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121.
Some azeto[2,1-a]isoquinolin-2-ones were synthesized from 2-(3,4-dimethoxyphenyl)ethylamine in three steps in good yield. 相似文献
122.
During radiotherapy of cancer, neighboring normal cells may receive sub-lethal doses of radiation. To investigate whether such low levels of radiation modulate normal cell responses to death stimuli, primary cultured human fibroblasts were exposed to various doses of gamma-rays. Analysis of cell viability using an exclusion dye propidium iodide revealed that the irradiation up to 10 Gy killed the fibroblasts only to a minimal extent. In contrast, the cells efficiently lost their viability when exposed to 0.5-0.65 mM H(2)O(2). This type of cell death was accompanied by JNK activation, and was reversed by the use of a JNK-specific inhibitor SP600125. Interestingly, H(2)O(2) failed to kill the fibroblasts when these cells were pre-irradiated, 24 h before H(2)O(2) treatment, with 0.25-0.5 Gy of gamma-rays. These cytoprotective doses of gamma-rays did not enhance cellular capacity to degrade H(2)O(2), but elevated cellular levels of p21(Cip/WAF1), a p53 target that can suppress H(2)O(2)-induced cell death by blocking JNK activation. Consistently, H(2)O(2)-induced JNK activation was dramatically suppressed in the pre-irradiated cells. The overall data suggests that ionizing radiation can impart normal fibroblasts with a survival advantage against oxidative stress by blocking the process leading to JNK activation. 相似文献
123.
Manojkumar TK Suh SB Oh KS Cho SJ Cui C Zhang X Kim KS 《The Journal of organic chemistry》2005,70(7):2651-2659
[reaction: see text] We present an ab initio study of the acid-promoted hydrolysis reaction mechanism of N-formylaziridine in comparison with formamide. Since the rate of amide hydrolysis reactions depends on the formation of the tetrahedral intermediate, we focused our attention mainly on the reactant complex, the tetrahedral intermediate, and the transition state connecting these two stationary points. Geometries were optimized using the density functional theory, and the energetics were refined using ab initio theory including electron correlation. Solvent effects were investigated by using polarizable continuum method calculations. The proton-transfer reaction between the O-protonated and N-protonated amides was investigated. In acidic media, despite that the N-protonated species is more stable than the O-protonated one, it is predicted that both N-protonated and O-protonated pathways compete in the hydrolysis reaction of N-formylaziridine. 相似文献
124.
Photophysical properties of porphyrin tapes 总被引:1,自引:0,他引:1
Cho HS Jeong DH Cho S Kim D Matsuzaki Y Tanaka K Tsuda A Osuka A 《Journal of the American Chemical Society》2002,124(49):14642-14654
The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials. 相似文献
125.
Dong Hyun KimHyun Il Cho Taehyoung ZyungLee-Mi Do Ki-Min BarkGap Chul Shin Sung Chul Shin 《European Polymer Journal》2002,38(1):133-137
New tetradentate Schiff-base polymers, in which phenylene units alternate with salicylideneiminato units, have been prepared by condensation of 2,5-(didodecyloxy)-1,4-bis(3-formyl-4-hydroxyphenyl)benzene (DFHB) with appropriate diamines in a mixed solution of CHCl3/toluene/acetic acid with 31-79% yields. DFHB as the key building block was prepared by the Suzuki reaction of 2,5-(didodecyloxy)benzene-1,4-diboronic acid with 5-bromosalicylaldehyde in a two-phase solution of tetrahydrofuran/water in the presence of NaHCO3/Pd(PPh3)4 in 45% yield. The molecular structures of the prepared compounds were identified by spectroscopy. Their absorption spectroscopic profiles have been analyzed. 相似文献
126.
The adsorption and reaction of pyridine on the Si(001) and Ge(001) surfaces are investigated by first-principles density-functional calculations within the generalized gradient approximation. On both surfaces the N atom of pyridine initially reacts with the down atom of the dimer, forming a single bond between the N atom and the down atom. On Ge(001) such an adsorption configuration is most favorable, but on Si(001) a further reaction with a neighboring dimer occurs, resulting in formation of a bridge-type configuration. Especially we find that on Ge(001) the bridge-type configuration is less stable than the gas phase. Our results provide an explanation for a subtle difference in the adsorption structures of pyridine on Si(001) and Ge(001), which was observed from recent scanning tunneling microscopy experiments. 相似文献
127.
Young Hyun Cho Wanno Lee Kun Ho Chung Geun Sik Choi Chang Woo Lee 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(3):531-538
The seasonal variation of the 7Be activities in air and the size distribution of the 7Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level
of 7Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m−3 and revealed a seasonal variation, in which the 7Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a
higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased
with increasing ambient 7Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h−1 were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the
high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and
the low 7Be content in the surface air. The AMAD of the 7Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological
and meteorological conditions. 相似文献
128.
In the hydrolysis reaction of dichlorosilanes having an intramolecular coordinating atom, dcisiloxane-1,3-diols, [(OH){o-(CH3)2NCH2-C6H4}RSi]2O(R=CH2CH (1), C6H5 (2), o-(CH3)2NCH2C6H4 (3), Me (4)), were obtained in high yields. The results of the crystal structure analyses of meso-2, rac-2a, rac-2b and 3 are reported. They showed strong intramolecular hydrogen bondings between the hydroxy group and the nitrogen atom. We have also found that the diastereomeric isomerization of meso-2 to rac-2 in CDCl3 solvent containing moisture occurred to result in the 55:45 equilibrium mixtures of the isomers and vice versa. 相似文献
129.
Abstract— The action spectrum for the generation of singlet oxygen (1 O2 ) from mitochondrial membranes under aerobic conditions was measured at wavelengths between 360 and 600 nm, using sub-mitochondrial particles (SMP) prepared from soybean hypocotyls. The spectrum, showing a peak at about 420 nm, remarkably resembles the absorption spectra of the Fe-S centers of nonheme iron proteins. Disruption of the Fe-S centers by treating SMP with mersalyl acid resulted in a substantial decrease in the efficiency of 1 O2 generation, leaving an action spectrum whose pattern is significantly similar to the absorption spectrum of flavins, at least in the region of near UV and blue light wavelengths. Estimating the contribution of the Fe-S centers to the generation of 1 O2 from SMP, we suggest that the Fe-S centers act as very important endogenous photosensitizers in plant cells, in so far as the type II mechanism is concerned. Possible involvement of mitochondrial flavoproteins in the generation of 1 O2 is also discussed. 相似文献
130.
Yoshida N Ishizuka T Yofu K Murakami M Miyasaki H Okada T Nagata Y Itaya A Cho HS Kim D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2854-2866
A series of zinc(II) porphyrin-imide dyads (ZP-Im), in which an electron donating ZP moiety is directly connected to an electron accepting imide moiety in the meso position, have been prepared for the examination of energy gap dependence of intramolecular electron transfer reactions with large electronic coupling. The nearly perpendicular conformation of the imide moiety towards the porphyrin plane has been revealed by Xray crystal structures. The energy gap for charge separation, 1ZP* - Im --> ZP+ - Im-, is varied by changing the electron accepting imide moiety to cover a range of about 0.8 eV in DMF. Definitive evidence for electron transfer has been obtained in three solvents (toluene, THF, and DMF) through picosecond-femtosecond transient absorption studies, which have allowed us to determine the rates of photoinduced charge separation, 1ZP* - Im --> ZP+ - Im-, and subsequent thermal charge recombination ZP+ - Im- --> ZP - Im. The free-energy gap dependence (energy gap law) has been probed from the normal to the nearly top region for the charge separation rate alone, and only the inverted region for the charge recombination rate. Although both of the energy gap dependencies can be approximately reproduced by means of the simplified semiclassical equation, when we take into consideration the effect of the high frequency vibrations replaced by one mode of averaged frequency, many features, including the effects of solvent polarity and the electron tunneling matrix element on the energy gap law, differ considerably from those of the previously studied porphyrin-quinone systems, which have weaker interchromophore electronic interactions. 相似文献