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981.
982.
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
983.
A sensitive technique for the determination of trace Cu(II) in various samples after column preconcentration by adsorbing
onto pulverized Amberlite XAD-4 loaded with N-benzoylphenylhydroxylamine (BPHA) was developed. Several experimental conditions,
such as the size of XAD-4, adsorption flow rate, pH of sample solution, and so forth, were optimized. The interfering effects
of diverse concomitant ions were investigated. Al(III), Fe(III), Ni(II), and Co(II) interfered, but the interference by these
ions was completely eliminated by adjusting the amount of XAD-4-BPHA resin to 0.30 g. The dynamic range, the correlation coefficient
(R2), and the detection limit obtained by the proposed technique were 1.0–60, 0.9953, and 0.83 ng/mL, respectively. For validating
the technique, the aqueous samples (stream water, reservoir water, and wastewater), the diluted brass sample, and the plastic
sample were used as real samples. Recovery yields of 94–102% were obtained. These measured data were not different from ICP-MS
data at the 95% confidence level. This method was also validated by rice flour CRM (normal, fortified) samples. Based on the
results of the experiment, it has been found that the proposed technique can be applied to the determination of Cu(II) in
various real samples.
The text was submitted by the authors in English. 相似文献
984.
Investigation of the root extract of Antidesma pentandrum var. barbatum led to the isolation of seven new compounds, antidesmol ( 1 ), antidesmanins E ( 2 ) and F ( 3 ), antidesnone ( 4 ), antidesnol ( 5 ), barbatumols A ( 6 ) and B ( 7 ), together with 14 known compounds including sodium aristolochate‐I ( 10 ) and aristolochic acid‐I methyl ester ( 11 ). 相似文献
985.
986.
Since alkynes have higher symmetry than olefins, it is not easy to infer the mechanism of a triplet carbene’s addition to
an alkyne by traditional product analysis studies. Specifically, no stereochemical information which might offer insight into
the carbene’s spin state can be extracted from the cyclopropene products. In 1971, Hendrick, Baron, and Jones showed that
diphenylcarbene reacts with terminal alkynes in solution to produce indenes via a “self-trapping” vinylcarbene. They also examined the diphenylcarbene reaction with disubstituted alkynes and found at most
trace amounts of the “self-trapping” indene product.
In this work, we report the direct observation by organic matrix EPR of the vinylcarbenes generated from triplet fluorenylidene
and terminal alkynes. Our efforts to confirm the identities of these intermediates by independent synthesis, intermolecular
trapping, and an intramolecular “self-trapping” method-halogen-migration-are also recounted. These findings are among the
few instances in which fluorenylidene undergoes carbon-carbon bond formation rather than atom abstraction reactions in a low-temperature
matrix, and in which the biradical adduct of a triplet carbene and a π-bonded substrate can be directly observed. 相似文献
987.
Yu JI Kim KH Bae IH Lee DY Kim DL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2640-2642
Photoreflectance measurements were performed to investigate the optical properties in the electron beam irradiation semi-insulating GaAs(e-beam irradiation GaAs) and semi-insulating GaAs(SI-GaAs). A considerable increase of the PR amplitudes has been registered after the e-beam irradiation in comparison with the GaAs. It is that result of a higher electron scattering on the lattice defects created by the e-beam. 相似文献
988.
Two novel octanortriterpenoids, micranoic acids A (1) and B (2), along with three known compounds, kadsuric acid (3), 3beta-hydroxy-lanost-9(11),24(25)-dien-26-oic acid (4) and schizandronic acid (5), were isolated from the leaves and stems of Schisandra micrantha. The structures of 1 and 2 were determined by 1D and 2D NMR spectroscopic analysis. Micranoic acids A and B represent a new group of triterpenes in which the entire C-17 side chain has lost. This is the first report of octanortriterpenoids isolated from the family Schisandraceae. 相似文献
989.
Lee L Wang JX Adzić RR Robinson IK Gewirth AA 《Journal of the American Chemical Society》2001,123(36):8838-8843
X-ray reflectivity, cyclic voltammetry, and scanning tunneling microscopy (STM) are used to examine the structure of alpha-SiW12O4(4-) or silicotungstic acid (STA) adsorbed on Ag(100) in acid solution. The voltammetry shows that STA passivates the Ag surface relative to electron transfer to a solution redox species. STM images reveal the formation of a series of lattice structures, one of which can be associated with a commensurate ( radical13x radical13)R33.69 degrees structural model. X-ray reflectivity measurements show uniquely that STA orients with its four-fold axis perpendicular to the Ag(100) surface and that the center of the STA molecule is 4.90 A above the top layer of the Ag substrate. Analysis of bond lengths leads to a footprint of STA on Ag(100), in which the four terminal O atoms are located near the hollow sites and have a Ag-O bond length of 2.06 A. This bond length is consistent with a strong covalent interaction between STA and the Ag surface. 相似文献
990.
A cytotoxic compound from the leaves of Juglans mandshurica 总被引:1,自引:0,他引:1
From Juglans mandshurica leaves, a new quinone compound was isolated through bioassay-guided fractionation. The structure elucidation of the compound was established based on spectroscopic studies, notably of the 2D NMR spectra. The compound exhibited moderate cytotoxic activities against Hela, MCF-7, BGC823 and 3T3-Llcell lines with IC50 ranges from 7.5 to 26.8 μmol/L. 相似文献