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31.
Synthesis, Constitution and Properties of Cage-like Vinyl- and Allylsilylated Silicic Acids By silyation of tetramethylammonium silicate [N(CH3)4]8Si8O20 · 69 H2O with vinyldimethylchlorosilane ( I ) and divinyltetramethyldisiloxane, respectively, or allyldimethylchlorosilane there were synthesized the crystalline silicic esters [CH2?CH(CH3)2Si]8Si8O20 and[CH2?CH? CH2(CH3)2Si]8Si8O20. By means of gas chromatography, mass spectrometry, 1H and 29Si NMR the two compounds were identified to be cage-like double four-ring(D4R)-silicic esters containing eight vinyldimethylsilyl- or allyldimethylsilyl groups, Silylation with a mixture of I and trimethylchlorosilane yields in dependence on the ratio of silanes vinyldimethylsilyltrimethylsilyl D4R silicic esters with average numbers of unsaturated groups < 8. 相似文献
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Reaction of the Cage-like Silicic Acid Derivative [(CH3)2HSi]8Si8O20 with Unsaturated Organic Compounds By 29Si, 1H, and 13C NMR investigations were shown that the eight HSi?groups of the double four-ring silicic acid derivative [(CH3)2HSi]8Si8O20 react with the following unsaturated compounds: vinylcyclohexene, allyl glycidyl ether, methyl methacrylate, octadecene-1, and styrene. The resulting oily products are soluble in organic solvents. The compounds were characterized by the chemical shifts of the 29Si, 1H, and 13C NMR signals. Their formulae are [C6H9(CH2)2Si(CH3)2]8Si8O20, [CH3OOCCH(CH3)CH2Si(CH3)2]8Si8O20, [CH3(CH2)17Si(CH3)2]8Si8O20 and [C6H5(CH2)2Si(CH3)2]8Si8O20, and [C6H5CH(CH3)Si(CH3)2]8 Si8O20, respectively. Mainly the addition reactions do not follow the Markovnikov rule. 相似文献
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Tiago de Oliveira F Bominaar EL Hirst J Fee JA Münck E 《Journal of the American Chemical Society》2004,126(17):5338-5339
[2Fe-2S] clusters found in the xanthine oxidase family of proteins exhibit an S = 1/2 EPR feature, called signal II, for which one g-value is significantly above g = 2.0. The g-values of signal II cannot be explained with the standard spin coupling model that has been so successful in describing the g = 1.94 signals of [2Fe-2S] ferredoxins. We have studied the EPR spectra of the Rieske protein from Thermus thermophilus at pH 14 and observed a signal II-type EPR spectrum, with g-values at 1.81, 1.94, and 2.14. It is shown that the g-values of signal II can be explained by including an antisymmetric exchange term, d.S1xS2, in the spin Hamiltonian. The presence of this term is sensed by EPR if the isotropic exchange coupling constant J is sufficiently small. For the Rieske protein we determined J = 43 cm-1 which is at least 4 times smaller than the J values reported for [2Fe-2S] clusters that yield standard g = 1.94 signals. 相似文献
35.
Püschl A Boesen T Zuccarello G Dahl O Pitsch S Nielsen PE 《The Journal of organic chemistry》2001,66(3):707-712
To preorganize PNA for duplex formation, a new cyclic pyrrolidinone PNA analogue has been designed. In this analogue the aminoethylglycine backbone and the methylenecarbonyl linker are connected, introducing two chiral centers compared to PNA. The four stereoisomers of the adenine analogue were synthesized, and the hybridization properties of PNA decamers containing one analogue were measured against complementary DNA, RNA, and PNA strands. The (3S,5R) isomer was shown to have the highest affinity toward RNA, and to recognize RNA and PNA better than DNA. The (3S,5R) isomer was used to prepare a fully modified decamer which bound to rU10 with only a small decrease in Tm (delta Tm/mod = 1 degree C) relative to aminoethylglycine PNA. 相似文献
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H. Fleck R. Warington W. A. Peake und Otto Pitsch 《Fresenius' Journal of Analytical Chemistry》1881,20(1):580-581
Ohne Zusammenfassung 相似文献
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Temperature‐Modulated Water Filtration Using Microgel‐Functionalized Hollow‐Fiber Membranes 下载免费PDF全文
Daniel Menne Fee Pitsch Dr. John E. Wong Prof. Andrij Pich Prof. Matthias Wessling 《Angewandte Chemie (International ed. in English)》2014,53(22):5706-5710
In the present work, we investigate the potential of aqueous polymer microgels in membrane technology, especially for filtration applications. The poly(N‐vinylcaprolactam)‐based microgels exhibit thermoresponsive behavior and were employed to coat hollow‐fiber membranes used for micro‐ and ultrafiltration. We discuss the preparation of microgel‐modified membranes (by “inside‐out” as well as “outside‐in” filtration in dead‐end mode). The clean‐water permeability and stability of these membranes was studied not only as a function of time, but also of temperature. The microgel‐modified membranes exhibit a reversible thermoresponsive behavior whereby both the resistance and the retention increased with decreasing temperature. 相似文献
40.
Prediction of local extinction and re-ignition effects in non-premixed turbulent combustion using a flamelet/progress variable approach 总被引:1,自引:0,他引:1
The flamelet/progress variable approach (FPVA) has been proposed by Pierce and Moin as a model for turbulent non-premixed combustion in large-eddy simulation. The filtered chemical source term in this model appears in unclosed form, and is modeled by a presumed probability density function (PDF) for the joint PDF of the mixture fraction Z and a flamelet parameter λ. While the marginal PDF of Z can be reasonably approximated by a beta distribution, a model for the conditional PDF of the flamelet parameter needs to be developed. Further, the ability of FPVA to predict extinction and re-ignition has also not been assessed. In this paper, we address these aspects of the model using the DNS database of Sripakagorn et al. It is first shown that the steady flamelet assumption in the context of FPVA leads to good predictions even for high levels of local extinction. Three different models for the conditional PDF of the flamelet parameter are tested in an a priori sense. Results obtained using a delta function to model the conditional PDF of λ lead to an overprediction of the mean temperature, even with only moderate extinction levels. It is shown that if the conditional PDF of λ is modeled by a beta distribution conditioned on Z, then FPVA can predict extinction and re-ignition effects, and good agreement between the model and DNS data for the mean temperature is observed. 相似文献