Chemistry Graduate Group, University of California, Davis, One Shields Avenue, Davis, California 95616, United States.
Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States.
J Phys Chem B. 2023 Aug 31;127(34):7497-7508. doi: 10.1021/acs.jpcb.3c01654. Epub 2023 Aug 16.
The hydrophobic effect, a ubiquitous process in biology, is a primary thermodynamic driver of amphiphilic self-assembly. It leads to the formation of unique morphologies including two highly important classes of lamellar and micellar mesophases. The interactions between these two types of structures and their involved components have garnered significant interest because of their importance in key biochemical technologies related to the isolation, purification, and reconstitution of membrane proteins. This work investigates the structural organization of mixtures of the lamellar-forming phospholipid 1-palmitoyl-2-oleoyl--glycero-3-phosphocholine (POPC) and two zwitterionic micelle-forming surfactants, being -dodecyl-,-dimethyl-3-ammonio-1-propanesulfonate (Zwittergent 3-12 or DDAPS) and 1-oleoyl-2-hydroxy--glycero-3-phosphocholine (O-Lyso-PC), when assembled by water vapor hydration with X-ray diffraction measurements, brightfield optical microscopy, wide-field fluorescence microscopy, and atomic force microscopy. The results reveal that multilamellar mesophases of these mixtures can be assembled across a wide range of POPC to surfactant (POPC:surfactant) concentration ratios, including ratios far surpassing the classical detergent-saturation limit of POPC bilayers without significant morphological disruptions to the lamellar motif. The mixed mesophases generally decreased in lamellar spacing () and headgroup-to-headgroup distance () with a higher concentration of the doped surfactant, but trends in water layer thickness () between each bilayer in the stack are highly variable. Further structural characteristics including mesophase topography, bilayer thickness, and lamellar rupture force were revealed by atomic force microscopy (AFM), exhibiting homogeneous multilamellar stacks with no significant physical differences with changes in the surfactant concentration within the mesophases. Taken together, the outcomes present the assembly of unanticipated and highly unique mixed mesophases with varied structural trends from the involved surfactant and lipidic components. Modulations in their structural properties can be attributed to the surfactant's chemical specificity in relation to POPC, such as the headgroup hydration and the hydrophobic chain tail mismatch. Taken together, our results illustrate how specific chemical complexities of surfactant-lipid interactions can alter the morphologies of mixed mesophases and thereby alter the kinetic pathways by which surfactants dissolve lipid mesophases in bulk aqueous solutions.
疏水作用是生物学中普遍存在的过程，是两亲自组装的主要热力学驱动力。它导致了独特形态的形成，包括两种非常重要的层状和胶束中间相。这两种结构及其相关成分之间的相互作用因其在与膜蛋白分离、纯化和重构相关的关键生化技术中的重要性而引起了极大的关注。这项工作研究了层状形成磷脂 1-棕榈酰-2-油酰基--甘油-3-磷酸胆碱（POPC）与两种两性离子胶束形成表面活性剂，即 -十二烷基-，-二甲基-3-氨丙基-1-丙磺酸（Zwittergent 3-12 或 DDAPS）和 1-油酰基-2-羟基--甘油-3-磷酸胆碱（O-Lyso-PC）混合物的结构组织，通过水蒸气水合作用进行组装，并用 X 射线衍射测量、明场光学显微镜、宽场荧光显微镜和原子力显微镜进行研究。结果表明，这些混合物的多层中间相可以在很宽的 POPC 到表面活性剂（POPC：表面活性剂）浓度比范围内组装，包括远远超过 POPC 双层经典去污剂饱和限制的浓度比，而对层状结构没有明显的形态破坏。混合中间相的层间距（）和头对头距离（）随着掺杂表面活性剂浓度的增加而减小，但堆叠中每个双层之间的水层厚度（）趋势变化很大。原子力显微镜（AFM）揭示了进一步的结构特征，包括中间相形貌、双层厚度和层状破裂力，显示出均匀的多层堆叠，在中间相的表面活性剂浓度变化时，没有明显的物理差异。总之，这些结果呈现了出人意料的、高度独特的混合中间相的组装，具有由涉及的表面活性剂和脂质成分引起的不同结构趋势。它们的结构特性的调制可以归因于表面活性剂与 POPC 的化学特异性，例如头基水合和疏水性链尾不匹配。总之，我们的结果说明了表面活性剂-脂质相互作用的特定化学复杂性如何改变混合中间相的形态，从而改变表面活性剂在体相水溶液中溶解脂质中间相的动力学途径。
