Cationic lipid membranes have recently attracted huge attention both from a fundamental point of view and due to their practical applications in drug delivery and gene therapy. The dynamical behavior of the lipids in the membrane is a key parameter controlling various physiological processes and drug release kinetics. Here, we review the dynamical and thermotropic phase behavior of an archetypal cationic lipid membrane, dioctadecyldimethylammonium bromide (DODAB), as studied using neutron scattering and molecular dynamics simulation techniques. DODAB membranes exhibit interesting phase behavior, specifically showing coagel, gel, and fluid phases in addition to a large hysteresis when comparing heating and cooling cycles. The dynamics of the lipid membrane is strongly dependent on the physical state of the bilayer. Lateral diffusion of the lipids is faster, by an order of magnitude, in the fluid phase than in the ordered phase. It is not only the characteristic times but also the nature of the segmental motions that differ between the ordered and fluid phases. The effect of different membrane active molecules including drugs, stimulants, gemini surfactants, and unsaturated lipids, on the dynamical and thermotropic phase behavior of the DODAB membrane, is also discussed here. Various interesting features such as induced synchronous ordering between polar head groups and tails, sub diffusive behavior, etc., are observed. The results shed light on the interaction between these additives and the membrane, which is found to be a complex interplay between the physical state of the membrane, charge, concentration, molecular architecture of the additives, and their location within the membrane.

中文翻译：

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双十八烷基二甲基溴化铵，细胞膜的表面活性剂模型：微观动力学的重要性


阳离子脂质膜最近从基本角度以及由于其在药物输送和基因治疗中的实际应用而引起了巨大的关注。膜中脂质的动力学行为是控制各种生理过程和药物释放动力学的关键参数。在这里，我们回顾了使用中子散射和分子动力学模拟技术研究的原型阳离子脂质膜双十八烷基二甲基溴化铵（DODAB）的动力学和热致相行为。 DODAB 膜表现出有趣的相行为，在比较加热和冷却循环时，除了大​​的滞后现象外，还特别显示了凝固凝胶、凝胶和流体相。脂质膜的动力学很大程度上取决于双层的物理状态。脂质的横向扩散在流体相中比在有序相中快一个数量级。有序相和流体相之间的差异不仅在于特征时间，而且在于分段运动的性质。本文还讨论了不同膜活性分子（包括药物、兴奋剂、双子表面活性剂和不饱和脂质）对 DODAB 膜动力学和热致相行为的影响。观察到各种有趣的特征，例如极性头部和尾部之间的诱导同步排序、亚扩散行为等。结果揭示了这些添加剂与膜之间的相互作用，发现这是膜的物理状态、电荷、浓度、添加剂的分子结构及其在膜内的位置之间复杂的相互作用。