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201.
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203.
Fe-sitting sites and the origin of magnetic order in YBa2(Cu0.95Fe0.05)3O7?δ have been studied by comparing the Mössbauer spectra observed before and after heat-treatments at 300°C in vacuum. Both of the major quadrupole doublets D-1 and D-2 are assigned to originate from Fe’s replacing Cu1’s. It is also suggested that fluctuations of Cu2 spins play an important role for inducing the magnetic order. 相似文献
204.
Fluorescence and electrochemical detection of pyrimidine/purine transversion by a ferrocenyl aminonaphthyridine derivative 总被引:1,自引:0,他引:1
A novel hydrogen bond-forming ligand for pyrimidine/purine transversion, which contains both a fluorescent naphthyridine moiety and a ferrocenyl group as an electrochemical indicator, is described. Hydrogen bond-mediated recognition for a target nucleobase at an abasic site in a DNA duplex is confirmed by both fluorescence and electrochemical measurements. The analysis by fluorescence titration reveals that the ligand shows significant fluorescent quenching upon formation of a 1 : 1 complex with the target nucleobase opposite the abasic site, and the selectivity is in the order of cytosine > thymine > adenine, guanine, reflecting the stability of the hydrogen bond formation. 相似文献
205.
[reaction: see text] The effect of anion templation is investigated for the photodimerization of a thymine-functionalized isothiouronium receptor. The receptor forms a photodimer at the thymine moiety in methanol upon UV irradiation, while the isothiouronium moiety works as an oxoanion binding site via a two-point hydrogen-bonding motif. As compared to the case of a free receptor, the presence of pyrophosphate (PPi) resulted in the preferential formation of the syn-type photodimer, which would be desirable for recognizing the templated PPi. 相似文献
206.
Itoh K Kudryashov I Yamagata J Nishizawa T Fujii M Osaka N 《The journal of physical chemistry. B》2005,109(1):271-276
Confocal Raman microscopic measurements were performed at room temperature on the Langmuir-Blodgett (LB) monolayer of 10,12-pentacosadiynoic acid (DA) prepared on surface enhanced Raman scattering (SERS) active Ag island films, two-dimensional (2D) Raman images of which exhibit bright and dim spots on a dark background. The measurements performed by focusing the excitation laser light (488 nm) on the dark background indicate the prompt appearance of the Raman bands (1515 and 2115 cm(-1)) due to polydiacetylene (PDA) in the red phase and subsequent diminution of the Raman bands. On the other hand, the spectra observed by focusing the excitation laser spot on the dim and bright spots exhibit almost random fluctuations, giving rather narrow Raman bands in the 1620-1000 cm(-1) region, which appear and disappear temporarily with varying intensities under the continuous irradiation at 488 nm. Broad Raman bands appear around 1580 and 1360 cm(-1), which are ascribable to amorphous carbon, at a later stage of the observation, the intensities from the bright spot being more than 100 times stronger than those from the dim spot. The narrow bands are ascribed to a series of carbonaceous intermediates such as polyenes, graphite sheets with various sizes, and folded or reorganized forms of the sheets including carbon nanotubes and fullerenes, which are formed during the conversion of PDA to amorphous carbon. The random spectral fluctuation was interpreted by considering that the intermediates undergo thermally activated diffusion and get temporarily in contact with the SERS-active site, resulting in the enhancement of their Raman bands and the fluctuation. 相似文献
207.
Hypacrone (1), a new seco-illudoid sesquiterpene, was isolated from a fern, Hypolepis punctata Mett., as its characteristic acrid principle. The structure is proposed on the spectral basis and the transformation into pterosins, illudoid constituents of the same plant. 相似文献
208.
Philippe Bühlmann Shigeru Amemiya Seiichi Nishizawa Kang Ping Xiao Yoshio Umezawa 《Journal of inclusion phenomena and macrocyclic chemistry》1998,32(2-3):151-163
The potential and limits of hydrogen-bonding ionophores and their use in chemical sensors are discussed. Several hydrogen-bonding bis-thiourea ionophores have been found to complex inorganic anions, among them most strongly H2PO4-. Using such ionophores, ion-selective electrodes for chloride and sulfate have been developed. Furthermore, hosts that bind nucleotides with up to five hydrogen bonds have been synthesized. They have been applied in nucleotide selective electrodes, optodes and voltammetric sensors mimicking ion channels. 相似文献
209.
Eric Bescher Y. Hoshino Yuka Nishizawa Kristen Cooley John D. Mackenzie 《Journal of Sol-Gel Science and Technology》2003,26(1-3):297-301
The thermal stability of organically modified silicates (Ormosils) is limited by that of their organic constituent. In the case of the polydimethylsiloxane (PDMS)-silica hybrids, degradation of the PDMS begins around 250°C, which restricts their range of applications. Several strategies have been used to stabilize PDMS, such as substitution of the methyl groups by phenyl groups. Another strategy is the addition of very small amounts (typically about 1 wt%) of iron. This technique has been used successfully in the stabilization of liquid silicones. In the case of PDMS-SiO2 hybrids, this small dopant concentration has a very significant effect on the thermal stability, increasing it by up to 200°C. However, very little is known of the mechanism of stabilization. In the present work we carry out an investigation of the materials in order to explain the mechanisms involved. The materials were investigated by liquid and solid state 29Si NMR, BET, SEM, TGA and DMA. The data indicates that Fe plays a most significant role at the solution stage already. The structures of the hybrids with and without Fe are very different. In other words, the thermal stabilization mechanism appears to be due not so much a direct redox process taking place in the solid state (as in the case of liquid silicones) but rather, to differences in chemical structures induced by Fe in the liquid. Specifically, PDMS chain cleavage and increased cross-linking to SiO2 appear to be the cause of the thermal stabilization. 相似文献
210.
Tetsuo Narumi Takuma Nishizawa Tomoyuki Imai Ryuji Kyan Hiroki Taniguchi Kohei Sato Nobuyuki Mase 《Tetrahedron》2018,74(45):6527-6533
Conjugated systems have versatile utilities in various fields including organic synthesis, pharmaceutical development, and material science. Such systems take advantage of their properties, which include their unique reactivity, relatively rigid structures, and low HOMO-LUMO gap energies. Their utility and the handling of conjugated systems however are both limited by excessively high photosensitivity and reactivity. We now report a novel molecular approach to the improvement of the chemical stability of the acyclic conjugated system against the photolysis and oxidation reactions simply by introduction of a chlorine atom into the conjugated system. Systematic studies of substrates with various substituents reveals that the improved chemical stability is based on the additive effects of the steric and electronic properties of the chlorine atom substituent. 相似文献