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The (17R,20S,22S,24S) C20-C29 segment of contignasterol has been stereoselectively prepared in 8 steps and 40% overall yield from (S)-carvone. Synthetic studies towards contignasterol's C/D ring functionalization/isomerization are also reported. 相似文献
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D. Drijard H. G. Fischer W. Geist P. G. Innocenti V. Korbel A. Minten A. Norton S. Stein O. Ullaland H. D. Wahl G. Fontaine C. Ghesquière G. Sajot P. Hanke W. Hofmann M. Panter K. Rauschnabel J. Spengler D. Wegener H. Frehse M. Heiden E. E. Kluge A. Putzer M. Della Negra D. Linglin R. Gokieli R. Sosnowski 《Zeitschrift fur Physik C Particles and Fields》1981,9(4):293-303
Inclusive production of ?0,f, andg 0 mesons and ofK s 0 ,K *0 (892), ? andK *0(1430)mesons has been measured at <y>~2.6 and <p T >~1.1 GeV/c in proton-proton interactions at \(\sqrt s = 52.5\) GeV. The negative particle from the two-body decays of these resonances were identified by a threshold Cerenkov counter and used for triggering. Starting from the measured differential cross section, total inclusive cross sections for the vector and tensor mesons were determined using various parametrizations for they andp T dependence of the differential cross section. The experimental results are discussed in the framework of production models based on the parton picture. The strangeness suppresion factor λ=(0.30±0.10) due toSU(3) symmetry breaking of the quark sea is derived. 相似文献
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Cardoso Daisy Alves Valle Eliana Maíra Agostini Codognoto Lucia 《Journal of Solid State Electrochemistry》2018,22(5):1549-1555
Journal of Solid State Electrochemistry - In this work, the interaction of the pesticide methyl parathion (MP) with the lead metal ion was evaluated using a carbon electrode reused from a zinc... 相似文献
47.
L. Hedjazi C.L. Martin S. Guessasma G. Della Valle R. Dendievel 《International Journal of Solids and Structures》2012,49(13):1893-1899
Crack propagation in a vitreous biopolymer material is simulated using the Discrete Element Method (DEM), which models the brittle material as an assembly of particles bonded together. The simulations are compared to experiments combining a high-speed camera monitoring of crack branching together with a micromechancial testing of samples where local mixture mode is generated by introducing a stress concentrator. Our experimental results show unstable crack propagation and branching occurring upon crack deviation by the action of the stress concentrator. The validity of the DEM simulations is checked by comparing its result to the Finite Element Method (FEM) and to an analytical expression under similar conditions. DEM results show a higher sensitivity to mixed mode compared to FEM and a better match with the analytical formulation. Finally, crack branching is correctly predicted using DEM without any specific criterion for the initiation of secondary cracks. 相似文献
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José J. Garrido-González Irene Boya del Teso Dr. Ángel L. Fuentes de Arriba Dr. Francisca Sanz Dr. Eva M. Martín del Valle Dr. Joaquín R. Morán Dr. Victoria Alcázar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14605-14609
Cleft type receptors showing the oxyanion hole motif have been prepared in a straightforward synthesis starting from the commercial 3,7-dihidroxy-2-naphthoic acid. The double H-bond donor pattern is achieved by the introduction of a sulfonamide group in the C-8 position of naphthalene and a carboxamide at the C-2 position. This cleft, for which the geometry resembles that of an oxyanion hole, is able to adjust to different guests, as shown by the analysis of the X-ray crystal structures of associates with methanol or acetic acid. Combination of hydrogen bonds and charge-transfer interactions led to further stabilization of the complexes, in which the electron-rich aromatic ring of the receptor was close in space to the electron-deficient dinitroaromatic guests. Modelling studies and bidimensional NMR experiments have been carried out to provide additional information. 相似文献
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Giovanna Delogu Ottorino De Lucchi Maria Paola Fois Giovanni Valle 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):417-425
Abstract Ketimines la-d derived from ortho-aminosubstituted phenylthioethers were prepared in order to determine the degree of chirality transfer from the chiral auxiliary to the sulfur atom in the formation of the sulfoxide or to the α-carbon atom in the reaction of the anion with alkyl halides or benzaldehyde. Oxidation to the sulfoxide occurred with little or no asymmetric induction. The crystalline benzyl sulfone 4c was deprotonated by alkyllithium or Grignard reagents and reacted with alkyl halides and benzaldehyde, in all cases with little to fair transfer of chirality. The major diastereoisomer from methylation of the anion of 4c with methyl iodide, was isolated, and afforded the enantiomerically pure amine 5 after removal of the chiral auxiliary. An X-ray structure determination of 4d allowed the assignment of the absolute configuration of the asymmetric carbon and revealed that the conformation of the ketimine in the crystal state is not homogeneous. 相似文献