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991.
Taisuke Imamura Takeshi Maehara Prof. Dr. Ryo Sekiya Prof. Dr. Takeharu Haino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3250-3254
By introducing slight structural modifications to a D4‐symmetric coordination capsule, we succeeded in isolating the nearly enantiopure capsules (P)‐ and (M)‐ 2 a (BF4)4. Chiral guest, dibenzyl 4,4′‐diacetoxy‐6,6′‐dimethyl‐[1,1′‐biphenyl]‐2,2′‐dicarboxylate ( 3 ) was encapsulated within the dissymmetric cavity of 2 a (BF4)4, resulting in a high diastereoselectivity of >99 % de. The encapsulated guest was successfully removed from the complex without racemization through precipitation of the empty capsule. CD spectra confirmed that the chirality of the capsule was maintained in THF and 1,4‐dioxane for long periods, whereas a small amount of acetonitrile accelerated racemization of the empty capsule. The activation parameters of the racemization reaction were determined in dichloromethane and 1,2‐dichloroethane, resulting in positive enthalpic contributions and large negative entropic contributions, respectively. Accordingly, the racemization fits a first‐order kinetic model. Mechanically coupled Cu+‐2,2′‐bipyridine coordination centers were responsible for the high‐energy barrier of racemization and led to the unique chiral memory of the dissymmetric cavity, which was turned off by the addition of acetonitrile. 相似文献
992.
Ryo Nadano Dr. Kohei Fuchibe Dr. Masahiro Ikeda Hiroki Takahashi Junji Ichikawa Prof. Dr. 《化学:亚洲杂志》2010,5(8):1875-1883
1‐(Trifluoromethyl)vinylation is accomplished in two protocols by the in situ generation of thermally unstable 3,3,3‐trifluoroprop‐1‐en‐2‐yllithium ( 1 ): 1) a rapid lithium–halogen‐exchange reaction of 2‐bromo‐3,3,3‐trifluoroprop‐1‐ene ( 2 ) takes effect with sec‐BuLi at ?105 °C to generate vinyllithium 1 , which reacts with more reactive electrophiles, such as aldehydes and N‐tosylimines before its decomposition, to afford 2‐(trifluoromethyl)allyl alcohols and N‐[2‐(trifluoromethyl)allyl] sulfoamides in good yield; 2) treatment of 2 with nBuLi at ?100 °C causes a slow lithium–halogen exchange of 2 , which gives rise to a mixture of 1 and nBuLi. Vinyllithium 1 is preferentially trapped with less reactive electrophiles, such as N,N‐dimethylamides in the presence of BF3?OEt2, to afford 1‐(trifluoromethyl)vinyl ketones in good yield. Versatility of the products toward syntheses of CF3‐containing ring‐fused cyclopentenones is also demonstrated by the Pauson–Khand reaction and the Nazarov cyclization. 相似文献
993.
994.
Synthesis, crystal structures and magnetic properties of metal telluromolybdates MxM′1?xTeMoO6 (M, M′ = Mn, Co, Cd) have been investigated. Their crystal structures have two-dimensional arrays of M and M′ atoms. From the powder X-ray diffraction measurements, MnxCo1?xTeMoO6 adopt an orthorhombic structure throughout the composition range (x = 0.0–1.0). On the other hand, MnxCd1?xTeMoO6 and CoxCd1?xTeMoO6 adopt two types of structures corresponding to their end members (orthorhombic for Mn- or Co-rich solid solutions; tetragonal for Cd-rich ones). In the intermediate compositions, it was found that two phases coexist with different metal components. Magnetic properties of these solid solutions were investigated. All the MnxCo1?xTeMoO6 exhibits an antiferromagnetic transition at ~23 K. The antiferromagnetic transition was also observed in MnxCd1?xTeMoO6 and CoxCd1?xTeMoO6. However, the Néel temperature rapidly decreases with increasing the concentration of Cd and disappeared below x = 0.6, which is characteristic for two-dimensional magnetic system. 相似文献
995.
This review presents the state of the art of DNA sensors (or genosensors) that utilize electrochemical impedance spectroscopy as the transduction technique. As issue of current interest, it is centered on the use of nanomaterials to develop or to improve performance of these specific biosensors. It will describe the different principles that may be employed in the measuring step and the different formats adopted for detection of a DNA sequence or confirmation or amplification of the finally obtained signal. The use of nanomaterials for the above listed aspects, viz. the use of carbon nanotubes or other nanoscopic elements in the construction of the electrodes, or the use of nanoparticles, mainly gold or quantum dots, for signal enhancement will be fully revised. 相似文献
996.
金涛 贾宏志 侯文玫 Ryo Yamamoto Norihiro Nagai Yusaku Fujii Koichi Maru Naoya Ohta Kazuhito Shimada 《中国光学快报(英文版)》2010,(6):601-605
<正>A practical method for evaluating the three-dimensional(3D) position and velocity of a moving object used in the parabolic flight experiment is developed by using the binocular stereo vision measurement theory. The camera calibration mathematic model without considering the lens distortion is introduced.The direct linear transformation(DLT) algorithm is improved to accomplish the camera calibration.The camera calibration result and optimization algorithm are used to calculate the object's world coordinate from image coordinate.The 3D position and the velocity of the moving object are obtained.The standard uncertainty in estimating the velocity is 0.0024 m/s,which corresponds to 1%level of the velocity of the object in the experiment.The results show that this method is very useful for the parabolic flight experiments. 相似文献
997.
We analyze the Thermodynamic Bethe Ansatz equations for the mirror model which determine the ground state energy of the light-cone AdS5×S5 superstring living on a cylinder. The light-cone momentum of string is equal to the circumference of the cylinder, and is identified with the inverse temperature of the mirror model. We show that the natural requirement of the analyticity of the Y-functions leads to the quantization of the temperature of the mirror model which has never been observed in any other models. 相似文献
998.
Stuart Pearce Ryo Yasuhara Akira Yoshida Toshiyuki Kawashima Hirofumi Kan 《Optics Communications》2009,282(11):2199-4985
A diode-pumped Master Oscillator Power Amplifier (MOPA) laser system based on cryogenic cooled Yb:YAG has been designed, developed and its output performance characterised. The laser system consists of a fibre oscillator, an active mirror regenerative amplifier and a four pass main amplifier. 2.4 mJ, 10 ns, 100 Hz seed pulses from the fibre oscillator/regenerative amplifier arrangement were amplified up to pulse energies of over 200 mJ by using the four pass main amplifier arrangement. As a further study we have obtained an increased slope efficiency of 40% and an optical-to-optical efficiency of 30% using a pinhole vacuum spatial filter/image relay for laser mode control. With 1.8 mJ input seed pulses, output pulse energies of around 150 mJ were achieved. 相似文献
999.
Shintani R Yashio K Nakamura T Okamoto K Shimada T Hayashi T 《Journal of the American Chemical Society》2006,128(9):2772-2773
A rhodium-catalyzed asymmetric isomerization of racemic alpha-arylpropargyl alcohols to beta-chiral indanones has been developed. High enantioselectivity has been realized by the use of a newly developed axially chiral bisphosphine ligand. This ligand is unique in the sense that its axial chirality is fixed to a single configuration upon complexation to a transition metal due to other chiral axes existing within the same molecule. 相似文献
1000.
A palladium-catalyzed [3 + 3] cycloaddition of trimethylenemethane (TMM) with azomethine imines has been developed to produce hexahydropyridazine derivatives under simple and mild conditions. The use of substituted TMM precursors highlights the difference of this system from previously reported [3 + 2] cycloaddition of TMMs under palladium catalysis. The present [3 + 3] cycloaddition reactions are also applicable to couplings with nitrones. 相似文献