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31.
Ulrich Schubert 《Journal of Sol-Gel Science and Technology》2003,26(1-3):47-55
Organically substituted metal alkoxides can be prepared by reaction of the parent alkoxides with complexing organic compounds. The chemical and structural consequences of such substitutions are discussed in this article. Examples are given showing how functional organic moieties, such as polymerizable groups, can be incorporated into sol-gel materials via the complexing ligands. Major structural differences between silica-based and metal-based hybrid materials originate from the different charge/coordination number ratios of silicon and most metals. This results in a high tendency for the molecular building blocks to aggregate. In many cases, metal oxide clusters are formed which are capped by the organic ligands. Such surface-modified clusters are themselves very valuable condensed matter units for materials syntheses. 相似文献
32.
Meier MA de Gans BJ van den Berg AM Schubert US 《Rapid communications in mass spectrometry : RCM》2003,17(20):2349-2353
Recently, a new multiple-layer matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) sample spotting technique for poly(ethylene glycol), offering improved analysis possibilities, was described. In this contribution the application of ink-jet printing to automated, multiple-layer MALDI-TOFMS sample preparation of synthetic polymers is presented, allowing accurate deposition of matrix, additive and analyte solutions. The new sample preparation technique was evaluated for poly(ethylene glycol) as well as poly(methyl methacrylate) standards, and optimized settings for both synthetic polymers have been obtained. 相似文献
33.
The hydrogenation of unsaturated organic substrates such as olefins and ketones is usually effected by homogeneous or heterogeneous transition-metal catalysts. On the other hand, a single case of a transition-metal-free and purely base-catalyzed hydrogenation of ketones was reported by Walling and Bollyky some 40 years ago. Unfortunately, the harsh reaction conditions (ca. 200 degrees C, >100 bar H(2), potassium tert-butoxide as base) limit the substrate spectrum of this reaction to robust, nonenolizable ketones such as benzophenone. We herein present a mechanistic study of this process as a basis for future rational improvement. The base-catalyzed hydrogenation of ketones was found to be irreversible, and it shows first-order kinetics with respect to the substrate ketone, hydrogen, and catalytic base. The rate of the reaction depends on the type of alkali ion present (Cs > Rb - K > Na > Li). Using D(2) instead of H(2) revealed a rapid base-catalyzed isotope exchange/equilibration between the gas phase and the solvent as a concomitant reaction. The degree of deuteration of the product alcohols did not indicate a significant kinetic isotope effect. It is proposed that both ketone reduction and isotope exchange proceed via similar six-membered cyclic transition states involving the H(2)(D(2))-molecule, the alkoxide base, and the ketone (solvent alcohol in the case of isotope exchange). Mechanistic analogies are pointed out which apparently exist between the base-catalyzed hydrogenation of ketones studied here and the Ru-catalyzed asymmetric ketone hydrogenation developed by Noyori. In both cases, heterolysis of the hydrogen molecule appears to be assisted by a Br?nsted-base (i.e., alkoxide), the latter being bound to the substrate ketone or the catalyst ligand, respectively, by a bridging Lewis-acidic alkali ion. 相似文献
34.
On Chalcogenolates. 159. Reaction of 1,2-Ethanedithiolates with Carbon Disulfide. 1. Synthesis and Characterization of 1,2-Ethane-bis(trithiocarbonates) The reaction of 1,2-ethanedithiolates with carbon disulfide forms the corresponding 1,2-ethane-bis(trithiocarbonates). The compounds M2[S2C? SCH2CH2S? CS2] with M = Li, Na, K, Rb, Cs, NH4, Tl have been characterized with chemical methods as well as by means of electron absorption, infrared, nuclear magnetic resonance (1H and 13C), and mass spectra. 相似文献
35.
Barbara Dogan Hans-Dieter Beckhaus Hermann Birkhofer Christoph Rüchardt 《欧洲无机化学杂志》1990,123(6):1365-1368
Effects of Substituents on the Strength of C - C Bonds, 81. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol -1, s. d. in parentheses) ΔH°c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔHv = 14.3 (± 0.3) and the heat of sublimation of 2 ΔHsub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (s) of 15.9 and 8.0 kcal mol-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group. 相似文献
36.
Reinhard Schubert Achim Ansmann Paul Bleckmann Bernhard Schrader 《Journal of Molecular Structure》1975,26(2):429-438
By using the values of the vibrational frequencies of normal and deuterated cyclopropenone (II-d0 , II-d2 ) and 16 O-and 18 O-substituted dimethylcyclopropenone (III) as -well as the infrared and Raman intensities of II a consistent set of force constants has been derived for the cyclopropenone skeleton. The derived values show that the zwitterionic form makes a substantial contribution to the electronic ground state of the molecule. The combined frequency and intensity calculation - simulation of the infrared and the Raman spectrum - is shown to be a good method for making a proper assignment of calculated and observed vibrations and deriving realistic sets of force constants. 相似文献
37.
Rudovsky J Hermann P Botta M Aime S Lukes I 《Chemical communications (Cambridge, England)》2005,(18):2390-2392
A marked increase of relaxivity has been observed upon rigidifying the internal frame of Gd-containing PAMAM dendrimers: the effect has been attained by either protonation of the dendrimer or by forming supramolecular adducts with cationic polyaminoacids. 相似文献
38.
Hermann M. Niemeyer 《Tetrahedron》1978,34(18):2757-2762
Chelates formed by carbocations and cyclic polyethers and polyamines are studied with semiempirical and ab initio MO methods. 相似文献
39.
Preparation of Acetatolead(1V) and Acetatotin(1V) Manganese Pentacarbonyls by Acidolysis of (C6H5)4?n M[Mn(CO)5]n (M ? Sn, Pb; n = 1, 2) with Acetic Acid By acidolysis of (C6H5)4?nM[Mn(CO)5]n (M ? Sn, Pb; n = 1, 2) with acetic acid no M? Mn bonds are broken, but M? C bonds. In this reaction (CH3COO)2M[Mn(CO)5]2 is formed from (C6H5)2M[Mn(CO)5]2, and (CH3COO)3SnMn(CO)5 and (CH3COO)2C6H5PbMn(CO)5 from (C6H5)3MMn-(CO)5. (CH3COO)2C6H5SnMn(CO)5 is prepared from Cl2C6H5SnMn(CO)5 and AgCH3COO. According to IR spectroscopic data the acetato ligands of the diacetato complexes are bidentate, while in (CH3COO)3SnMn(CO)5 bi- and monodentate carboxylate groups are present. For the central atoms Sn and Pb octahedral coordination is proposed. 相似文献
40.
Study of the development of thermoresistance in human pancreatic carcinoma cell lines using proteome analysis 总被引:3,自引:0,他引:3
In order to find candidate proteins that are potentially associated with the thermoresistant phenotype in combination with drug resistance, we analyzed the differential protein expression in vitro in the human pancreatic cancer cell line EPP85-181-P and classical and atypical multidrug-resistant variants and their thermoresistant counterparts using proteomics. This study identifies sets of proteins that may lead to the development of thermoresistance. These results provide a fundamental basis to elucidate the molecular mechanism of thermoresistance and chemoresistance phenomena that may assist the therapy of inoperable cancers. 相似文献