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1.
Summary The acid-catalysed decarboxylation of thecis-- andcis--[CoL(CO3)]+ complexes (L = 3,6-dimethyl-1,8-diamino-3,6-diazaoctane) have been studied over a range of HClO4 concentrations and the temperatures 25, 35 and 45° at I = 1.0 mol dm–3 (NaClO4). The rate expression takes the form kobs = k0 + k1[H+] where kobs is the observed first order rate constant at constant hydrogen ion concentration. The k0 term makes only a minor contribution to the overall reaction. Both complexes display solvent deuterium isotope effects ofca. 2.6 for the acid-catalysed decarboxylation, consistent with a rapid proton pre-equilibrium mechanism. Activation parameters have been determined and the mechanism of the reaction discussed. The magnitude of the solvent isotope effect is consistent with an A-1 type mechanism involving formation of a 5-coordinate intermediate. 相似文献
2.
M. A. Bakir T. Yaseen A. Sarheel I. Othman 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(3):607-612
The aim of this study was to investigate the relationship of selenium concentration in blood components and tumour tissues
of breast cancer patients and healthy volunteers (control), in Syria, using instrumental neutron activation analysis (INAA).
Red blood cells and serum selenium concentrations were determined in 50 healthy volunteers aged 25-70 years and 70 breast
cancer patients aged 25-84 years. Selenium levels were also measured in malignant and adjacent normal tissues from breast
cancer patients. The accuracy of the analysis was evaluated by co-analyses of international reference materials. The results
showed that selenium concentration in serum and RBC was significantly lower among breast cancer patients compared to healthy
volunteers (P<0.001). The results also showed that the selenium concentration was significantly higher in the cancer tissues compared to
adjacent normal tissues (P<0.001). We conclude that there is a good indication for selenium deviation in blood and malignant tissue of breast cancer
patients compared to that of healthy volunteers.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Kanda S. Ramasamy Farid Bakir Brenda Baker P. Dan Cook 《Journal of heterocyclic chemistry》1993,30(5):1373-1377
The synthesis of benzylated N2-(4,7,10,13-tetraazatridec-1-yl)-2′-deoxyguanosines 4 was accomplished by a key nucleophilic reaction of the novel unsymmetrical polyamine 2 , with 3′,5′-O-(tetraisopropyldisiloxane-1,3-diyl)-2-chloro-2′-deoxyinosine ( 1 ). 相似文献
4.
Alya A. Dawood Martin C. Grossel Robert M. Richardson Bakir A. Timimi Neil J. Wells 《Liquid crystals》2017,44(1):106-126
ABSTRACTOne of the current challenges in liquid crystal science is to understand the molecular factors leading to the formation of the intriguing twist-bend nematic phase (NTB) and determine its properties. During our earlier hunt for the NTB phase created on cooling directly from the isotropic phase and not the nematic phase, we had prepared 30 symmetric liquid crystal dimers. These had odd spacers and methylene links to the two mesogenic groups; desirable but clearly not essential features for the formation of the NTB. Here, we report the phases that the dimers exhibit and their transition temperatures as functions of both the lengths of the spacer and the terminal chains. In addition we describe the transitional entropies, their optical textures, the X-ray scattering patterns and the 2H NMR spectra employed in characterising the phases. All of which may lead to important properties of the twist-bend nematic phase. 相似文献
5.
Dr. Waqar Rizvi Naxhije Berisha Dr. Christopher Farley Dr. N. V. S. Dinesh K. Bhupathiraju Dr. Chrysafis Andreou Emaad Khwaja German V. Fuentes Dr. Moritz F. Kircher Dr. Ruomei Gao Dr. Charles Michael Drain 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(64):14517-14521
Distortion of nominally planar phthalocyanine macrocycles affects the excited state dynamics in that most of the excited-state energy decays through internal conversion. A click-type annulation reaction on a perfluorophthalocyanine platform appending a seven-membered ring to the β-positions on one or more of the isoindoles distorts the macrocycle and modulates solubility. The distorted derivative enables photoacoustic imaging, photothermal effects, and strong surface-enhanced resonance Raman signals. 相似文献
6.
The next-nearest-neighbour (NNN) effect in tetranuclear iron(II) complexes of thiacalixarene macrocycles using the isotropic
Heisenberg model has been investigated in order to understand its effects on the observed plateau of magnetization. Although
NNN effect is generally very weak in these kinds of systems, it was calculated that its response is quite significant to the
external perturbations in certain temperature regions. Using the isotropic Heisenberg exchange Hamiltonian, zero-field energy
spectra have been calculated for this particular tetranuclear system. The average magnetic moments with and without next-nearest-neighbour
interactions were also calculated. In order to verify the calculations, the results were compared with experimental data taken
from the literature, whence, it is suggested that observed magnetic behaviour can be improved by taking into account the NNN
effect. 相似文献
7.
Bakir Farhi 《Comptes Rendus Mathematique》2005,340(2):103-106
We present here an elementary proof of a quantitatively improved version of the Mordell's Conjecture which is now Faltings's Theorem. For the count of the ‘large points’ of (see below for the notations) we use Vojta's method which was simplified by Bombieri and then by T. de Diego, G. Rémond. To count the points of small heights of , we use a result of S. David and P. Philippon, allowing to us estimate the number of points of small height of the bigger set . To cite this article: B. Farhi, C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
8.
Reaction between Re(CO)5Cl and dpknph in PhMe under reflux gave fac-Re(CO)3(dpknph)Cl in good yield. Both dpknph and fac-Re(CO)3(dpknph)Cl exhibit rich electro-optical properties that are sensitive to their surroundings and point to the potential use of these compounds in nonlinear optics and molecular sensing. Spectroscopic and electrochemical measurements on solutions of dpknph and fac-Re(CO)3(dpknph)Cl show that the metal complex undergoes faster electron/charge-transfer than the free ligand. Solvent variations show that the rate increases in the following order: DMSO>DMF>MeCN. 相似文献
9.
Belkacem Manser Idir Belaidi Abderrachid Hamrani Sofiane Khelladi Farid Bakir 《Comptes Rendus Mecanique》2019,347(2):141-165
A wisely chosen geometry of micro textures with the favorable relative motion of lubricated surfaces in contacts can enhance tribological characteristics. In this paper, a computational investigation related to the combined influence of bearing surface texturing and journal misalignment on the performances of hydrodynamic journal bearings is reported. To this end, a numerical analysis is performed to test three texture shapes: square “SQ”, cylindrical “CY”, and triangular “TR”, and shaft misalignment variation in angle and degree. The Reynolds equation of a thin viscous film is solved using a finite differences scheme and a mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. Preliminary results are compared with benchmark data and are consistent with a positive enhancement in misaligned bearing performances (load carrying capacity and friction). The results suggest that the micro-step bearing mechanism is a key parameter, where the micro-pressure recovery action present in dimples located at the second angular part of the bearing (from 180° to 360°) can compensate for the loss on performances caused by shaft misalignment, while the micro-pressure drop effect at the full film region causes poor performances. Considering the right arrangement of textures on the contact surface, their contours geometries can have a significant impact on the performance of misaligned journal bearings, particularly at high eccentricity ratios, high misalignment degrees and when the misalignment angle α approaches to or . 相似文献
10.