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排序方式: 共有216条查询结果,搜索用时 15 毫秒
1.
A new method involving efficient, widely applicable, and highly selective alpha-chlorination of simple silyl enolate with Lewis acid and an alpha,alpha-dichloro-1,3-dicarbonyl controller unit was reported. Diastereoselectivity and enantioselectivity of the reaction were investigated. High reactivity and selectivity were achieved by using alpha,alpha-dichlorinated malonic ester. 相似文献
2.
Spin preference and S-T gaps of localized 1,3-diradicals were studied by an orbital phase theory and theoretical calculations. The orbital phase theory was applied to rationalize thermodynamic and kinetic stabilities of diradicals. We theoretically designed some singlet localized 1,3-diradicals, substituted trimethylenes, which are more stable than the lowest triplets. Some diradicals with the four-membered rings, 2,4-disilacyclobutane-1,3-diyls, were designed and shown to have singlet ground states and to be more stable than the sigma-bonded isomers, 2,4-disilabicyclo[1.1.0]butanes. The ab initio calculations supported predictions of the stable carbon-centered localized singlet 1,3-diradicals. 相似文献
3.
Masaki Takeguchi Kazutaka Mitsuishi Miyoko Tanaka Kazuo Furuya 《Microscopy and microanalysis》2004,10(1):134-138
About 1 monolayer of palladium was deposited onto a silicon (111) 7 x 7 surface at a temperature of about 550 K inside an ultrahigh vacuum transmission electron microscope, resulting in formation of Pd2Si nanoislands and a 1 x 1 surface layer. Pd clusters created from an excess of Pd atoms on the 1 x 1 surface layer were directly observed by in situ plan view high-resolution transmission electron microscopy. When an objective aperture was introduced so that electron diffractions less than 0.20 nm were filtered out, the lattice structure of the 1 x 1 surface with 0.33 nm spacing and the Pd clusters with a trimer shape were visualized. It was found that image contrast of the 1 x 1 lattice on the specific height terraces disappeared, and thereby an atomic structure of the Pd clusters was clearly observed. The appearance and disappearance of the 1 x 1 lattice was explained by the effect of the kinematical diffraction. It was identified that a Pd cluster was composed of three Pd atoms without a centered Si atom, which is consistent with the model proposed previously. The feature of the Pd clusters stuck at the surface step was also described. 相似文献
4.
Gold-dendrimer nanocomposites are prepared in aqueous solutions in the presence of poly(amidoamine)dendrimers (PAMAM) (generation 3 and 5) or poly(propyleneimine)dendrimers (PPI) (generation 3 and 4) by wet chemical NaBH(4) method. Thus prepared gold-dendrimer nanocomposites are irradiated by laser at 532 nm. UV-vis absorption spectroscopy and transmission electron microscopy reveal that the gold nanoparticles grow with the laser irradiation time as well as the fluence of the laser; in particular, the gold nanoparticles prepared at lower concentrations of PAMAM dendrimer as well as lower generations of PAMAM grow significantly. On the other hand, in the case of PPI dendrimers, the gold nanoparticles hardly grow by irradiation. In addition, dynamic light-scattering measurements show that the laser irradiation markedly promotes the association of the gold-PAMAM G3 dendrimer nanocomposites compared to that of the gold-PAMAM G5 dendrimer nanocomposites, while the sizes of association for the gold-PPI G3, G4 dendrimer nanocomposites hardly change by laser irradiation. 相似文献
5.
5,11-Diazadibenzo[hi,qr]tetracene: Synthesis,Properties, and Reactivity toward Nucleophilic Reagents
Dr. Keisuke Fujimoto Satoshi Takimoto Shota Masuda Dr. Toshiyasu Inuzuka Kazutaka Sanada Prof. Dr. Masami Sakamoto Prof. Dr. Masaki Takahashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(35):8951-8955
5,11-Diazadibenzo[hi,qr]tetracene was synthesized as a new nitrogen-substituted polycyclic heteroaromatic compound by Pd-catalyzed cycloisomerization of an alkyne precursor followed by oxidative cyclization with bis(trifluoroacetoxy)iodobenzene. The substitution of imine-type nitrogen atoms significantly enhanced its electron-accepting character and facilitated the direct nucleophilic addition of arylamines under strongly basic conditions to afford the desired amino-substituted products. The introduction of amino groups induced a remarkable red-shift in their absorption spectra; the tetrasubstituted product exhibited intense near-infrared absorbing property. Furthermore, the π-electronic system, which includes a redox-active 1,4-diazabutadiene moiety, underwent reversible interconversion to its corresponding reduced form upon reduction with NaBH4 and aerobic oxidation. 相似文献
6.
Hirakawa K 《Analytical and bioanalytical chemistry》2006,386(2):244-248
Hydrogen peroxide (H2O2) is one of the most important reactive oxygen species. In the present study, a fluorometry method for detecting H2O2 utilizing folic acid was evaluated. Folic acid was decomposed by H2O2 in the presence of Cu(II) into pterine-6-carboxylic acid, leading to strong fluorescence enhancement. In the absence of the
metal ion, superoxide and H2O2 could not decompose folic acid. Also, H2O2 plus sodium hypochlorite (a source of singlet oxygen) could not induce fluorescence enhancement. These results demonstrate
that H2O2 can be selectively detected using folic acid plus Cu(II). The limit of detection (LOD; at S/N=3) for H2O2 is 0.5 μM. This method based on the fluorescence enhancement of folic acid was applied in order to determine small amounts
of H2O2 generated through the autooxidation of semicarbazide (generation rate: ∼0.01 μM min−1), a carcinogenic compound.
相似文献
7.
We study the spectral properties of a chiral random banded matrix (chRBM) with elements decaying as a power-law Hij|i−j|−. This model is equivalent to a chiral 1D Anderson Hamiltonian with long range power-law hopping. In the weak disorder limit we obtain explicit nonperturbative analytical results for the density of states (DoS) and the two-level correlation function (TLCF) by mapping the chRBM onto a nonlinear σ model. We also put forward, by exploiting the relation between the chRBM at =1 and a generalized chiral random matrix model, an exact expression for the above correlation functions. We give compelling analytical and numerical evidence that for this value the chRBM reproduces all the features of an Anderson transition. Finally we discuss possible applications of our results to quantum chromodynamics (QCD). 相似文献
8.
Izumi T Naitou Y Shimbo Y Takanishi Y Takezoe H Watanabe J 《The journal of physical chemistry. B》2006,110(47):23911-23919
The mesomorphic behavior and phase structure were examined in the mixture of two kinds of dimeric compounds, alpha,omega-bis(4-alkoxyanilinebenzylidene-4'-carbonyloxy)pentane (mOAM5AMOm), by optical microscopy, X-ray diffraction, polarization switching, and second-harmonic generation measurements. One compound is 4OAM5AMO4 with a short terminal alkyl chain that forms a single-layer smectic phase (SmCAs) with a random mixing of spacer and tail groups. Another compound is 16OAM5AMO16 with a long terminal alkyl chain that forms a chiral, anticlinic, and antiferroelectric bilayer phase (SmCAb) with the bent molecules tilted to the bilayer. By mixing these two compounds, the SmCAs phase of 4OAM5AMO4 is easily destabilized, leading to the wide content region of the bilayer phases. In the bilayer regime, three other smectic phases are newly induced. Two of them are antiferroelectric and ferroelectric phases in which the molecules lie perpendicularly with respect to the layer. The other shows no polar response to an external electric field and behaves like a smectic A. The new appearance of these bilayer phases is discussed as a mixing effect of long and short tail groups. 相似文献
9.
Hiroshi Nagai Minami Watanabe Shingo Sato Mioko Kawaguchi Yue-Yun Xiao Kazutaka Hayashi Ryuichi Watanabe Hajime Uchida Masayuki Satake 《Tetrahedron》2019,75(17):2486-2494
The marine cyanobacterium Moorea producens is a rich source of diverse compounds that possess a variety of biological activities. In the present study, eight new aplysiatoxin derivatives, namely 6, 8–13, and 15, along with aplysiatoxin (1), debromoaplysiatoxin (2), 3-methoxyaplysiatoxin (3), anhydroaplysiatoxin (4), anhydrodebromoaplysiatoxin (5), oscillatoxin B2 (7), and 30-methyloscillatoxin D (14) were isolated and identified from the Okinawan M. producens. In cytotoxicity and diatom growth inhibition tests, the fifteen compounds tested (1–15) showed moderate or no activity at a concentration of 10?μg/mL. 相似文献
10.
UVA, which accounts for approximately 95% of solar UV radiation, can cause mutations and skin cancer. Based mainly on the results of our study, this paper summarizes the mechanisms of UVA-induced DNA damage in the presence of various photosensitizers, and also proposes a new mechanism for its chemoprevention. UVA radiation induces DNA damage at the 5'-G of 5'-GG-3' sequence in double-stranded DNA through Type I mechanism, which involves electron transfer from guanine to activated photosensitizers. Endogenous sensitizers such as riboflavin and pterin derivatives and an exogenous sensitizer nalidixic acid mediate DNA photodamage via this mechanism. The major Type II mechanism involves the generation of singlet oxygen from photoactivated sensitizers, including hematoporphyrin and a fluoroquinolone antibacterial lomefloxacin, resulting in damage to guanines without preference for consecutive guanines. UVA also produces superoxide anion radical by an electron transfer from photoexcited sensitizers to oxygen (minor Type II mechanism), and DNA damage is induced by reactive species generated through the interaction of hydrogen peroxide with metal ions. The involvement of these mechanisms in UVA carcinogenesis is discussed. In addition, we found that xanthone derivatives inhibited DNA damage caused by photoexcited riboflavin via the quenching of its excited triplet state. It is thus considered that naturally occurring quenchers including xanthone derivatives may act as novel chemopreventive agents against photocarcinogenesis. 相似文献