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排序方式: 共有785条查询结果,搜索用时 281 毫秒
731.
Kogen H Toda N Tago K Marumoto S Takami K Ori M Yamada N Koyama K Naruto S Abe K Yamazaki R Hara T Aoyagi A Abe Y Kaneko T 《Organic letters》2002,4(20):3359-3362
Highly efficient acetylcholinesterase (AChE) and serotonin transporter (SERT) dual inhibitors, (S)-4 and (R)-13 were designed and synthesized on the basis of the hypothetical model of AChE active site. Both compounds showed potent inhibitory activities against AChE and SERT. [structure: see text] 相似文献
732.
Formic acid-phosphorus pentoxide was effective for the preparation of 5,7-dimethyl[1,3,4]thiadiazolo- and -[1,3]thiazolo[3,2-a]pyrimidin-4-ium salts. Further, the pyrimidine ring transformation and the isocyanation of 5imino-6H-[1,3,4]thiadiazolo- and -[1,3]thiazolo[3,2-a]pyrimidin-7-ones were carried out in the presence of formic acid and triethyl orthoformate, respectively. 相似文献
733.
Analysis of the artificial radionuclide 99Tc in environmental samples requires a chemical separation due to its low concentration, and therefore the use of a chemical yield tracer is peremptory. From a practical viewpoint, Re can be used for this purpose, due to its chemical similarities with Tc. Thus, the use of a radioactive tracer for Tc recovery calculation can be avoided. However, results from a recent intercomparison exercise showed that using of Re as a chemical yield tracer appears to underestimate the Tc concentration relative to the result obtained with isotopes of Tc. In the present work, the methodology used to design a simple separation method for the measurement of 99Tc in environmental samples is described. Tc recovery is estimated throughout the Re recovery calculation by the isotope dilution technique coupled with ICP-MS (ID-ICP-MS) technique. For chemical separation, a chromatographic resin is used. Interfering elements are removed using a resin washing step carefully designed to avoid any element fractionation between Re and Tc; the care taken in this step is of major importance to assure the equivalence of the chemical recoveries for both elements. Agreement is tested using five replicates of five seaweed samples. The average recoveries for 95mTc and Re were 93±6 and 95±7%, respectively, those are within the uncertainty intervals for each other. The results explained here demonstrate the possibility of applying Re chemical recoveries to calculate the Tc concentrations with the advantage of not introducing systematic errors. 相似文献
734.
Seiichi Miyajima Keisuke Nakazawa Keiko Niikura Yasuhiro Ujiiye Makiko Yashiro Takehiko Chiba 《Liquid crystals》1990,8(5):707-718
The nature of smectic A liquid crystals and the phase transitions from smectic A to nematic phases are studied in the homologous series of 4-(4'-octyloxy-benzoyloxy)benzylidene-4'-substituted anilines, in which the substituents are H, F, Cl, Br, I, NO2 and CN. Measurements have been performed for the dipole moment of the molecule, the smectic A lattice period, the temperatures and the entropies of phase transitions, and the temperature dependence of the orientational order parameter, all of which provide information on the intermolecular pair potentials. It is shown that the introduction of a terminal polar substituent brings about counteracting contributions to the stability of the smectic A state. It is suggested that the reentrant nematic phase transition can appear in the strongly polar mesogens if the extent of antiparallel association of the molecules increases on lowering the temperature. 相似文献
735.
736.
B. A. Arbuzov A. A. Kamalyutdinova-Salikhova S. M. Shostakovskii A. A. Retinski V. V. Keiko S. G. Vul'fson A. N. Vereshchagin 《Russian Chemical Bulletin》1978,27(12):2526-2529
Conclusions The meso- and dl-bis-2,2-dichlorocyclopropyl ethers exist in solution in a gauche-gauche type of conformation, with the three-membered rings arranged along different sides of the C-O-C plane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2828–2831, December, 1978. 相似文献
737.
Shoji Murai Satoshi Imajo Hiroaki Inumaru Keiko Takahashi Kenjiro Hattori 《Journal of colloid and interface science》1997,190(2):488
The adsorption and recovery of ionic surfactants, such as dodecylbenzenesulfonic acid (DBS) and benzalkonium chloride (BKC), from an aqueous solution were studied using the β-cyclodextrin polymer (β-CDP). BKC always demonstrated a higher adsorption efficiency than DBS in batch tests, isotherms, and column tests. The adsorption characteristics of the surfactants seemed to be caused by inclusion into β-CD, and they were easily determined using the Langmuir adsorption isotherm. Furthermore, the surfactants adsorbed by β-CDP were easily released by shaking it with a mixture of water and methanol. Recovery efficiency was dependent on the mixture ratio of the solvent, and regenerated β-CDP was reusable as an adsorbent. 相似文献
738.
Suzuki AZ Watanabe T Kawamoto M Nishiyama K Yamashita H Ishii M Iwamura M Furuta T 《Organic letters》2003,5(25):4867-4870
Caged compounds can be used to regulate the spatial and temporal dynamics of signaling molecules in live cells. Photochemical properties of coumarin-4-ylmethoxy carbonates (1a-d) are investigated to construct caged compounds of hydroxy-containing molecules. All the compounds possess desired properties as phototriggers for alcohols and phenols. The 6-bromo-7-hydroxycoumarin-4-ylmethoxycarbonyl (Bhcmoc) group has the highest photochemical efficiency and is applied to make caged compounds of 1,2-dioctanoylglycerol (diC(8)), Tyr-OMe, and adenosine. [reaction: see text] 相似文献
739.
A high-performance liquid chromatographic method involving postcolumn fluorescence derivatization is described for the quantification of five fragment peptides (methionine-enkephalin-Thr-Ser-Glu-Lys, methionine-enkephalin-Lys, methionine-enkephalin-Arg, leucine-enkephalin-Lys and leucine-enkephalin-Arg) released by tryptic digestion from the opioid peptide precursors (proopiomeranocortin and proenkephalins A and B) in rat brain tissues. The tissue proteins containing the precursors are hydrolyzed with trypsin to the fragment peptides. The peptides are separated on an Asahipak ODP-50 column and on-line detected fluorometrically by using hydroxylamine, cobalt(II) and borate buffer reagents. The detection limits (S/N = 3) for the peptides are 0.7-2.8 pmol per 100 microliters injected. The distribution of the precursors in the brain tissues was also discussed on the basis of the determined values of the fragment peptides. 相似文献
740.
In situ chemical aminoacylation with amino acid thioesters linked to a peptide nucleic acid 总被引:1,自引:0,他引:1
Ninomiya K Minohata T Nishimura M Sisido M 《Journal of the American Chemical Society》2004,126(49):15984-15989
tRNA-specific chemical aminoacylation was achieved with nonnatural amino acids. A nonnatural amino acid was activated as a thioester derivative, and the latter was linked through a spacer to the N-terminal of a 9-mer peptide nucleic acid that is complementary to the 3'-terminal region of yeast phenylalanine tRNA. Efficient aminoacylation was observed when the amino acid thioester-spacer-PNA conjugate was mixed with the tRNA. The PNA-assisted aminoacylation was also successful in an Escherichia coli in vitro protein synthesizing system that contained an orthogonalized tRNA. The in situ aminoacylation/in vitro translation gave a mutant protein in which the nonnatural amino acid was incorporated into the position directed by a CGGG 4-base codon/anticodon pair. 相似文献