Crowned dendron: ion-responsive flexibility of macromolecules induced by integrated crown ether moieties

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• 作者：Mutsuo Tanaka ; Yoshihiro Higuchi ; Naoki Adachi ; Yasuhiko Shibutani ; Saleh A. Ahmed ; Shinpei Kado ; Makoto Nakamura and Keiichi Kimura
• 关键词：Dendron ; Ion-responsive flexibility ; Crown ether
• 刊名：Tetrahedron
• 出版年：2005
• 出版时间：2005
• 年：2005
• 卷：61
• 期：34
• 页码：8159-8166
• 全文大小：390 K

文摘

Polybenzyl ether type dendrons bearing the crown ether moieties at the periphery, namely, crowned dendrons were synthesized, and the effect of complex formation on their flexibility with metal-ion binding properties was examined. Upon addition of Na⁺, ¹H NMR spectra of the crowned dendrons in CD₃CN were significantly broadened, reflecting the flexibility restriction of the crowned dendrons by the complex formation with Na⁺. Such a significant flexibility restriction was observed only with Na⁺, although ESI-MS studies revealed that the crowned dendrons formed 1:2 complexes (a metal ion:the crown ether moiety) regardless of the kind of metal ions. The flexibility restriction became significant with increasing dendron generation on the basis of ¹H NMR spectra and spin-lattice relaxation time (T₁) measurements. Binding constants of the crowned dendrons with metal ions in CD₃CN decreased with the increase of the dendron generation, reflecting an influence of the charge repulsion as well as a dendrimer effect to cause the steric hindrance. The examination of UV–vis absorption spectra for complexes of the crowned dendron with metal picrates in THF displayed the formation of a loose ion-pair complex with Na⁺, namely, a typical sandwich type complex. However, in CH₃CN, all metal picrates were solvated to be in a loose ion-pair even without complex formation. These results suggested that the control of macromolecular flexibility with metal ions is feasible by the integration of crown ether moieties with a dendritic structure.