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201.
Loquet A Laage S Gardiennet C Elena B Emsley L Böckmann A Lesage A 《Journal of the American Chemical Society》2008,130(32):10625-10632
A two-dimensional proton-mediated carbon-carbon correlation experiment that relies on through-bond heteronuclear magnetization transfers is demonstrated in the context of solid-state NMR of proteins. This new experiment, dubbed J-CHHC by analogy to the previously developed dipolar CHHC techniques, is shown to provide selective and sensitive correlations in the methyl region of 2D spectra of crystalline organic compounds. The method is then demonstrated on a microcrystalline sample of the dimeric protein Crh (2 x 10.4 kDa). A total of 34 new proton-proton contacts involving side-chain methyl groups were observed in the J-CHHC spectrum, which had not been observed with the conventional experiment. The contacts were then used as additional distance restraints for the 3D structure determination of this microcrystalline protein. Upon addition of these new distance restraints, which are in large part located in the hydrophobic core of the protein, the root-mean-square deviation with respect to the X-ray structure of the backbone atom coordinates of the 10 best conformers of the new ensemble of structures is reduced from 1.8 to 1.1 A. 相似文献
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Jean‐Raphaël Caille Antoine Debuigne Robert Jrme 《Journal of polymer science. Part A, Polymer chemistry》2005,43(13):2723-2733
Styrene has been polymerized by a Quinone Transfer Radical Polymerization (QTRP) based on the redox reaction of an ortho‐quinone and a metal catalyst. Several metal acetylacetonates have been tested in this work. The radical polymerization of styrene is largely controlled when phenanthrenequinone (PhQ) is used with catalytic amounts of Co(acac)2, Ni(acac)2, Mn(acac)2 or 3, and Al(acac)3. As a rule, in the presence of all these metallic complexes, the polystyrene molar mass increases with the monomer conversion, and polydispersity (Mw/Mn) is in the 1.3–1.6 range (at least until 40% monomer conversion). Styrene polymerization has also been resumed by polystyrene chains prepared by QTRP. In the specific case of manganese acetylacetonates, an amine or phosphine ligand has to be added for the control to be effective. Finally, two mechanistic hypotheses have been proposed, depending on whether the oxidation state of the metal can be easily changed or not. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2723‐2733, 2005 相似文献
204.
Abdelkrim El-Ghayoury Laurent Douce Raymond Ziessel Rachid Seghrouchni Antoine Skoulios 《Liquid crystals》1996,21(1):143-146
5,5'-[(4-Hexadecyloxyphenyl)ethynyl]-2,2'-bipyridine was synthesized by a palladium(O) cross-coupling reaction. Its thermotropic liquid crystalline behaviour was analysed using differential scanning calorimetry, polarizing microscopy, and X-ray diffraction. Three enantiotropic tilted smectic phases were identified upon heating: SF, SI, and SC. 相似文献
205.
During high amplitudes of vibration, nonlinearities affect the electroacoustical behavior of electrodynamic transducers and are responsible for audible distortions. We distinguish two types of nonlinearities: electrical and mechanical. In this study, attention is paid to the mechanical and geometrical properties of loudspeaker-like structures. The loudspeaker is viewed as a combination of an annular plate with a circular plate. Nonlinear vibrations of such a structure are investigated, using the dynamic analog of the Von-Kármán equations. Furthermore, the influence of both material properties and geometrical parameters is studied. It is shown that nonlinear effects can be substantially reduced by choosing appropriate material and geometrical parameters. 相似文献
206.
Boris Aronov Mark de Berg Otfried Cheong Joachim Gudmundsson Herman Haverkort Michiel Smid Antoine Vigneron 《Computational Geometry》2008,40(3):207-219
Given a set S of n points in , and an integer k such that 0k<n, we show that a geometric graph with vertex set S, at most n−1+k edges, maximum degree five, and dilation O(n/(k+1)) can be computed in time O(nlogn). For any k, we also construct planar n-point sets for which any geometric graph with n−1+k edges has dilation Ω(n/(k+1)); a slightly weaker statement holds if the points of S are required to be in convex position. 相似文献
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Photolysis of germanium azides gives rise to transient germa-imines which have been quantitatively trapped by pinacol. Evidence for the formation of diphenylgermylene in the photolysis of hexaphenylcyclodigermazane is also reported. 相似文献