Seddon John M, Squires Adam M, Conn Charlotte E, Ces Oscar, Heron Andrew J, Mulet Xavier, Shearman Gemma C, Templer Richard H
Department of Chemistry, Imperial College London, London SW7 2AZ, UK.
Philos Trans A Math Phys Eng Sci. 2006 Oct 15;364(1847):2635-55. doi: 10.1098/rsta.2006.1844.
In this paper, we give an overview of our studies by static and time-resolved X-ray diffraction of inverse cubic phases and phase transitions in lipids. In [section sign] 1, we briefly discuss the lyotropic phase behaviour of lipids, focusing attention on non-lamellar structures, and their geometric/topological relationship to fusion processes in lipid membranes. Possible pathways for transitions between different cubic phases are also outlined. In [section sign] 2, we discuss the effects of hydrostatic pressure on lipid membranes and lipid phase transitions, and describe how the parameters required to predict the pressure dependence of lipid phase transition temperatures can be conveniently measured. We review some earlier results of inverse bicontinuous cubic phases from our laboratory, showing effects such as pressure-induced formation and swelling. In [section sign] 3, we describe the technique of pressure-jump synchrotron X-ray diffraction. We present results that have been obtained from the lipid system 1:2 dilauroylphosphatidylcholine/lauric acid for cubic-inverse hexagonal, cubic-cubic and lamellar-cubic transitions. The rate of transition was found to increase with the amplitude of the pressure-jump and with increasing temperature. Evidence for intermediate structures occurring transiently during the transitions was also obtained. In [section sign] 4, we describe an IDL-based 'AXcess' software package being developed in our laboratory to permit batch processing and analysis of the large X-ray datasets produced by pressure-jump synchrotron experiments. In [section sign] 5, we present some recent results on the fluid lamellar-Pn3m cubic phase transition of the single-chain lipid 1-monoelaidin, which we have studied both by pressure-jump and temperature-jump X-ray diffraction. Finally, in [section sign] 6, we give a few indicators of future directions of this research. We anticipate that the most useful technical advance will be the development of pressure-jump apparatus on the microsecond time-scale, which will involve the use of a stack of piezoelectric pressure actuators. The pressure-jump technique is not restricted to lipid phase transitions, but can be used to study a wide range of soft matter transitions, ranging from protein unfolding and DNA unwinding and transitions, to phase transitions in thermotropic liquid crystals, surfactants and block copolymers.
在本文中，我们概述了通过静态和时间分辨X射线衍射对脂质中反立方相和相变进行的研究。在第1节中，我们简要讨论了脂质的溶致相行为，重点关注非层状结构及其与脂质膜融合过程的几何/拓扑关系。还概述了不同立方相之间转变的可能途径。在第2节中，我们讨论了静水压力对脂质膜和脂质相变的影响，并描述了如何方便地测量预测脂质相变温度压力依赖性所需的参数。我们回顾了我们实验室早期关于反双连续立方相的一些结果，展示了诸如压力诱导形成和膨胀等效应。在第3节中，我们描述了压力跃变同步加速器X射线衍射技术。我们展示了从脂质体系1:2二月桂酰磷脂酰胆碱/月桂酸获得的立方-反六方、立方-立方和层状-立方转变的结果。发现转变速率随压力跃变幅度和温度升高而增加。还获得了转变过程中瞬时出现的中间结构的证据。在第4节中，我们描述了我们实验室正在开发的基于IDL的“AXcess ”软件包，用于对压力跃变同步加速器实验产生的大型X射线数据集进行批处理和分析。在第5节中，我们展示了关于单链脂质1-单油酸甘油酯的流体层状-Pn3m立方相转变的一些最新结果，我们通过压力跃变和温度跃变X射线衍射对其进行了研究。最后，在第6节中，我们给出了这项研究未来方向的一些指标。我们预计最有用的技术进步将是开发微秒时间尺度上的压力跃变装置，这将涉及使用一堆压电压力致动器。压力跃变技术不仅限于脂质相变，还可用于研究广泛的软物质转变，从蛋白质解折叠、DNA解旋和转变，到热致液晶、表面活性剂和嵌段共聚物中的相变。
