Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, Eindhoven 5600 MB, The Netherlands.
Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin 14195, Germany.
J Am Chem Soc. 2020 Oct 14;142(41):17644-17652. doi: 10.1021/jacs.0c08179. Epub 2020 Sep 29.
Supramolecular fibers in water, micrometers long and several nanometers in width, are among the most studied nanostructures for biomedical applications. These supramolecular polymers are formed through a spontaneous self-assembly process of small amphiphilic molecules by specific secondary interactions. Although many compounds do not possess a stereocenter, recent studies suggest the (co)existence of helical structures, albeit in racemic form. Here, we disclose a series of supramolecular (co)polymers based on water-soluble benzene-1,3,5-tricarboxamides (BTAs) that form double helices, fibers that were long thought to be chains of single molecules stacked in one dimension (1D). Detailed cryogenic transmission electron microscopy (cryo-TEM) studies and subsequent three-dimensional-volume reconstructions unveiled helical repeats, ranging from 15 to 30 nm. Most remarkable, the pitch can be tuned through the composition of the copolymers, where two different monomers with the same core but different peripheries are mixed in various ratios. Like in lipid bilayers, the hydrophobic shielding in the aggregates of these disc-shaped molecules is proposed to be best obtained by dimer formation, promoting supramolecular double helices. It is anticipated that many of the supramolecular polymers in water will have a thermodynamic stable structure, such as a double helix, although small structural changes can yield single stacks as well. Hence, it is essential to perform detailed analyses prior to sketching a molecular picture of these 1D fibers.
在水中，长数微米、宽数纳米的超分子纤维是生物医学应用中研究最多的纳米结构之一。这些超分子聚合物是通过特定的次级相互作用，由小的两亲性分子自发自组装形成的。尽管许多化合物没有手性中心，但最近的研究表明，尽管是外消旋形式，但存在螺旋结构。在这里，我们公开了一系列基于水溶性苯-1,3,5-三甲酰胺（BTAs）的超分子（共）聚合物，这些聚合物形成了双螺旋，而这些纤维长期以来一直被认为是一维堆叠的单分子链。详细的低温透射电子显微镜（cryo-TEM）研究和随后的三维体积重建揭示了螺旋重复，范围从 15 到 30nm。最显著的是，通过共聚物的组成可以调整螺距，其中具有相同核心但不同外围的两个不同单体以不同比例混合。与脂质双层一样，这些盘状分子聚集物中的疏水屏蔽被认为通过二聚体形成得到最佳，从而促进超分子双螺旋的形成。预计许多在水中的超分子聚合物将具有热力学稳定的结构，例如双螺旋，尽管微小的结构变化也可以产生单堆叠。因此，在描绘这些一维纤维的分子图像之前，进行详细的分析是至关重要的。
