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941.
Atila Kaya Lothar Jakisch Hartmut Komber Gisela Pompe Jürgen Pionteck Brigitte Voit Ulrich Schulze 《Macromolecular rapid communications》2000,21(17):1267-1271
Using two different zirconocene/MAO catalyst systems, propene was copolymerized with the comonomers 2‐(9‐decene‐1‐yl)‐1,3‐oxazoline and 2‐(4‐(10‐undecene‐1‐oxo)phenyl)‐1,3‐oxazoline, respectively. The catalysts used were rac‐Et[Ind]2ZrCl2 and rac‐Me2Si[2‐Me‐4, 5‐BenzInd]2ZrCl2. Up to 0.53 mol‐% oxazoline could be incorporated into polypropene. Oxazoline content, molecular weight, degree of isotacticity and melting behavior were dependent on the catalyst system, comonomer structure and comonomer concentration in the feed. 相似文献
942.
943.
Ulrich Riebel 《Particle & Particle Systems Characterization》1998,15(6):251-256
The discrete nature of particles leads to fluctuations, in both space and time, of the radiation transmitted through a disperse system. The result of a transmission or extinction measurement is commonly expressed, however, as an average value and consecutively converted to a concentration measurement. The experiment discussed here shows that different concentration measures (volume concentration and surface concentration) can be obtained from the same measurement, depending on which level of the signal treatment the averaging procedure is introduced. 相似文献
944.
Chloroselenates with Di- and Tetravalent Selenium: 77Se-NMR-Spectra, Syntheses, and Crystal Structures of (PPh4)2SeCl6 · 2 CH2Cl2, (NMe3Ph)2SeCl6, (K-18-crown-6)2SeCl6 · 2 CH3CN, PPh4Se2Cl9, (NEt4)2Se2Cl10, (PPh4)2Se3Cl8 · CH2Cl2, and (PPh4)2Se4Cl12 · CH2Cl2 The title compounds were obtained from reactions of selenium and selenium tetrachloride with PPh4Cl, NEt4Cl, NMe3PhCl, or (K-18-crown-6)Cl in dichloromethane or acetonitrile. (PPh4)2Se3Cl8 · CH2Cl2 was also formed from GeSe, PPh4Cl and chlorine in acetonitrile. The 77Se-NMR spectra of the solutions show the presence of dynamical equilibria which, depending on composition, mainly contain SeCl2, SeCl4, Se2Cl2, SeCl62–, Se2Cl62–, and/or Se2Cl102–. Solutions of AsCl3 and (PPh4)2Se4 in acetonitrile upon chlorination with Cl2 or PPh4AsCl6 yielded (PPh4)2Se2Cl6, while (PPh4)2As2Se4Cl12 was the product after chlorination with SOCl2. According to the X-ray crystal structure analyses the ions SeCl62–, Se2Cl9–, and Se2Cl102– have the known structures with octahedral coordination of the Se atoms. The structure of the Se3Cl82– ion corresponds to that of Se3Br82– consisting of three SeCl2 molecules associated via two Cl– ions. (PPh4)2Se4Cl12 · CH2Cl2 is isotypic with the corresponding bromoselenate and contains anions in which three SeCl2 molecules are attached to a SeCl62– ion; there is a peculiar Se–Se interaction. 相似文献
945.
Ulrich Reineke Jens Schneider-Mergener 《Angewandte Chemie (International ed. in English)》1998,37(6):769-771
A short peptide as mimic for the hemopoietic growth factor erythropoietin (containing 165 amino acids) could be identified with the aid of peptide libraries on phage surfaces (phage display). The crystal structure of a peptide dimer complexed with two erythropoietin receptors (shown on the right) provides an insight into the molecular basis of this protein mimicry. 相似文献
946.
Heiko Kalpen Wolfgang Hnle Mehmet Somer Ulrich Schwarz Karl Peters Hans Georg von Schnering Roger Blachnik 《无机化学与普通化学杂志》1998,624(7):1137-1147
Bismuth(II) Chalcogenometallates(III) Bi2M4X8, Compounds with Bi24+ Dumbbells (M = Al, Ga and X = S, Se) The ternary bismuth(II) chalcogenometallates(III) Bi2M4X8 (with M = Al, Ga and X = S, Se) were synthesized from the binary chalcogenides M2X3 and Bi2X3 and elementary bismuth. All compounds are diamagnetic semiconductors with Eg (opt.) = 1.8–2.7 eV. The phases (except Bi2Al4Se8) are thermodynamically stable and decompose peritectically above 965–1020 K. Bi2Al4Se8 is metastable below 825 K and is obtained only by rapid quenching from T > 825 K. The isotypic compounds crystallize in a new tetragonal tP28 structure type (P4/nnc). The characteristic unit is the hitherto unknown clustercation Bi24+, with the mean bond length d(Bi–Bi) = 314.2 pm, the Raman frequency 102 cm–1 ≤ νs ≤ 108 cm–1, and the mean force constant of f = 0.68 N · cm–1. The Electron Localization Function, ELF, shows the covalent Bi–Bi bond, the lone electron pairs of the ψ-octahedrally coordinated Bi(II) cations, and the polar character of the Bi–X bonds. 相似文献
947.
948.
D. C. Barbacci D. H. Russell J. A. Schultz J. Holocek S. Ulrich W. Burton M. Van Stipdonk 《Journal of the American Society for Mass Spectrometry》1998,9(12):1328-1333
An electrospray ionization ion source coupled to a time-of-flight mass analyzer incorporating a multi-anode time-to-digital converter is described. High-speed data acquisition (kHz mass spectral acquisition) rates are achieved. The four-anode detector produces a significant increase in detection/counting efficiency over that for a single-anode detector. In this work a 2.5 times increase in detection efficiency is demonstrated. The multi-anode detector is also used as a diagnostic tool to optimize transmission of the ion optics. 相似文献
949.
950.