Biomimetic Zinc Funnel Complexes Based on Calix[6]N3ArO Ligands: An Acid-Base Switch for Guest Binding

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• 作者：Olivier Sé ; nè ; que ; Marie-Noë ; lle Rager ; Michel Giorgi ; Thierry Prangé ; Alain Tomas ; and Olivia Reinaud
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：October 26, 2005
• 年：2005
• 卷：127
• 期：42
• 页码：14833 - 14840
• 全文大小：363K
• 年卷期：v.127,no.42(October 26, 2005)
• ISSN：1520-5126

文摘

The coordination chemistry of Zn in an N₃ArOH environment has been explored. The ligandsare based on calix[6]arenes that present two imidazole arms and an amino phenol moiety at the narrowrim. Three different types of complexes have been characterized. One is dicationic with Zn²⁺ coordinatedto the three nitrogen atoms and to the oxygen of the phenol group of the calix[6]ligand. This complex isvery sensitive to exogenous coordinating molecules and exists as a 5-coordinate species due to the endo-complexation of a guest. The second species is a monocationic complex for which the phenol group hasbeen deprotonated. The resulting N₃ArOZn complex can also bind a guest ligand albeit with a lower affinitythan the dicationic complex. The third species is neutral. It can be obtained upon reaction with a base toyield a hydroxo complex or with an anion such as a chloride that coordinates the metal center from theoutside of the calixarene cavity. The simultaneous binding of two anionic donors decreases the Zn Lewisacidity, allowing an impressive conformational reorganization of the system. One imidazole arm is releasedby the metal center. The other one undergoes self-inclusion into the -basic calixarene cavity because thelow affinity of the metal center for neutral ligand does not allow the endo-coordination of an exogenousguest. Hence, the calix[6]N₃ArOH-based Zn complexes act as an acid-base switch for guest binding. Severalaspects of this system appear reminiscent of Zn-peptidases of the astacin and serralisin families.