Institute of Chemistry - Physical Chemistry, Martin-Luther-University Halle-Wittenberg , D-06120, Halle/Saale, Germany.
J Phys Chem B. 2012 Apr 26;116(16):4871-8. doi: 10.1021/jp207996r. Epub 2012 Apr 17.
The T-shaped amphiphilic molecule A6/6 forms a columnar hexagonal liquid-crystalline phase between the crystalline and the isotropic liquid when studied in bulk (Chen et al., 2005). Because of the hydrophilic and flexible oligo(oxyethylene) side chain terminated by a 1-acylamino-1-deoxy-d-sorbitol moiety attached to a rigid terphenyl core with terminal hexyloxy alkyl chains, it was expected that also formation of lyotropic phases could be possible. We therefore studied the behavior of A6/6 in water and also in mixtures with bilayer-forming phospholipids, such as dipalmitoyl-phosphatidylcholine (DPPC), using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and solid-state nuclear magnetic resonance (ssNMR). DSC showed for the pure A6/6 suspended in water a phase transition at ca. 23 °C. TEM and cryo-TEM showed vesicular as well as layered structures for pure A6/6 in water below and above this phase transition. By atomic force microscopy (AFM), the thickness of the layer was found to be 5-6 nm. This leads to a model for a bilayer formed by A6/6 with the laterally attached polar side chains shielding the hydrophobic layer built up by the terphenyl core with the terminal alkyl chains of the molecules. For DPPC:A6/6 mixtures (10:1), the DSC curves indicated a stabilization of the lamellar gel phase of DPPC. Negative staining TEM and cryo-TEM images showed planar bilayers with hexagonal morphology and diameters between 50 and 200 nm. The hydrodynamic radius of these aggregates in water, investigated by dynamic light scattering (DLS) as a function of time and temperature, did not change indicating a very stable aggregate structure. The findings lead to the proposition of a new bicellar structure formed by A6/6 with DPPC. In this model, the bilayer edges are covered by the T-shaped amphiphilic molecules preventing very effectively the aggregation to larger structures.
T 型两亲分子 A6/6 在本体中研究时形成结晶态和各向同性液态之间的柱状六方液晶相（Chen 等人，2005 年）。由于亲水且柔性的聚（氧乙烯）侧链由末端酰氨基-1-去氧-d-山梨糖醇部分终止，并连接在带有末端己氧基烷基链的刚性三联苯核上，因此预计也可以形成溶致液晶相。因此，我们研究了 A6/6 在水中的行为，以及与双层形成磷脂，如二棕榈酰磷脂酰胆碱（DPPC）的混合物中的行为，使用差示扫描量热法（DSC）、透射电子显微镜（TEM）、冷冻透射电子显微镜（cryo-TEM）、动态光散射（DLS）和固态核磁共振（ssNMR）。DSC 显示，在纯 A6/6 悬浮在水中时，在约 23°C 处发生相变。TEM 和 cryo-TEM 显示，在低于和高于该相变的纯 A6/6 水中，存在囊泡和层状结构。通过原子力显微镜（AFM），发现层的厚度为 5-6nm。这导致了一个由 A6/6 形成的双层模型，其中侧向附着的极性侧链屏蔽了由分子的三联苯核和末端烷基链构成的疏水性层。对于 DPPC:A6/6 混合物（10:1），DSC 曲线表明 DPPC 的层状凝胶相得到稳定。负染色 TEM 和 cryo-TEM 图像显示出具有六边形形态的平面双层，直径在 50 至 200nm 之间。这些在水中的聚集物的水动力半径，通过动态光散射（DLS）作为时间和温度的函数进行研究，没有变化，表明聚集物结构非常稳定。这些发现导致了由 A6/6 和 DPPC 形成的新型双胶束结构的提出。在这个模型中，双层边缘被 T 型两亲分子覆盖，有效地阻止了聚集到更大的结构。
