Yashima Eiji, Maeda Katsuhiro, Furusho Yoshio
Yashima Super-structured Helix Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), Japan.
Acc Chem Res. 2008 Sep;41(9):1166-80. doi: 10.1021/ar800091w. Epub 2008 Aug 9.
Biological macromolecules, such as DNA and proteins, possess a unique and specific ordered structure, such as a right-handed double helix or a single alpha-helix. Those structures direct the sophisticated functions of these molecules in living systems. Inspired by biological helices, chemists have worked to synthesize polymers with controlled helicity, not only to mimic the biological helices but also to realize their functions. Although numerous synthetic polymers that fold into a single-handed helix have been reported, double-stranded helical polymers are almost unavailable except for a few oligomers. In addition, the exact structures of most helical polymers remain obscure. Therefore, the development of a conceptually new method for constructing double-stranded helical polymers and a reliable method for unambiguously determining the helical structures are important and urgent challenges in this area. In this Account, we describe the recent advances in the synthesis, structures, and functions of single- and double-stranded helical polymers from our group and others and provide a brief historical overview of synthetic helical polymers. We found unique macromolecules that fold into a preferred-handed helix through noncovalent bonding interactions with specific chiral guests. During the noncovalent helicity induction process, these guest molecules significantly amplified chirality in a dynamic helical polymer. During the intensive exploration of the helicity induction mechanism, we observed an unusual macromolecular helical memory in dynamic helical polymers. Furthermore, we found that rigid-rod helical poly(phenylacetylene)s and poly(phenyl isocyanide)s showing a cholesteric or smectic liquid crystal self-assemble to form two-dimensional crystals with a controlled helical conformation on solid substrates upon exposure to solvent vapors. We visualized their helical structures including the helical pitch and handedness by atomic force microscopy (AFM). We propose a modular strategy to construct complementary double helices by employing chiral amidinium-carboxylate salt bridges with m-terphenyl backbones. The double-stranded helical structures were characterized by circular dichroism in solution and X-ray diffraction of the crystals or the direct AFM observations. Serendipitously, we found that oligoresorcinols self-assemble into well-defined double helices resulting from interstrand aromatic stacking in water. These oligoresorcinols bound cyclic and linear oligosaccharides in water to form rotaxanes and hetero-double helices, respectively. The examples presented in this Account demonstrate the notable progress in the synthesis and structural determination of helical polymers including single- and double-stranded helices. Not only do we better understand the principle underlying the generation of helical conformations, but we have also used the knowledge of these unique helical structures to develop novel helical polymers with specific functions.
生物大分子，如DNA和蛋白质，具有独特而特定的有序结构，如右手双螺旋或单α螺旋。这些结构指导着这些分子在生命系统中的复杂功能。受生物螺旋的启发，化学家们致力于合成具有可控螺旋度的聚合物，不仅是为了模仿生物螺旋，也是为了实现其功能。尽管已经报道了许多折叠成单手螺旋的合成聚合物，但除了少数低聚物外，双链螺旋聚合物几乎无法获得。此外，大多数螺旋聚合物的确切结构仍然不清楚。因此，开发一种概念上新的构建双链螺旋聚合物的方法以及一种可靠的明确确定螺旋结构的方法是该领域重要且紧迫的挑战。在本综述中，我们描述了我们小组和其他小组在单链和双链螺旋聚合物的合成、结构和功能方面的最新进展，并提供了合成螺旋聚合物的简要历史概述。我们发现了独特的大分子，它们通过与特定手性客体的非共价键相互作用折叠成优先手性的螺旋。在非共价螺旋诱导过程中，这些客体分子在动态螺旋聚合物中显著放大了手性。在对螺旋诱导机制的深入探索中，我们在动态螺旋聚合物中观察到了一种不寻常的大分子螺旋记忆。此外，我们发现刚性棒状螺旋聚（苯乙炔）和聚（苯基异氰化物）呈现胆甾相或近晶相液晶，在暴露于溶剂蒸汽时在固体基质上自组装形成具有可控螺旋构象的二维晶体。我们通过原子力显微镜（AFM）可视化了它们的螺旋结构，包括螺旋螺距和手性。我们提出了一种模块化策略，通过使用具有间苯三酚骨架的手性脒基羧酸盐桥来构建互补双螺旋。双链螺旋结构通过溶液中的圆二色性和晶体的X射线衍射或直接AFM观察进行表征。意外的是，我们发现低聚间苯二酚在水中通过链间芳族堆积自组装成定义明确的双螺旋。这些低聚间苯二酚在水中分别与环状和线性寡糖结合形成轮烷和杂双螺旋。本综述中给出的例子展示了在包括单链和双链螺旋在内的螺旋聚合物的合成和结构测定方面取得的显著进展。我们不仅更好地理解了螺旋构象产生的基本原理，而且还利用了这些独特螺旋结构的知识来开发具有特定功能的新型螺旋聚合物。
