"Molecular flasks" are well-defined supramolecular cages that can encapsulate one or more molecular guests within their cavities and, in so doing, change the physical properties and reactivities of the guests. Although molecular flasks are powerful tools for manipulating matter on the nanoscale, most of them are limited in their scope because of size restrictions. Recently, however, increasingly large and diverse supramolecular cages have become available with enough space in their cavities for larger chemical systems such as polymers, nanoparticles, and biomolecules. Here we report how a class of metallosupramolecular cages known as M12L24 polyhedra have been adapted to serve as nanometer-scale containers for solutions of a pseudorotaxane host-guest complex based on a tetracationic cyclophane host, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), and a 1,5-dioxynaphthalene (DNP) guest. Remarkably, the hierarchical integration of pseudorotaxanes and M12L24 superhosts causes the system to express stimulus-responsive behavior, a property which can be described as emergent because neither the DNPCCBPQT(4+) nor the M12L24 assemblies exhibit this behavior independently. The DNP-containing M12L24 molecular flasks are effectively "sealed off" to CBPQT(4+) until ions are added as a stimulus to "open" them. The electrolyte stimulus reduces the electrostatic screening distance in solution, allowing favorable DNPCCBPQT(4+) host-guest interactions to overcome repulsive Coulombic interactions between the cationic M12L24 cages and CBPQT(4+) rings. This unusual example of ion-gated transport into chemical nanocontainers is reminiscent of transmembrane ion channels which act as gates to the cell, with the important difference that this system is reversible and operates at equilibrium.
"分子瓶"是超分子化合物中的明确界定的笼状结构,能够在其空腔内包裹一个或多个分子客体,通过这一过程改变客体分子的物理性质和反应性。尽管分子瓶在纳米尺度上操纵物质方面表现出强大的能力,但大多数分子瓶由于尺寸限制,在应用范围上受到限制。然而,近年来,随着超分子笼结构的增大和多样化,其空腔内已具备容纳较大
化学系统(如聚合物、纳米粒子和
生物分子)的空间。在这篇文章中,我们报告了一种被称为 M12
L24 多面体的
金属超分子笼类如何被改造为纳米尺度的容器,用于包裹基于四阳离子环状 hosts 的伪轮烷主-客体复合物的溶液。此复合物由四阳离子的环状 hosts(环双(对位苯醌-p-苯撑)CBPQT^4+)与 1,5-二氧
萘(DNP)客体分子组成。值得注意的是,伪轮烷与 M12
L24 超宿主之间的分级整合使整个系统表现出刺激响应行为,而这一特性可被描述为突然出现,因为无论是 DNP-CBPQT^4+ 复合物,还是 M12
L24 組裝体,单独存在时都不会呈现这样的行为。含有 DNP 的 M12
L24 分子瓶在未添加离子刺激的情况下,会有效地"隔绝"CBPQT^4+ 直到添加刺激物"开启"它们。电解质刺激减少了溶液中的静电屏蔽距离,从而使得有利的 DNP-CBPQT^4+ 主客体相互作用能够克服带电 M12
L24 笼与 CBPQT^4+ 环之间的排斥库仑力。这一罕见的离子门控运输进入
化学纳米容器的例子,类似于跨膜离子通道的作用,这种结构充当细胞膜上的"门",但重要区别在于,该系统是可逆的,并且在平衡状态下运行。