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排序方式: 共有334条查询结果,搜索用时 31 毫秒
71.
Masaru Kihara Kuniyoshi Ohnishi Shigeru Kobayashi 《Journal of heterocyclic chemistry》1988,25(1):161-165
(8R) and (8S)-Hydroxy-6-methyl-5,6,7,8-tetrahydrodibenz[c,e]azocines (R- and S- 1 ) were synthesized by oxidative kinetic resolution of N-(2-iodobenzyl)-β-(2-iodophenyl)ethanolamine ( 8 ), followed by cyclization of the optically active acetates (R- and S- 6 ) of R- and S- 8 with zero-valent nickel to (8R)- and (8S)-acetoxyazocines (R- and S- 7 ), and by hydrolysis of the acetates ( R - and S- 7 ). 相似文献
72.
Abstract The effects of ultraviolet C (UVC) irradiation on nucleosome assembly and its stability were investigated quantitatively using an in vitro nucleosome assembly system comprising a plasmid DNA of pBR322 and core histones isolated from rat ascites hepatoma cells. Nucleosomal formation was estimated by analyzing the resulting DNA supercoils. When UVC-irradiated (3000 J/m2 ) DNA was used as a substrate for the nucleosome assembly system, the nucleosomal formation efficiency was reduced by half compared with nonirradiated DNA. On the other hand, when the reconstituted nucleosomes (minichromosomes) on the nonirradiated DNA were irradiated with UVC (3000 J/m2 ), about half each were disrupted and retained. These results indicate that it is difficult for UV-damaged DNA regions to supercoil around the histone octamers to form nucleosomes and that the histone octamers in the UV-damaged nucleosomes tend to be dissociated from DNA. 相似文献
73.
Zhe Wang Rikuo Akisaka Sohshi Yabumoto Tatsuo Nakagawa Sayaka Hatano Manabu Abe 《Chemical science》2021,12(2):613
Localised singlet diradicals are key intermediates in bond homolysis processes. Generally, these highly reactive species undergo radical–radical coupling reaction immediately after their generation. Therefore, their short-lived character hampers experimental investigations of their nature. In this study, we implemented the new concept of “stretch effect” to access a kinetically stabilised singlet diradicaloid. To this end, a macrocyclic structure was computationally designed to enable the experimental examination of a singlet diradicaloid with π-single bonding character. The kinetically stabilised diradicaloid exhibited a low carbon–carbon coupling reaction rate of 6.4 × 103 s−1 (155.9 μs), approximately 11 and 1000 times slower than those of the first generation of macrocyclic system (7.0 × 104 s−1, 14.2 μs) and the parent system lacking the macrocycle (5 × 106 s−1, 200 ns) at 293 K in benzene, respectively. In addition, a significant dynamic solvent effect was observed for the first time in intramolecular radical–radical coupling reactions in viscous solvents such as glycerin triacetate. This theoretical and experimental study demonstrates that the stretch effect and solvent viscosity play important roles in retarding the σ-bond formation process, thus enabling a thorough examination of the nature of the singlet diradicaloid and paving the way toward a deeper understanding of reactive intermediates.An extremely long-lived localised singlet diradical with π-single bonding character is found in a macrocyclic structure that retards the radical–radical coupling reaction by the “stretch and solvent-dynamic effects”. 相似文献
74.
Amenomori M Cao Z Ding LK Feng ZY Hibino K Hotta N Huang Q Huo AX Jia HY Jiang GZ Jiao SQ Kajino F Kasahara K Labaciren Mei DM Meng L Meng XR Mimaciren Mizutani K Mu J Nanjo H Nishizawa M Nusang Oguro A Ohnishi M Ohta I Ren JR Saito T Sakata M Shi ZZ Shibata M Shirai T Sugimoto H Sun XX Tai A Taira K Tan YH Tateyama N Torii S Wang H Wen CZ Yamamoto Y Yao XY Yu GC Yuan P Yuda T Zeng JG Zhang CS Zhang HM Zhang L Zhasang Zhaxiciren Zhou WD 《Physical review D: Particles and fields》1993,47(7):2675-2681
75.
The glass-forming composition regions of aqueous tetraalkylammonium nitrate solutions (alkyl = ethyl and n-propyl) were determined by a simple DTA method with a cooling rate of about 600 K-min–1. The glass transition temperatures Tg of these solutions vary in a different manner from those for simple inorganic salt solutions such as aqueous LiCl, MgCl2,and AlCl3 solutions. Liquid-liquid immiscibilities are observed in these solutions at low temperatures. 相似文献
76.
Structural changes of graphite surfaces induced by femtosecond (fs) laser excitation at a fluence regime above 75 mJ/cm2 are reported. Direct imagings of excited surfaces by means of scanning tunneling microscopy have revealed that fs-excitations induce nanometer-scaled craters, together with sp3-type interlayer-bonded domains. The nano-craters are characterized by atomically-flat bottom and two atomic-steps in depth, indicating the exfoliation of fragmentary intact-sheets of double-layer of graphite. The theoretical simulation has shown that the required energy for the double-layer ablation is much lowered by the help of interlayer-bond formation, compared to the sequential removal of individual graphene layers. Based on the experimental and theoretical results, the exfoliation of double graphite layers, that is a novel mode of laser-ablation observed first, indicates clearly that the formation of strong interlayer bonds between the two atomic layers is a crucial step in the ablation process. 相似文献
77.
Zimmer JP Kim SW Ohnishi S Tanaka E Frangioni JV Bawendi MG 《Journal of the American Chemical Society》2006,128(8):2526-2527
We have developed a size series of unusually small, water-soluble (InAs)ZnSe (core)shell quantum dots (QDs) that emit in the near-infrared and exhibit new behavior in vivo, including multiple sequential lymph node mapping and extravasation from the vasculature. The biological utility of these fluorescent probes resulted from our intentional choice to match the semiconductor material and water-soluble ligand with a desired final hydrodynamic diameter and emission wavelength. 相似文献
78.
We present the analysis of elliptic flow at
=130 A GeV energy in a hadron-string cascade model. We find that the final hadronic yields are qualitatively described. The
elliptic flow v
2 is reasonably well-described at low transverse momentum (p
t<1 GeV/c) in mid-central collisions. On the other hand, this model does not explain v
2 at high p
t or in peripheral collisions and thus generally, it underestimates the elliptic flow at RHIC energy. 相似文献
79.
Horiuchi M Tokuda H Ohnishi K Yamashita M Nishino H Maoka T 《Natural product research》2006,20(2):161-166
To search for possible cancer chemopreventive agents from natural sources, we performed primary screening of metabolites of Alternaria porri by examining their possible inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. The ethyl acetate extract of A. porri showed the inhibitory effect on EBV-EA activation. Three porritoxins (1-3) were obtained as inhibitory active compounds for EBV-EA from ethyl acetate extract. 6-(3',3'-Dimethylallyloxy)-4-methoxy-5-methylphthalide (2) showed the strongest activity among them. Inhibitory effect of porritoxin (1) and (2) was superior to that of beta-carotene, a well-known anti-tumor promoter. Furthermore, the structure-activity correlation of porritoxins and their related compounds were discussed. 相似文献
80.
E.S.R. spectra of PF4 radicals were investigated with single crystals of PF3 made at a low temperature and irradiated with γ-rays. The angular dependence of the spectral lines was satisfactorily analysed in terms of the second-order equations for large couplings of one 31P nucleus and two magnetically equivalent 19F nuclei and of the first-order equation for two 19F nuclei with small couplings. We conclude that the two magnetically equivalent fluorine nuclei occupy the axial positions of the trigonal bipyramidal structure of the PF4 radical and the other two fluorine nuclei are in the equatorial positions. Furthermore, the unpaired electron of the PF4 radical was shown to occupy an orbital consisting mainly of the 2p orbital of each of the two axial fluorine atoms along the F-P-F axis and the 3s and 3p orbitals, directed towards the vacant equatorial position of the central phosphorus atom. The orbital of the unpaired electron can be reasonably represented as a Rundle three-centre non-bonding orbital. The results obtained for the PF4 radicals not only strongly support the results given for POCl3 - radicals, but also allow us to discuss the electronic structure of phosphoranyl radicals in more detail. 相似文献