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81.
A new family of enantiomerically pure (1S,2R)-1-alkyl-2-(dialkylamino)-3-(R-oxy)-1-propanols containing a very bulky alkyl substituent (tert-butyl or 1-adamantyl) on their hydrocarbon chains has been synthesized from the corresponding enantiopure epoxy alcohols, arising from the catalytic Sharpless epoxidation, by protection of the primary hydroxy group and subsequent regioselective ring opening of the epoxide by a secondary cyclic amine (C-2 attack). The performance of these amino alcohols as ligands for the catalytic enantioselective addition of diethylzinc to benzaldehyde has been studied, with enantioselectivities of 92-96% being recorded. The best performing ligands, those with a bulky R-oxy group, also depict a convenient activity and selectivity profile in the addition of Et(2)Zn to a representative family of aldehydes. An anomalous structure/enantioselectivity relationship of some ligands in the tert-butyl series has been studied using PM3 calculations, and conclusions have been drawn on the possible effects of including in modular designs structural fragments giving rise to a variety of rotameric transition states. 相似文献
82.
Maria Hoffmann Antoni Konitz Artur Sikorski Urszula Lesińska Maria Bocheńska 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(3-4):137-142
The synthesis and characterization of the lower rim bis-phosphorylatedtetrakis-p-tert-butyl-25,27-bis(methoxy)calix[4]arenas(compounds 2–4) is presented. The studied compounds were examined as ionophores in ion-selective membrane electrodes, showing selectivity for rubidium, potassium, and for the large and flat guanidinium cations (G+). The correlation wasstudied between the stereochemical structure of the ligands andpotentiometrically determined ion-selectivity. Complex formationconstants in the PVC/BEHS (bis(ethyl)hexyl sebacate) membranes weredetermined. The crystal and molecular structures of compound 4 have been determined by single crystal X-ray diffraction study. 相似文献
83.
In this paper we study the direct decomposability of free Tarski algebras. We
show that infinite freely generated Tarski algebras are directly indecomposable, whereas
finite freely generated Tarski algebras can only be decomposed into a direct product of two
factors, one of which is the two-element Tarski algebra. 相似文献
84.
85.
86.
Luca Stabellini Wei Lu Alfredo De Rossi Thomas Antoni Mathieu Carras Stefano Trillo Gaetano Bellanca 《Optical and Quantum Electronics》2008,40(14-15):1085-1090
A Finite Difference Time Domain approach is used to design and to optimize quantum-well based infrared photodetectors. Results showing the influence of some parameters on the performance of these devices are presented and discussed. 相似文献
87.
Antoni Orlowski 《Fresenius' Journal of Analytical Chemistry》1872,11(1):38-43
Ohne Zusammenfassung 相似文献
88.
Hugo Peluffo Laia Acarin Anna Arís Pau González Antoni Villaverde Bernardo Castellano Berta González 《BMC neuroscience》2006,7(1):35
Background
Superoxide mediated oxidative stress is a key neuropathologic mechanism in acute central nervous system injuries. We have analyzed the neuroprotective efficacy of the transient overexpression of antioxidant enzyme Cu/Zn Superoxide dismutase (SOD) after excitotoxic injury to the immature rat brain by using a recently constructed modular protein vector for non-viral gene delivery termed NLSCt. For this purpose, animals were injected with the NLSCt vector carrying the Cu/Zn SOD or the control GFP transgenes 2 hours after intracortical N-methyl-D-aspartate (NMDA) administration, and daily functional evaluation was performed. Moreover, 3 days after, lesion volume, neuronal degeneration and nitrotyrosine immunoreactivity were evaluated. 相似文献89.
Limage S Krägel J Schmitt M Dominici C Miller R Antoni M 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):16754-16761
In the present work, we focus on the bulk rheology of mixtures consisting of surfactant modified silica nanoparticles in water. Depending on the ratio of surfactant and nanoparticle concentrations, significant modifications in the measured rheology are evidenced. A domain where the dispersions behave like viscoelastic media is observed. Outside this domain, the dispersions exhibit viscous properties. The changes in the bulk rheology characteristics are discussed in terms of interaction effects between the surfactant and the particles. The results obtained are seen in the context of diluted emulsions' properties and characteristics. 相似文献
90.
Antoni T Kuhn AG Briant T Cohadon PF Heidmann A Braive R Beveratos A Abram I Le Gratiet L Sagnes I Robert-Philip I 《Optics letters》2011,36(17):3434-3436
We have designed photonic crystal suspended membranes with optimized optical and mechanical properties for cavity optomechanics. Such resonators sustain vibration modes in the megahertz range with quality factors of a few thousand. Thanks to a two-dimensional square lattice of holes, their reflectivity at normal incidence at 1064?nm reaches values as high as 95%. These two features, combined with the very low mass of the membrane, open the way to the use of such periodic structures as deformable end mirrors in Fabry-Perot cavities for the investigation of cavity optomechanical effects. 相似文献