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排序方式: 共有80条查询结果,搜索用时 236 毫秒
1.
A. Parlier H. Rudler N. Platzer M. Fontanille A. Soum 《Journal of organometallic chemistry》1985,287(1):c8-c12
Treatment of VO(acac)2 with the facial-tridentate organometallic ligand [η-CpCo{P(O)(OEt)2}3]? affords a new binuclear compound [η-CpCo{P(O)(OEt)2}3VO(acac)] (I). This compound undergoes protonation with HPF6 in the presence of 1,10-phenanthroline (phen), or 2,2′-bipyridyl (bipy), to yield binuclear cationic derivatives [η-CpCo{P(O)(OEt)2}3VO(phen))]+PF6? (II), and [η-CpCo{P(O)(OEth)2}3VO(bipy)]+PF6? (III). The X-ray crystal structure determination and full characterization of I has been performed. The catalytic oxygenation and oxygen transfer to 3,5-di-t-butylcatechol in the presence of I, II+, or III+ complexes is reported. 相似文献
2.
Michele Daney Henry Bouas-Laurent Bernard Calas Louis Giral Nicole Platzer 《Journal of organometallic chemistry》1980,188(3):277-291
The structure of the 9,10-dihydroanthracenyl anion and of a series of 9-alkyl-10-lithio-9-10-dihydroanthracenes (9-R-10-LiDHA, I–V where R = H, Me, Et, i-Pr, t-Bu) was studied in solution by electronic absortion spectrometry and proton magnetic resonance. Our electronic absorption results, in addition to those of other authors, show that the contact ion pairs (c.i.p.) have an absorption at λmax}- 400 nm (I–III) and 415 nm (V) whereas the loose ion pairs (l.i.p.) absorb at λmax}- 450 nm (I–V). In the NMR the chemical shift of the proton para with respect to the carbanionic center was examined as a function of solvent (THF, THF/HMPA, and in some cases ether or pure HMPA) and temperature (+20 to ?40°C). The para proton is shielded significantly with regard to the aromatic protons of the hydrocarbon (Δδ(Hpara) ca. 1–1.7 ppm). The weakest shielding was observed in ether, in agreement with the existence of c.i.p. The largest shielding (THF/HMPA or pure HMPA) is in connection with the presence of l.i.p. where the negative charge is less localised at position 10. Moreover, in the same solvent, and at the same temperature, Δδ(Hpara) was observed to increase with the substituent bulk, up to the point that there are only l.i.p. present. As found previously (namely for the fluorenyl anion) the l.i.p./c.i.p. ratio increases when temperature decreases. The results of this structural study allow to rationalize the protonation stereochemistry of 9-alkyl-10-lithio-9,10-dihydroanthracenes in the above-mentioned solvents. 相似文献
3.
G. Krausch T. Detzel H. Bielefeldt R. Fink B. Luckscheiter R. Platzer U. Wöhrmann G. Schatz 《Applied Physics A: Materials Science & Processing》1991,53(4):324-329
Growth and melting behaviour of thin indium films on Ge(100) have been investigated by Auger-electron spectroscopy (AES), atomic force microscopy (AFM) and perturbed angular correlation (PAC) spectroscopy, respectively. At room temperature inidium is found to grow in three-dimensional islands even at submonolayer coverages. A very rough film surface is observed for thicknesses up to 230 ML. The melting behaviour of such films has been studied by PAC. A reduction of the melting temperature T
m as well as a strong supercooling of the films is observed. The electric field gradient for 111In(111Cd) in the indium islands is determined as a function of temperature and is used to monitor the local crystalline order of the films up to temperatures just below the melting point. 相似文献
4.
Melanie Platzer Sandra Kiese Thomas Herfellner Ute Schweiggert-Weisz Oliver Miesbauer Peter Eisner 《Molecules (Basel, Switzerland)》2021,26(5)
Numerous assays were developed to measure the antioxidant activity, but each has limitations and the results obtained by different methods are not always comparable. Popular examples are the DPPH and ABTS assay. Our aim was to study similarities and differences of these two assay regarding the measured antioxidant potentials of 24 phenolic compounds using the same measurement and evaluation methods. This should allow conclusions to be drawn as to whether one of the assays is more suitable for measuring specific subgroups like phenolic acids, flavonols, flavanones, dihydrochalcones or flavanols. The assays showed common trends for the mean values of most of the subgroups. Some dihydrochalcones and flavanones did not react with the DPPH radical in contrast to the ABTS radical, leading to significant differences. Therefore, to determine the antioxidant potential of dihydrochalcone or flavanone-rich extracts, the ABTS assay should be preferred. We found that the results of the flavonoids in the DPPH assay were dependent on the Bors criteria, whereas the structure–activity relationship in the ABTS assay was not clear. For the phenolic acids, the results in the ABTS assay were only high for pyrogallol structures, while the DPPH assay was mainly determined by the number of OH groups. 相似文献
5.
Michaela Dobeneck Ramandeep Kaur Benedikt Platzer Prof. Dr. Dirk M. Guldi Prof. Dr. Andreas Hirsch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(32):8325-8336
A modified synthetic pathway towards perylene-perylene dimers and a facile purification method to obtain the regioisomerically pure syn- and anti-isomers are reported. In addition, a novel perylene-naphthalene heterodimer with 30 conjugated π-electron pairs was designed and synthesized on the basis of a previously described precursor and the resulting regioisomers were separated from each other. Thereby, the opto-electronic properties of the linearly elongated chromophores could be investigated regarding the differences in length of their aromatic system and the configuration of the isomers. Further tuning of their energy gaps was realized via protonation and methylation of the dibenzimidazole-bridging unit. Extraordinary red-shifts of the absorption maxima of 62 nm for the methylated and 92 nm for the protonated perylene-perylene anti-isomer could be achieved. Moreover, the maxima for the syn-isomer could be shifted bathochromically by 87 and 113 nm, respectively. 相似文献
6.
The experimental technique presented is designed to obtain detailed local heat transfer data on both stationary as well as rotating disc-cavity surfaces applicable to gas turbines. The method employed utilizes thin coatings of thermochromic liquid crystals (TLC) as surface temperature indicators under aerodynamically steady but thermally transient experimental conditions. The color display of the liquid crystals is monitored by a video camera. The video signals are captured in real time by a computer-based color recognition system to extract areal temperature and heat transfer information. Some typical results are presented and compared with-literature data to illustrate the potential of the system.
List of symbols
Symbols Unit Physical property a m2/s thermal diffusivity - B - blue color signal - G - green color signal - G - rotor/stator spacing ratio z/r o - Nu ro - Nusselt number r o/ - r m radial location - r o m disc radius - R - red color signal - Re m - mass flow Reynolds number V/2zv - Re ro - rotational Reynolds number r o 2/v - t s time - T o K initial temperature - T ref K convecting fluid temperature - T s K disc surface temperature - U - color difference signal - V - color difference signal - Y - luminance signal - z m rotor/stator spacing - - spectral weight factor - W/m2 K local heat transfer coefficient - 1/K volumetric expansion coefficient - - spectral weight factor - - scaling factor - ij - Kronecker-Delta - - scaling factor - - spectral weight factor - W/m K thermal conductivity - v m2/s fluid kinematic viscosity - kg/m3 fluid density 相似文献7.
8.
9.
We report a comparison of electric-field gradients (EFGs) measured at the group-III sites on epitaxially-grown surfaces of
2×2-reconstructed GaAs and InAs crystals. For this purpose, we used 111In→111Cd perturbed-angular-correlation (PAC) spectroscopy. Sharp spectral lines characterize the perturbation functions corresponding
to both surfaces. On GaAs surface, we observe only one well-defined nuclear electric-quadrupole interaction (NQI); and on
the InAs surface, we observe a primary and a secondary NQI. Very similar but experimentally-distinguishable values of the
EFG-parameters characterize the primary interactions corresponding to the GaAs and InAs surfaces. Specifically, for the GaAs
and InAs surfaces, ω
Q
=28.0±0.2 Mrad s−1 and η=0.43±0.02 and ω
Q
=28.8±0.2 Mrad s−1 and η=0.39±0.02, and the angles between EFG z-axis and the (111) direction are 65°±3° and β=53°±3°, respectively. These unexpected results indicate that the so-called
lattice contribution to the EFG is not significant. Moreover, for the primary NQIs on both surfaces, the similar parameter
values demonstrate that chemical differences between the 111In probe and the indigenous Ga surface atoms cause no large quantitative effects. This information indicates that impurity
probes and PAC spectroscopy can be used effectively to investigate III–V surfaces.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
10.
We have investigated epitaxial YBCO films by Perturbed γγ-Angular Correlation Spectroscopy (PAC) using 111In probe atoms. The probes substitute on the yttrium lattice site and hyperfine parameters have been determined unambiguously.
Excellent agreement is achieved with full potential electric field gradient (efg) calculations. Good reproducibility has been
achieved by our preparation method allowing us to study the influence of oxygen motion on the structural orthorhombic to tetragonal
phase transition.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献