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131.
The dc electrical conductivity of pure and doped ammonium perchlorate (AP) has been studied in two different crystal orientations, with the electric field applied perpendicularly to either (001) or (210) planes. The conductivity along the direction of the c axis was found to be lower than that normal to (210) by a factor of 5 to 10. The dc electrical conductivity of AP is decreased by Pb2+ ions but increased by SO2?4 and CrO2?4 ions. The conductivity of pure AP and of Pb2+-doped AP displays two regions with activation energies for conduction of 0.56 and 0.87 eV, respectively. The conductivity of the anion-doped crystals has a single activation energy, 0.66 eV for SO2?4 and 0.72 eV for CrO2?4. Exposure to ammonia enhances the conductivity of pure AP. A proton conduction mechanism is proposed that takes due regard of the structure of AP. The effect of the various additives on the conductivity are attributed to their influences on the formation of charge-carrying protons. 相似文献
132.
An electrochemical strategy for running nitrogen-transfer reactions on chemically inert anode surfaces has been developed. The generation and trapping of highly reactive nitrene-transfer reagents can be accomplished under mild conditions on platinum electrodes. The key factor that accounts for the high levels of chemoselectivity in this process is the phenomenon of overpotential. We have found that molecules that are similar in terms of propensity toward oxidation can be differentiated on the basis of their affinity to a given electrode surface. Thereby, reactive species can be selectively generated in the presence of acceptor molecules of interest. Specifically, a wide range of structurally dissimilar olefins can be transformed into the corresponding aziridines in the presence of N-aminophthalimide. Likewise, nitrene generation in the presence of sulfoxides leads to their chemoselective transformation into the corresponding sulfoximines. In this paper we discuss the underlying mechanistic foundation of these reactions. 相似文献
133.
The values nJ (195Pt, 14N) are shown to be measurable directly from the 195Pt spectrum for a variety of complexes containing nitrogen ligands. The sample temperature can play an important role in determining the width of the 195Pt signal. 195Pt chemical shifts for the complexes trans-[PtCl2(C2H4) (substituted pyridine)] have been measured. Methyl substitution at the 2- and 6-positions produces a relatively large downfield shift. 相似文献
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Palitha P. Wickramanayake K. W. Michael Siu Shier S. Berman 《Journal of mass spectrometry : JMS》1986,21(5):279-282
A corona discharge atmospheric pressure ionization source generates the reagent ions, OH? and O? ions in addition to better known O2? ions, when ambient air is used as the carrier. All three ions are gas-phase bases that could form negative ions from organics via proton abstraction. Ionization of simple aromatic hydrocarbons by O2? is thermodynamically not feasible. Simple aromatic hydrocarbons are ionized only by O? and/or OH? to form [M ? H]? ions. However, [M ? H]? ions do not appear in the mass spectrum as they undergo stabilization via clustering with predominantly oxygen atoms. 相似文献
136.
Crude palm oil contains 600 to 1000 ppm of tocols in the form of tocopherols and tocotrienols. These palm tocols have been isolated and analyzed in the past by various chromatographic techniques such as open column chromatography, high-performance liquid chromatography, as well as thin-layer chromatography. Supercritical fluid chromatography (SFC) has emerged as a more advanced chromatographic technique in recent years. The tocols present in palm oil are successfully isolated using SFC. Identification of these tocols is supported by various spectroscopic techniques such as 1H NMR, 13C NMR, and mass spectrometry. 相似文献
137.
Multiply charged anions of some 30 species containing multiple carboxylic, sulphonic and/or phosphoric groups generated by ionspray were studied by using tandem mass spectrometry (MS/MS). Two trends emerged: (1) lower-charged ions are preferentially evaporated, and (2) for more highly charged ions, evaporability is a function of ion size. Triply and quadruply charged ions were observed for azo dyes with molecular masses in the 700-900 Dalton range. Daughter-ion mass spectra of selected multiply charged ions are presented. 相似文献
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Hyun‐Woo Shim Ah‐Hyeon Lim Jae‐Chan Kim Gwang‐Hee Lee Prof. Dong‐Wan Kim 《化学:亚洲杂志》2013,8(11):2851-2858
A phase‐pure MnWO4‐based nanocomposite, MnWO4@MWCNTs (MWCNTs=multiwalled carbon nanotubes), was successfully synthesized through a simple hydrothermal reaction at 180 °C by adjusting the pH of the precursor medium. The resulting nanocomposite maintains the original flowerlike morphology of MnWO4 with hierarchical structures composed of numerous single‐crystalline nanorods that drive growth preferentially along the [001] direction. The growth mechanism for the flowerlike formations is also discussed. In addition, the Li electroactivity of pure MnWO4 and MnWO4@MWCNTs electrodes was investigated. As an anode for Li‐ion batteries, the MnWO4@MWCNTs nanocomposite showed enhanced electrochemical performance in reversible Li storage relative to that shown by bare MnWO4 electrodes, including a high capacity of 425 mAh g?1 and superior rate performance. This performance can be attributed to the synergistic effect of the nanocomposite combined with the MWCNTs, which provide efficient electron transport in their role as a conductor. 相似文献