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951.
Nikolay Youhnovski Laurent Bigler Christa Werner Manfred Hesse 《Helvetica chimica acta》1998,81(9):1654-1671
A H2O/MeOH extract of the pollen of Hippeastrum x hortorum (Amaryllidaceae) was analyzed. A mixture of different compounds (at the most 84) was found, namely the geometrically ((E,E), (E,Z), (Z,E), and (Z,Z) and structurally isomeric N,N′-dicoumaroyl (=N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]), N,N′-diferuloyl (=N,N′-bis[3-(4-hydroxy-3-methoxyphenyl)prop-2-enoyl]), N,N′-disinapoyl (=N,N′-bis[3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enoyl]), N-coumaroyl-N′-feruloyl, and N-feruloyl-N′-sinapoyl derivatives of spermidine (=4-azaoctane-1,8-diamine=N-(3-aminopropyl)butane-1,4-diamine). Their structures were proven by using on-line-coupled high-performance liquid chromatography and atmospheric-pressure chemical-ionization mass spectrometry (HPLC-UV(DAD)/APCI-MS and MS/MS), UV-induced (E)⇌(Z) photoisomerization, and catalytic hydrogenation, as well by comparing their spectra and chromatographic behavior with those of synthetic standards. According to the physicochemical properties of these natural compounds, a proposed biological function is discussed. 相似文献
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The random phase approximation has been used to extend the Leibler theory for the stability limit of a homogeneous melt of A–B diblock copolymers to examine the onset of microphase and macrophase separation in a variety of ABC block copolymer systems. The stability limit is located by the divergence of the collective structure factor of the melt. We introduce and analyze three models for ABC block copolymers: linear triblocks, random comb copolymers where a fixed number of A and B teeth are placed randomly along a C backbone, and statistical comb copolymers, with A or B teeth spaced regularly, but with sequences constructed using a two parameter Markov process. We compute order-disorder stability boundaries for the segregation strength parameter χABN at threshold as a function of χACN, χBCN, composition, and other model parameters, and compare the results for the three different architectural models. An interesting “reentrant order-disorder transition” is located in several model phase diagrams, and is associated with a peculiar situation in which more incompatibility causes less segregation. In the case of statistical combs, macrophase separation into two liquid phases can be favored over microphase separation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 849–864, 1997 相似文献
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Astrid M. Müller Stefan Lochbrunner Wolfram E. Schmid Werner Fuß 《Angewandte Chemie (International ed. in English)》1998,37(4):505-507
What is the standard course of the cis – trans isomerization of nonpolar polyenes? Many results support a pathway in which only a central CH group rotates out of the plane, while the remaining parts of the molecule reorient within the plane (“hula-twist” mechanism). The intermediate structure through which the molecule passes corresponds to the geometry predicted for the conical intersection of the S1 and S0 potential energy surfaces (see picture). 相似文献