Controlled Hierarchical Self-Assembly of Catenated Cages

Constructing hierarchical superstructures to achieve comparable complexity and functions to proteins with four-level hierarchy is challenging, which relies on the elaboration of novel building blocks with complex structures. We present a series of catenated cages with unique structural complexity and tailorability. The rational design was realized as such: A catenane of two symmetric cages (CSC), CSC-1, with all rigid imine panels was converted to a catenane of two dissymmetric cages (CDC), CDC-1, with two exterior flexible amine panels, and CDC-5 was tailored from CDC-1 by introducing an additional methyl group on each blade to increase lateral hindrance. CDC-1s with the most irregular and flexible configuration formed supramolecular dimers, which self-organized into 3D continuous wavelike plank with a three-level hierarchy, previously undiscovered by conventional building blocks. A drastically different 3D triclinic crystalline phase with a four-level hierarchy and trigonal phase with a three-level hierarchy were constructed of distorted CSC-1s and the most symmetric CDC-5s, respectively. The wavelike plank exhibited the lowest order, and the triclinic phase had a lower order than the trigonal phase which had the highest order. It correlates with the configuration of the primary structures, namely, the most disordered shape of CDC-1, the low-order configuration of CSC-1, and the most ordered geometry of CDC-5. The catenated cages with subtle structural differences therefore provide a promising platform for the search of emerging hierarchical superstructures that might be applied to proton conductivity, ferroelectricity, and catalysis.构建可与具有四级层级结构的蛋白质媲美的复杂度与功能的分级超结构极具挑战，该过程依赖于具有复杂结构的新型构筑基元的精准设计与制备。我们报道了一系列具有独特结构复杂度与可调控性的连环笼（catenated cages）。其合理设计思路如下：由两个对称笼构成的索烃（catenane）CSC（全称Catenane of Two Symmetric Cages）-1，即CSC-1，其全部板块均为刚性亚胺板块（imine panels）；该索烃可被转化为由两个非对称笼构成的索烃CDC（全称Catenane of Two Dissymmetric Cages）-1，即CDC-1，后者带有两个外侧柔性胺基板块（amine panels）；而CDC-5则是通过在CDC-1的每个叶片上引入额外甲基（methyl group）以增大空间位阻（lateral hindrance），从CDC-1衍生得到的结构。构型最不规则且最为柔性的CDC-1可形成超分子二聚体（supramolecular dimers），这些二聚体进一步自组装形成具有三级层级结构的三维连续波浪状板层，该结构此前从未通过常规构筑基元被制备得到。分别以扭曲的CSC-1与对称性最高的CDC-5为构筑基元，可构建出具有四级层级结构的三维三斜晶相（triclinic crystalline phase），以及具有三级层级结构的三方晶相（trigonal phase），二者结构差异显著。该波浪状板层的有序度最低，三斜晶相的有序度低于三方晶相，而三方晶相的有序度最高。这一有序度规律与初级结构的构型密切相关：即CDC-1的构型最无序，CSC-1的有序度较低，而CDC-5的几何构型最为规整。因此，这类具有细微结构差异的连环笼为探索新型分级超结构提供了极具潜力的平台，这类超结构有望应用于质子传导性（proton conductivity）、铁电性（ferroelectricity）及催化（catalysis）领域。