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71.
The fission track technique has been applied to the determination of uranium on Dowex 1 x 8 after chemical separation from silicates. Standard rock and several stone meteorite samples were treated by this method and satisfactory results were obtained. The procedure is applicable to natural waters. 相似文献
72.
Summary: We observed the negative electrorheological phenomenon on swollen silicone gels containing barium titanate. Contrary, no negative electrorheological effect was observed in unswollen silicone gels containing barium titanate and silicon gels without barium titanate. The change in storage modulus increased with increasing DC electric field strength. The effects of frequency, degree of swelling, and the field strength have been investigated.
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74.
Ritesh Haldar Mariana Kozlowska Michael Ganschow Samrat Ghosh Marius Jakoby Hongye Chen Farhad Ghalami Weiwei Xie Shahriar Heidrich Yusuke Tsutsui Jan Freudenberg Shu Seki Ian A. Howard Bryce S. Richards Uwe H. F. Bunz Marcus Elstner Wolfgang Wenzel Christof Wll 《Chemical science》2021,12(12):4477
Charge carrier mobility is an important figure of merit to evaluate organic semiconductor (OSC) materials. In aggregated OSCs, this quantity is determined by inter-chromophoric electronic and vibrational coupling. These key parameters sensitively depend on structural properties, including the density of defects. We have employed a new type of crystalline assembly strategy to engineer the arrangement of the OSC pentacene in a structure not realized as crystals to date. Our approach is based on metal–organic frameworks (MOFs), in which suitably substituted pentacenes act as ditopic linkers and assemble into highly ordered π-stacks with long-range order. Layer-by-layer fabrication of the MOF yields arrays of electronically coupled pentacene chains, running parallel to the substrate surface. Detailed photophysical studies reveal strong, anisotropic inter-pentacene electronic coupling, leading to efficient charge delocalization. Despite a high degree of structural order and pronounced dispersion of the 1D-bands for the static arrangement, our experimental results demonstrate hopping-like charge transport with an activation energy of 64 meV dominating the band transport over a wide range of temperatures. A thorough combined quantum mechanical and molecular dynamics investigation identifies frustrated localized rotations of the pentacene cores as the reason for the breakdown of band transport and paves the way for a crystal engineering strategy of molecular OSCs that independently varies the arrangement of the molecular cores and their vibrational degrees of freedom.Pentacene assembled into 1D arrays using a metal–organic framework (MOF) approach. This cofacial packing motif, which is not present in pentacene bulk, shows an interesting interplay of band-like and hopping-type transport. 相似文献
75.
Conformational structures of solvated cobalt(II) ions in several amides and trimethyl phosphate (TMP) have been studied by the X-ray diffraction method using the isomorphous substitution technique. The amides used are formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N,N-dimethylpropioamide (DMPA). From the analysis of radial distribution functions around Co2+, the distances from Co2+ to each atom of coordinated solvent molecules were obtained and the coordination numbers were determined to be six, except for DMPA where four-coordinate species coexist. The Co—O bond distances are 2.09(1)–2.11(1) Å for six-coordinate species but is 1.96(2) Å for the four-coordinate species. In the amide solutions the Co—O—C bond angles are 126(3)° (FA), 123(2)° (NMF), 123(2)° (DMF), 134(3)° (DMA), and 137(4)–138(4)° (DMPA). The Co—O—C—N dihedral angles were also estimated to discuss the conformational distortion on the Co2+-amide interactions. For TMP solutions the Co—O—P angle was determined to be 150(4)°, and the conformational structure on the Co2+–TMP interaction is discussed. 相似文献
76.
Tadatomi Nishikubo Atsushi Kameyama Hiroto Kudo Kousuke Tsutsui 《Journal of polymer science. Part A, Polymer chemistry》2002,40(9):1293-1302
New photoreactive calixarene derivatives containing spiro ortho ester groups (calixarenes 3a–3c ) were synthesized by the reaction of 2‐bromomethyl‐1,4,6‐trioxaspiro[4.4]nonane with 2,8,14,20‐tetramethyl‐4,6,10,12,16,18,22,24‐octakis(carboxymethoxy)calix[4]resorcinarene, 5,11,17,23,29,35‐hexamethyl‐37,38,39,40,41,42‐hexakis(carboxymethoxy)calix[6]arene, and 5,11,17,23,29,35,41,47‐octa‐tert‐butyl‐49,50,51,52, 53,54,55,56‐octakis‐(carboxymethoxy)calix[8]arene, which were prepared by the reaction of C‐methylcalix[4]resorcinarene, p‐methylcalix[6]arene, and p‐tert‐butylcalix[8]arene, respectively. The thermal stability of the obtained calixarene derivatives containing spiro ortho ester groups was examined with thermogravimetric analysis, and it was found that these calixarene derivatives had good thermal stability. The photoinitiated cationic polymerization of spiro ortho ester groups in calixarene derivatives 3a–3c was examined with certain photoacid generators in the film state. Interestingly enough, the reaction of calixarene derivatives did not proceed with only photoirradiation; however, the reaction proceeded smoothly when the photoirradiation was followed by heating. Furthermore, calixarene 3a , composed of a C‐methylcalix[4]resorcinarene structure, showed the highest photochemical reactivity in this reaction system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1293–1302, 2002 相似文献
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79.
Tsutsui H Abe T Nakamura S Anada M Hashimoto S 《Chemical & pharmaceutical bulletin》2005,53(10):1366-1368
An efficient and reliable procedure for the preparation of dirhodium(II) tetrakis[N-phthaloyl-(S)-tert-leucinate], Rh2(S-PTTL)(4), a universally effective catalyst for a range of enantioselective carbene transformations, is described. The N-phthaloylation of (S)-tert-leucine by the method of Bose with essentially no racemization is a key to this process. 相似文献
80.
Kei Kamada Takayuki Yanagida Jan Pejchal Martin Nikl Takanori Endo Kousuke Tsutumi Yoshiyuki Usuki Yutaka Fujimoto Akihiro Fukabori Akira Yoshikawa 《Journal of Crystal Growth》2012,352(1):84-87
Pr:Gd3(Ga,Al)5O12 single crystals were grown by the micro-pulling down (μ-PD) method. All grown crystals were greenish and transparent with 3.0 mm in diameter, 15–30 mm in length. Neither visible inclusions nor cracks were observed. Luminescence and scintillation properties were measured. The substitution at the Al3+ sites by Ga3+ in garnet structure has been studied. In these crystals, Pr3+ 5d–4f emission is observed with 340 nm wavelength. Pr1%:Gd3Ga3Al2O12 shows highest emission intensity. The light yield of Pr:Gd3Ga3Al2O12 sample with 3 mmφ×1 mm size was around 4500 photon/MeV. Scintillation decay time was 7.9 ns (0.5%), 46 ns (0.7%) and 214 ns (98.8%). 相似文献