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Phase metastability and supercooled metastable state of diundecanoylphosphatidylethanolamine bilayers 总被引:3,自引:0,他引:3
Aqueous dispersons of L-alpha-phosphatidylethanolamine (PE) with identical saturated acyl chains are known to exhibit gel-state metastability. It is also known that the metastability in PE becomes more pronounced with decreasing acyl chain-length. In an attempt to study the metastable phase behavior of PE, we have synthesized diundecanoylphosphatidylethanolamine (diC11PE) and examined its polymorphic phase behavior. A single endothermic transition at 38 degrees C is detected between 10 and 55 degrees C by DSC for the nonheated sample of diC11PE in excess water. An immediate second heating scan done after cooling slowly of the same sample from the liquid-crystalline state shows a smaller endothermic transition at a lower temperature, 18 degrees C. However, the high-temperature transition at 38 degrees C can be detected, if the sample which has been heated above 38 degrees C is quench cooled from the liquid-crystalline to a temperature between 18 and 38 degrees C. Furthermore, two endothermic transitions at 18 and 38 degrees C and an exothermic transition at 19 degrees C are recorded for diC11PE after quench supercooling of the sample from the liquid-crystalline state to an appropriate temperature below 10 degrees C. The gel-state metastability of diC11PE can be most appropriately explained in terms of changes in interbilayer headgroup-headgroup interactions. It is suggested that the kinetically trapped supercooled metastable state may be a multilamellar structure with melted acyl chains but with strong interbilayer headgroup-headgroup interactions. 相似文献
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日本学者长尾照义(1978)用原生质体融合获得普通烟草与黄花烟草的体细胞杂种植株。1980年陈家玉等在国内首先获得普通烟草(Copus Yeusuku No.4)和黄花烟草(Yellow Flower)的体细胞杂种植株。之后,中国农科院烟草所(1981)也得到相同的结果。陈家玉等(1983)对上述杂种进行了形态学、细胞学和同工酶的分析并取得一定的结果。Dlineee等(1975)分析比较了用等电聚焦技术分离的过氧 相似文献
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The repopulation kinetics of the irradiated lip mucosa of mice has been investigated. Split-dose experiments showed that, in this tissue, repopulation starts within 3 days after the first irradiation and increases exponentially within 10 days. To assess the relative importance of protraction and distribution of irradiations as a function of time, 10 fractions were given in (1) 3 days (three irradiations per day with a 4-hr interval), (2) 11 days (daily fractions), or (3) two short courses, each consisting of five fractions given in 1.5 days separated by a rest period of 8 days, with an overall time of 11 days. The results show that by protracting the treatment from 3 to 11 days (with daily irradiations) repopulation accounts for recovery of approximately 13 Gy. Delivering the radiation in two short courses separated by a rest period leads to an additional recovery of approximately 5 Gy. The most plausible explanation for this observation is that repopulation is much more efficient during the rest period between the two courses than during continuous daily irradiation. Although the regimen of two short courses with a rest period spares the acute reaction, it will not enhance the late tolerance. Before thorough knowledge about the repopulation kinetics of the tumors can be gained, caution should be observed for indiscriminate use of split-course multiple-fraction-per-day (MFD) regimens for treating various tumors. 相似文献