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51.
Gil M. Barretto Peter J. Collings Dirk Bennemann Detlef L
tzsch Gerd Heppke 《Liquid crystals》2001,28(4):629-635
Optical activity measurements in the isotropic phase of two antiferroelectric liquid crystal systems in which the chirality can be varied reveal unusual behaviour of the short range order. In one system the phase sequence as the chirality is increased is smectic A, smectic C*A, and smectic Q. In the other system the phase sequence is smectic C*, smectic C*A, and smectic Q as the chirality is increased. The short range order of the isotropic phase behaves similarly for these systems, showing mean field behaviour at low chirality and far above the phase transition, but deviating from this behaviour significantly as the chirality is increased and the phase transition is approached. These optical activity results indicate how different is the short range order in the isotropic phase for these antiferroelectric liquid crystal systems and demonstrates the crucial role played by chirality. Past theoretical work that includes smecticlike fluctuations in the calculation of short range order in the isotropic phase is capable of qualitatively explaining these results. 相似文献
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Burkhard Butschke Maria Schlangen Detlef Schröder Helmut Schwarz 《Helvetica chimica acta》2008,91(10):1902-1915
Mechanistic details for the formation of methane from the title compound as well as the combined elimination of (CH3)2S/CH4 are derived from various mass‐spectrometric experiments including deuterium‐labeling studies and DFT calculations. For the first process, i.e., methane formation, we have identified three competing pathways in which the intact, Pt‐bonded methyl group combines with a H‐atom that originates from a phenyl substituent (ca. 7%), the dimethyl sulfide ligand (ca. 41%), and a methyl group of the diazabutadiene backbone (ca. 52%). In contrast, in the combined (CH3)2S/CH4 elimination, the methane is specifically formed from the Pt‐bound CH3 group and a H‐atom provided by one of the phenyl groups (‘cyclometalation’). 相似文献
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Xiangli Liu Ping Fan Ming Chen Hossam Hefesha GerhardK.E. Scriba Detlef Gabel Alfred Fahr 《Helvetica chimica acta》2010,93(2):203-211
The objective of this study was to investigate drug–membrane interaction by immobilized liposome chromatography (ILC; expressed as lipophilicity index log Ks) and the comparison with lipophilicity indices obtained by liposome/H2O, octan‐1‐ol/H2O, and immobilized artificial membrane (IAM) systems. A set of structurally diverse monofunctional compounds and drugs (nonsteroidal anti‐inflammatory drugs and β‐blockers) were selected in this study. This set of solutes consists of basic or acidic functionalities which are positively or negatively charged at physiological pH 7.4. No correlation was found between log Ks from ILC and lipophilicity indices from any of the other membrane model systems for the whole set of compounds. For structurally related compounds, significant correlations could be established between log Ks from ILC and lipophilicity indices from IAM chromatography and octan‐1‐ol/H2O. However, ILC and liposome/H2O systems only yield parallel partitioning information for structurally related large molecules. For hydrophilic compounds, the balance between electrostatic and hydrophobic interactions dominating drug partitioning is different in these two systems. 相似文献
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