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11.
Temperature-dependent intensity data for two-photon excitation and second harmonic generation signals phase matched onto the polariton branches of the single a-exciton of naphthalene are presented. The data are shown be in quantitative agreement with the polariton fusion model which accounts for strong exciton-photon coupling. In this model the polariton scattering frequency and group velocity determine the branching ratios for the above signals. 相似文献
12.
THE PHOTOREACTIVITY OF PYRIMIDINE-PURINE SEQUENCES IN SOME DEOXYDINUCLEOSIDE MONOPHOSPHATES AND ALTERNATING DNA COPOLYMERS 总被引:2,自引:0,他引:2
Abstract— A reversed-phase HPLC system has been developed which separates the common nucleo-bases from the 6-methylimidazo[4,5- b ]pyridin-5-one (6-MIP) produced on acid hydrolysis of a thymine-adenine photoadduct (TA*) that is formed between adjacent thymine and adenine bases in UV-irradiated polydeoxyribonucleotides. By measuring the relative amounts of adenine and 6-MIP in acid hydrolysates, this system has been used to investigate how polynucleotide conformation affects the yield of TA* in poly(dA-dT) irradiated at 254 nm. The photoreactivity of other pyrimidine-purine sequences has been examined with the deoxydinucleoside monophosphates d(TpI) and d(m5 CpA) and with the alternating DNA copolymers poly(dA-dU), poly(dI-dC), poly(dG-dC) and poly(dA-dC).poly(dG-dT). Samples were irradiated at 254 nm in aqueous solution and in ice, and at wavelengths >290 nm with acetone as photosensitizer. A photoproduct resembling TA*, and giving 6-MIP on acid hydrolysis, was isolated from d(TpI) irradiated at 254 nm in solution or in ice; d(m5 CpA) was comparatively unreactive. Acid hydrolysates of the irradiated DNA copolymers were screened by HPLC and by TLC and paper electrophoresis, for the presence of imidazo[4,5- b ]pyridin-5-one, 6-MIP, or other species attributable to specific photoproduct formation. By this criterion, however, none of the copolymers showed evidence of significant photoreactivity in either their single- or double-stranded conformational states. The formation of mixed pyrimidine-purine photoadducts in DNA is therefore probably restricted to T-A doublets. 相似文献
13.
Catalytic hydrogenation of dihydroindolizidinone occurred preferentially from the endo-face giving rapid entry to (8R,8aS)-8-methylhexahydroindolizin-5-one, a key intermediate in the synthesis of 5,8-disubstituted indolizidines and deoxypumiliotoxin 251H. The selectivity could be improved further by diimide reduction though this also resulted in some oxidation of the alkene to the diene. The basis of the unusual stereoselectivity in the diimide reduction is believed to be stereoelectronic in origin. 相似文献
14.
Two new mixed-metal tellurites, Na1.4Nb3Te4.9O18 and NaNb3Te4O16, have been synthesized by standard solid-state techniques using Na2CO3, Nb2O5, and TeO2 as reagents. The structures of Na1.4Nb3Te4.9O18 and NaNb3Te4O16 were determined by single-crystal X-ray diffraction. Both of the materials exhibit three-dimensional structures composed of NbO6 octahedra, TeO4, and TeO3 polyhedra. The Nb5+ and Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn-Teller (SOJT) effects. The Nb5+ cations undergo an intraoctahedral distortion toward a corner (local C4 direction), whereas the Te4+ cations are in distorted environments owing to their nonbonded electron pair. Infrared and Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dielectric measurements were also performed on the reported materials. Crystal data: Na1.4Nb3Te4.9O18, monoclinic, space group C2/m (No. 12), with a = 32.377(5) A, b = 7.4541(11) A, c = 6.5649(9) A, beta = 95.636(5) degrees, V = 1576.7(4) A3, and Z = 4; NaNb3Te4O16, monoclinic, space group P2(1)/m (No. 11), with a = 6.6126(13) A, b = 7.4738(15) A, c = 14.034(3) A, beta = 102.98(3) degrees, V = 675.9(3) A3, and Z = 2. 相似文献
15.
Shiv Poojan Seung-Hyun Bae Jae-Woong Min Eun Young Lee Yura Song Hee Yeon Kim Hye Won Sim Eun-Kyung Kang Young-Ho Kim Hae-Ock Lee Yourae Hong Woong-Yang Park Hyonchol Jang Kyeong-Man Hong 《Experimental & molecular medicine》2020,52(7):1102
To elucidate the epigenetic mechanisms of drug resistance, epigenetically reprogrammed H460 cancer cells (R-H460) were established by the transient introduction of reprogramming factors. Then, the R-H460 cells were induced to differentiate by the withdrawal of stem cell media for various durations, which resulted in differentiated R-H460 cells (dR-H460). Notably, dR-H460 cells differentiated for 13 days (13dR-H460 cells) formed a significantly greater number of colonies showing drug resistance to both cisplatin and paclitaxel, whereas the dR-H460 cells differentiated for 40 days (40dR-H460 cells) lost drug resistance; this suggests that 13dR-cancer cells present short-term resistance (less than a month). Similarly, increased drug resistance to both cisplatin and paclitaxel was observed in another R-cancer cell model prepared from N87 cells. The resistant phenotype of the cisplatin-resistant (CR) colonies obtained through cisplatin treatment was maintained for 2–3 months after drug treatment, suggesting that drug treatment transforms cells with short-term resistance into cells with medium-term resistance. In single-cell analyses, heterogeneity was not found to increase in 13dR-H460 cells, suggesting that cancer cells with short-term resistance, rather than heterogeneous cells, may confer epigenetically driven drug resistance in our reprogrammed cancer model. The epigenetically driven short-term and medium-term drug resistance mechanisms could provide new cancer-fighting strategies involving the control of cancer cells during epigenetic transition.Subject terms: Tumour heterogeneity, Epigenetics 相似文献
16.
Summary The analysis of several phenylurea herbicides in different waters is described using an immunoaffinity column clean-up and
determination by high performance liquid chromatography. The pesticides were selectively retained on a solid phase extraction
column containing antibodies to chlortoluron and to isoproturon immobilised onto silica. Selected phenylureas were eluted
using a simple phosphate buffered saline/ethanol mixture at low pH. The immunoaffinity approach gave extracts free of interfering
substances and allowed detection limits comparable to those required for pesticides in water in the European Community. The
proposed method was successfully applied to the determination of chlortoluron, isoproturon, linuron and chlorbromuron in tap
and river water.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
17.
Bozlee BJ Misra AK Sharma SK Ingram M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(10):2342-2348
In the present study, we investigated remote laser-induced fluorescence (LIF), at a distance of 4.8 m, of a variety of natural minerals and rocks, and Hawaiian Ti (Cordyline terminalis) plant leaves. These minerals included calcite cleavage, calcite onex and calcite travertine, gypsum, fluorapatite, Dover flint and chalk, chalcedony and nephelene syenite, and rubies containing rock. Pulsed laser excitation of the samples at 355 and 266 nm often resulted in strong fluorescence. The LIF bands in the violet-blue region at approximately 413 and approximately 437 nm were observed only in the spectrum of calcite cleavage. The green LIF bands with band maxima in the narrow range of approximately 501-504 nm were observed in the spectra of all the minerals with the exception of the nephelene syenite and ruby rocks. The LIF red bands were observed in the range approximately 685-711 nm in all samples. Excitation with 532 nm wavelength laser gave broad but relatively low fluorescence background in the low-frequency region of the Raman spectra of these minerals. One microsecond signal gating was effective in removing nearly all background fluorescence (with peak at approximately 610 nm) from calcite cleavage Raman spectra, indicating that the fluorescence was probably from long-lifetime inorganic phosphorescence. 相似文献
18.
A general route to 2-arylbenzofurans, consisting of reaction of an o-halogenophenol ester with a cuprous arylacetylide, was employed to synthesize medicagol methoxybenzofuran. 2,4-Diraethoxyacetophenone was converted to 2,4-dimethoxyphenylacetylene in three steps and reaction of the cuprous salt with 2-iodo-4,5-methylenedioxyphenyl acetate gave the desired 2-(2′,4′-dimethoxyphenyl)-5,6-methylenedioxybenzofuran. 相似文献
19.
F. E. G. Henn R. M. Buchanan N. Jiang D. A. Stevenson 《Applied Physics A: Materials Science & Processing》1995,60(5):515-519
Alternating current (ac) conductivity and permittivity measurements were carried out on yttriastabilized cubic zirconia, with yttria varying from 9.6 to 25.5 mol%. In this composition range, the dielectric constant measured at 103 Hz decreased from 29.8 to 23.2 as the yttria concentration increased. A plot of the ac conductivity versus frequency exhibited a plateau conductivity (dc) and a frequency () dependent term '(). An analysis of '() with a suitable theoretical approach based on a pairs-approximation model, resulted in a calculated binding energy for the yttrium-associated oxygen vacancy of 0.29±0.05 eV, which compares favorably with values obtained by different means in previous studies. The experimental determination of the frequency dependence of the conductivity and its analysis provides an effective basis for understanding the ionic conductivity mechanism. 相似文献
20.