Direct correlation of structure changes and thermal events in hydrated lipid established by simultaneous calorimetry and time-resolved x-ray diffraction.
Direct correlation of structure changes and thermal events in hydrated lipid established by simultaneous calorimetry and time-resolved x-ray diffraction.
复制标题
通过同时量热法和时间分辨 X 射线衍射建立了水合脂质结构变化和热事件的直接关联。
DOI：
10.1016/s0006-3495(92)81621-1
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发表时间：
1992
影响因子：
3.4
通讯作者：
Caffrey,M
中科院分区：
文献类型：
--
作者：
Chung,H;Caffrey,M
在许多脂质系统中，多晶型和介晶行为取决于样品的热历史。为了明确确定此类系统中吸热和放热事件的结构起源，我们进行了同步量热和时间分辨 X 射线衍射 (SCALTRD)。为此，使用铝量热坩埚来容纳水合脂质样品，并且安装量热计时，坩埚底部垂直于同步加速器衍生的聚焦单色 X 射线束，用于 SCALTRD 数据收集。使用密封坩埚中的水合单反油蛋白和 1,2-二反油酰基-sn-甘油-3-磷酸乙醇胺 (DEPE) 进行测量。使用 X 射线图像增强器/视频系统和包含 X 射线敏感图像板和/或胶片的条纹相机收集时间分辨 X 射线衍射 (TRXRD) 数据。水合单油蛋白中层状凝胶到层状液晶相变的 SCALTRD 分析通过量热法和 TRXRD 在 1 ℃/min 的扫描速率下给出了相同的进度曲线。在更快的速率下，量热法显示出更广泛的相变，其开始温度比 TRXRD 观察到的温度更低，结束温度更高。出现这种差异的部分原因是 TRXRD 中使用的 X 射线束仅询问样品的一小部分，而量热计则对整个样品体积做出响应。由于数据收集时间相对较长，辐射损伤是 SCALTRD 测量的一个重要的潜在问题。使用DEPE/水观察到这种效应，因为TRXRD显示层状凝胶到层状液晶相变发生在比量热法观察到的温度更低的温度下。我们推测，由于辐射损伤，样品在局部积累了杂质，辐射损伤具有降低 X 射线束询问部位的相变温度的效果。这种“组合方法”SCALTRD 方法有利于在相同的热历史条件下将同一样品中的结构重排和热事件直接关联起来。由此得出的数据的信息内容远远超过单独使用的任何一种方法所提供的信息内容。
In many lipid systems, polymorphic and mesomorphic behavior depends on sample thermal history. To establish unequivocally the structural origin of endothermic and exothermic events in such systems, we have performed simultaneous calorimetry and time-resolved x-ray diffraction (SCALTRD). To this end, aluminum calorimetry crucibles were used to contain the hydrated lipid sample, and the calorimeter was mounted with the base of the crucible oriented perpendicular to a synchrotron-derived focused monochromatic x-ray beam for SCALTRD data collection. Measurements were made with hydrated monoelaidin and 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) contained in hermetically sealed crucibles. Time-resolved x-ray diffraction (TRXRD) data were collected using an x-ray image intensifier/video system and a streak camera containing an x-ray sensitive image plate and/or film. SCALTRD analysis of the lamellar gel to lamellar liquid crystalline phase transition in hydrated monoelaidin gives identical progress curves by calorimetry and TRXRD at a scan rate of 1 degree C/min. At faster rates, calorimetry shows a broader phase transition that starts at a lower and ends at a higher temperature than is observed by TRXRD. The disparity arises in part because the x-ray beam used in TRXRD interrogates only a small portion of the sample, whereas the calorimeter responds to the entire sample volume. Because data collection times are relatively long, radiation damage is an important potential problem for SCALTRD measurements. Such an effect was observed with DEPE/water in that TRXRD shows the lamellar gel to lamellar liquid crystalline phase transition occurring at a lower temperature than observed by calorimetry. We speculate that the sample accumulates impurities locally as a result of radiation damage that has the effect of lowering the phase transition temperature at the site of interrogation by the x-ray beam. This "methods-in-combination" SCALTRD approach facilitates the direct correlation of structure rearrangements and thermal events in the same sample under identical conditions of thermal history. The information content of the data so derived far surpasses that available from either method used in isolation.