Anion Binding Modes in meso-Substituted Hexapyrrolic Calix[4]pyrrole Isomers

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• 作者：Kai-Chi Chang ; Tsuyoshi Minami ; Petr Koutnik ; Pavel Y. Savechenkov ; Yuanli Liu ; Pavel Anzenbacher ; Jr.
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：January 29, 2014
• 年：2014
• 卷：136
• 期：4
• 页码：1520-1525
• 全文大小：424K
• ISSN：1520-5126

文摘

We report on the synthesis of a new receptor for anions, meso-substituted hexapyrrolic calix[4]pyrrole 1. The calix[4]pyrrole鈥檚 core features two additional pyrrole side-arms suspended above or below the calix[4]pyrrole core. This hexapyrrolic calix[4]pyrrole 1 is formed as cis- and trans-configurational isomers, the structures of which have been determined by single crystal X-ray diffraction. The anion binding experiments revealed interesting difference in the binding mode: The cis-1 isomer binds anions in a mixed binding mode featuring a combination of hydrogen bonding and anion鈭捪€ interactions resulting in an unexpected strong binding. On the other hand, the trans-1 isomer displays only hydrogen bonding and lower affinity for anions. This is unexpected as one would assume both isomers to display the same binding modes. Overall, the titrations of 1 using UV spectrophotometry and NMR titrations by anions reveal that cis-isomer 1 displays higher affinity (10⁵鈥?0⁶ M^鈥?) and cross-reactivity for anions, while the trans-isomer 1 shows a more selective response to anions. Such differences in binding mode in configurational isomers are so far unexplored and a feature deserving further study.