DPPC双层膜中浓度依赖的膜不稳定化：氯仿和醇类的插入机制与应力再分配
Concentration-Dependent Membrane Destabilization in DPPC Bilayers: Distinct Insertion Mechanisms and Stress Redistribution by Chloroform and Alkanols
AI总结：
研究通过分子动力学模拟揭示了溶质浓度和分子化学如何影响DPPC双层膜从饱和到不稳定化的转变，发现浓度增加导致面积压缩模量降低和应力再分配，不同溶剂表现出不同的插入机制。
摘要：
溶质浓度和分子化学如何调控膜从饱和到不稳定化的转变？本文通过微秒级分子动力学模拟研究了氯仿和一系列醇类在0-50%浓度范围内对DPPC双层膜的影响。尽管1000 ns内未观察到完全熔化，但所有系统均表现出不稳定化前兆，包括厚度波动增强、脂质有序度降低和机械变软。氯仿引起显著变薄和大波动，与深插入一致。甲醇主要扰动头部区域，乙醇有中间行为，部分插入。辛醇在高浓度下保持双层厚度，因类脂质插入但显著增加波动和互嵌。所有系统中，浓度增加导致面积压缩模量和氘有序参数降低，伴随横向压力分布平滑，表明应力再分配。自由能分析显示膜分区增加和转移动能降低，最强见于辛醇，最弱见于甲醇。这些结果表明膜不稳定化由插入深度、界面拥挤和脂质排列破坏的相互作用决定。
英文摘要：
How do solute concentration and molecular chemistry govern the transition from membrane saturation to destabilization? We address this using microsecond-scale molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) bilayers with chloroform (CHCl$_3$) and a homologous series of alkanols (methanol, ethanol, octanol) over $0-50\%$ concentrations. Although complete membrane melting is not observed within $1000\, ns$, all systems exhibit clear precursors of destabilization, including enhanced thickness fluctuations, reduced lipid order, and mechanical softening. Chloroform induces pronounced thinning and large fluctuations, consistent with deep, transient insertion. Methanol perturbs primarily the headgroup region, while ethanol shows intermediate behavior with partial insertion. Octanol preserves bilayer thickness at high concentrations due to lipid-like insertion but significantly increases fluctuations and interdigitation. Across all systems, increasing concentration decreases the area compressibility modulus and deuterium order parameter, accompanied by smoothing of lateral pressure profiles, indicating stress redistribution. Free energy analysis reveals increased membrane partitioning and reduced translocation barriers with concentration, strongest for octanol and weakest for methanol. These results demonstrate that membrane destabilization is governed by the interplay of insertion depth, interfacial crowding, and lipid packing disruption.
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