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331.
Trukhan NN Panchenko AA Roduner E Mel'gunov MS Kholdeeva OA Mrowiec-Białoń J Jarzebski AB 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10545-10554
The surface acidity of different mesoporous titanium-silicates, such as well-organized hexagonally packed Ti-MMM, Ti-MMM-2, Ti-SBA-15, and amorphous TiO(2)-SiO(2) mixed oxides (aerogels and xerogels), was studied by means of FTIR spectroscopy of CO adsorbed at 80 K and CD(3)CN adsorbed at 293 K. The surface hydroxyl groups of mesoporous titanium-silicates with 2-7 wt % Ti revealed a Br?nsted acidity slightly higher to that of pure silicate. TiO(2)-SiO(2) xerogels revealed the highest Br?nsted acidity among the titanium-silicates studied. CO adsorption revealed two additional sites on the surface in comparison to pure silicate, characterized by nu(CO) from 2185 (high pressure) to 2178 (low pressure) cm(-1) and from 2174 (high pressure) to 2170 (low pressure) cm(-1). These bands are due to CO adsorbed on isolated titanium cations in the silica surrounding or having one Ti(4+) cation in their second coordination sphere and due to CO interactions with Ti-OH groups, respectively. CD(3)CN adsorption similarly revealed the existence of two additional sites, which were not detected for pure silicate: at 2289 cm(-1) due to CD(3)CN interaction with titanol groups and from 2306 (low pressure) to 2300 (high pressure) cm(-1) due to acetonitrile interaction with isolated framework titanium cations with probably one Ti(4+) cation in their second coordination shell. The spectroscopic results are compared with computational data obtained on cluster models of titanium-silicate with different titanium content. According to the IR data, the Ti accessibility on the surfaces for mesoporous titanium-silicates with similar Ti loading (2 wt %) was found to fall in the order TiO(2)-SiO(2) aerogel approximately TiO(2)-SiO(2) xerogel > Ti-MMM approximately Ti-MMM-2 > Ti-SBA-15. This order (except TiO(2)-SiO(2) xerogel) correlates with the catalytic activity found previously for titanium-silicates in 2,3,6-trimethylphenol oxidation with H(2)O(2). 相似文献
332.
Gary M. Coppola Emil W. Fu Michael J. Shapiro Goetz E. Hartdmann 《Journal of heterocyclic chemistry》1983,20(5):1427-1429
The reaction of N-methylisatoic anhydride with 1-cyanoacetylpiperidine in the presence of sodium hydride produces a tautomeric mixture of 4a and 4b , with 4b predominating. When heated in xylene, 4 is converted to the piperidine adduct 5 whereas heating in dimethylsulfoxide furnishes 3 . Spectral data for 4 and 5 are also discussed. 相似文献
333.
Emil Makovicky 《Journal of solid state chemistry》1983,49(1):85-92
Phase transformations and thermal expansion of Cu3BiS3 were studied up to 300°C using heated Weissenberg and Guinier cameras. At 118.5°C a transformation takes place from the P212121 to a modulated Pn21a or Pnma polymorph. The modulation changes continuously, with decreasing intensities of X-ray satellites, from ~3.14c at 118.5°C toward ~2c at 190°C. At 191°C an unmodulated, high Pnma polymorph is formed. The lattice parameters are a = 7.705, b = 10.400, and c = 6.720 Å at room temperature. They expand only slightly in the low form; a and c contract in the intermediate form, and c contracts further in the high form. The unit cell volume remains nearly constant between 25 and 300°C. The observed phenomena result from redistributions of copper atoms over available structural sites and, at above ~135°C, from the conversion of these atoms from a stationary to a mobile state. 相似文献
334.
Emil D. Krumov Dimitar G. Popov Nikolay S. Starbov 《Central European Journal of Chemistry》2005,3(4):668-673
Thick aluminum oxide films are prepared on Al plates by anodizing. On the ceramic surface thus obtained a very thin Ag film
is deposited via vacuum thermal evaporation. The Ag/Al2O3/Al samples prepared are irradiated by Nd:YAG laser through a suitable metal mask in order to remove the top metal film in
the exposed areas. Thus, a negative silver image of the copied mask is obtained. Further, the samples are processed in Ni
electroless chemical bath activated by the rest of silver. All processing steps are studied by scanning electron microscopy
(SEM). EDS X-ray mapping is applied to study the final distribution of Al and Ni in the processed areas. In addition, the
DC conductivity of the fabricated Ni wires obtained is measured. The proposed new method for selective chemical deposition
of electroconductive Ni onto laser microstructured Ag/Al2O3/Al samples is simple, versatile and not restricted to the metal/ceramic system studied as well as to the electroless deposited
metal. 相似文献
335.
Hernandez EA Posada B Irizarry R Castro ME 《The journal of physical chemistry. B》2005,109(15):7251-7257
We present evidence, based on scanning and transmission electron microscopy measurements, for the formation of nanofibers from silver-thiol materials treated with water. Mercapto acetic acid, a thiol with a carboxylic acid group at one end, was employed for the experiments presented here. Nanoparticles, with diameters as large as 1 nm, fill the nanofibers and are responsible for absorption bands between 2 and 5.5 eV in UV-visible absorption spectroscopy measurements. The nanofibers disappear at pH values larger than the first pK(a) of the acid, while rods are observed for pH values between 3.6 and 7. This result is interpreted in the context of hydrogen bonding interactions playing an important role in driving the one-dimensional growth of the fibers, a proposal that is supported by the vibrational frequency of the carbonyl stretching mode in surface reflection Fourier transform infrared measurements on dry deposits of aqueous dispersions of the thiol-silver material. 相似文献
336.
Emil Cherbuliez Br. Baehler O. Espejo H. Jindra B. Willhalm J. Rabinowitz 《Helvetica chimica acta》1967,50(1):331-346
3-Aminopropanol reacts with aryl(or aralkyl or alkyl)isothiocyanates R? N?C?S to yield the corresponding thio-ureas R? NH? CS? NH? (CH2)3OH which, refluxed with hydrochloric acid, are cyclized by elimination of water. The cyclization products are identical with the hydrothiazines resulting by elimination of sulfate or phosphate from the sulfuric or phosphoric monoesters of these thio-ureas. The resulting hydrothiazines are either 2-(R-imino)-tetrahydro-m-thiazines (I) or 2-(R-amino)-dihydro-Δ2-m-thiazines (II). Their structure has been established by comparison of their spectra with those of model compounds in one of which the C?N double bond is certainly endocyclic (2-methyl-dihydro-Δ2-m-thiazine), the other presenting an exocyclic C?N double bond (3-methyl-2-phenylimino-tetrahydro-m-thiazine). When R is an aryl group, the C?N double bond is exocyclic (structure I with >C?N? Ar), and one may presume that this structure is stabilized by resonance. When R is an aralkyl or an alkyl group, the C?N double bond is endocyclic (structure II). The nmr spectra were taken with three types of solvent: CDCl3 or CCl4; (CD3)2SO; CF3COOH. In CF3COOH solution the benzylic protons of the hydrothiazine with R = pF? C6H4CH2? couple with NH (J=5,5cps) which confirms the endocyclic position of the C?N double bond in this case. 相似文献
337.
Reductive elimination of alkane from a silylated bis-indenyl zirconium isobutyl hydride affords a zirconium sandwich complex with an unusual eta6 indenyl ligand. Crystallographic characterization of its adduct with tetrahydrofuran has been achieved and reveals significant localization in the six-membered ring. Complexation of more potent ligands such as carbon monoxide and diphenylacetylene are effective in promoting haptotropic rearrangement of the eta6 indenyl ligand and provides familiar bent zirconocene derivatives. The zirconium sandwich compound also undergoes oxidative addition of carbon-hydrogen bonds of pyridyl ligands, resulting in a crystallographically characterized dimethylamino pyridyl hydride complex of zirconium. 相似文献
338.
Emil B. Milosavljević Ljiljana Solujić John H. Nelson James L. Hendrix 《Mikrochimica acta》1985,87(5-6):353-360
Summary
Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System
A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml–1 and 0.67% for Cr(III) (0.10,g ml–1) and the corresponding limits of detection were 85 ng ml–1, and 16 ng ml–1, respectively.On leave from University of Belgrade. 相似文献
339.
Subhadeep Kal Emil Stoyanov Thomas L. Groy Ulrich Hussermann 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):i96-i98
Single crystals of strontium undecazinc, SrZn11, were obtained when decomposing SrZn2 under conditions of high pressure and high temperature. The new binary Sr–Zn compound crystallizes in the space group I41/amd (BaCd11 structure type) with one Sr position (m2) and three Zn sites (m2, .2/m., 1). The structure is described in terms of all‐face‐capped Zn8 tetrahedra as the central building unit, defined by the Zn atoms on .2/m. and 1. The building units are condensed into chains by the central tetrahedra sharing edges, and the chains are interconnected by shared capping atoms. The resulting three‐dimensional framework of Zn atoms yields channels that are occupied by Sr and Zn atoms on the high‐symmetry m2 positions. 相似文献
340.
Gerhard Englert Klaus Noack Emil A. Broger Ernst Glinz Max Vecchi Reinhard Zell 《Helvetica chimica acta》1991,74(5):969-982
Developmental efforts to improve the yield of the chemical synthesis of (3R,3′R)-zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by 1H-NMR, UV/VIS, and CD spectrosocpy of eleven (Z/E)-isomers of zeaxanthin: (7Z)-, (9Z), (13Z)-, (15Z)-, (7Z,7′Z)-, (9Z,9′Z)- (7Z,9Z,7Z)-, (7Z,11Z,7′Z)-, (9Z,13Z,9′Z)-, (7Z,9Z,7′Z,9′Z)-, and (7Z,9Z,11Z,7′Z,9′Z)-zeaxanthin. Five of these isomers were obtained by specific synthesis, namely the (7Z)-, (7Z,7′Z)-, (9Z,9′Z)-, (7Z,9Z,7′Z)-, and (7Z,9Z,7′Z-9Z)-isomers. 相似文献