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171.
ZHENG Hong WANG Shaoqing & CHENG Huiming Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang China 《中国科学B辑(英文版)》2004,47(3):222-227
Hydrogen is a kind of clean, sustainable and renewable energy carrier. Of the problems to be solved for the utilization of hydrogen energy, how to store and transport hydrogen has been given high priority on the research agenda. Recently, carbon nanotubes (CNTs) were reported to be very promising candidates for hydrogen uptake[1], which may have possibility to satisfy the benchmark set by the US Department of Energy (DOE) Hydrogen Plan for fuel cell powered vehicles: a gravimetric density … 相似文献
172.
Cadmium colloids have been prepared by Chemical Liquid Deposition (CLD). The metal is evaporated to yield atoms which are solvated at liquid nitrogen temperature, and upon warming, stable liquid colloids are formed with particle size ranging between 25–100 Å. Zeta potentials were calculated according to the conversion of Hunter and the Hückel equation, for ethanol and dimethyl sulphoxide. UV/VIS measurement of most of the black colloids showed absorption band around 280 nm. For comparison, we prepared CdS colloid with size 400–625 Å. The colloids are stable to oxidation in air and/or oxygen bubbling. The synthesis of colloids and films from Cd with acetone, 2-butanone, ethanol, 2-propanol, 2-methoxyethanol, DMF and DMSO is reported. Transmission Electron Microscopy (TEM) allows us to determine particle size. 相似文献
173.
174.
An overview is given on recent advances of density functional theory (DFT) as applied to the calculation of nuclear magnetic
resonance (NMR) chemical shifts and electron spin resonance (ESR) g-tensors. This is a new research area that has seen tremendous progress and success recently; we try to present some of these
developments. DFT accounts for correlation effects efficiently. Therefore, it is the only first-principle method that can
handle NMR calculations on large systems like transition-metal complexes. Relativistic effects become important for heavier
element compounds; here we show how they can be accounted for. The ESR g-tensor is related conceptually to the NMR shielding, and results of g-tensor calculations are presented. DFT has been very successful in its application to magnetic properties, for metal complexes
in particular. However, there are still certain shortcomings and limitations, e.g., in the exchange-correlation functional,
that are discussed as well.
Received: 24 October 1997 / Accepted: 19 December 1997 相似文献
175.
A novel method using liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry in the
negative selected ion monitoring mode has been developed and validated for rapid simultaneous determination of triptolide
and tripdiolide in the extract of Tripterygium wilfordii Hook. f. The molecular ions m/z [M–H]− 359 and 375 were selected for the quantification in selected ion monitoring mode for triptolide and tripdiolide. Standard
calibration curve was linear over the concentration range of 0.12–24 and 0.15–30 μg mL−1 for triptolide and tripdiolide. The relative standard deviations of intra- and inter-day were in the range of 4.7–9.9 and
8.9–12.6%. The average recoveries were between 96.4 and 104.6%. The limits of quantitation were 2.0 × 10−3 and 2.5 × 10−3 μg mL−1 for triptolide and tripdiolide. 相似文献
176.
I. V. Korol’kov A. I. Gubanov K. V. Yusenko I. A. Baidina S. A. Gromilov 《Journal of Structural Chemistry》2007,48(3):486-493
Several non-equilibrium solid solutions belonging to the platinum-osmium systems Os0.9Pt0.1, Os0.8Pt0.2, Os0.5Pt0.5, Os0.7Pt0.3, Os0.75Pt0.25 are prepared and studied. The thermal decomposition of [Pt(NH3)4][OsCl6] in the hydrogen and helium atmosphere is investigated. It is found that the Pt0.5Os0.5 solid solution develops through the formation of (NH4)2[OsCl6] and a metallic phase based on Pt. The crystal structure of a double complex salt [Pt(NH3)4][OsCl6] is studied (X8-APEX Bruker, 1508 independent reflections, R = 2.04%). Crystal data for PtOsN4Cl6H12 are: a = 11.6216(5) Å, b = 11.0016(5) Å, c = 10.3819(5) Å, V = 1327.4(1) Å3, space group Cmca, Z = 4, d x = 3.333 g/cm3. The coordination polyhedron around Os is octahedral: 〈Os-Cl〉 2.357 Å, ∠Cl-Os-Cl 89.5–90.5°, while around Pt it is square-planar: Pt-N 2.046 Å, ∠ N-Pt-N 89.59° and 90.41°. 相似文献
177.
Published data on methods for the synthesis of indole derivatives (isogramines) containing a dimethylamino group at positions 1, 2 and also at various positions of the benzene ring in the indole bicycle and their chemical properties are reviewed.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 483–504, April, 2005. 相似文献
178.
A.?Ya.?NeimanEmail author N.?N.?Pestereva A.?R.?Sharafutdinov Yu.?P.?Kostikov 《Russian Journal of Electrochemistry》2005,41(6):598-611
The conduction and transport numbers of charge carriers for composites in the systems MeWO4-WO3 (Me = Ca, Sr, Ba) are studied as a function of the temperature and the activity of oxygen in a gas phase. The transport numbers are determined by an emf method and are estimated from dependences of conductance on the activity of oxygen in a gas phase. The deficiencies of the given procedure as applied to investigation of properties of composite phases are analyzed. The materials under study are classified with a class of metacomposites. The concentration intervals of the ionic, mixed, and electronic conductions are determined. The conduction of composites of compositions (100 − x)MeWO4 ⋅ xWO3 is predominantly ionic at x ≤ 10 (Me = Ca), x ≤ 60 (Me = Sr), and x ≤ 45 (Me = Ba). The obtained data are explained in the framework of a model that represents a composite as a distributed matrix system where a film of surface phase MeW-s with a high mobility of oxygen ions plays the role of a connected matrix. It is presumed that the surface phase MeW-s possesses double-sided surface activity (α MeW-s ≤
) and a higher mobility with respect to MeWO4 and WO3. The discovered anomalies of dependences
(T) and partial dependences
, σel(T) are explained by a change in the stoichiometry, morphology, and the degree of connectedness of surface phase MeW-s caused by with a change in the temperature and composition of composites.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 680–693.Original Russian Text Copyright © 2005 by Neiman, Pestereva, Sharafutdinov, Kostikov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004). 相似文献
179.
Balandina A Kalinin A Mamedov V Figadère B Latypov S 《Magnetic resonance in chemistry : MRC》2005,43(10):816-828
(1)H, (13)C and (15)N NMR chemical shifts for a variety of novel quinoxalines were determined by different 2D methods and were calculated using the GIAO DFT approach. Comparison with experimental data shows good correlations in the case of (1)H, (13)C and (15)N chemical shifts. Different combinations of basis sets were tested. In non-polar solvents quinoxalines exist as dimers owing to strong hydrogen bonding. Calculations for dimers improve the correlation between experiment and theory. Additive empirical methods for estimating chemical shifts have drawbacks and have to be used with a great care for this type of compound. 相似文献
180.
Viana FA Pouliquen YB Andrade-Neto M Santiago GM Pessoa OD Rodrigues-Filho E Braz-Filho R 《Magnetic resonance in chemistry : MRC》2004,42(8):695-699
A detailed NMR study and full assignments of the 1H and 13C spectral data for two novel triterpenoid saponins isolated from the stem bark of Pentaclethra macroloba (Willd.) Kuntze are described. Their structures were established using a combination of 1D and 2D NMR techniques including 1H,1H-COSY, TOCSY, NOESY, gs-HMQC and gs-HMBC, and also electrospray ionization mass spectrometry and chemical methods. The structures were established as 3beta-O-([O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)]-[O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->4)])-alpha-L-arabinopyranosylhederagenin (1) and 3beta-O-)[O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)]-[O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->4)])-alpha-L-arabinopyranosyloleanolic acid (2). 相似文献