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排序方式: 共有434条查询结果,搜索用时 343 毫秒
381.
Gerald A Metselaar Erik Schwartz René de Gelder Martin C Feiters Serge Nikitenko Grigory Smolentsev Galina E Yalovega Alexander V Soldatov Jeroen J L M Cornelissen Alan E Rowan Roeland J M Nolte 《Chemphyschem》2007,8(12):1850-1856
The structure of the active complex in the Ni-catalyzed polymerization of isocyanides to give polyisocyanides is investigated. It is shown by X-ray absorption spectroscopy (XAS), including EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure), and single-crystal X-ray diffraction, to contain a carbene-like ligand. This is the first structural characterization of a crucial intermediate in the so-called merry-go-round mechanism for Ni-catalyzed isocyanide polymerization. 相似文献
382.
The synthesis and aggregation behavior of cavity-containing facial amphiphiles is described. The molecules consist of a glycoluril-based rigid cavity functionalized with two water-soluble benzoate groups. By specific molecular recognition processes in water, the amphiphilic hosts self-assemble in a hierarchical process to form arrays of molecules. Depending on the counterions, these arrays can be assembled into well-defined aggregates of mesoscopic size. The size and shape of the aggregates can be tuned by variations in the size and substitution pattern of the cavities of the host molecules. 相似文献
383.
Be(II), Mg(II), Ca(II), Sr(II) and Ba(II) can be separated by elution from a cation-exchange column in the ammonium form with increasing concentrations of ammonium malonate. A typical elution sequence for a 60-ml column (volume in H+-form) of AG50-X8 resin is: 200 ml of 0.20 N ammonium malonate plus 0.10 N malonic acid for Be(II); 300 ml of 0.50 N, 450 ml of 0.70 N, 350 ml of 1.10 N ammonium malonate for Mg(II), Ca(II) and Sr(II), respectively, and 200 ml of 3.0 N nitric acid for Ba(II). Separations are sharp and quantitative for element pairs in weight ratios from 1:1000 to 1000:1. Distribution coefficients, elution curves and quantitative separations are presented. 相似文献
384.
385.
E. Nolte T. Faestermann A. Gillitzer G. Korschinek D. Müller V. M. Novikov A. A. Pomansky A. Ljubicic D. Miljanic 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(4):411-413
The Pauli exclusion principle was tested by searching with accelerator mass spectrometry for non-Paulian atoms with three electrons in theK-shell and for non-Paulian nuclei with three protons or three neutrons in the nuclear 1 s1/2 shell. For non-Paulian atoms of
and
the following limits have been obtained:
and
. For non-Paulian nuclei of
and
with three protons or three neutrons, respectively, in the nuclear 1 s1/2 shell the following limits have been measured:
for a range of proton separation energies of
between 0 and 50 MeV and
for neutron separation energies between 0 and 32 MeV. The result for5Li is used to deduce a limit for the probability 2/2 of finding two colliding protons in the symmetric state with respect to exchange to be 2/2<>–32.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday. Supported by the BMFT 相似文献
386.
387.
A. N. Davies R. Kuckuk W. Hill J. Nolte P. Burba 《Journal of Analytical and Applied Pyrolysis》2001,60(2):145-157
The interpretation of the results of pyrolysis studies of humic substances is fraught with difficulties if only a single analytical technique is employed for substructure analyses. In this paper we have carried out investigations into humic substances utilising the additional information from the combination of gas chromatography/infrared spectroscopy and gas chromatography/mass spectrometry detection following Curie-point pyrolysis at five different temperatures. The results were compared to those obtained from conventional flash pyrolysis. The aim was to ensure the validation of the results of the compounds identified by at least one other spectroscopic technique. Some 30 substances have been positively identified by infrared spectroscopy, although their appearance is dependent on pyrolysis method and temperature. Most assignments were validated by mass spectrometry or the substance class confirmed. 相似文献
388.
Dreisow F Szameit A Heinrich M Pertsch T Nolte S Tünnermann A Longhi S 《Physical review letters》2008,101(14):143602
Control of optical tunneling via modulation of the coupling to the continuum is experimentally reported in femtosecond laser written waveguide arrays. The experiment demonstrates for optical tunneling in photonic lattices the universal mechanism of decay control recently proposed for quantum systems by Kofman and Kurizki [Phys. Rev. Lett. 87, 270405 (2001)]. In particular, we prove that the formation of a dressed discrete-continuum bound state in the regime of fractional decay can be suppressed by dynamic modulation of discrete-to-continuum coupling. 相似文献
389.
Yingfeng Tu Fei Peng Josje M. Heuvelmans Shuwen Liu Roeland J. M. Nolte Daniela A. Wilson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(26):8779-8783
Controlling the motion of artificial self‐propelled micro‐ and nanomotors independent of the fuel concentration is still a great challenge. Here we describe the first report of speed manipulation of supramolecular nanomotors via blue light‐responsive valves, which can regulate the access of hydrogen peroxide fuel into the motors. Light‐sensitive polymeric nanomotors are built up via the self‐assembly of functional block copolymers, followed by bowl‐shaped stomatocyte formation and incorporation of platinum nanoparticles. Subsequent addition of β‐cyclodextrin (β‐CD) leads to the formation of inclusion complexes with the trans‐isomers of the azobenzene derivatives grafted from the surfaces of the stomatocytes. β‐CDs attachment decreases the diffusion rate of hydrogen peroxide into the cavities of the motors because of partly blocking of the openings of the stomatocyte. This results in a lowering of the speed of the nanomotors. Upon blue light irradiation, the trans‐azobenzene moieties isomerize to the cis‐form, which lead to the detachment of the β‐CDs due to their inability to form complexes with the cis‐isomer. As a result, the speed of the nanomotors increases accordingly. Such a conformational change provides us with the unique possibility to control the speed of the supramolecular nanomotor via light‐responsive host–guest complexation. We envision that such artificial responsive nano‐systems with controlled motion could have potential applications in drug delivery. 相似文献
390.
Nils Metzler‐Nolte 《Nachrichten aus der Chemie》2006,54(10):966-970