A pressure-jump time-resolved x-ray diffraction study of cubic-cubic transition kinetics in monoolein
A pressure-jump time-resolved x-ray diffraction study of cubic-cubic transition kinetics in monoolein
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DOI：
10.1021/la7023378
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发表时间：
2008-03-18
期刊：
影响因子：
3.9
通讯作者：
Seddon, John M.
中科院分区：
文献类型：
--
作者：
Conn, Charlotte E.;Ces, Oscar;Seddon, John M.
在过去的二十年里，两亲体系中的反双连续立方相之间的转化所涉及的几何路径已经被广泛的理论建模。然而，很少有实验数据存在的纯脂质系统中的三次-立方变换。我们已经使用压力跳跃时间分辨的X射线衍射，以调查的螺旋Q（II）（G）和双金刚石Q（II）（D）相之间的过渡1-单油酸甘油酯在30重量%的水的混合物。我们发现，该系统中，没有任何可检测的中间结构的情况下发生的立方-立方过渡。此外，我们已经确定了动力学的过渡，在向前和向后的方向，作为一个函数的压力跳跃幅度，温度和水含量。最近开发的模型允许（至少在原则上）从这些数据的脂质相变的活化能的计算。仅当至少在一个样品内实现动力学再现性时，该分析才适用，并且在此通过进行延长的压力循环来显示这种动力学再现性的实现。的转化率显示出明确的和一致的趋势与压力跃变的幅度，温度，和水含量，所有这些都被证明是在协议的热力学参数的变化后，在位置上的移动的效果的立方相边界。
In the past two decades, the geometric pathways involved in the transformations between inverse bicontinuous cubic phases in amphiphilic systems have been extensively theoretically modeled. However, little experimental data exists on the cubic-cubic transformation in pure lipid systems. We have used pressure-jump time-resolved X-ray diffraction to investigate the transition between the gyroid Q(II)(G) and double-diamond Q(II)(D) phases in mixtures of 1-monoolein in 30 wt% water. We find for this system that the cubic-cubic transition occurs without any detectable intermediate structures. In addition, we have determined the kinetics of the transition, in both the forward and reverse directions, as a function of pressure-jump amplitude, temperature, and water content. A recently developed model allows (at least in principle) the calculation of the activation energy for lipid phase transitions from such data. The analysis is applicable only if kinetic reproducibility is achieved, at least within one sample, and achievement of such kinetic reproducibility is shown here, by carrying out prolonged pressure-cycling. The rate of transformation shows clear and consistent trends with pressure-jump amplitude, temperature, and water content, all of which are shown to be in agreement with the effect of the shift in the position of the cubic-cubic phase boundary following a change in the thermodynamic parameters.