Biological membranes predominantly consist of fluid lipid phases featuring lateral mobility and a considerable disorder of their hydrocarbon chains. Langmuir monolayers of lipids at the air/water interface are versatile model systems for fundamental physicochemical and biophysical membrane investigations. Grazing-incidence X-ray diffraction (GIXD) is a powerful tool for the structural characterization of such monolayers but has so far been used almost exclusively for lipid phases of crystalline ordering giving rise to sharp diffraction peaks. Here, we use GIXD for the characterization of fluid monolayers of phospholipids and of water-soluble surfactants. We find that these layers feature spatiotemporally localized, structurally correlated hydrocarbon chain regions that involve only a few molecules and have only a small extension vertically. The abundance of these regions increases with increasing lateral packing density due to compression until the transition into an ordered phase occurs.

中文翻译：

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掠入射 X 射线衍射阐明了脂质和表面活性剂的流体单层中的结构相关性


生物膜主要由具有横向迁移性和相当无序的烃链的液态脂质相组成。空气/水界面处的 Langmuir 脂质单层是用于基础物理化学和生物物理膜研究的通用模型系统。掠入射 X 射线衍射 （GIXD） 是此类单分子层结构表征的强大工具，但迄今为止几乎专门用于产生尖锐衍射峰的结晶有序脂质相。在这里，我们使用 GIXD 来表征磷脂的流体单层和水溶性表面活性剂。我们发现这些层具有时空定位的、结构相关的烃链区域，这些区域仅涉及几个分子，并且在垂直方向上只有一个很小的延伸。由于压缩，这些区域的丰度随着横向堆积密度的增加而增加，直到过渡到有序相。