Dipartimento di Chimica, Università di Roma La Sapienza, P. le A. Moro 5, 00185 Roma, Italy.
Phys Chem Chem Phys. 2013 May 28;15(20):7560-6. doi: 10.1039/c3cp00121k. Epub 2013 Apr 15.
Tubules formed by self-assembly of organic molecules have vast potential for nanotechnology applications, and the introduction of sensitivity to stimuli into self-assembly tubules represents a particularly attractive feature. Here we report the preparation and characterization of a molecule obtained by chemical modification of a natural bile acid, a biological surfactant, that self-assembles in pH sensitive tubules in aqueous solutions. The tubules, which are rigid, single-walled and with a diameter of 60 nm, form at pH 8-9 and open up when the pH is increased. The transition is reversible, it occurs in the pH range of 9-10 with an opening mechanism that is remarkably different from those so far proposed in the literature. It involves a release of wall layers similar to leaves, and is determined by a drastic pH-triggered change in the molecular arrangement, which in turn induces a radical modification of the wall curvature. The description of the morphological transformation is provided by means of cryogenic transmission electron microscopy and represents, to our knowledge, the first detailed visualization of pH stimulated tubule opening. UV and circular dichroism spectroscopies are used to investigate the evolution at the molecular level.
由有机分子自组装形成的管状结构在纳米技术应用方面具有巨大的潜力，而将对刺激的敏感性引入自组装管中则代表了一个特别有吸引力的特性。在这里，我们报告了一种通过对天然胆汁酸（一种生物表面活性剂）进行化学修饰而获得的分子的制备和表征，该分子在水溶液中 pH 敏感的管状结构中自组装。这些管状结构刚性、单壁且直径为 60nm，在 pH 8-9 时形成，当 pH 值增加时会打开。这种转变是可逆的，它发生在 pH 值为 9-10 的范围内，其打开机制与迄今为止文献中提出的机制明显不同。它涉及到类似于叶片的壁层释放，并且由分子排列的剧烈 pH 触发变化决定，这反过来又导致壁曲率的根本修饰。通过低温透射电子显微镜对形态转变进行了描述，据我们所知，这是首次对 pH 刺激管状结构打开的详细可视化。使用紫外和圆二色性光谱来研究分子水平的演变。
