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排序方式: 共有997条查询结果,搜索用时 31 毫秒
981.
Kiyoshi Sawada Eiji Takahashi Tomokazu Horie Keiichi Satoh 《Monatshefte für Chemie / Chemical Monthly》2001,36(4):1439-1450
The distribution of tetraalkylammonium ions (C n H 2n+1 )4N+ (R +, TAAn +, n = 4–7) with picrate ion (pic −) and inorganic anions X −, (Cl−, Br−, ClO− 4), into various inert organic solvents was studied at 25.0°C. The distribution data were analyzed by taking into consideration the distribution of ion pairs, R + · X −, and the dimerization of the ion pairs, (R + · X −)2, in the organic phase. The ion-pair, distribution constant, K dist, increases with increasing chain length of the tetraalkylammonium ion and with increasing ionic radius of the anion. The values of K dist show a good correlation with the E T value of solvent, i.e. the solvation ability with respect to the anion, and smoothly increase with increasing E T. The effect of the solvent on the dimerization constants, K dim, is markedly different between the ion pairs of picrate ion and inorganic anions. In the case of picrate, K dim significantly decreases with decreasing length of the alkyl chain of the tetraalkylammonium ion, but hardly changes by changing the solvent. On the other hand, in the case of ion pairs of inorganic anions the value of K dim decreases with decreasing E T and is almost constant for all anions. These results were reasonably explained by the difference of the solvation of the anion moieties of the monomeric and dimeric ion pairs. 相似文献
982.
Ryusei Hoshikawa Ryoji Mitsuhashi Eiji Asato Jianqiang Liu Hiroshi Sakiyama 《Molecules (Basel, Switzerland)》2022,27(2)
Only a limited number of multinucleating ligands can stably maintain multinuclear metal structures in aqueous solutions. In this study, a water-soluble dinucleating ligand, 2,6-bis{[N-(carboxylatomethyl)-N-methyl-amino]methyl}-4-methylphenolate ((sym-cmp)3−), was prepared and its copper(II) complexes were structurally characterized. Using the single-crystal X-ray diffraction method, their dimer-of-dimers type defect cubane tetranuclear copper(II) structures were characterized for [Cu4(sym-cmp)2Cl2(H2O)2] and [Cu4(sym-cmp)2(CH3O)2(CH3OH)2]. In the complexes, each copper(II) ion has a five-coordinate square-pyramidal coordination geometry. The coordination bond character was confirmed by the density functional theory (DFT) calculation on the basis of the crystal structure, whereby we found the bonding and anti-bonding molecular orbitals. From the cryomagnetic measurement and the magnetic analysis, overall antiferromagnetic interaction was observed, and this magnetic behavior is also explained by the DFT result. Judging from the molar conductance and the electronic spectra, the bridging chlorido ligand dissociates in water, but the dinuclear copper(II) structure was found to be maintained in an aqueous solution. In conclusion, the tetranuclear copper(II) structures were crystallographically characterized, and the dinuclear copper(II) structures were found to be stabilized even in an aqueous solution. 相似文献
983.
H. Parhat N.J. Vasa M. Kidosaki T. Okada M. Maeda T. Mizunami O. Uchino 《Applied physics. B, Lasers and optics》2000,70(3):361-366
We describe a comparative study related to an influence of a feedback coupling on operating characteristics of a cw Cr3+:LiSrAlF6 (Cr3+:LiSAF) laser using an end-coupled fiber grating with different coupling configurations. To achieve a compact construction,
a direct butt-coupling of the fiber grating at the pump end of the Cr3+:LiSAF laser and pumping through the same fiber was considered. The feedback provided by the coupled fiber grating through
an end mirror was responsible for a spectrally narrowed output with a slope efficiency of 11%. However, the performance critically
depended on an amount of the feedback coupling. The feedback-coupling condition was improved considerably by using a lens-coupled
fiber grating at the pump end of the Cr3+:LiSAF crystal. A spectrally narrowed output of ≈0.15 cm-1 was obtained, and the output slope efficiency was measured as 27%. Theoretical modeling was also performed to understand
the effect of the feedback coupling and the results agreed well with the experimental observations.
Received: 23 April 1999 / Revised version: 3 August 1999 / Published online: 30 November 1999 相似文献
984.
985.
986.
Kazuki Matsuo Tadashi Yoshitake Eiji Yamaguchi Akichika Itoh 《Molecules (Basel, Switzerland)》2021,26(22)
We have developed a photochemical ATRA/ATRC reaction that is mediated by halogen bonding interactions. This reaction is caused by the reaction of malonic acid ester derivatives containing bromine or iodine with unsaturated compounds such as alkenes and alkynes in the presence of diisopropylethylamine under visible light irradiation. As a result of various control experiments, it was found that the formation of complexes between amines and halogens by halogen-bonding interaction occurs in the reaction system, followed by the cleavage of the carbon–halogen bonds by visible light, resulting in the formation of carbon radicals. In this reaction, a variety of substrates can be used, and the products, cyclopentenes and cyclopentanes, were obtained by intermolecular addition and intramolecular cyclization. 相似文献
987.
Keisuke Seto Hiromu Yamada Takayoshi Kobayashi Eiji Tokunaga 《Annalen der Physik》2020,532(9):2000241
Absorption spectroscopy, coupled with photothermal super-resolution microscopy, is enabled by the frequency division multiplexing of the pump-light (Pu) wavelength whose spectral component is discriminated by the modulation frequency. This demonstrates a great advantage in availing multicolor image information. However, the response gain of the thermal lens signal to the spectral components is not uniform because of the limited relaxation rate of the thermal lens, i.e., the gains of the components assigned to the high-frequency modulations are diminished, thus resulting in a distorted absorption spectrum. In this study, white-pump light (Pu) is multiplexed by pseudonoise sequences (PNSs) to avoid the distortion. The frequency bandwidth of the PNSs is equalized, and the gains of the thermal lens generation to the respective wavelength components are balanced. The obtained results indicate that the modulation-waveform deformation due to the slow responses of the sample can also distort spectra. To mitigate the problem, the countermeasures required to compensate for this distortion are also discussed. 相似文献
988.
Daiki Yamane Satsuki Onitsuka Suyong Re Hikaru Isogai Rui Hamada Tadanari Hiramoto Eiji Kawanishi Kenji Mizuguchi Naoya Shindo Akio Ojida 《Chemical science》2022,13(10):3027
The coronavirus disease 2019 (COVID-19) pandemic has necessitated the development of antiviral agents against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The main protease (Mpro) is a promising target for COVID-19 treatment. Here, we report an irreversible SARS-CoV-2 Mpro inhibitor possessing chlorofluoroacetamide (CFA) as a warhead for the covalent modification of Mpro. Ugi multicomponent reaction using chlorofluoroacetic acid enabled the rapid synthesis of dipeptidic CFA derivatives that identified 18 as a potent inhibitor of SARS-CoV-2 Mpro. Among the four stereoisomers, (R,R)-18 exhibited a markedly higher inhibitory activity against Mpro than the other isomers. Reaction kinetics and computational docking studies suggest that the R configuration of the CFA warhead is crucial for the rapid covalent inhibition of Mpro. Our findings highlight the prominent influence of the CFA chirality on the covalent modification of proteinous cysteines and provide the basis for improving the potency and selectivity of CFA-based covalent inhibitors.Chlorofluoroacetamide (CFA) was used as the warhead for covalent targeting of SARS-CoV-2 Mpro. The chirality at CFA showed marked influence on inhibitory activity, suggesting stereospecific activation of CFA for cysteine modification in the protein. 相似文献
989.
990.
Several new phenylcarbamate derivatives of cellulose and amylose having fluoro and methyl groups or 4-trimethylsilyl substituent on the phenyl groups were prepared and their chiral recognition abilities as chiral stationary phases for HPLC were evaluated. These derivatives are soluble in chloroform and exhibit chiral discrimination in 1H NMR spectroscopy. Based on the above results and molecular mechanics calculation of interaction energies between the derivatives and enantiomers, the mechanism of chiral discrimination is discussed. 相似文献