共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
3.
4.
侧链型偶氮聚合物液晶在不同波长激发条件下的光致取向 总被引:4,自引:0,他引:4
合成了聚甲基丙烯酸 (6 [4 (4 氰基偶氮苯 )苯氧基 ]己酯 ) (Poly(6 [4 (4 cyanophenylazo)phenoxy]hexylmethacrylate) (PM6ABCN) ) ,采用溶液挥发法在玻璃载片上成膜 ,研究了薄膜样品在Tg 温度以下的光致取向 .用波长分别为 36 6、40 0和 436nm的偏振光照射 ,发现PM6ABCN薄膜的光致取向过程不仅依赖于光的强度 ,还依赖所使用的偏振光的波长 .在低于Tg 的温度下 ,用波长为 40 0nm ,功率为 2 0mW cm2 的光照射 10 0s可以使样品的取向达到饱和 ,而用 36 6nm的光导致的取向程度要小于 40 0nm和 436nm的光 ,因为 36 6nm的光会在稳态时产生更多数目的cis异构体 相似文献
5.
添加助剂,用碱/酸两步处理(4 ̄6mol NaOH,1mol HCl,助剂浓度1 ̄2%W),在常压,100℃左右时,对四种煤(大同、神木、平朔、太西)进行了脱矿物质的研究。最佳条件下可得到Ad为0.34%的超净煤。矿物质脱除率分别可达81.89%、88.96%、88.57%、76.35%。本文重点考察了助剂种类和浓度、碱浓度、反应时间等过程参数对YA的影响。并采用X射线衍射、红外光谱和电镜分析等手 相似文献
6.
PHOTOSENSITIZATION BY ANTITUMOR AGENTS—1. PRODUCTION OF SINGLET OXYGEN DURING IRRADIATION OF ANTHRAPYRAZOLES WITH VISIBLE LIGHT 总被引:1,自引:0,他引:1
Krzysztof Reszka Petros G. Tsoungas J. William Lown 《Photochemistry and photobiology》1986,43(5):499-504
Abstract— Oxygen consumption, photoinduced by visible light, and sensitized by novel anthrapyrazole antitumor agents has been observed. Generation of singlet oxygen upon irradiation of ethanolic solutions of the drugs with visible light (480–520 nm) was demonstrated using a specific 1 O2 acceptor, 2.5-dimethylfuran and a quencher, sodium azide. An electron paramagnetic resonance method was employed to measure the rate of oxygen consumption. Significant differences were found in the sensitizing properties among the anthrapyrazoles studied. Intramolecular hydrogen bonding within the chro-mophore is one of the structural factors that determine the efficacy of a given anthrapyrazole in 1 O2 generation 相似文献
7.
CONDITIONS AFFECTING THE EARLY THYMINELESS DEATH OCCURRING AFTER ULTRAVIOLET IRRADIATION OF ESCHERICHIA COLI B3 总被引:1,自引:0,他引:1
Abstract— Exposure of the thymine requiring bacterium Escherichia coli strain B3 to ultraviolet light (u.v.) prior to incubation in the absence of thymine shortens the lag period normally observed before the onset of death due to lack of thymine. Culture conditions promoting synthesis of new kinds of enzymes at the time of thymineless challenge after u.v. irradiation enhance this effect. The effect can be reversed either by the addition of thymine or photo-reactivation. Possible mechanisms for these phenomena are discussed. 相似文献
8.
Abstract— Bacteriophage SP02c12 and its isolated DNA were irradiated at 254 nm in tryptophan solutions. At a concentration of 10 m M , the amino acid exerted a protective effect on intact virus. The magnitude of this effect depended upon the length of time elapsed between mixing and irradiation. No protection was observed for solutions irradiated immediately after mixing. Tryptophan did not have a significant effect on UV sensitivity of the isolated viral DNA. No covalent crosslinking of tryptophan to DNA was observed. 相似文献
9.
10.
11.
Abstract— Degradation of the DNA of a rec- mutant of Escherichia coli K12 (JC1569 b) induced by u.v. light was investigated. The rate of degradation was much larger by growing bacteria than by stationary cells. When growing bacteria were starved for amino acids, their DNA became resistant to irradiation. The mode of u.v.-induced degradation was investigated by comparing the time course of release from the acid-insoluble fraction of the label for two growing cultures; the one was pulse-labeled with 3 H-thymidine and the other was pulse-labeled and chased thereafter for 12 min. It was found that the label incorporated into the former culture begins to be lost from the acid-insoluble fraction prior to the loss of the label incorporated into the latter culture. It was concluded that breakdown of the replicating point precedes degradation of the bulk of the DNA. This result suggested that the replicating point is a sensitive site to irradiation and the u.v.-induced degradation of DNA seemed to be influenced by the state of chromosome at the time of irradiation. Experiments of centrifugation of lysed spheroplasts of bacteria uniformly labeled with 3 H-thymidine in alkaline sucrose demonstrated that DNA of low molecular weight appeared after irradiation with only 5 ergs/ mm2 , and that the molecular weight could not be restored by post-irradiation incubation. Considering these results, an hypothesis is proposed concerning the initiation of induced degradation of the DNA of the rec- mutant. 相似文献
12.
13.
14.
Jacques Kagan Xinsheng Chen Tian P. Wang P. Forlo 《Photochemistry and photobiology》1992,56(2):185-193
Supercoiled (SC) pBR322 was used to probe the recent claim that 5-geranoxylpsoralen (5-GOP) did not photoreact with DNA. Contrary to expectations, 5-GOP was found to damage DNA in the presence of UV-A through two competing pathways: (a) single strand breaks, identified by the conversion of supercoiled into open circular and linear DNA, and (b) cross-linking, revealed by the fluence-dependent decrease in the extent of denaturation of the double stranded supercoiled DNA to single stranded circular DNA. In addition, a fluence-dependent modification reduced the ability of the restriction enzyme EcoR I to linearize the photosensitized DNA, and alkali-labile lesions were generated. Psoralen, 5-methoxypsoralen, and 8-methoxypsoralen, which are well-known to undergo cycloaddition to DNA, had a more pronounced effect on supercoiled DNA. Single strand breaks occurred more readily than with 5-GOP, and the surviving SC form remaining had reduced electrophoretic mobility in agarose gels. In all cases, the DNA damage was more prominent when oxygen was absent. 相似文献
15.
16.
ACUTE SKIN RESPONSE IN ALBINO MICE FOLLOWING PORPHYRIN PHOTOSENSITIZATION UNDER OXIC AND ANOXIC CONDITIONS 总被引:4,自引:0,他引:4
Abstract Acute normal skin toxicity induced by porphyrin photosensitization has been examined using albino mice. Oxic and anoxic (clamped) skin was exposed to red light (630 nm) 24 h following administration of hematoporphyrin derivative (HpD) or Photofrin II (the active component of HpD). Experiments were also performed to determine the effect of sodium pentobarbital anesthesia on HpD and Photofrin II photosensitization of normal skin. Results from this study demonstrated that comparable levels of acute skin damage were induced by HpD and Photofrin II under oxic conditions but neither porphyrin produced any apparent phototoxicity under anoxic conditions. In addition, the level of skin damage induced by porphyrin photosensitization was not affected by sodium pentobarbital anesthesia. 相似文献
17.
PHOTODYNAMIC INHIBITION OF ESCHERICHIA COLI DNA POLYMERASE I BY 8-METHOXYPSORALEN PLUS NEAR ULTRAVIOLET IRRADIATION 总被引:1,自引:0,他引:1
Abstract— Morphological abnormality due to the UV irradiation of sperm and its modification by photoreactivation (PR) were studied in the sea urchin, Hemicentrotus pukherrimus. When sperm was UV-irradiated and allowed to fertilize unirradiated eggs, the effect of the UV was manifested as an abnormal morphology of embryos in the gastrula or later stages. The UV-induced morphological abnormality was prevented by photoreactivation when the fertilized eggs were illuminated with visible light. In the experiments on a stage-dependent change of PR effectiveness, it was found that an illumination sufficed to effect a nearly complete PR when applied up to the onset of the first DNA synthetic phase, while the PR effectiveness declined thereafter. Illumination after the completion of DNA synthesis had little effect for PR. 相似文献
18.
A. Castellano J. P. Catteau A. Lablache-Combier G. Allan 《Photochemistry and photobiology》1974,20(1):27-31
Abstract —Ultraviolet irradiation of pyrimidine and 4- and 5-methylpyrimidine in methanol at 113 K gave the corresponding semiquinone radicals in a monophotonic process. It is likely that this process involves an n * triplet state of the photoexcited pyrimidines. 相似文献
19.
乙酰苯胺在超声波作用下的N—烷基化 总被引:2,自引:0,他引:2
超声波作为一种新型能量形式用于许多有机反应。我们对乙酰苯胺的相转移催化N-烷基化反应进行了研究。发现超声波作用能使反应在室温下顺利进行,反应产率令人满意。 所用试剂除卤代正丁烷为化学纯外均为分析纯。超声波装置为上海超声波仪器厂CQ-250型超声波清洗仪。红外光谱由岛津IR-408型仪器测定。 在圆底烧瓶中加入乙酰苯胺2.7g(0.02mol),适量相转移催化剂(PTC),50mL苯,4g氢氧 相似文献
20.
The electrochemistry of polyaniline synthesized electrochemically in acidic solution under light irradiation has been studied as a function of the applied potentials, the concentration and acidity of electrolyte as well as pH at applied potentials in the rang+0.40 to-0.5V vs. SCE. It is concluded that under selected experimental conditions the reduced repeat groups in polyaniline are oxidized by air in the dark and that this oxidation process can be strongly photocatalyzed. 相似文献