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61.
Rudolf Schmida Symon Antoulas August Rüttimann Max Schmid Max Vecchi Harald Weiserb 《Helvetica chimica acta》1990,73(5):1276-1299
All four stereoisomers of (E)-vitamin Kb i. e. (21E, 7R, 111R)-l (= 1a), (21E, 71 R, l11S)-1 (= 1b), (21E, 71 S, 111S) 1 ( = 1c), and (21E, 71S, 111R)-l ( = Id), have been synthesized in a state of high chemical and stereoisomeric purity. The synthesis of stereoisomers lb-d relied on the use of the optically active Cf1* and C*10-building blocks (R)- or (S)-4-(benzyloxy)-3-methylbutanal ((R)- or (S)-2) and (R)- or (S)-citronellal ((R)- or (S)- 3 ) which had been secured by the Rh1-catalyzed allylamine-to-enamine isomerization technology. For the synthesis of the natural (E)-vitamin-K1 stereoisomer 1a , a new route starting from natural phylol was developed, based on an O-alkylation/rearrangement procedure. A HPLC method was developed which separates with remarkable efficiency all four stereoisomers of (E)- as well as three out of the four stereoisomers of (Z)-vitamin K1 on optically active poly(trityl methacrylate) as the chiral stationary phase supported on Nucleosil. By this method, the stereoisomeric content of the stereoisomers 1b-d synthesized was shown to be in the range of 96-98 %, while the natural isomer 1a was configurationally uniform. The biological activity of the four (E)-vitamin-K1 stereoisomers was determined by means of the curative prothrombin time test with vitamin-K-depleted chicks. A high precision of the results was obtained with the recently introduced up-and-down organization of the test and the statistical evaluation according to an estimation procedure. With the natural (E)-vitamin-K1 stereoisomer 1a as standard (set at 1. 0), activities of 0. 93, 1. 19, and 0. 99 were found for stereoisomers 1b, 1c , and 1d , respectively. Within the confidence limits, these activity ratios can be regarded as identical, A very similar efficacy was obtained by comparison of (E, all-rac )-vitamin K1 ((21E, RS, 11′ RS)- 1 ; equimolar mixture of the four stereoisomers 1a-d) with the natural (E)-vitamin-K1 stereoisomer 1a ). A synergistic effect was not detectable, as was the case with the eight α-tocopheryl-acetate stereoisomers. 相似文献
62.
Ab initio theoretical ground state potentials of diatomic molecules calculated with the use of the variational CI-MO (configuration interaction method based on molecular orbitals) are analyzed with the use of the RPC (reduced potential curve) method. It is shown on a series of examples that the following statement is true even for inaccurateab initio calculations: in reduced form, the theoretical potential coincides to a high degree of accuracy with the reduced RKR (Rydberg-Klein-Rees) potential calculated from the spectroscopic data. Thus, with the use of the RPC method, even inaccurateab initio calculations (in particular for heavier molecules) may be used for the construction of rather accurate internuclear potentials and hence obtain a practical significance. The statement also holds for excited states if strong perturbations are not present. 相似文献
63.
August W. Bosse Scott W. Sides Kirill Katsov Carlos J. García-Cervera Glenn H. Fredrickson 《Journal of polymer science. Part A, Polymer chemistry》2006,44(18):2495-2511
In recent years, there has been increased interest in using microphase-separated block copolymer thin films as submicrometer/suboptical masks in next generation semiconductor and magnetic media fabrication. With the goals of removing metastable defects in block copolymer thin film simulations and potentially examining equilibrium defect populations, we report on two new numerical techniques that can be used in field-theoretic computer simulations: (1) a spectral amplitude filter (SF) that encourages the simulation to relax into high symmetry states (representing zero defect states), and (2) different variants of force-biased, partial saddle point Monte Carlo algorithms that allow for barrier crossing toward lower energy defect-free states. Beyond their use for removing defects, the force-biased Monte Carlo algorithms will be seen to provide a promising tool for studying equilibrium defect populations. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2495–2511, 2006 相似文献
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August Florian 《Aequationes Mathematicae》2009,77(1-2):147-170
67.
Georg August Koenig 《Fresenius' Journal of Analytical Chemistry》1900,39(8):508-511
Ohne ZusammenfassungMit Tafel III. 相似文献
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August J Weidner 《Fuzzy Sets and Systems》1981,6(1):61-72
A connection between fuzzy sets and Boolean-valued universes is made by developing a formal axiomatic system for fuzzy sets among whose models are suitably interpreted Boolean-valued universes. The formal system is an independent first-order axiomatization of fuzzy set theory which parallels the Zermelo-Fraenkel development of classical set theory. 相似文献