Specific Cooperative Effect of a Macrocyclic Receptor for Metal Ion Transfer into an Ionic Liquid

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• 作者：Hiroyuki Okamura ; Atsushi Ikeda-Ohno ; Takumi Saito ; Noboru Aoyagi ; Hirochika Naganawa ; Naoki Hirayama ; Shigeo Umetani ; Hisanori Imura ; Kojiro Shimojo
• 刊名：Analytical Chemistry
• 出版年：2012
• 出版时间：November 6, 2012
• 年：2012
• 卷：84
• 期：21
• 页码：9332-9339
• 全文大小：376K
• 年卷期：v.84,no.21(November 6, 2012)
• ISSN：1520-6882

文摘

An intramolecular cooperative extraction system for the removal of strontium cations (Sr²⁺) from water by use of a novel macrocyclic receptor (H₂尾DA18C6) composed of diaza-18-crown-6 and two 尾-diketone fragments in ionic liquid (IL) is reported, together with X-ray spectroscopic characterization of the resulting extracted complexes in the IL and chloroform phases. The covalent attachment of two 尾-diketone fragments to a diazacrown ether resulted in a cooperative interaction within the receptor for Sr²⁺ transfer, which remarkably enhanced the efficiency of Sr²⁺ transfer relative to a mixed 尾-diketone and diazacrown system. The intramolecular cooperative effect was observed only in the IL extraction system, providing a 500-fold increase in extraction performance for Sr²⁺ over chloroform. Slope analysis and potentiometric titration confirmed that identical extraction mechanisms operated in both the IL and chloroform systems. Extended X-ray absorption fine structure spectroscopy revealed that the average distance between Sr²⁺ and O atoms in the Sr²⁺ complex was shorter in IL than in chloroform. Consequently, Sr²⁺ was held by H₂尾DA18C6 more rigidly in IL than in chloroform, representing an important factor dominating the magnitude of the intramolecular cooperative effect of H₂尾DA18C6 for Sr²⁺. Furthermore, competitive extraction studies with alkaline earth metal ions revealed that the magnitude of the intramolecular cooperative effect depended on the suitability between metal ion size and the cavity size of H₂尾DA18C6. Sr²⁺ was successfully recovered from IL by controlling the pH in the receiving phase, and the extraction performance of H₂尾DA18C6 in IL was maintained after five repeated uses.