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21.
Ramaswamy K Saito H Murakami H Shiba K Suga H 《Journal of the American Chemical Society》2004,126(37):11454-11455
Fx3 is an artificial ribozyme with the ability to aminoacylate various tRNAs with phenylalanine and its nonnatural derivatives. Herein we report a simple strategy to build tRNA specificity into the generic Fx3, by appending to its 3'-end a tRNA-specific sequence (TSS), which is complementary to the acceptor stem of the cognate tRNA. This new designer ribozyme, referred to as Fx10, is able to recognize its cognate tRNA via a 10-base-pair interaction that is formed after the invasion of the tRNA acceptor stem by the TSS. We have demonstrated that Fx10 can aminoacylate its cognate tRNA with a high degree of specificity and also discriminate against the noncognate tRNAs. Because the tRNA specificity can be easily programmed into Fx10, it is a custom-made catalyst to generate nonnatural aminoacyl-tRNAs. 相似文献
22.
Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 A) and partially oxidized Ru microclusters (diameter less than 10 A). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 A in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed. 相似文献
23.
Friggeri A Gronwald O van Bommel KJ Shinkai S Reinhoudt DN 《Journal of the American Chemical Society》2002,124(36):10754-10758
The synthesis of a new saccharide-based gelator (2) containing a donor moiety has been described. Gelation experiments of a dual-component gel consisting of a saccharide-based gelator bearing an acceptor group (1) and of 2 have been performed in a variety of organic solvents and water. Moreover, gelation tests at different molar ratios of 1 and 2 have been performed in water, octanol, and diphenyl ether. In these last two solvents a gel color change was observed, from colorless to yellow, upon cooling of the sample to room temperature. This phenomenon was further investigated by UV-visible spectroscopy, which revealed the presence of charge-transfer interactions in the gel, in octanol. Temperature-dependence UV spectroscopy confirmed that such interactions occur in the gel but not in the corresponding solution sample. Furthermore, T(gel) measurements show that dual-component gels of 1 and 2 present increased thermal stability at a 50:50 ratio of the two gelators, in dependence of the solvent. Transmission electron microscopy (TEM) images of the single-component gels in diphenyl ether revealed that they consist of a fibrous network, while the dual-component gel presents a novel, helical, fibrous-bundle structure. 相似文献
24.
Toru Sakaki Takaaki Harada Yohko Kawahara Seiji Shinkai 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(4):377-392
A criterion for the selection of a suitable plasticizer for calix[n]arene-based ion-selective electrodes is discussed. The cation selectivity of plasticized membranes without the ligand was first measured as a reference. The membranes can be roughly classified into two groups. The first group shows cation selectivity in the order Cs++>K+>Na+>Li+. The membranes in the second group are made of phosphorus plasticizers, which show a selectivity in the reverse order. The plasticizers in the first group featured a linear relationship between the dipole moment of the plasticizer (calculated by a PM3 method) and the ratio of cesium selectivity to lithium selectivity. The linear relationship supports the view that the polar membrane which includes a soft plasticizer with a large dipole moment shows selectivity for Cs+, whereas the nonpolar membrane including the soft plasticizer with the small dipole moment shows much lower selectivity for Cs+. Next, 2-fluorphenyl-2-nitrophenyl ether (FPNPE) which showed the highest Cs+ selectivity and tris(2-ethylhexyl)phosphate (TEHP) which showed the highest Li+ selectivity were mixed in an appropriate ratio to make membranes with a different affinity for hard ions. The metal selectivities of several crown-based and calixarene-based ionophores were examined in these membranes. Although a few exceptions exist, the polar soft membrane is favorable when the interfering metal ion is hard, whereas the hard membrane is favorable when the interfering metal ion is soft. 相似文献
25.
Technical problems in the design and construction of small sample adiabatic calorimeters are pointed out and solutions to them discussed. Two calorimeters constructed on the design principle are described with illustrative examples of data obtained with them. Hard and soft wares for fully automatic operation of the two calorimeters are described in some detail. 相似文献
26.
Tetsuji Kametani Kazuo Kigasawa Mineharu Hiiragi Haruhide Ishimaru Seiji Haga Keiko Shirayama 《Journal of heterocyclic chemistry》1978,15(3):369-375
2-[4-(1-Oxo-2-isoindolinyl)phenyl]propanoic acid ( 1 ) having a potent analgesic and anti-inflammatory activity could be obtained by three methods, which were found to provide extremely useful ways for the synthesis of 1 from the industrial point of view. (E)- and (Z)-Isomers of 2-butenoic acid and oxiranecarboxylic acid derivatives as the intermedaites in the synthesis of 1 were separated and characterized. Furthermore, the optical resolution of (±)-2-[4-(1-oxo-2-isoindolinyl)phenyl]propanoic acid was successfully achieved using cinchonidine as a resolution reagent. 相似文献
27.
Hara K Wang ZS Sato T Furube A Katoh R Sugihara H Dan-Oh Y Kasada C Shinpo A Suga S 《The journal of physical chemistry. B》2005,109(32):15476-15482
We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO(2) solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-800 nm. A solar energy-to-electricity conversion efficiency (eta) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm(-2)) with a mask: short-circuit current density (J(sc)) = 13.5 mA cm(-2); open-circuit voltage (V(oc)) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity. 相似文献
28.
The free-radical-induced reactions of cyclohexene oxide in the presence of maleic anhydride have been found to lead to polyether in presence of AIBN and to a mixture of polyether, ester, and maleic anhydride adduct of polyether with di-tert-butyl peroxide (DTBP), the amounts of the mixture components depending on the concentration of DTBP and the temperature. Analogous reactions in the presence of succinic anhydride lead to no polyether. The obtained polyether has no hydroxyl group. The reaction appears to consist of three different steps, radical initiation, cationic propagation, and radical termination. 相似文献
29.
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