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31.
Maram R. Al-Dweik Jalal A. Zahra Monther A. Khanfar Mustafa M. El-Abadelah Klaus-Peter Zeller Wolfgang Voelter 《Monatshefte für Chemie / Chemical Monthly》2009,45(4):221-228
Abstract
A series of ethyl 2-(substituted)-9-cyclopropyl-4-fluoro-6-oxo-1H-imidazo[4,5-h]quinoline-7-carboxylates has been prepared from ethyl 7,8-diamino-1,4-dihydroquinoline-3-carboxylate via thermally induced reactions with model alkanoic acids or via microwave-assisted cyclocondensation with some arene carboxaldehydes. Acid-catalysed hydrolysis of the resulting ester derivatives furnished the corresponding imidazoquinoline-7-carboxylic acids. The structures of these new acid and ester derivatives are based on microanalytical and spectral (IR, MS, and NMR) data. 相似文献32.
33.
Ccile Alberola Bernhard Blümich Detlef Emeis Klaus-Peter Wittern 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,290(1-3):247-255
The present work investigates the phase transitions of monoglyceride emulsifier systems and pearlescent effects in cosmetic creams using 13C-NMR spectroscopy and DSC. The four phases of monoglyceride emulsifier systems – the coagel, gel phase, liquid-crystalline lamellar phase, and cubic phase – can be characterized in creams at appropriate temperatures by NMR spectroscopy. The phase transition temperatures were determined by DSC. Cross polarization (13C-CP)-magic angle spinning (MAS) measurements confirmed that the formation of the coagel is responsible for the pearlescence of creams. It could be shown that the proportions of monoglyceryl laurate and monoglyceryl myristate in the emulsifier system influence the phase transitions and the intensity of the pearlescence of creams. Furthermore, the coagel forms directly from the liquid-crystalline lamellar phase without transition through the gel phase if the cream is at a temperature higher than that of gel phase formation. These insights into the monoglyceride-emulsifier system of creams make it possible to more closely study the pearlescent effect of the coagel. Especially, the amount of emulsifier system in the coagel can be quantified. It could be shown that for a typical pearlescent cream more than 27% of the emulsifier system must be found in the coagel in order for pearlescence to be detectable optically. Moreover, the increase in the intensity of pearlescence over time after fabrication of a cream correlated with the increase in the amount of emulsifier system in the coagel. This ripening process can take up to approximately 15 months. 相似文献
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35.
Gerhard Bringmann Doris Feineis Katja Maksimenka Kim Messer Klaus-Peter Gulden Karl Peters 《Tetrahedron》2004,60(37):8143-8151
Separation and stereochemical attribution of the two enantiomers of the neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo) has been achieved by applying chromatography on a chiral phase HPLC column in hyphenation with circular dichroism (CD) spectroscopy (LC-CD coupling). Assignment of the absolute configuration of TaClo and its N-methyl analog has been achieved by quantum chemical CD calculations and has finally been confirmed by single-crystal X-ray diffraction analyses of the two enantiomers of N-formyl-TaClo as obtained in enantiomerically pure form by crystallization. 相似文献
36.
Systematic optical hyperfine interaction studies in various isotope series gave first indications to the possibility of single-particle
and collective motions of nucleons in atomic nuclei and the variation of the nuclear radius with the mass number and deformation
(isotope shift). Indeed, the careful studies by Schmidt (1908–1986), which he performed together with Schüler in Potsdam,
revealed the existence of both nuclear quadrupole deformation and single-particle magnetic moments (Schmidt lines). These
findings were essential as a basis for the nuclear vibrational and rotational models and the single particle shell model,
respectively. The talk reviews some of the achievements of Schmidt and Kopfermann (1895–1963) and sheds some light on their
working conditions before, during and after World War II.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
37.
Dibenzoylketene 5 undergoes degenerate 1,3-shifts of the phenyl group between acyl and ketene carbon atoms, thus interconverting it with 6 and 7. This 1,3-shift takes place in the gas phase under flash vacuum thermolysis (FVT) conditions, but not in solution at 110-145 degrees C. Imidoyl(benzoyl)ketene 13 undergoes degenerate 1,3-shift of the phenyl group on FVT, thus interconverting it with 14, but the ketenimine isomer 15 is not formed, and none of these shifts take place in the solid state at 250 degrees C. Imidoyl(p-toluoyl)ketene 21 undergoes a 1,3-p-tolyl shift, interconverting it with ketene 22 but not with ketenimine 23. The imidoyl(p-toluoyl)ketene rotamer 25 cyclizes to 4-toluoyloxyquinoline 28 and 4-quinolone 29. The cyclization of imidoyl(benzoyl)ketene 13 to 4-benzoyloxyquinoline 18, and of 25 to 28 involves 1,3-C-to-O shifts of benzoyl (toluoyl) groups. Calculations of the transition states for the transformations at the B3LYP/6-31G** level of theory are in agreement with the observed reaction preferences. 相似文献
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