Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology , 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.
Langmuir. 2016 May 10;32(18):4546-53. doi: 10.1021/acs.langmuir.6b00713. Epub 2016 Apr 27.
Topology of amphiphiles is important to control physicochemical properties of supramolecular assemblies. Nature demonstrates higher stability of membrane composed of lipids with a macrocyclic aliphatic tail than those with linear tails, which likely results from the restricted molecular structures of the macrocyclic lipids, allowing for closer molecular packing. In contrast, here we report that a PEG-containing macrocyclic amphiphile shows lower stability of vesicles than the corresponding acyclic one. The macrocyclic amphiphile consists of an aromatic hydrophobic part with chirality in which both ends are strapped by octaethylene glycol via phosphoric ester groups, while the acyclic amphiphile bears tetraethylene glycol chains attached to both ends of the hydrophobic part. Because of the thermoresponsive property of PEG to change its conformation, the hydrophobic part of the macrocyclic amphiphile undergoes a larger thermal conformational change than that of the acyclic one. In addition, the cyclic amphiphile has a larger molecular area, which likely reduces the vesicular stability compared with the acyclic one. Such a contrasting topological effect caused by macrocyclization at the aliphatic part seen in the natural system and at the hydrophilic part demonstrated in this study leads to expand the molecular design of amphiphiles for both increasing and decreasing the stability of vesicles by molecular topology.
两亲物的拓扑结构对于控制超分子组装的物理化学性质很重要。自然界表明，具有大环脂肪族尾部的脂质组成的膜比具有线性尾部的脂质组成的膜具有更高的稳定性，这可能是由于大环脂质的受限分子结构，允许更紧密的分子堆积。相比之下，我们在这里报告说，含有 PEG 的大环两亲物形成的囊泡比相应的无环两亲物更不稳定。该大环两亲物由具有手性的芳香疏水性部分组成，其两端通过磷酸酯基团通过 8 个氧乙烯基固定，而无环两亲物则在疏水性部分的两端连接有 4 个氧乙烯基链。由于 PEG 的温度响应特性会改变其构象，因此大环两亲物的疏水性部分会经历比无环两亲物更大的热构象变化。此外，环状两亲物具有更大的分子面积，这可能会降低囊泡的稳定性，与无环两亲物相比。这种在自然界中亲脂部分看到的大环化和在本研究中亲水部分看到的拓扑对比效应导致可以通过分子拓扑结构来扩展两亲物的分子设计，从而增加和降低囊泡的稳定性。
