Czeslik C, Winter R, Rapp G, Bartels K
University of Dortmund, Institute of Physical Chemistry I, Germany.
Biophys J. 1995 Apr;68(4):1423-9. doi: 10.1016/S0006-3495(95)80315-2.
We used x-ray and neutron diffraction to study the temperature- and pressure-dependent structure and phase behavior of the monoacylglycerides 1-monoelaidin (ME) and 1-monoolein (MO) in excess water. The monoacylglycerides were chosen for investigation of their phase behavior because they exhibit mesomorphic phases with one-, two-, and three-dimensional periodicity, such as lamellar, an inverted hexagonal and bicontinuous cubic phases, in a rather easily accessible temperature and pressure range. We studied the structure, stability, and transformations of the different phases over a wide temperature and pressure range, explored the epitaxial relations that exist between different phases, and established a relationship between the chemical structure of the lipid molecules and their phase behavior. For both systems, a temperature-pressure phase diagram has been determined in the temperature range from 0 to 100 degrees C at pressures from ambient up to 1400 bar, and drastic differences in phase behavior are found for the two systems. In MO-water dispersions, the cubic phase Pn3m extends over a large phase field in the T,p-plane. At temperatures above 95 degrees C, the inverted hexagonal phase is found. In the lower temperature region, a crystalline lamellar phase is induced at higher pressures. The phases found in ME-water include the lamellar crystalline Lc phase, the L beta gel phase, the L alpha liquid-crystalline phase, and two cubic phases belonging to the crystallographic space groups Im3m and Pn3m. In addition, the existence of metastable phases has been exploited. Between coexisting metastable cubic structures, a metric relationship has been found that is predicted theoretically on the basis of the curvature elastic energy approximation only.
我们利用X射线和中子衍射研究了单酰基甘油1-反油酸甘油酯（ME）和1-油酸甘油酯（MO）在过量水中随温度和压力变化的结构及相行为。选择单酰基甘油来研究其相行为，是因为它们在相当容易达到的温度和压力范围内会呈现出具有一维、二维和三维周期性的介晶相，如层状相、反六角相和双连续立方相。我们在很宽的温度和压力范围内研究了不同相的结构、稳定性及转变，探索了不同相之间存在的外延关系，并建立了脂质分子化学结构与其相行为之间的联系。对于这两个体系，已确定了在0至100摄氏度温度范围、从环境压力到1400巴压力下的温度-压力相图，并且发现这两个体系的相行为存在显著差异。在MO-水体系中，立方相Pn3m在T-p平面上延伸至很大的相区。在温度高于95摄氏度时，会出现反六角相。在较低温度区域，在较高压力下会诱导出结晶层状相。在ME-水体系中发现的相包括层状结晶Lc相、Lβ凝胶相、Lα液晶相以及属于晶体学空间群Im3m和Pn3m的两个立方相。此外，还利用了亚稳相的存在。在共存的亚稳立方结构之间，发现了一种仅基于曲率弹性能近似理论预测的度量关系。
