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991.
Previously, thiols have been determined indirectly by cathodic stripping voltammetry (CSV) after accumulation as their mercury and copper(I) salts. Following a previous report of the first use of the catalytic nickel peak (for the determination of cysteine), this paper reports the first use of the catalytic cobalt peak in CSV (for the determination of 2-mercaptobenzothiazole (MBT)): only a very ill-defined catalytic cobalt peak had been observed previously with cysteine, and was unreported. MBT is accumulated at pH 4 (Britton-Robinson buffer) as its cobalt(II) complex at -0.1 V, and is then determined indirectly by observing the reduction of the cobalt(II) in the complex at -0.95 V, i.e., with a much lowered overpotential: hydrated cobalt(II) is reduced at -1.2 V. The peak is catalytic because the thiol released on reduction of the complex complexes further cobalt ions and causes their reduction. The detection limit for the determination of MBT was calculated to be 2.5 x 10(-9) M (3sigma) using an accumulation time of 1 min. The sensitivity is about three times that obtained with the corresponding catalytic nickel peak. 相似文献
992.
Lauricella R Allouch A Roubaud V Bouteiller JC Tuccio B 《Organic & biomolecular chemistry》2004,2(9):1304-1309
A new kinetic approach to the evaluation of rate constants for the spin trapping of superoxide/hydroperoxyl radical by nitrones in buffered media is described. This method is based on a competition between the superoxide trapping by the nitrone and the spontaneous dismutation of this radical in aqueous media. EPR spectra are recorded as a function of time at various nitrone concentrations, and kinetic curves are obtained after treatment of these spectra using both singular value decomposition and pseudo-inverse deconvolution methods. Modelling these curves permits the determination of the rate constants k(T) and k(D) for the superoxide trapping and the adduct decay reactions, respectively. Kinetics parameters thus obtained with six nitrones, namely the 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (EMPO), the 5-diethoxyphosphoryl-5-methyl-3,4-dihydro-5H-pyrrole N-oxide (DEPMPO), the 5,5-dimethyl-3,4-dihydro-5H-pyrrole N-oxide (DMPO), the 1,3,5-tri[(N-(1-diethylphosphono)-1-methylethyl)-N-oxy-aldimine]benzene (TN), the N-benzylidene-1-ethoxycarbonyl-1-methylethylamine N-oxide (EPPN), and the N-[(1-oxidopyridin-1-ium-4-yl)methylidene]-1-ethoxycarbonyl-1-methylethylamine N-oxide (EPPyON), indicate that cyclic nitrones trapped superoxide faster than the linear ones. However, the low k(T) values obtained for compounds show that there is still a need for new molecules with better spin trapping capacities. 相似文献
993.
994.
995.
Ardeshir Khazaei Mahsa Tavasoli Ahmad Reza Moosavi-Zare 《Research on Chemical Intermediates》2018,44(10):5893-5910
996.
Sk. Safique Ahmad 《Linear and Multilinear Algebra》2013,61(9):1244-1266
We discuss the perturbation analysis for eigenvalues and eigenvectors of structured homogeneous matrix polynomials with Hermitian, skew-Hermitian, H-even and H-odd structure. We construct minimal structured perturbations (structured backward errors) such that an approximate eigenvalue and eigenvector pair (finite or infinite eigenvalues) is an exact eigenvalue eigenvector pair of an appropriately perturbed structured matrix polynomial. We present various comparisons with unstructured backward errors and previous backward errors constructed for the non-homogeneous case and show that our results generalize previous results. 相似文献
997.
Sze-Mun Lam Jin-Chung Sin Ahmad Zuhairi Abdullah Abdul Rahman Mohamed 《Chemical Papers》2013,67(10):1277-1284
Ag2O/ZnO heterostructure has been recently synthesized using a facile chemical-precipitation method. X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy results confirmed the Ag2O nanoparticles loading on ZnO nanorods. The Ag2O addition increased the visible light absorption ability and a red shift for Ag2O/ZnO heterostructure appeared when compared to pure ZnO. Photoluminescence spectra showed lower emission yield on the Ag2O/ZnO heterostructure than on pure ZnO. Such a decrease in the emission yield represents the fraction of the excited state Ag2O sensitizer involved in the charge injection process. Under compact fluorescent lamp irradiation, the Ag2O/ZnO heterostructure demonstrated higher photocatalytic activity than pure ZnO in the degradation of resorcinol, which can be attributed to the high separation efficiency of the photogenerated electron-hole pairs based on the cooperative roles of Ag2O loading on ZnO nanarods. All these characteristics represent a significant contribution of the Ag2O/ZnO heterostructure to the practical applications in indoor environmental remediation. 相似文献
998.
Muhammad Rafiq Muhammad Khalid Muhammad Nawaz Tahir Muhammad Umair Ahmad Muhammad Usman Khan Muhammad Moazzam Naseer Ataualpa Albert Carmo Braga Shabbir Muhammad Zahid Shafiq 《应用有机金属化学》2019,33(11)
Present study advocates the joint experimental and computational studies of two potent benzoimidazole‐based hydrazones with chemical formula C23H18F2N4O ( 5a ) and C25H22FN5O3 ( 5b ). Both 5a and 5b were synthesized and resolved into their crystal structures using SC‐XRD for the assessment of bond lengths, bond angles, unit cells and space groups. The structures of 5a and 5b were chemically characterized using infrared (FT‐IR), UV–Visible, nuclear magnetic resonance (1H‐NMR and 13C‐NMR), EIMS and elemental analysis. DFT at M06‐2X/6‐31G(d,p) level of theory was performed to get optimized structures and countercheck the experimental findings. Overall, DFT findings show excellent concurrence with the experimental data which confirms the purity of both compounds. FMO, NBO analysis, MEP surfaces and nonlinear optical (NLO) properties were explored at same level of theory. UV–Vis analysis at TDDFT/M06‐2X/6‐31G(d,p) level of theory showed that 5b is red shifted with λmax 331.69 nm as compared to 5a with λmax 240.25 nm. Global reactivity parameters were estimated using energy of FMOs indicated the greater harness value than the softness values of 5a and 5b . NBO analysis confirmed that the presence of non‐covalent interactions, hydrogen bonding and hyper conjugative interactions are pivotal cause for the existence of 5a and 5b in the solid‐state. NLO results of 5a and 5b were observed better than standard molecule recommended the NLO activity of said molecules for optoelectronic applications. 相似文献
999.
Johann Pierrel Ahmad Ibrahim Cline Croutx‐Barghorn Gildas L'Hostis Xavier Allonas 《Journal of polymer science. Part A, Polymer chemistry》2019,57(13):1440-1447
The effect of a two‐step free‐radical photopolymerization of an acrylate resin on the polymer properties in the presence of glass fibers is studied. It is found that a first irradiation leading to a partial conversion is effective for the fabrication of a preimpregnated glass‐fiber composite, which can be further processed and fully polymerized through a second irradiation. DMA analysis evidences the formation of a first relatively soft polymer embedding unreacted double bonds during the preirradiation. Further process allows the completion of the photopolymerization together with a reinforcement of the polymer network. This obviously affects the final mechanical properties of the photocomposite. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1440–1447 相似文献
1000.
Zaheer Khan Shaeel Ahmed Al-Thabaiti F.M. Al-Nowaiser Abdullah Yousif Obaid Abdulrahman O. Al-Youbi Maqsood Ahmad Malik 《Arabian Journal of Chemistry》2012,5(4):453-459
In this paper we report the effect of poly(vinyl alcohol) (PVA) on the silver nanoparticles formation of different morphologies by using silver nitrate and citric acid as the oxidant and reductant, respectively, for the first time. Our transmission electron microscopy (TEM) results suggest that the presence of PVA has significant impact on the size, shape, and the size distribution of the silver nanoparticles. The reaction follows a zero-order kinetics in [citric acid] as well as in [silver(I)] in the absence and presence of PVA. It was found that PVA and cetyltrimethylammonium bromide (CTAB) concentrations show no significant effects on the rate of CTAB-stabilized silver nanoparticles formation, whereas in presence of PVA, the reaction rate increases with (CTAB). Both spectrophotometric and TEM measurement demonstrated that the orange silver sol consists of aggregates, whereas the purple sol does not contain the aggregated arrangement. On the basis of various observations, the most plausible mechanism has been envisaged. 相似文献