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191.
192.
Eduard Bernhardt David J. Brauer Martin Köckerling Prof. Dr. Gottfried Pawelke Dr. 《无机化学与普通化学杂志》2007,633(7):947-954
Trimethylamine‐tris(pentafluoroethyl)borane [(C2F5)3BNMe3] ( 1 ) reacts at 190 °C with water under displacement of the trimethylamine ligand to yield the hydroxy‐tris(pentafluoroethyl)borate [(C2F5)3BOH]? ( 2 ). In tributylamine 1 reacts with alkynes HC≡CR to form novel ethynyl‐tris(pentafluoroethyl)borate anions [(C2F5)3BC≡CR]? – R = C6H5 ( 3 ), C6H4CH3 ( 4 ), Si(CH(CH3)2)3 ( 5 ) – in moderate yields. Compound 3 adds water across the triple bond to form the novel anion [(C2F5)3BCH2(CO)C6H5]? ( 6 ). The structures of [(C2F5)3BNMe3], [NMe4][(C2F5)3BOH] and K[(C2F5)3BCH2(CO)C6H5] have been determined by x‐ray crystallography. 相似文献
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Bernd Mayer Giancarlo Marconi Christian Klein Gottfried Köhler Peter Wolschann 《Journal of inclusion phenomena and macrocyclic chemistry》1997,29(1):79-93
Complexation trajectories and the variation ofinduced circular dichroism are calculated for thedocking of phenol and 2,4,6-trimethyl-phenol with-cyclodextrin. The results are compared toexperimental chirality data to elucidate themechanism of nonspecific molecular recognitionprocesses in aqueous solution. Large geometricalchanges along nearly isoenergetic Dynamic Monte Carlotrajectories show the conformational flexibility ofsuch host–guest systems. This proves diffuseintermolecular interactions, van der Waals orelectrostatic in nature, as the main contributions to thebinding energy. The number and position of the methylsubstituents of the guest reduces the complexityof the conformational space as the guests positionbecomes fixed by steric constraints.The solvation free energy is calculated from thesolvent accessible surface area weighted byrespective atomic solvation parameters. Consideringthe solvation term in the dynamic simulationsrestricts the conformational flexibility of themacromolecular system. The relative importance ofvarious contributions to the solvation energy isdiscussed and it is shown that those terms arisingfrom the interaction of hydrophobic groups with theaqueous environment are essential for thedetermination of the complex structure. Consideringthese terms in the dynamic simulation model, the signand strength of the calculated rotatory strength isin perfect agreement with induced circular dichroismobtained from experimentally determined averagedspectra. The results demonstrate the accuracy of thegeometrical properties of host–guest systems obtainedfrom these simulations. 相似文献
196.
Structural optimization of an asymmetric automotive brake disc with cooling channels to avoid squeal
Brake squeal is still a major issue in the automotive industry due to comfort complaints of passengers and resulting high warranty costs. Many measures to avoid squeal have been discussed in the engineering community reaching from purely passive measures like the increase of damping, e.g. by the application of shims, to the active or semiactive suppression of squeal. While active measures can be effective but are elaborate and therefore more expensive, passive measure are less complex in most cases. This leads to the necessity to develop passive, economic and robust measures to avoid squeal. Asymmetry of the brake rotor has been proposed to achieve this goal and the resulting split of all double eigenfrequencies of the brake rotor has lately been shown to stabilize the system. 相似文献
197.
Gottfried Spelsberg-Korspeter 《Journal of sound and vibration》2012,331(19):4259-4268
Brake squeal is still a challenge for design engineers and scientists. Due to cost reasons for the avoidance of brake noise only passive measures are meaningful for a broad industrial range. Many countermeasures against squeal are based on the introduction of damping, for example by using shims. In the literature on the modeling of brake squeal, the structural properties of the brake disc are most often not considered. It has however been shown analytically and experimentally that the stiffness properties of the disc are important and that splitting of double modes of the disc has a stabilizing effect. This knowledge can be used for structural optimization of brake rotors. The goal of this paper is to exploit the potential and to discuss some mathematical difficulties. Furthermore, experimental evidence for the relation of rotor asymmetry and squeal is given. 相似文献
198.
Martin Schmid Andre Kaftan Hans-Peter Steinrück J. Michael Gottfried 《Surface science》2012,606(11-12):945-949
The electronic states of submonolayers and multilayers of cobalt(II) phthalocyanine (CoPc) adsorbed on Ag(111) were examined with photoelectron spectroscopy to obtain insight into the details of the substrate–adsorbate interaction. UV photoelectron spectroscopy (UPS) reveals the presence of two interaction-related valence states in the direct vicinity of the Fermi edge, in agreement with previous DFT calculations. X-ray photoelectron spectra indicate that the substrate–adsorbate interaction results in transfer of electron density from the substrate to the Co(II) ion. Substantial changes in the Co 2p multiplet structure, a spectral pattern induced by the open-shell character of the central Co(II) ion, indicate a complete quenching of the molecular spin. While pristine CoPc molecules are paramagnetic with S = 1/2, molecules in direct contact to the Ag(111) substrate appear to be in a diamagnetic state. 相似文献
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Dreisewerd K Kölbl S Peter-Katalinić J Berkenkamp S Pohlentz G 《Journal of the American Society for Mass Spectrometry》2006,17(2):139-150
We have recently presented a new method for direct coupling of high-performance thin-layer chromatography (HPTLC) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), illustrated by the analysis of a complex ganglioside mixture. In the current communication, an adaptation of this procedure to mixtures of native oligosaccharides from human and from elephant milk is described. The key features in this method are (1) glycerol as a liquid matrix, to provide a homogeneous wetting of the silica gel and a simple and fast MALDI preparation protocol, (2) an infrared (IR) laser for volume material ablation and particular soft desorption/ionization conditions, and (3) an orthogonal time-of-flight mass spectrometer for a high mass accuracy, independent of any irregularity of the silica gel surface. Chromatographic "mobility profiles" were determined by scanning the laser beam across the analyte bands. The current limit of detection for the MS analysis was determined to approximately 10 pmol of individual oligosaccharides spotted for chromatography. A liquid composite matrix, containing glycerol and the ultraviolet (UV-)MALDI matrix alpha-cyano-4-hydroxycinnamic acid, allows a direct HPTLC-MALDI-MS analysis with a 337 nm-UV laser as well. Compared to the IR-MALDI mode, the analytical sensitivity in UV-MALDI was found to be lower by one order of magnitude, whereas unspecific analyte ion fragmentation as well as adduct formation was found to be more extensive. 相似文献