Self-Assembly of [n]Rotaxanes Bearing Dendritic Stoppers

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• 作者：David B. Amabilino ; Peter R. Ashton ; Vincenzo Balzani ; Christopher L. Brown ; Alberto Credi ; Jean M. J. Fré ; chet ; Jeffrey W. Leon ; Franç ; isco M. Raymo ; Neil Spencer ; J. Fraser Stoddart ; and
• 刊名：Journal of the American Chemical Society
• 出版年：1996
• 出版时间：December 4, 1996
• 年：1996
• 卷：118
• 期：48
• 页码：12012 - 12020
• 全文大小：465K
• 年卷期：v.118,no.48(December 4, 1996)
• ISSN：1520-5126

文摘

We have developed a synthetic approach to the self-assembly of[2]-, [3]-, and [4]rotaxanes, incorporatingbis-p-phenylene-34-crown-10 as the ring component(s)surrounding bipyridinium-based dumbbell-shaped componentsbearing dendritic stoppers at both ends. As a result of thehydrophobic dendritic framework, these [n]rotaxanesaresoluble in a wide range of organic solvents, despite the polycationicnatures of their bipyridinium-based backbones.In all cases, they could be purified by means of columnchromatography employing relatively low polar eluants.The molecular shuttling action of the[2]rotaxane containing two bipyridinium units on the rod portionof the dumbbell-shaped component has been investigated by variable-temperature¹H-NMR spectroscopy in a range of solvents[CDCl₃,CD₂Cl₂, THF-d₈, and(CD₃)₂CO] for the first time. Thisinvestigation reveals a marked dependence of the rate ofthe shuttling process upon the polarity of the media.On going from CDCl₃ to(CD₃)₂CO, the rate constantincreasesfrom ca. 200 to 33000 times per second. Moleculardynamics simulations, performed in CHCl₃ andMe₂CO on the[2]rotaxane, suggest that significant conformational changesoccur upon changing the polarity of the medium resultingin both steric and electronic hindrance of the shuttlingprocess in CHCl₃. Three-dimensional representations,aswell as the approximate sizes-i.e. overall lengths andmolecular volumes which range from 3 to 6 nm and from 4to 6 nm³, respectively-of these molecular compounds, wereobtained by means of molecular modeling studies.Thus, these nanometer-scale dendritic rotaxanes resemblenaturally-occurring chemical systems incorporating anactive component, in so far as the rotaxane-like core with itsdistinctive recognition features is surrounded by amolecular shell in the form of the dendritic framework.