Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 6AD.
Faraday Discuss. 2009;143:205-20; discussion 265-75. doi: 10.1039/b900684b.
A novel type of tweezer molecule containing electron-rich 2-pyrenyloxy arms has been designed to exploit intramolecular hydrogen bonding in stabilising a preferred conformation for supramolecular complexation to complementary sequences in aromatic copolyimides. This tweezer-conformation is demonstrated by single-crystal X-ray analyses of the tweezer molecule itself and of its complex with an aromatic diimide model-compound. In terms of its ability to bind selectively to polyimide chains, the new tweezer molecule shows very high sensitivity to sequence effects. Thus, even low concentrations of tweezer relative to diimide units (< 2.5 mol %) are sufficient to produce dramatic, sequence-related splittings of the pyromellitimide proton NMR resonances. These induced resonance-shifts arise from ring-current shielding of pyromellitimide protons by the pyrenyloxy arms of the tweezer-molecule, and the magnitude of such shielding is a function of the tweezer-binding constant for any particular monomer sequence. Recognition of both short-range and long-range sequences is observed, the latter arising from cumulative ring-current shielding of diimide protons by tweezer molecules binding at multiple adjacent sites on the copolymer chain.
一种新型的镊子分子，含有富电子的 2-蒽氧基臂，被设计用来利用分子内氢键稳定超分子络合的优先构象，以与芳香共聚酰亚胺中的互补序列结合。这种镊子构象通过镊子分子本身及其与芳香二酰亚胺模型化合物的复合物的单晶 X 射线分析得到证明。就其对聚酰亚胺链选择性结合的能力而言，新型镊子分子对序列效应表现出非常高的灵敏度。因此，即使相对于二酰亚胺单元，镊子分子的浓度（<2.5mol%）较低，也足以产生显著的、与序列相关的均苯四甲酰亚胺质子 NMR 共振分裂。这些诱导的共振位移源于吡喃氧基臂的环电流屏蔽均苯四甲酰亚胺质子，并且这种屏蔽的大小是任何特定单体序列的镊子结合常数的函数。观察到短程和远程序列的识别，后者源于通过在共聚物链上多个相邻位置结合的镊子分子对二酰亚胺质子的累积环电流屏蔽。
