Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
J Am Chem Soc. 2015 Jan 21;137(2):876-85. doi: 10.1021/ja5111305. Epub 2015 Jan 8.
We report the synthesis of a series of homologous oligoviologens in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, as a prelude to investigating how their radical cationic forms self-assemble both in solution and in the solid state. The strong radical-radical interactions between the radical cationic forms of the BIPY(2+) units-namely, BIPY(•+)-in these oligoviologens induce intra- or intermolecular folding of these homologues. UV/Vis/NIR spectroscopic studies and DFT quantum mechanics indicate that the folding of the shorter oligoviologens is dominated by intermolecular radical-radical interactions. In addition to intermolecular interactions, strong intramolecular radical-radical interactions, which give rise to an NIR absorption band at 900 nm, tend to play a crucial role in governing the folding of the longer oligoviologens. The solid-state superstructure of the oligoviologen with three BIPY(2+) units reveals that two intertwining chains fold together to form a dimer, stabilized by intermolecular radical-radical interactions. These dimers continue to stack in an infinite column through intermolecular radical-radical interactions between them. This research features an artificial biomimetic system which sustains delicate secondary and tertiary structures, reminiscent of those present in nucleic acids and proteins.
我们报告了一系列同系寡聚紫精的合成，其中不同数量的 4,4'-联吡啶（BIPY(2+))单元通过对二甲撑桥连接，作为研究其阳离子自由基形式如何在溶液中和固态中自组装的前奏。BIPY(2+)单元的阳离子自由基形式之间的强自由基-自由基相互作用——即 BIPY(•+)——在这些寡聚紫精中诱导这些同系物的分子内或分子间折叠。紫外/可见/近红外光谱研究和密度泛函理论量子力学表明，较短寡聚紫精的折叠主要由分子间自由基-自由基相互作用主导。除了分子间相互作用外，强分子内自由基-自由基相互作用导致在 900nm 处出现近红外吸收带，这往往在控制较长寡聚紫精的折叠中起着关键作用。具有三个 BIPY(2+)单元的寡聚紫精的固态超结构表明，两个交织的链折叠在一起形成二聚体，通过分子间自由基-自由基相互作用稳定。这些二聚体通过它们之间的分子间自由基-自由基相互作用继续堆积成无限的柱状物。这项研究的特点是一种人工仿生系统，它维持着精细的二级和三级结构，让人联想到核酸和蛋白质中存在的结构。
