The efficient transformation of D-glucal to (2R)-hydroxymethyldihydropyridinone 5 in seven steps and 35 % overall yield is reported. Dihydropyridone 5 constitutes a versatile chiral building block for the synthesis of various piperidine alkaloids. In this regard, 5 was converted to piperidinol 13 and piperidinone 15, that may be further elaborated for the syntheses of (+)-desoxoprosophylline (1) and deoxymannojirimycin (3) or D-mannolactam (4), respectively. 相似文献
Summary: The effect of peroxide vulcanization on organoclay dispersion in hydrogenated nitrile rubber (HNBR)/organo‐montmorillonite (organo‐MMT) nanocomposites was investigated. Three types of organoclays were tested, one containing a primary amine and two bearing quaternary intercalants. In contrast to sulfur vulcanization, which in combination with primary amine intercalants produced a confined/deintercalated clay structure, the peroxide curing yielded well‐ordered intercalated nanocomposites. The tensile mechanical performance and oxygen permeability of the HNBR nanocomposites were determined.
Oxygen permeability coefficient ratio for the different HNBR films tested at 0 and 60% relative humidity (i.e., dry and wet conditions, respectively). 相似文献
Furocoumarins 3,5 and pyranocoumarin 7 were synthesized from the reaction of furonaphthalenediones 2,4 and pyranonaphthalenedione 6 respectively with carbethoxymethylene(triphenyl)phosphorane in refluxing DCM for 3‐6 hours or under microwave irradiation in toluene for a few minutes. Compounds 3,5,7 and their precursors were tested as anti‐inflammatory/antioxidant agents. They were found to compete significantly high DMSO for OH radicals, to scavenge O2? and to inhibit lipoxygenase to a high extent. 相似文献
A new synthesis of hexamethyltungsten involves the reaction of WCl6 and AlMe3, while interaction of AlMe3 and ReOMe4 gives ReMe6; a dioxorhenium(VII) methyl, ReO2 Me3, is reported. 相似文献
The linearized buckling response of uniform steel beam-columns resting on a Pasternak foundation type is dealt with in this work. The corresponding two-point boundary value problem depends on the two parameters associated with the foundation model, that is, shear layer constant and Winkler spring coefficient, as well as on the axial loading. The fourth-order differential equation of buckling and the consequent characteristic one yield exact values of the buckling loads, which may lead to shape functions, being either one sinusoidal waveform or the sum of two different waveforms. The former case is associated with a single-mode response, while the latter with mode coupling. The conditions for which each of these cases characterizes the beam-column behavior are fully assessed and the dependence on the combination of the aforementioned parameters on the response is discussed in detail. It is found that regardless of the order of coupling, the corresponding mode is not related to rational values of buckling loads and hence this unfavorable phenomenon is excluded in structural design. 相似文献
A non conventional source or receiver of THz and above THz electromagnetic radiation is proposed. Specifically, electron or hole oscillations in DNA dimers (two interacting DNA base‐pairs or monomers) are predicted, with frequency in the range 0.25–100 THz (period 10–4000 fs) i.e. potentially absorbing or emitting electromagnetic radiation mainly in the mid‐ and far‐infrared with wavelengths ≈ 3–1200 μm. The efficiency of charge transfer between the two monomers which make up the dimer is described with the maximum transfer percentage p and the pure maximum transfer rate . For dimers made of identical monomers , but for dimers made of different monomers . The investigation is extended to DNA trimers (three interacting DNA base‐pairs or monomers). For trimers made of identical monomers the carrier oscillates periodically with 0.5–33 THz ( 30–2000 fs); for 0 times crosswise purines , for 1 or 2 times crosswise purines . For trimers made of different monomers the carrier movement may be non periodic. Generally, increasing the number of monomers above three, the system becomes more complex and periodicity is lost; even for the simplest tetramer the carrier movement is not periodic. 相似文献
The fundamental paradox of the incompatibility of the observed large-scale uniformity of the Universe with the fact that the age of the Universe is finite is overcome by the introduction of an initial period of superluminal expansion of space, called cosmic inflation. Inflation can also produce the small deviations from uniformity needed for the formation of structures in the Universe such as galaxies. This is achieved by the conjunction of inflation with the quantum vacuum, through the so-called particle production process. This mechanism is explained and linked with Hawking radiation of black holes. The nature of the particles involved is discussed and the case of using massive vector boson fields instead of scalar fields is presented, with emphasis on its distinct observational signatures. Finally, a particular implementation of these ideas is included, which can link the formation of galaxies, the standard model vector bosons and the observed galactic magnetic fields. 相似文献
We completely solve diophantine equations of the form where is a positive integer, using a reduction to some quartic elliptic equations, which can be solved with well known methods.
