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31.
Kent Morrill Robert E. Linder Edith M. Bruckmann Günter Barth Edward Bunnenberg Carl Djerassi Lloyd Seamans Albert Moscowitz 《Tetrahedron》1977,33(8):907-911
The magnetic CD spectra of a number of Me substituted trans-2-decalones and bicyelo[2.2.2]octan-2-ones were measured. The results showed a large, and sometimes dominant, contribution to the MCD intensity which could be correlated with the presence of α-substituents lying outside of the plane of the carbonyl chromophore. 相似文献
32.
Rubinshtein I. Zaltzman B. Pretz J. Linder C. 《Russian Journal of Electrochemistry》2002,38(8):853-863
The paper is concerned with convection at an ion-exchange electrodialysis membrane induced by nonequilibrium electroosmosis as a source of overlimiting conductance current through the membrane. Derivation of nonequilibrium electroosmotic slip condition is recapitulated along with the results of linear stability analysis of quiescent electrodiffusion through a flat ion-exchange membrane. Results of numerical calculation pertaining to nonlinear convection, developing from the respective instability, are reported along with those of recent experiments with modified membranes. These latter rule in favor of electroosmotic versus bulk electroconvective origin of overlimiting conductance through ion-exchange membranes. 相似文献
33.
Depecker G Patino N Di Giorgio C Terreux R Cabrol-Bass D Bailly C Aubertin AM Condom R 《Organic & biomolecular chemistry》2004,2(1):74-79
A cyclic molecule including a hexameric PNA sequence has been designed and synthesized in order to target the TAR RNA loop of HIV-1 through the formation of a "kissing complex". For comparison, its linear analogue has also been investigated. The synthesis of the cyclic and linear PNA has been accomplished following a liquid-phase strategy using mixed PNA and fully N-protected (aminoethylglycinamide) fragments. The interactions of this cyclic PNA and its linear analogue with TAR RNA have been studied and the results indicate clearly that no interaction occurs between the cyclic antisense PNA and TAR RNA, whereas a tenuous interaction has been detected with its linear PNA analogue. 相似文献
34.
Christophe Vande Velde Evi Bultinck Karla Tersago Christian Van Alsenoy Frank Blockhuys 《International journal of quantum chemistry》2007,107(3):670-679
Unhindered ortho‐dimethoxy‐substituted phenyl rings often display a coplanar conformation. A theoretical study of a series of methoxybenzenes consisting of methoxybenzene (anisole), the three dimethoxybenzenes, and 1,2,4,5‐tetramethoxybenzene, at the DFT/B3LYP/6‐311++G** level of theory, allows us to identify the factors influencing the conformational preference and attribute the coplanarity of such methoxy groups to mesomeric effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
35.
For polystyrene–poly(ethylene oxide) (PS–PEO) diblock copolymers, as micellar dispersions in aqueous medium, the formation of complexes with anionic surfactants, such as sodium dodecylsulfate (SDS) could be confirmed. The number of SDS molecules fixed per EO unit is close to the values reported for the SDS–PEO homopolymer interaction. Advantage of this type of complexation was taken to develop a controlled agglomeration process for SDS stabilized PS and PVC latexes by using as agglomerants ‘hairy’ latexes of PS and PVC that have been synthesized in the presence of PS–PEO block copolymers and that carry therefore a fringe of PEO sequences on their surface. The complexation of SDS by these surface-anchored PEO chains leads to the destabilization of the anionic latex, which has a tendency to precipitate onto the surface of the agglomerant latex. The average particle size and the size distribution of the agglomerated particles were studied as a function of the weight and number ratio of the two types of latexes involved in the agglomeration process, as well as in function of the surface coverage by SDS and PEO respectively. By adjusting these parameters, it was possible to obtain, with an efficiency of almost 100%, latex agglomerates with a monomodal distribution in the size range of 1 to 40 μm. An agglomeration mechanism could be outlined taking into account the complexation capacity and the specific surface of the agglomerating ‘hairy’ latex. To cite this article: P. Peter et al., C. R. Chimie 6 (2003). 相似文献
36.
(−)-Neplanocin F, the natural isomer of a component of the neplanocin family was enantioselectively synthesized starting from d-γ-ribonolactone. The synthetic approach was based on the preparation of a suitable carbocyclic precursor bearing three hydroxyl groups orthogonally protected. The key steps of the synthesis were the regioselective protection of a secondary allylic alcohol over a homoallylic one and the coupling of the nucleobase with a triflate intermediate. 相似文献
37.
Under Friedel-Crafts conditions, meso-tetraarylporphyrins give porphyrin spiro dimers in good yield. This reaction involves acylation, acid-catalyzed cyclization, and dimerization. A stable dimer possessing three additional six-membered rings could be isolated and its structure determined. By modifying the substrate and reagents, intermediates could be isolated and characterized. The reactivity of the substrates, the side-reactions, and the concentration requirements to form the dimers, all explain why this reaction remained apparently unexplored in the widely used meso-tetraarylporphyrin series. [reaction: see text] 相似文献
38.
Thoma G Streiff MB Katopodis AG Duthaler RO Voelcker NH Ehrhardt C Masson C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):99-117
Polyvalent carbohydrate-protein interactions occur frequently in biology, particularly in recognition events on cellular membranes. Collectively, they can be much stronger than corresponding monovalent interactions, rendering it difficult to control them with individual small molecules. Artificial macromolecules have been used as polyvalent ligands to inhibit polyvalent processes; however, both reproducible synthesis and appropriate characterization of such complex entities is demanding. Herein, we present an alternative concept avoiding conventional macromolecules. Small glycodendrimers which fulfill single molecule entity criteria self-assemble to form non-covalent nanoparticles. These particles-not the individual molecules-function as polyvalent ligands, efficiently inhibiting polyvalent processes both in vitro and in vivo. The synthesis and characterization of these glycodendrimers is described in detail. Furthermore, we report on the characterization of the non-covalent nanoparticles formed and on their biological evaluation. 相似文献
39.
Enantiomerically pure syn-anti and syn-syn configured triol units are efficiently synthesized by the SnCl4 mediated allylation of chiral α-benzyloxyaldehydes with the uniquely functionalised allylstannane 9. Remarkably, the stereochemistry of the adducts is solely governed by the amount of Lewis acid employed. 相似文献
40.
Jian Yang Vernica Postils Michael I. Lipschutz Meg Fasulo Christophe Raynaud Eric Clot Odile Eisenstein T. Don Tilley 《Chemical science》2020,11(19):5043
A cationic nickel complex of the bis(8-quinolyl)(3,5-di-tert-butylphenoxy)phosphine (NPN) ligand, [(NPN)NiCl]+, is a precursor to efficient catalysts for the hydrosilation of alkenes with a variety of hydrosilanes under mild conditions and low catalyst loadings. DFT studies reveal the presence of two coupled catalytic cycles based on [(NPN)NiH]+ and [(NPN)NiSiR3]+ active species, with the latter being more efficient for producing the product. The preferred silyl-based catalysis is not due to a more facile insertion of alkene into the Ni–Si (vs. Ni–H) bond, but by consistent and efficient conversions of the hydride to the silyl complex.A cationic nickel complex of the bis(8-quinolyl)(3,5-di-tert-butylphenoxy)phosphine (NPN) ligand, [(NPN)NiCl]+, is a precursor to efficient catalysts for the hydrosilation of alkenes with hydrosilanes under mild conditions and low catalyst loadings. 相似文献