements were made in a quasiequilibrium cell using the collisional cooling technique. Cross sections for broadening of the metastable (J,K)=(1, 1), (2, 2) and (3, 3) inversion transitions ranged from 67.5 A2 for (1, 1) at 20.0 K to 100.1 A2 for (3, 3) at 25.0 K. The J=0, ortho-D2 cross sections were found to be consistently larger than previously measured cross sections for low temperature broadening of NH3 by both He and H2. 相似文献
29.
Ayoko Godwin Adefikayo Iyun Johnson Femi El-Idris Ibrahim Faskari 《Transition Metal Chemistry》1992,17(1):46-49
Transition Metal Chemistry - The kinetics of the silver(I) ion catalysed reduction of peroxodisulphate by 12-tungstocobaltate(II) anion in aqueous HC1O4 has been studied. Although the reaction in... 相似文献
30.
Mohamed M. Shoukry Ibrahim M. Kenawy Ibrahim H. El-Haj 《Transition Metal Chemistry》1991,16(6):637-640
Summary The formation and equilibria of the binary and ternary palladium(II) complexes of diethylenetriamine (dien) with other selected amines have been investigated. The results of pH titration measurements allowed the calculation of equilibrium constants, characteristic for the binary and ternary complexes formed. The concentration distribution of various complex species was evaluated and the chelation mode ascertained by conductivity measurements. 相似文献