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排序方式: 共有237条查询结果,搜索用时 46 毫秒
71.
Hagen V Bendig J Frings S Wiesner B Schade B Helm S Lorenz D Kaupp UB 《Journal of photochemistry and photobiology. B, Biology》1999,53(1-3):91-102
New caged derivatives of hydrolysis-resistant 8-bromoadenosine cyclic 3',5'-monophosphate (8-Br-cAMP) and 8-bromoguanosine cyclic 3',5'-monophosphate (8-Br-cGMP) are described. The compounds are the axial and equatorial isomers of the (7-methoxycoumarin-4-yl)methyl (MCM) esters of cyclic nucleotides. Synthesis is accomplished by treatment of 4-bromomethyl-7-methoxycoumarin with the tetra-n-butylammonium salts of the 8-bromo-substituted cyclic nucleotides or with the free acids of 8-Br-cAMP and 8-Br-cGMP in the presence of silver(I) oxide. MCM-caged 8-Br-cAMP and MCM-caged 8-Br-cGMP liberate 8-Br-cAMP and 8-Br-cGMP during irradiation with ultraviolet light within a few nanoseconds. They show favorable absorption properties and quantum yields and are resistant to hydrolysis in aqueous buffer solutions. The moderate fluorescence properties of the caged compounds in comparison with the strongly fluorescent 4-hydroxymethyl-7-methoxycoumarin (MCM-OH) photoproduct allow the indirect estimation of the amount of photolytically released cyclic nucleotides in aqueous buffer solutions using fluorescence measurements. Their usefulness for physiological studies has been examined in a mammalian cell line expressing the cyclic nucleotide-gated ion channel of bovine olfactory sensory neurons using the patch-clamp technique and confocal laser scanning microscopy. The caged compounds serve as efficient and rapid intracellular sources of 8-Br-cAMP and 8-Br-cGMP. However, at least in HEK 293 cells, fluorescence signals cannot be used to monitor the photolysis of MCM-caged 8-Br-cAMP and 8-Br-cGMP, due to quenching of the fluorescence of MCM-OH. 相似文献
72.
73.
J. W. Saalmueller H. W. Long T. Volkmer U. Wiesner G. G. Maresch H. W. Spiess 《Journal of Polymer Science.Polymer Physics》1996,34(6):1093-1104
The motion of nitroxide spin probes and spin labels in amorphous polymers is studied below the glass transition temperature with a two-dimensional pulsed electron double-resonance experiment. Polystyrene and a liquid crystalline side group polymer are studied using both spin probes and spin labels covalently bound to specific sites along the polymer chain. Two methyl acrylic polymers differing only in their side group structure and polyvinylacetate are compared and large differences in the molecular dynamics deduced from both the nuclear and the electron spin relaxation rates are observed as the glass transition is approached. The results demonstrate the complexity of small amplitude motion in simple polymers below the glass transition temperature and show that it is very sensitive to the packing in the polymer. © 1996 John Wiley & Sons, Inc. 相似文献
74.
G. Krabbes G. Auerswald A. Bartl H. Eschrig B. Lippold M. Ritschel H. Vinzelberg E. Wolf U. Wiesner 《Crystal Research and Technology》1988,23(9):1161-1168
The relationship between stoichiometry in YBa2Cu3Ox and oxygen potential was investigated by barometry and compared with in-situ X-ray diffraction experiments between 300 and 1000 °C (6 < x < 7). The physical properties are influenced even by small deviations in x. Y2BaCuO5 was included in the investigations and found to be antiferromagnetic with TN ≈ 30 K. 相似文献
75.
76.
77.
Hua Chen Daniel F. Schmidt Marinos Pitsikalis Nikos Hadjichristidis Yuangming Zhang Ulrich Wiesner Emmanuel P. Giannelis 《Journal of polymer science. Part A, Polymer chemistry》2003,41(24):3264-3271
In addition to phase morphology, diffusion, and dynamics in the bulk, the behavior of block copolymers in the confined state has been of great interest. Although random and graft copolymers have been used in polymer-layered silicate nanocomposites, well-defined block copolymers have received relatively little attention. In this study, the kinetics of intercalation of a series of poly(styrene-b-isoprene) block copolymers into a layered silicate were examined via X-ray diffraction. Intercalation was observed even when the copolymer was in the ordered state, with no discontinuity around the order–disorder transition of the copolymer. As the size of the polystyrene block was increased, slower intercalation kinetics were observed, possibly because of the increased glass-transition temperature of the polystyrene segment. Finally, the clearing temperature of the copolymer in the nanocomposites as measured by small-angle X-ray scattering showed a large heating-rate dependence suggesting that the nanoparticles act as kinetics barriers to the disordering of the copolymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3264–3271, 2003 相似文献
78.
79.
T.W. Donnelly D. Hitlin M. Schwartz J.D. Walecka S.J. Wiesner 《Physics letters. [Part B]》1974,49(1):8-12
The use of neutrino excitation of nuclear levels to study weak neutral currents is examined. 相似文献
80.
H. Rebel G. Hauser G.W. Schweimer G. Nowicki W. Wiesner D. Hartmann 《Nuclear Physics A》1974,218(1):13-42
Differential cross sections have been measured for the elastic and inelastic scattering of 104 MeV α-particles from46, 48, 49Ti. The experimental results are analyzed in terms of coupled channels on the basis of various limiting models of the collective behavior of these nuclei: symmetric rotator (46Ti), asymmetric rotator (48Ti) and anharmonic vibrator (50Ti). The analysis uses both the usual extended optical model and a semimicroscopic folding model. Prolate-oblate and γ-asymmetry effects are studied and confirm prolate deformation of 46Ti and 48Ti. Hexadecapole transitions (0+ → 41+) are found. 相似文献