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971.
S Umemoto S Im J Zhang M Hagihara A Murata Y Harada T Fukuzumi T Wazaki S Sasaoka K Nakatani 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(32):9999-10008
A series of xanthone and thioxanthone derivatives with aminoalkoxy substituents were synthesized as fluorescent indicators for a displacement assay in the study of small-molecule-RNA interactions. The RNA-binding properties of these molecules were investigated in terms of the improved binding selectivity to the loop region in the RNA secondary structure relative to 2,7-bis(2-aminoethoxy)xanthone (X2S) by fluorimetric titration and displacement assay. An 11-mer double-stranded RNA and a hairpin RNA mimicking the stem loop IIB of Rev response element (RRE) RNA of HIV-1 mRNA were used. The X2S derivatives with longer aminoalkyl substituents showed a higher affinity to the double-stranded RNA than the parent molecule. Introduction of a methyl group on the aminoethoxy moiety of X2S effectively modulated the selectivity to the RNA secondary structure. Methyl group substitution at the C1' position suppressed the binding to the loop regions. Substitution with two methyl groups on the amino nitrogen atom resulted in reducing the affinity to the double-stranded region by a factor of 40%. The effect of methyl substitution on the amino nitrogen atom was also observed for a thioxanthone derivative. Titration experiments, however, suggested that thioxanthone derivatives showed a more prominent tendency of multiple binding to RNA than xanthone derivatives. The selectivity index calculated from the affinity to the double-stranded and loop regions suggested that the N,N-dimethyl derivative of X2S would be suitable for the screening of small molecules binding to RRE. 相似文献
972.
A new method is described for the regioselective synthesis of multisubstituted pyridine derivatives. Treatment of N-acetyl β-enamino ketones with alkynes in the presence of the rhenium catalyst, Re(2)(CO)(10), gives multisubstituted pyridines regioselectively. In this reaction, the N-acetyl moieties are important for the selective formation of the multisubstituted pyridines. This reaction proceeds via insertion of alkynes into a carbon-carbon single bond of β-enamino ketones, intramolecular nucleophilic cyclization, and elimination of acetic acid. 相似文献
973.
Amakawa K Wrabetz S Kröhnert J Tzolova-Müller G Schlögl R Trunschke A 《Journal of the American Chemical Society》2012,134(28):11462-11473
The depth of our understanding in catalysis is governed by the information we have about the number of active sites and their molecular structure. The nature of an active center on the surface of a working heterogeneous catalyst is, however, extremely difficult to identify and precise quantification of active species is generally missing. In metathesis of propene over dispersed molybdenum oxide supported on silica, only 1.5% of all Mo atoms in the catalyst are captured to form the active centers. Here we combine infrared spectroscopy in operando with microcalorimetry and reactivity studies using isotopic labeling to monitor catalyst formation. We show that the active Mo(VI)-alkylidene moieties are generated in situ by surface reaction of grafted molybdenum oxide precursor species with the substrate molecule itself gaining insight into the pathways limiting the number of active centers on the surface of a heterogeneous catalyst. The active site formation involves sequential steps requiring multiple catalyst functions: protonation of propene to surface Mo(VI)-isopropoxide species driven by surface Br?nsted acid sites, subsequent oxidation of isopropoxide to acetone in the adsorbed state owing to the red-ox capability of molybdenum leaving naked Mo(IV) sites after desorption of acetone, and oxidative addition of another propene molecule yielding finally the active Mo(VI)-alkylidene species. This view is quite different from the one-step mechanism, which has been accepted in the community for three decades, however, fully consistent with the empirically recognized importance of acidity, reducibility, and strict dehydration of the catalyst. The knowledge acquired in the present work has been successfully implemented for catalyst improvement. Simple heat treatment after the initial propene adsorption doubled the catalytic activity by accelerating the oxidation and desorption-capturing steps, demonstrating the merit of knowledge-based strategies in heterogeneous catalysis. Molecular structure of active Mo(VI)-alkylidene sites derived from surface molybdena is discussed in the context of similarity to the highly active Schrock-type homogeneous catalysts. 相似文献
974.
Employing an aero-acoustic levitator, the Fe2O3-16.5 mol% La2O3 eutectic alloy was levitated, melted, undercooled and then solidified under a containerless condition when a continuous laser beam heating system was incorporated. By revealing the surface and cross-sectional microstructures, copious nucleation is confirmed to take place in the undercooled melts solidified by either an external seeding or spontaneous crystallization. The nucleation behaviour of eutectic alloys is summarized, indicating that copious nucleation may be an intrinsic attribute of a eutectic system with the exact eutectic composition in unconstrained solidification. Considering the complexity level of crystal structures of eutectic oxide phases in the Fe2O3-La2O3 alloy, the linear kinetic constants are approximately estimated and the growth kinetics are discussed. The sluggish growth kinetics of the perovskite-type phase, that is LaFeO3 with a higher complexity level in a unit cell leads to a decoupled growth within a single eutectic colony when the melt is undercooled to exceed the critical undercooling ΔT = 125 K. It is the decoupled growth that results in the formation of anomalous eutectics. The present concept based on the kinetic constant of different phases can also be applicable to account for the growth behaviour of other oxide eutectics when considering the stable and metastable eutectic reactions in different solidification conditions. The nucleation behaviour and growth modes in some oxide eutectic systems have been predicted in the free solidification from an undercooled state. 相似文献
975.
Abstract A nuclear microprobe combined with Rutherford backscattering (RBS) has been applied to analysis of silicide formation processes and a multi-layered structure. Lateral overgrowth of cobalt silicide layers on silicon was found to be suppressed by an additional ion beam mixing process, though residual cobalt atoms were found on insulating mask layers by ion beam mixing. Energy shift arising from RBS kinematics was found to deform tomographic images of multi-layered structures. Such deformation was easily corrected by simple data processing. 相似文献
976.
Keisuke Nose Yasuyuki Ozeki Yasuo Kanematsu Yoshizo Takai Kazuyoshi Itoh 《Optical Review》2014,21(4):425-428
We demonstrate that an RF spectral fringe appears when a nonpolarized optical noise and its delayed replica are combined and photo-detected without any polarization control. A theoretical analysis explains the visibility of the fringe and its insensitivity to polarization. 相似文献
977.
Shiro Kubuki Koya Shibano Kazuhiko Akiyama Zoltán Homonnay Ernő Kuzmann Mira Ristić Tetsuaki Nishida 《Hyperfine Interactions》2013,218(1-3):47-52
Decomposition mechanism of methylene blue (MB) caused by a mixture of metallic iron-maghemite (Fe0-γFe2O3) was investigated by means of 57Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), Ultraviolet-Visible Absorption Spectroscopy (UV-vis) and electrospray-ionization mass spectroscopy (ESI-MS). Ten day-leaching test of 10 μmol L???1 MB aqueous solution and Fe0-γFe2O3 mixture (mass ratio 3:7) showed a decrease in the concentration from 10.5 to 4.45 μmol L???1 with first-order rate constant (k) of $1.5_{7} \times 10^{-1}$ day???1. An ESI-MS study of Fe0-γFe2O3 mixture (3:7) after the leaching test revealed new peaks at m/z of 100, 110 and 137 due to fragmentation of MB, in addition to those observed at m/z of 284, 270 and 256 which were ascribed to MB, Azure B and Azure A, respectively. 57Fe-Mössbauer spectra of Fe0-γFe2O3 mixture (3:7) resulted in a decrease in absorption area (A) for Fe0 (δ?=?0.00±0.01 mm s???1, H int?=?33.0±0.1 T) from 37.5 to 21.3, 9.7, 7.9, 7.0 and 4.5±0.5 %, together with an increase in A from 0.0 to 5.0, 13.8, 17.2, 21.0 and 22.4±0.5 % for octahedral (O h) iron (FeII?+?FeIII) of Fe3O4. XRD study of these samples indicated that the peak intensity at 2Θ of 44.7° being ascribed to Fe0 was decreased, while that of 35.6° due to Fe3O4 was almost constant; relative peak ratio of Fe $^{0}/\mathrm{Fe}_{3}$ O4 was decreased from 26.3 to 2.76 after the leaching, indicating that Fe0 in the Fe0-γFe2O3 mixture was oxidized to Fe3O4. These experimental results suggest that Fe0-γFe2O3 mixture could be utilized for the cleaning or decomposition of toxic organic compounds like trichloroethylene. 相似文献
978.
In this article, we shall prove that Gorenstein isolated quotient singularities of odd prime dimension are cyclic. In the case where the dimension is bigger than 1 and is not an odd prime number, then there exist Gorenstein isolated noncyclic quotient singularities. 相似文献
979.
Kenta Takai 《Tetrahedron》2009,65(28):5596-5932
We developed an efficient, practical, and robust method for stereoselective preparations of (Z)-ketene trimethylsilyl (TMS) thioacetals from thioesters and alkyl (1Z)- or (1Z,3E)-1,3-bis(TMS)dienol ethers from alkyl β-ketoesters. The former preparation was performed by convenient procedure (LDA-TMSCl, 0-5 °C, 2.5 h), while the latter preparation involved convenient method A (2NaHMDS-2TMSCl) and cost-effective method B (NaH, NaHMDS-2TMSCl). The first catalytic NaOH-catalyzed crossed-Claisen condensation between ketene silyl acetals and methyl esters proceeded successfully to give a variety of α-monomethyl β-ketoesters and inaccessible α,α-disubstituted β-ketoesters. For further extension, a couple of Claisen-aldol tandem reactions of the obtained β-ketoester analogues utilizing TiCl4 and TiCl4-Bu3N reagents smoothly proceeded with good to excellent stereoselectivity. 相似文献
980.
K. Ando K. Shinke S. Yamada T. Koyama T. Takai S. Nakaji T. Ogino 《Colloids and surfaces. B, Biointerfaces》2009,71(2):255-259
Bilirubin adsorption on carbon nanotube surfaces has been studied to develop a new adsorbent in the plasma apheresis. Powder-like carbon nanotubes were first examined under various adsorption conditions such as temperatures and initial concentrations of bilirubin solutions. The adsorption capacity was measured from the residual concentrations of bilirubin in the solution after the adsorption process using a visible absorption spectroscopy. We found that multi-walled carbon nanotubes (MWCNTs) exhibit greater adsorption capacity for bilirubin molecules than that of single-walled carbon nanotubes (SWCNTs). To guarantee the safety of the adsorbents, we fabricated carbon nanotube sheets in which leakage of CNTs to the plasma is suppressed. Since SWCNTs are more suitable for robust sheets, a complex sheet consisting of SWCNTs as the scaffolds and MWCNTs as the efficient adsorbents. CNT/polyaniline complex sheets were also fabricated. Bilirubin adsorption capacity of CNTs has been found to be much larger than that of the conventional materials because of their large surface areas and large adsorption capability for polycyclic compound molecules due to their surface structure similar to graphite. 相似文献