Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
J Phys Chem B. 2013 Aug 8;117(31):9248-57. doi: 10.1021/jp405342v. Epub 2013 Jul 25.
Biocompatible molecules that undergo self-assembly are of high importance in biological and medical applications of nanoscience. Peptides and bile acids are among the most investigated due to their ability to self-organize into many different, often stimuli-sensitive, supramolecular structures. With the aim of preparing molecules mixing the aggregation properties of bile acid and amino acid-based molecules, we report on the synthesis and self-association behavior of two diastereomers obtained by substituting a hydroxyl group of cholic acid with a l-phenylalanine residue. The obtained molecules are amphoteric, and we demonstrate that they show a pH-dependent self-assembly. Both molecules aggregate in globular micelles at high pH, whereas they form tubular superstructures under acid conditions. Unusual narrow nanotubes with outer and inner cross-section diameters of about 6 and 3 nm are formed by the derivatives. The diasteroisomer with α orientation of the substituent forms in addition a wider tubule (17 nm cross-section diameter). The ability to pack in supramolecular tubules is explained in terms of a wedge-shaped bola-form structure of the derivatives. Parallel or antiparallel face-to-face dimers are hypothesized as fundamental building blocks for the formation of the narrow and wide nanotubes, respectively.
在纳米科学的生物和医学应用中，自组装的生物相容性分子非常重要。由于能够自组装成许多不同的、通常对刺激敏感的超分子结构，因此肽和胆汁酸是研究最多的两种物质。为了制备混合胆汁酸和基于氨基酸的分子的聚集特性的分子，我们报告了通过用 l-苯丙氨酸残基取代胆酸的一个羟基而得到的两种非对映异构体的合成和自组装行为。所得到的分子是两性的，我们证明它们表现出 pH 依赖性自组装。两种分子在高 pH 下聚集形成球状胶束，而在酸性条件下形成管状超结构。由衍生物形成具有约 6nm 和 3nm 内外截面直径的异常窄纳米管。取代基具有α取向的非对映异构体还形成了更宽的管（17nm 截面直径）。超分子管的包装能力可以用衍生物的楔形 bola 形结构来解释。平行或反平行面对面二聚体被假设为形成窄纳米管和宽纳米管的基本构建块。
