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991.
A microcanonical analysis of the extended kinetic method is performed using statistical rate calculations based on orbiting transition state theory. The model systems simulate polydentate bases M which exhibit losses of entropy upon protonation of up to 35 kJ mol(-1) K(-1). It is shown that the correlations using the natural logarithm of the ratio of rate constants vs the proton affinity of the reference bases, at several effective temperatures, lead to correct proton affinity and protonation entropy of the base M of interest. A systematic underestimate of the latter quantity (by 5-15%), mainly due to the use of a linear rather than a polynomial curve fitting procedure, is noted, however. When considering experimental data, more severe underestimates are observed for the protonation entropies of polydentate bases (by 50-90%). The origins of these considerable discrepancies are beyond the limits of the present modeling and remain to be determined. 相似文献
992.
Loones KT Maes BU Dommisse RA Lemière GL 《Chemical communications (Cambridge, England)》2004,(21):2466-2467
A new strategy for the synthesis of the title compounds via a regio- and chemoselective one-pot inter- and intramolecular Buchwald-Hartwig amination of 2-chloro-3-iodopyridine with aminoazines and -diazines is reported. 相似文献
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997.
Valérie?Serre Bernadette?Penverne Jean-Luc?Souciet Serge?Potier Hedeel?Guy David?Evans Patrick?Vicart Guy?HervéEmail author 《BMC biochemistry》2004,5(1):6
Background
The S. cerevisiae carbamylphosphate synthetase – aspartate transcarbamylase multifunctional protein catalyses the first two reactions of the pyrimidine pathway. In this organism, these two reactions are feedback inhibited by the end product UTP. In the present work, the mechanisms of these integrated inhibitions were studied. 相似文献998.
[reaction: see text] The asymmetric synthesis of 2,7-cis-disubstituted oxepanes bearing a sulfoxide is achieved from commercially available precursors in only five steps. The key step is the highly diastereoselective Et3SiH/TMSOTf-promoted reductive cyclization of enantiopure hydroxysulfinyl aryl or alkyl ketones. 相似文献
999.
Schaffner-Hamann C von Zelewsky A Barbieri A Barigelletti F Muller G Riehl JP Neels A 《Journal of the American Chemical Society》2004,126(30):9339-9348
Chiral, facial tris-cyclometalated Ir(III) complexes, fac-Delta-Ir(pppy)(3), fac-Lambda-Ir(pppy)(3), fac-Lambda-IrL (where pppy is (8R,10R)-2-(2'-phenyl)-4,5-pinenopyridine and L is a tripodal ligand comprising three pppy moieties connected through a mesityl spacer) have been synthesized and characterized. In IrL, NMR and CD studies indicate that only one diastereomer is formed, with the Lambda configuration at the metal center, whereas enantiopure pppy yields the fac-Lambda- and the fac-Delta-stereoisomer in a ratio 2:3. fac-Lambda-IrL was structurally characterized using X-ray crystallography. The luminescence properties including CPL, of the three complexes and their sensitivity to dioxygen were examined. 相似文献
1000.
Mshvildadze V Elias R Faure R Rondeau D Debrauwer L Dekanosidze G Kemertelidze E Balansard G 《Chemical & pharmaceutical bulletin》2004,52(12):1411-1415
Five new triterpenoid saponins, pastuchoside A (1), B (3), C (5), D (7) and E (9), were isolated from the leaves of Hedera pastuchowii. They have oleanolic acid or hederagenin as aglycone. The structures were established by NMR spectroscopy including gs (gradient selected)-COSY, gs-HSQC, gs-HSQC-TOCSY and gs-HMBC experiments, and mass spectrometry (ESI-HR-MS). Heptaoside saponins, compounds 1 and 3, are described for the first time in the genus Hedera. 相似文献