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排序方式: 共有189条查询结果,搜索用时 15 毫秒
81.
Tosaki SY Hara K Gnanadesikan V Morimoto H Harada S Sugita M Yamagiwa N Matsunaga S Shibasaki M 《Journal of the American Chemical Society》2006,128(36):11776-11777
A kinetic resolution of tertiary nitroaldols derived from simple ketones is described. Mixed BINOL/biphenol La-Li heterobimetallic complexes gave the best selectivity in retro-nitroaldol reactions of racemic tertiary nitroaldols. By using a mixture of La-Li3-(1a)3 complex (LLB 2a) and La-Li3-(1b)3 (LLB* 2b) complex in a ratio of 2/1, chiral tertiary nitroaldols were obtained in 80-97% ee and 30-47% recovery yield. 相似文献
82.
Matsuo Sekine Katsumi Sugita Yoshiwo Okamoto 《International Journal of Theoretical Physics》1997,36(6):1409-1412
Based on a preon model satisfying both theSU(2) and Lorentz invariances, it is shown thatCP is violated, and anomalies are also eliminated. 相似文献
83.
2 Σ+,H′ 2Π±(v′=2), and 4dσ,πO2Σ+,O′ 2Π±(v′=0) Rydberg states of NO molecules are described. The analyses of the two-photon excitation functions and infrared emission
spectra revealed that only the 2Π- component was involved in PFWM. This is in good accordance with the absence of amplified spontaneous emission (ASE) in the
2Σ+ and 2Π+ components due to their predissociative character. Results provide some support for the mechanism that the generation of
the vacuum ultraviolet radiation was brought by PFWM in which ASE served as a third driving wave.
Received: 6 January 1998 相似文献
84.
Masanobu Mori Toshinobu Suzuki Tsuyoshi Sugita Daisuke Nagai Kazuo Hirayama Makoto Onozato Hideyuki Itabashi 《Analytica chimica acta》2014
This study aimed to evaluate the heavy metal adsorptivity of calcium-alginate-modified diethylenetriamine-silica gel (CaAD) and incorporate this biosorbent into a flow analytical system for heavy metal ions using flame atomic absorption spectrometry (FAAS). The biosorbent was synthesized by electrostatically coating calcium alginate onto diethylenetriamine (dien)-silica gel. Copper ion adsorption tests by a batch method showed that CaAD exhibited a higher adsorption rate compared with other biosorbents despite its low maximum adsorption capacity. Next, CaAD was packed into a 1 mL microcolumn, which was connected to a flow analytical system equipped with an FAAS instrument. The flow system quantitatively adsorbed heavy metals and enriched their concentrations. This quantitative adsorption was achieved for pH 3–4 solutions containing 1.0 × 10−6 M of heavy metal ions at a flow rate of 5.0 mL min−1. Furthermore, the metal ions were successfully desorbed from CaAD at low nitric acid concentrations (0.05–0.15 M) than from the polyaminecarboxylic acid chelating resin (Chelex 100). Therefore, CaAD may be considered as a biosorbent that quickly adsorbs and easily desorbs analyte metal ions. In addition, the flow system enhanced the concentrations of heavy metals such as Cu2+, Zn2+, and Pb2+ by 50-fold. This new enrichment system successfully performed the separation and determination of Cu2+ (5.0 × 10−8 M) and Zn2+ (5.7 × 10−8 M) in a river water sample and Pb2+ (3.8 × 10−9 M) in a ground water sample. 相似文献
85.
Hiroyuki Kawai Yutaka Sugita Etsuko Tokunaga Hiroyasu Sato Motoo Shiro Norio Shibata 《ChemistryOpen》2014,3(1):14-18
Highly functionalized 5-trifluoromethyl-2-isoxazoline derivatives featuring a triflyl (SO2CF3) group at the 4-position were successfully synthesized via diastereoselective trifluoromethylation and halogenation of isoxazole triflones using the Ruppert– Prakash reagent. The trifluoromethylation is quite general in terms of the substrates including 3,5-diaryl isoxazole triflones and 3-aryl-5-styrylisoxazole triflones to provide products in high yields with excellent diastereoselectivities. The highly functionalized 5-trifluoromethyl-2-isoxazoline derivatives are expected to be a new class of antiparasiticides. Thus the triflyl group both activates isoxazoles and the 4-postion of CF3 adducts, and has a potential biological function. 相似文献
86.
Ono M Sugita F Shigematsu S Takamura C Yoshimitsu H Miyashita H Ikeda T Nohara T 《Chemical & pharmaceutical bulletin》2007,55(7):1093-1096
Three new steroid glycosides named trikamsterosides C, D and E were isolated from the underground parts of Trillium kamtschaticum PALL. (Liliaceae) along with two known 18-norspirostanol glycosides trillenosides A and B. Their chemical structures were determined on the basis of spectroscopic data and chemical evidence. 相似文献
87.
Katsumi Sugita Yoshiwo Okamoto Matsuo Sekine 《International Journal of Theoretical Physics》1997,36(6):1309-1316
We consider a simple Lagrangian which is constructed by only the preon and antipreon fields. By introducing the auxiliary
fields φμ, φ
μ
†
, and ϕμ, it is shown that φμ, φ
μ
†
, and ϕμ correspond to the electroweak gauge bosonsW
μ
+
,W
μ
−
, andW
μ
3
, respectively, which are composite particles of preons and antipreons. 相似文献
88.
Yoshiaki Inaki Shin-Ichi Sugita Tohru Takahara Kiichi Takemoto 《Journal of polymer science. Part A, Polymer chemistry》1986,24(12):3201-3217
Acrylamide and methacrylamide derivatives of nucleic acid bases were prepared from the corresponding aminoethyl derivatives. Free-radical polymerization of these monomers in water or in organic solvents gave their polymers. From the studies of the polymer complex formation by UV spectroscopy, it was found that extremely stable polymer complexes were formed between complementary polymers containing nucleic acid bases. 相似文献
89.
The 13C-selective infrared multiple-photon decomposition (IRMPD) of mixtures of CHClF2 and HI was examined in collimated and focused beam geometries using a CO2TEA laser. The carbon-containing products were CH2F2 and CHF2I. The former product showed remarkably high 13C atom concentrations beyond 95% under selected experimental conditions, while the latter contained 25% or less. The observed results can be explained satisfactorily in terms of the consecutive two-stage IRMPD process occurring in a single irradiation procedure, where the first-stage IRMPD of natural CHClF2 produces 13C-enriched CHF2I via the insertion of the initial decomposition fragment CF2 into HI, and the second stage is the subsequent 13C-selective IRMPD of the CHF2I to form a CHF2 radical and an I atom. The CHF2 radical reacts with HI to form CH2F2. Decomposition probabilities of 12CHClF2 and 13CHClF2 were measured as a function of laser fluence to optimize enrichment conditions. Furthermore, partial decomposition probabilities or relative production yields were measured as functions of laser line, pressure of HI, and pressure of CHClF2. Both stages showed high 13C selectivities in the irradiation with the laser radiation around 1040 cm–1 and at fluences below 4 J cm–2. This mixture is one of the most promising chemical systems for the production of highly enriched 13C. 相似文献
90.
Suyong Re Takashi Imai Jaewoon Jung Seiichiro Ten‐No Yuji Sugita 《Journal of computational chemistry》2011,32(2):260-270
Reversible phosphorylation of proteins is a post‐translational modification that regulates diverse biological processes. The molecular mechanism underlying phosphoryl transfer catalyzed by enzymes remains a subject of active debate. In particular, the nature of transition state (TS), whether it has an associative or dissociative character, has been one of the most controversial issues. Structural evidence supports associative TS, whereas physical organic studies point to a dissociative character. Here we perform hybrid quantum mechanics/molecular mechanics simulations for the reversible phosphorylation of phosphoserine phosphatase (PSP) to study the nature of the TS. Both phosphorylation and dephosphorylation reactions are investigated based on the two‐dimensional energy surfaces along phosphoryl and proton transfer coordinates. The structures of the active site at TS in both reactions reveal compact geometries, consistent with crystal structures of PSP with phosphate analogues. However, the electron density of the phosphoryl group in both TS structures slightly decreases compared with that in the reactant states. These findings suggest that the TS of PSP has a geometrically associative yet electronically dissociative character and strongly depends on proton transfer being coupled with phosphoryl transfer. Structure and literature database, which searches on phosphotransferases, suggest that such a hybrid TS is consistent with many structures and physical organic studies and likely holds for most enzymes catalyzing phosphoryl transfer. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 相似文献