Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850 United States.
Langmuir. 2020 Jul 7;36(26):7609-7618. doi: 10.1021/acs.langmuir.0c01210. Epub 2020 Jun 19.
Mixtures of cationic-anionic surfactants have been shown to spontaneously form ordered monolayers at hydrophobic-hydrophilic boundaries, including air-water and oil-water interfaces. In this work, confocal Raman microscopy is used to investigate the structure of hybrid-supported surfactant bilayers (HSSBs) formed by deposition of a distal leaflet of mixed cationic-anionic surfactants onto a proximal leaflet of -alkane (C) chains on the interior surfaces of chromatographic silica particles. The surface coverage of the two surfactants in a hybrid bilayer was determined from carbon analysis and the relative Raman scattering of their respective head-groups. Within the measurement uncertainty, the stoichiometric ratio of the two surfactants is one-to-one, equivalent to mixed-charge-surfactant monolayers at air-water and oil-water interfaces and consistent with the role of the head-group electrostatic interactions in their formation. When self-assembled on the hydrophobic surface, pairs of oppositely charged alkyl chain surfactants resemble a phospholipid (phosphatidylcholine) molecule, with its zwitterionic head-group and two hydrophobic acyl chain tails. Indeed, the structure of these hybrid-supported surfactant bilayers on C-modified silica surfaces is similar to that of hybrid-supported lipid bilayers (HSLBs) on the same supports, but with denser and more-ordered -alkyl chains. Hybrid-supported surfactant bilayers exhibit a melting phase transition (gel to liquid-crystalline phase) with structural and energetic characteristics similar to those of hybrid-supported bilayers prepared from a zwitterionic phospholipid of the same alkyl chain length. These mixed-charge surfactants on -alkane-modified silica are stable in water over time (months), results that suggest the potential use of these hybrid bilayers for generating supported lipid-bilayer-like surfaces or for separation applications.
混合阳离子-阴离子表面活性剂已被证明可在疏水-亲水界面处自发形成有序的单层，包括气-水和油-水界面。在这项工作中，共焦拉曼显微镜被用于研究通过将混合阳离子-阴离子表面活性剂的远端单层沉积到内部表面的 -烷烃（C）链的近端单层上而形成的混合支撑表面活性剂双层（HSSB）的结构。通过碳分析和各自头部基团的相对拉曼散射来确定双层中两种表面活性剂的表面覆盖率。在测量不确定度范围内，两种表面活性剂的化学计量比为一比一，相当于气-水和油-水界面处的混合电荷表面活性剂单层，并且与它们形成中头部基团静电相互作用的作用一致。当在疏水性表面上自组装时，带相反电荷的烷基链表面活性剂类似于磷脂（磷脂酰胆碱）分子，其具有两性离子头部基团和两个疏水性酰基链尾部。实际上，这些在 C 修饰的硅胶表面上的混合支撑表面活性剂双层的结构与在相同支撑物上的混合支撑脂质双层（HSLB）相似，但具有更密集和更有序的 - 烷基链。混合支撑表面活性剂双层表现出熔融相变（凝胶到液晶相），其结构和能量特征与具有相同烷基链长度的两性离子磷脂制备的混合双层相似。这些在 - 烷烃修饰的硅胶上的混合电荷表面活性剂在水中长时间（数月）稳定，这表明这些混合双层在生成类似支撑脂质双层的表面或用于分离应用方面具有潜在用途。
