Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
Department of Polymer Science, The University of Akron, Akron, OH, 44325, USA.
Angew Chem Int Ed Engl. 2019 Oct 7;58(41):14708-14714. doi: 10.1002/anie.201907668. Epub 2019 Sep 13.
Nanotubes assembled from macrocyclic precursors offer a unique combination of low dimensionality, structural rigidity, and distinct interior and exterior microenvironments. Usually the weak stacking energies of macrocycles limit the length and mechanical strength of the resultant nanotubes. Imine-linked macrocycles were recently found to assemble into high-aspect ratio (>10 ), lyotropic nanotubes in the presence of excess acid. Yet these harsh conditions are incompatible with many functional groups and processing methods, and lower acid loadings instead catalyze macrocycle degradation. Here we report pyridine-2,6-diimine-linked macrocycles that assemble into high-aspect ratio nanotubes in the presence of less than 1 equiv of CF CO H per macrocycle. Analysis by gel permeation chromatography and fluorescence spectroscopy revealed a cooperative self-assembly mechanism. The low acid concentrations needed to induce assembly enabled nanofibers to be obtained by touch-spinning, which exhibit higher Young's moduli (1.33 GPa) than many synthetic polymers and biological filaments. These findings represent a breakthrough in the design of inverse chromonic liquid crystals, as assembly under such mild conditions will enable the design of structurally diverse and mechanically robust nanotubes from synthetically accessible macrocycles.
由大环前体制备的纳米管提供了低维性、结构刚性以及独特的内外微观环境的独特组合。通常情况下，大环的弱堆积能限制了所得纳米管的长度和机械强度。最近发现亚胺键合的大环在过量酸的存在下组装成高纵横比（>10）的溶致性纳米管。然而，这些苛刻的条件与许多官能团和加工方法不兼容，而较低的酸负载反而会催化大环的降解。在这里，我们报告了吡啶-2,6-二亚胺键合的大环，在每大环不到 1 当量的 CF3COOH 存在下就能组装成高纵横比的纳米管。凝胶渗透色谱和荧光光谱分析揭示了一种协同自组装机制。在这种温和的条件下，需要的低酸浓度可以诱导组装，从而获得纳米纤维，其杨氏模量（1.33 GPa）高于许多合成聚合物和生物纤维。这些发现代表了反色晶液晶设计的突破，因为在如此温和的条件下进行组装将能够从可合成的大环设计出结构多样和机械坚固的纳米管。
