Department of Chemistry, Fudan University, Shanghai 200438, China.
Acc Chem Res. 2021 Jul 20;54(14):2959-2968. doi: 10.1021/acs.accounts.1c00254. Epub 2021 Jul 2.
Nanopore structures in nature play a crucial role in performing many sophisticated functions such as signal transduction, mass transport, ion channel, and enzyme reaction. Inspired by pore-forming proteins, considerable effort has been made to design self-assembling molecules that are able to form nanostructures with internal pores in aqueous media. These nanostructures offer ample opportunity for applications because their internal pores are able to perform a number of unique functions required for a confined nanospace. However, unlike nanopore assembly in nature, the synthetic nanopore structures are mostly based on a fixed pore that impedes performing adaptable regulation of properties to environmental change. This limitation can be overcome by integration of hydrophilic oligo(ethylene oxide) dendrons into aromatic building blocks for nanopore self-assembly, because the dendritic chains undergo large conformational changes triggered by environmental change. The transition of the oligoether chains triggers the aromatic nanopore assembly to undergo reversible pore deformation through closing, squeezing, and shape change without structural collapse. These switching properties allow the aromatic nanopore structures to perform adaptable, complex functions which are difficult to achieve using a fixed pore assembly.In this Account, we summarize our recent progress in the development of switchable nanopore structures by self-assembly of rigid aromatic amphiphiles grafted by hydrophilic oligo(ethylene oxide) dendrons in aqueous media. We show that combining oligoether chains into aromatic segments generates switchable aromatic nanopore structures in aqueous media such as hollow tubules, toroidal structures, and 2D porous sheets depending on the shape of the aromatic building block. Next, we discuss the chemical principle behind the switching motion of the aromatic nanopore structures triggered by external stimuli. We show that the internal pores of the aromatic nanostructures are able to undergo reversible switching between open-closed or expanded-contracted states triggered by external stimuli such as temperature, pH, and salts. In the case of toroidal structures, closed ring-like aromatic frameworks can be spirally open triggered by heat treatment, which spontaneously initiate helical polymerization. Additionally, we discuss switchable functions carried out by the aromatic nanopores such as driving helicity inversion of DNA, consecutive enzymatic action, reversible actuation of lipid vesicles, and pumping of captured guests out of internal pores. By understanding the underlying chemical principle required for dynamic mechanical motion, aromatic assembly can be exploited more broadly to create emergent nanopore structures with functions as complex as those of biological systems.
自然界中的纳米孔结构在执行许多复杂功能方面发挥着至关重要的作用，例如信号转导、质量传输、离子通道和酶反应。受孔形成蛋白的启发，人们付出了相当大的努力来设计能够在水介质中形成具有内部孔的自组装分子。这些纳米结构为应用提供了充足的机会，因为它们的内部孔能够执行许多独特的功能，这些功能对于受限的纳米空间是必需的。然而，与自然界中的纳米孔组装不同，合成的纳米孔结构主要基于固定的孔，这阻碍了对环境变化进行适应性调节的性质。通过将亲水性的聚（氧化乙烯）树枝状分子整合到芳香族构筑块中用于纳米孔自组装，可以克服这种限制，因为树枝状链会发生大的构象变化，从而触发环境变化。聚醚链的转变触发芳香族纳米孔自组装通过关闭、挤压和形状变化而无需结构坍塌来进行可逆的孔变形。这些开关特性允许芳香族纳米孔结构执行适应性强的复杂功能，而使用固定孔组装很难实现这些功能。在本综述中，我们总结了我们最近在通过在水介质中自组装接枝有亲水性聚（氧化乙烯）树枝状分子的刚性芳香族两亲分子来开发可切换纳米孔结构方面的进展。我们表明，将聚醚链结合到芳香族片段中可以根据芳香族构筑块的形状在水介质中生成可切换的芳香族纳米孔结构，例如空心管、环形结构和二维多孔片。接下来，我们讨论了外部刺激触发的芳香族纳米孔结构的开关运动背后的化学原理。我们表明，芳香族纳米结构的内部孔能够在外部刺激（如温度、pH 值和盐）的触发下在打开-关闭或膨胀-收缩状态之间进行可逆切换。在环形结构的情况下，环形芳香族框架可以通过热处理螺旋打开，从而自发引发螺旋聚合。此外，我们还讨论了芳香族纳米孔执行的可切换功能，例如驱动 DNA 的螺旋反转、连续的酶促反应、脂质囊泡的可逆驱动以及将捕获的客体从内部孔中泵出。通过了解动态机械运动所需的基本化学原理，可以更广泛地利用芳香族组装来创建具有与生物系统一样复杂功能的新兴纳米孔结构。
