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151.
152.
Yasuaki Kawamura Satoshi Nagai Juichi Hirose Yasaku Wada 《Journal of Polymer Science.Polymer Physics》1969,7(9):1559-1575
Dielectric constant and dielectric loss of copolymers of methyl methacrylate (MMA) with n-butyl methacrylate (nBMA) and isobutyl methacrylate (iBMA) have been measured in the frequency range 30 cps to 1 Mcps at temperatures from 70°K to 370°K. Results lead, together with those of previously published investigations on copolymers of MMA, to the following conclusions. (1) The loss-peak temperature attributed to side-chain relaxation (β peak) of PMMA varies with the comonomer ratio when the comonomer does not have an α-methyl group, but remains almost unchanged for comonomers having an α-methyl group. (2) In both cases, the β peak height of PMMA decreases with increasing ratio of comonomer B and completely vanishes for poly-B, and the loss peak temperature plotted against the fraction of B does not extrapolate to the β peak of poly-B. It is suggested on the basis of the above facts that the moving unit in the side-chain relaxation consists of a single side chain with a segment of the backbone chain and that the change in mobility of the side chain upon copolymerization results from the distortion of the helical structure of the backbone chain due to random distribution of α-methyl groups. Dielectric studies of the low-temperature side-chain relaxation (β2 peak) in PnBMA, poly(n-octyl methacrylate), and poly(n-dodecyl methacrylate) (130°K at 1 kcps) have been made and an interpretation is offered for the molecular nature of this relaxation. 相似文献
153.
The new nonlinear destabilization process is found in the nonlinear phase of the double tearing mode (DTM). This process causes the abrupt growth of DTM and subsequent collapse after long-time-scale evolution in the Rutherford-type regime. The nonlinear growth of the DTM is triggered when the triangular deformation of magnetic islands with sharp current point at the X point exceeds a certain value. Hence, the mode can be called the structure-driven one. Decreasing the resistivity increases the sharpness of the triangularity and the spontaneous growth rate in the abrupt-growth phase is almost independent of the resistivity. 相似文献
154.
Zenkoh T Hatori H Tanaka H Hasegawa M Hatakeyama M Kabe Y Setoi H Kawaguchi H Handa H Takahashi T 《Organic letters》2004,6(14):2477-2480
[structure: see text] We describe the design and synthesis of latex particles attached to an FR225659 derivative to identify its receptor proteins. Two key building blocks were prepared by two-step degradation of FR225659 under basic conditions. The designed ligand showed an acceptable level of biological activity to make it of potential value for use in affinity-supported receptor identification. Affinity purification of FR225659-binding proteins using the latex nanoparticles provided three candidate receptor peptides for the biological activity. 相似文献
155.
Shunya Takahashi Yasuaki Suda Takemichi Nakamura Koji Matsuoka Hiroyuki Koshino 《合成通讯》2017,47(1):22-28
Vialinin B is a natural 3-phenyldibenzo[b,d]furan product with a powerful inhibitory activity against tumor necrosis factor (TNF)–α production. This article describes the synthesis of three types of biotinylated p-terphenyls designed for clarifying the target molecule of vialinin B. Construction of the carbon backbone of the core was accomplished by stepwise Suzuki–Miyaura coupling while the phenyl dibenzofuran moiety was built up by the Ullmann reaction. The biotinyl unit was attached through click chemistry. 相似文献
156.
Maeda H Nanai Y Mizuno K Chiba J Takeshima S Inouye M 《The Journal of organic chemistry》2007,72(23):8990-8993
3-(1-Alkynyl)perylenes undergo oxygenation when subjected to irradiation with visible light under aerated conditions. The structures of novel oxygenated products formed in this manner are assigned as regioisomeric dibenzo[jk,mn]phenanthrene-4,5-diones. 相似文献
157.
Jeong-Sik Lee Mitsuru Sugisaki Hong-Wen Ren Shigeo Sugou Yasuaki Masumoto 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
In0.45Ga0.55As/GaAs multistacking quantum dot (QD) structures were fabricated on a GaAs (n 1 1)B (n=2–4) substrate by metalorganic vapor-phase epitaxy. QDs spontaneously aligned in the [0 1 1] direction were observed on stacked QDs, whereas QDs were randomly distributed in the initial In0.45Ga0.55As layer growth. The formation mechanism of this self-alignment was studied by changing the number of In0.45Ga0.55As/GaAs multilayers and crystallographic arrangement. Photoluminescence spectra showing clear polarization dependence indicate carrier coupling in the QD arrays. This growth technique results in spontaneously aligned InGaAs QDs without any preprocessing technique prior to growth. 相似文献
158.
Kenneth M. Light Yasuaki Yamanaka Masafumi Odaka Edward I. Solomon 《Chemical science》2015,6(11):6280-6294
Nitrile hydratases (NHases) are mononuclear nonheme enzymes that catalyze the hydration of nitriles to amides. NHase is unusual in that it utilizes a low-spin (LS) FeIII center and a unique ligand set comprised of two deprotonated backbone amides, cysteine-based sulfenic acid (RSO(H)) and sulfinic acid (RSO2–), and an unmodified cysteine trans to an exogenous ligand site. Electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD) and low-temperature absorption (LT-Abs) spectroscopies are used to determine the geometric and electronic structures of butyrate-bound (NHaseBA) and active (NHaseAq) NHase. These data calibrate DFT models, which are then extended to explore the mechanism of nitrile hydration by NHase. In particular, the nitrile is activated by coordination to the LS FeIII and the sulfenate group is found to be deprotonated and a significantly better nucleophile than water that can attack the coordinated nitrile to form a cyclic species. Attack at the sulfenate S atom of the cyclic species is favorable and leads to a lower kinetic barrier than attack by water on coordinated, uncyclized nitrile, while attack at the C of the cyclic species is unfavorable. The roles of the unique ligand set and low-spin nature of the NHase active site in function are also explored. It is found that the oxidized thiolate ligands are crucial to maintaining the LS state, which is important in the binding and activation of nitrile susbtrates. The dominant role of the backbone amidate ligands appears to be as a chelate in keeping the sulfenate properly oriented for nucleophilic attack on the coordinated substrate. 相似文献
159.