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11.
Wang XB Niu S Yang X Ibrahim SK Pickett CJ Ichiye T Wang LS 《Journal of the American Chemical Society》2003,125(46):14072-14081
The cubane [4Fe-4S] is the most common multinuclear metal center in nature for electron transfer and storage. Using electrospray, we produced a series of gaseous doubly charged cubane-type complexes, [Fe4S4L4]2- (L = -SC2H5, -SH, -Cl, -Br, -I) and the Se-analogues [Fe4Se4L4]2- (L = -SC2H5, -Cl), and probed their electronic structures with photoelectron spectroscopy and density functional calculations. The photoelectron spectral features are similar among all the seven species investigated, revealing a weak threshold feature due to the minority spins on the Fe centers and confirming the low-spin two-layer model for the [4Fe-4S](2+) core and its "inverted level scheme". The measured adiabatic detachment energies, which are sensitive to the terminal ligand substitution, provide the intrinsic oxidation potentials of the [Fe4S4L4]2- complexes. The calculations revealed a simple correlation between the electron donor property of the terminal thiolate as well as the bridging sulfide with the variation of the intrinsic redox potentials. Our data provide intrinsic electronic structure information of the [4Fe-4S] cluster and the molecular basis for understanding the protein and solvent effects on the redox properties of the [4Fe-4S] active sites. 相似文献
12.
Saad S. M. Hassan 《Fresenius' Journal of Analytical Chemistry》1973,266(4):272-274
Summary The solid state ion-selective chloride and bromide electrodes are used for the microdetermination of chlorine and bromine in organic compounds. After combustion in an oxygen-filled flask, potentiometric titration with silver nitrate at pH 5–7 in presence of 50% dioxan is carried out. Results accurate to ±0.3% absolute are obtained with some partially and highly halogenated compounds.
Mikrobestimmung von Chlor und Brom in einigen organischen Verbindungen mit Hilfe von ionenselektiven Elektroden
Zusammenfassung Chlorid- und bromidselektive Festkörperelektroden wurden zur Chlor- und Brombestimmung in teilweise bzw. hochhalogenierten organischen Verbindungen benutzt. Nach Verbrennung im Sauerstoffkolben erfolgt eine potentiometrische Titration mit Silbernitrat bei pH 5–7 in Gegenwart von 50% Dioxan. Die erhaltenen Ergebnisse sind auf ±0,3 % genau.相似文献
13.
14.
Ahmad Al-Alousy Saad Alshehri John Burgess Maria del Mar Graciani Maria-Luisa Moya Ernestina Muñoz Amalia Rodriguez Francisco Sanchez 《Transition Metal Chemistry》1993,18(2):179-181
Summary Dependences of rate constants on pressure (up to 1 kbar) and on added salt concentration (up to 6.0 mol dm–3 LiNO3, NaNO3, NaCl, Na2SO4 or KNO3) have been established for dissociative substitution of pentacyanoferrates(II), [Fe(CN)5L]3– with L = 4-cyanopyridine, 4,4-bipyridyl, 4-phenylpyridine and 4-t-butylpyridine. Activation volumes derived directly from pressure effects, and indirectly from salt effects via surface tension dependences and derived surfaces of activation, are reported, compared and discussed. 相似文献
15.
S. M. Al-Jobori R. K. Itawi A. Saad K. M. Shihab M. Jalil S. S. Farhan 《Journal of Radioanalytical and Nuclear Chemistry》1990,144(3):229-239
As a part of the Iraqi Food Analysis Programme /I.F.A.P./ the concentration of Na, Mg, P, Cl, K, Ca, Zn, Se, Br, Rb and I in natural milk collected from different regions of Iraq, and in milk powder samples have been determined by using the NAA technique. It was found that except for the elements I, Rb and Br the concentration of the elements was approximately identical in both the natural milks and milk powders. 相似文献
16.
Salama Tarek A. El-Ahl Abdel-Aziz S. Khalil Abdel-Galil M. Girges Margret M. Lackner Bernd Steindl Christian Elmorsy Saad S. 《Monatshefte für Chemie / Chemical Monthly》2003,134(9):1241-1252
Summary. Several new 1-aryl-, aralkyl-, and heteroaryl-5-(4-phenylbuta-1,3-dienyl)tetrazole derivatives and annulated tetrazole derivatives were efficiently and regiospecifically prepared in nearly quantitative yield via a facile one step reaction of dienones with a combination of tetrachlorosilane and sodium azide in acetonitrile under mild conditions. A complete structure assignment of three representative examples of the tetrazoles was achieved by advanced 2D NMR measurements including COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY experiments.Received March 17, 2003; accepted March 18, 2003
Published online July 28, 2003 相似文献
17.
Tarek A. Salama Abdel-Aziz S. El-Ahl Abdel-Galil M. Khalil Margret M. Girges Bernd Lackner Christian Steindl Saad S. Elmorsy 《Monatshefte für Chemie / Chemical Monthly》2003,20(5):1241-1252
Several new 1-aryl-, aralkyl-, and heteroaryl-5-(4-phenylbuta-1,3-dienyl)tetrazole derivatives and annulated tetrazole derivatives were efficiently and regiospecifically prepared in nearly quantitative yield via a facile one step reaction of dienones with a combination of tetrachlorosilane and sodium azide in acetonitrile under mild conditions. A complete structure assignment of three representative examples of the tetrazoles was achieved by advanced 2D NMR measurements including COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY experiments. 相似文献
18.
A reasonably sensitive and highly selective spectrophotometric method for the determination of mercury(II) is proposed. The method is based on the extraction of the ion-associate formed by a mercury(II) thiacrown ether cationic complex with Bromocresol Green as the anionic counter-ion using chloroform as the extracting solvent. The effect of thiacrown ethers of different cavity sizes, namely 1,4,7,10,13-pentathiacyclopentadecane (PTP) and 1,4,7,10,13,16-hexathiacyclooctadecane (HTO), the thiacrown ether concentration, the extracting solvent, the bromocresol green concentration and the aqueous phase pH on the extraction were investigated. Measurement of the absorbance at the lambda(max) (420 nm) of the extracted ion-associate reveals that Beer's law is obeyed over 0.5-12.0 ppm mercury(II) for both ligands. Slight interference from copper(II) and cadmium(II) is exhibited by the PTP ligand, while HTO is negligibly affected by these metal ions. Strong interference from silver(I) is evident for both ligands while alkali, alkaline earth and other transition metals tested posed negligible interference. Analysis of mercury in synthetic complex mixtures was satisfactory. 相似文献
19.
Osmotic and activity coefficients in the aqueous quaternary system sodium chloride-potassium chloride-calcium chloride were derived from isopiestic measurements at 25°C. The isopiestic data were treated by the various procedures of Scatchard, Friedman, and Reilly, Wood, and Robinson. The results obtained showed good agreement with those obtained by pseudo-ternary transforms. Interaction parameters obtained indicated the preponderance of pairwise interactions. Excess Gibbs free energies of mixing were calculated. 相似文献
20.
The chiroptical properties and transient rheological behavior of (acetyl)(ethyl)cellulose (AEC) m-cresol liquid crystalline solutions have been investigated. Chiroptical properties were manipulated through (i) increasing degree of acetylation of ethyl cellulose (EC), and (ii) blending AEC with EC. At the same average degree of acetylation (DA), the chiroptical properties of pure AEC were different from those of the EC/AEC mixtures. However, at the same DA, the AEC and mixed AEC/EC solutions showed similar steady state flow and oscillatory behaviors, but the transient behaviors were different. At high flow rates the mixed AEC/EC solutions exhibited double recoil after cessation of steady-state flow, whereas the AEC solutions showed double recoil only in the high DA AEC solutions. All solutions, pure and mixed, had the same stress relaxation behavior. Both pitch and handedness affected the transient behavior. After cessation of high shear rate flow, the rate of modulus evolution decreased with increasing pitch, and was faster in right-handed mesophases than in left-handed ones at a similar pitch. 相似文献