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51.
52.
Rapp A Schnell I Sebastiani D Brown SP Percec V Spiess HW 《Journal of the American Chemical Society》2003,125(43):13284-13297
Advanced solid-state NMR methods under fast magic-angle spinning (MAS) are used to study the structure and dynamics of large supramolecular systems, which consist of a polymer backbone with dendritic side groups and self-assemble into a columnar structure. The NMR experiments are performed on as-synthesized samples, i.e., no isotopic enrichment is required. The analysis of (1)H NMR chemical-shift effects as well as dipolar (1)H-(1)H or (1)H-(13)C couplings provide site-specific insight into the local structure and the segmental dynamics, in particular, of phenyl rings and -CH(2)O- linking units within the dendrons. Relative changes of (1)H chemical shifts (of up to -3 ppm) serve as distance constraints and allow protons to be positioned relative to aromatic rings. Together with dipolar spinning sideband patterns, pi-pi packing phenomena and local order parameters (showing variations between 30% and 100%) are selectively and precisely determined, enabling the identification of the dendron cores as the structure-directing moieties within the supramolecular architecture. The study is carried out over a representative selection of systems which reflect characteristic differences, such as different polymer backbones, sizes of dendritic side groups, or length and flexibility of linking units. While the polymer backbone is found to have virtually no effect on the overall structure and properties, the systems are sensitively affected by changing the generation or the linkage of the dendrons. The results help to understand the self-assembly process of dendritic moieties and aid the chemical design of self-organizing molecular structures. 相似文献
53.
Söldner FX McCormick K Eckhartt D Kornherr M Leuterer F Bartiromo R Becker G Bosch HS Brocken H Derfler H Eberhagen A Fussmann G Gehre O Gernhardt J Gierke Gv Giuliana A Glock E Gruber O Haas G Hesse M Hofmann J Izvozchikov A Janeschitz G Karger F Keilhacker M Klüber O Lackner K Lenoci M Lisitano G Mast F Mayer HM Meisel D Mertens V Müller ER Münich M Murmann H Niedermeyer H Pietrzyk A Poschenrieder W Rapp H Riedler H Röhr H Ryter F Schmitter KH Schneider F Setzensack C Siller G Smeulders P 《Physical review letters》1986,57(9):1137-1140
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P. A. Leclercq H. M. J. Snijders C. A. Cramers K. H. Maurer U. Rapp 《Journal of separation science》1989,12(10):652-656
Identification and detection limits for scanning and non-scanning mass spectrometers are discussed. It is theoretically deduced and experimentally confirmed that these limits are on the low pico-and femtogram levels, respectively, when using conventional secondary electron multiplier-amplifier systems. The sensitivity can be increased at least tenfold by pulse-counting techniques, instead of current amplification, provided the chemical noise is sufficiently low. The potential advantages of a detection system for simultaneous ion detection in a significant mass range, for obtaining complete mass spectra in fast GC/MS analyses, are demonstrated. A double focusing mass spectrometer was constructed, using the well-proven Mattauch-Herzog principles. By application of an “electronic photoplate”, substance identification in the low femtogram range on a millisecond time scale, so far only accessible for single ion monitoring techniques, is feasible. 相似文献
57.
Steinmetz K Noterdaeme J Wagner F Wesner F Bäumler J Becker G Bosch HS Brambilla M Braun F Brocken H Eberhagen A Fritsch R Fussmann G Gehre O Gernhardt J v Gierke G Glock E Gruber O Haas G Hofmann J Hofmeister F Izvozchikov A Janeschitz G Karger F Keilhacker M Klüber O Kornherr M Lackner K Lisitano G van Mark E Mast F Mayer HM McCormick K Meisel D Mertens V Müller ER Murmann H Niedermeyer H Poschenrieder W Puri S Rapp H Röhr H Ryter F Schmitter K Schneider F Setzensack C Siller G Smeulders P 《Physical review letters》1987,58(2):124-127
58.
P. MORLIÉRE M. BAZIN L. DUBERTRET R. SANTUS T. SA E. MELO G. HÜPPE J. HAIGLE P. FORLOT A. BERNARD 《Photochemistry and photobiology》1991,53(1):13-19
5-Geranoxypsoralen, commonly called bergamottin, a major furocoumarin contained in bergamot oil, is reported in vitro as a highly photoreactive psoralen. In ethanol, it exhibits quite a high triplet state quantum yield (approximately 0.37). The triplet state is involved in subsequent photochemistry which depends on the initial concentration and on the presence of oxygen. In contrast to most psoralens, absorption and fluorescence data suggest that 5-geranoxypsoralen does not interact with DNA in the dark. No UVA-induced interstrand cross-links in DNA were shown. 相似文献
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Paul Degener G. Kottmann und Tollens Rapp 《Fresenius' Journal of Analytical Chemistry》1884,23(1):100-102
Ohne Zusammenfassung 相似文献