The internal profile across the bilayer reveals important structural information regarding the crystallinity of acyl chains or the positions of encapsulated species. Here, we demonstrate that a simple five-layer-core-shell discoidal model can be employed to best fit the extended-q small angle X-ray scattering (SAXS) data and resolve the bilayer internal structure (with sub-nanometer resolution) of a nanoscale discoidal system comprised of a mixture of long- and short- chain lipids (known as “bicelles”). In contrast to the traditional core-shell discoidal model, the detailed structure in the hydrophobic core such as the methylene and methyl groups can be distinguished via this model. The refined model is validated by the SAXS data of bicelles whose electron scattering length density of the hydrophobic core is adjusted by the addition of a long-chain lipid with a fluorine-end group. The higher resolution of the bilayer internal structure can be employed to advance our understanding of the interaction and conformation of the membrane and associated molecules, such as membrane-associated proteins and locations of entrapped species in the lipid nanoparticles.

双层的内部轮廓揭示了有关酰基链结晶度或封装物质位置的重要结构信息。在这里，我们证明了一个简单的五层核壳盘状模型可以用来最好地拟合扩展的q小角度 X 射线散射 (SAXS) 数据并解析由长链和短链脂质（称为“bicelles”）混合物组成的纳米级盘状系统的双层内部结构（具有亚纳米分辨率）。与传统的核壳盘状模型相比，通过该模型可以区分疏水核中的详细结构，例如亚甲基和甲基。改进后的模型通过 bicelles 的 SAXS 数据进行验证，其疏水核心的电子散射长度密度通过添加具有氟端基的长链脂质进行调整。双层内部结构的更高分辨率可用于促进我们对膜和相关分子的相互作用和构象的理解，