Institute of Chemistry, Physical Chemistry , MLU Halle-Wittenberg , Von-Danckelmann-Platz 4 , 06120 Halle , Germany.
Institute of Pharmacy, Biophysical Pharmacy , MLU Halle-Wittenberg , Wolfgang-Langenbeck-Str. 4 , 06120 Halle , Germany.
J Phys Chem B. 2019 Feb 21;123(7):1566-1577. doi: 10.1021/acs.jpcb.8b11945. Epub 2019 Feb 7.
The nanofiber formation in aqueous suspension of two classes of symmetric single-chain bolaamphiphiles with different polar headgroups and a diacetylene-modified alkyl chain with a length of 32, 34, and 36 C atoms was investigated by differential scanning calorimetry, transmission electron microscopy, and small-angle neutron scattering. As observed before for other bolalipids with phosphocholine (PC) and dimethyl-phosphoethanolamine (MePE) headgroups, the molecules form fibers when suspended in water at low temperatures but disassemble into micellar-like aggregates upon heating. The introduction of a diacetylene group in the middle of the long chain leads to a perturbation of chain packing so that this fiber-micelle transition occurs at lower temperature compared to the other bolalipids having unmodified alkyl chains. The aim of our project was the introduction of diacetylene groups into alkyl chains to be able to polymerize the fibers at low temperature. This should enhance the fiber stability and prevent the disassembly into micellar aggregates at higher temperature. Polymerization of aggregates containing diacetylene-modified bolaamphiphiles can be easily traced by UV/vis spectroscopy as colored products are formed. We found that polymerization of bolaamphiphiles with PC headgroups leads to a breakdown of most fibers into micellelike aggregates, and only some longer fibers segments are still detectable. In contrast, the use of MePE headgroups improves polymerizability and length of the polymerized fibers. The compound with 36 C atoms in the chain could be polymerized at low temperatures, and the fibers remained stable at least up to a temperature of 60 °C. This shows that the perturbation of the chain packing due to the diacetylene groups in the chains can be overcome by elongation of the chains, so that thermostable fibers with a diameter of the length of the bolalipid molecule can be successfully formed.
两类具有不同极性头基的对称单链双冠醚两亲分子在水中的纳米纤维形成以及一个二乙炔修饰的烷基链（长度为 32、34 和 36 个碳原子）的形成通过差示扫描量热法、透射电子显微镜和小角中子散射进行了研究。如以前观察到的其他具有磷酸胆碱 (PC) 和二甲基磷酸乙醇胺 (MePE) 头基的 bolalipids 一样，当这些分子在低温下悬浮在水中时，它们会形成纤维，但在加热时会分解成类似胶束的聚集体。在长链中间引入二乙炔基团会导致链堆积的扰动，使得这种纤维-胶束转变发生在比具有未修饰烷基链的其他 bolalipids 更低的温度下。我们项目的目的是将二乙炔基团引入烷基链中，以便能够在低温下聚合纤维。这应该会增强纤维的稳定性，并防止在较高温度下分解成胶束聚集体。聚合含有二乙炔修饰的 bolaamphiphiles 的聚集体可以通过 UV/vis 光谱很容易地追踪到，因为会形成有色产物。我们发现，PC 头基的 bolaamphiphiles 的聚合导致大多数纤维断裂成类似胶束的聚集体，并且只能检测到一些较长的纤维段。相比之下，使用 MePE 头基可以提高聚合性和聚合纤维的长度。具有 36 个碳原子的链的化合物可以在低温下聚合，并且纤维在至少 60°C 的温度下保持稳定。这表明，由于链中二乙炔基团的存在而导致的链堆积的扰动可以通过链的伸长来克服，从而可以成功形成具有 bolalipid 分子长度的热稳定纤维。
