College of Chemistry , Beijing Normal University , Beijing 100875 , China.
Department of Chemistry , University at Buffalo, The State University of New York , Buffalo , New York 14260 , United States.
J Am Chem Soc. 2020 Feb 12;142(6):2915-2924. doi: 10.1021/jacs.9b11536. Epub 2020 Jan 10.
Supramolecular chemistry in aqueous media is an area with great fundamental and practical significance. To examine the role of multiple noncovalent interactions in controlled assembling and binding behavior in water, the self-association of five water-soluble hexakis(-phenylene ethynylene) (-PE) macrocycles, along with the molecular recognition behavior of the resultant assemblies, is investigated with UV-vis, fluorescence, CD, and NMR spectroscopy, mass spectrometry, and computational studies. In contrast to their different extents of self-aggregation in organic solvents, all five macrocycles remain aggregated in water at concentrations down to the micromolar (μM) range. CD spectroscopy reveals that and , two macrocycles carrying chiral side chains and capable of H-bonded self-association, assemble into tubular stacks. The tubular stacks serve as supramolecular hosts in water, as exemplified by the interaction of macrocycles and and guests through , each having a rod-like oligo(-phenylene ethynylene) (-PE) segment flanked by two hydrophilic chains. Fluorescence and H NMR spectroscopy revealed the formation of kinetically stable, discrete assemblies upon mixing and a guest. The binding stoichiometry, determined with fluorescence, H NMR, and ESI-MS, reveals that the discrete assemblies are novel pseudorotaxanes, each containing a pair of identical guest molecules encased by a tubular stack. The two guest molecules define the number of macrocyclic molecules that comprise the host, which curbs the "infinite" stack growth, resulting in a tubular stack with a cylindrical pore tailoring the length of the -PE segment of the bound guests. Each complex is stabilized by the action of multiple noncovalent forces including aromatic stacking, side-chain H-bonding, and van der Waals interactions. Thus, the interplay of multiple noncovalent forces aligns the molecules of macrocycles and into tubular stacks with cylindrical inner pores that, upon binding rod-like guests, lead to tight, discrete, and well-ordered tubular assemblies that are unprecedented in water.
水相超分子化学具有重要的基础和实际意义。为了研究多种非共价相互作用在水中控制组装和结合行为中的作用，我们用紫外可见光谱、荧光光谱、圆二色光谱、核磁共振波谱、质谱和计算研究了五种水溶性六（对苯乙炔基）苯大环（-PE）的自组装以及所得组装体的分子识别行为。与它们在有机溶剂中不同程度的自聚集相比，所有五种大环在浓度低至微摩尔（μM）的范围内仍在水中聚集。圆二色光谱表明，两种带有手性侧链且能够通过氢键自组装的大环 和 组装成管状堆积。管状堆积在水中充当超分子主体，例如大环 和 与客体 通过 相互作用，每个客体都有一个棒状寡聚（对苯乙炔基）苯（-PE）片段，两侧带有两个亲水链。荧光和 H NMR 光谱表明，在混合 和客体时，形成了动力学稳定的离散组装体。用荧光、H NMR 和 ESI-MS 确定的结合化学计量比表明，这些离散组装体是新颖的假轮烷，每个组装体都包含一对由管状堆积封装的相同客体分子。两个客体分子定义了构成主体的大环分子的数量，从而限制了“无限”堆积的生长，导致管状堆积具有圆柱形孔，定制了结合客体的 -PE 片段的长度。每个配合物都通过多种非共价力稳定，包括芳构化堆积、侧链氢键和范德华相互作用。因此，多种非共价力的相互作用将大环 和 的分子排列成具有圆柱形内孔的管状堆积，当结合棒状客体时，导致紧密、离散和有序的管状组装体，这在水中是前所未有的。
