Recognition, Encapsulation, and Selective Fluorescence Sensing of Nitrate Anion by Neutral C3-Symmetric Tripodal Podands Bearing Amide Functionality
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- 作者：Ashutosh S. Singh ; Shih-Sheng Sun
- 刊名：The Journal of Organic Chemistry
- 出版年：2012
- 出版时间：February 17, 2012
- 年：2012
- 卷：77
- 期：4
- 页码：1880-1890
- 全文大小：622K
- 年卷期：v.77,no.4(February 17, 2012)
- ISSN：1520-6904
文摘
A series of neutral C3-symmetric acyclic artificial receptors incorporating amide functionality has been designed, synthesized, and fully characterized. Upon protonation, these conformationally flexible N-bridged tripodal podands 1鈥?b>5 form in situ cone shape conformation through hydrogen bonding and C鈥揌路路路蟺 interactions. The protonation-induced interior preorganized cavity is capable of entrapping nitrate anions through the amide N鈥揌 bonds to form discrete nitrate complexes (1a鈥?b>5a), which were fully characterized by NMR, HRESI mass spectra, and single crystal structures. By incorporating suitable fluorophores at each branch of the tripod receptor, the resulting fluorescent receptor 5 selectively recognized nitrate anions by fluorescent quenching in a DMSO solution and displayed one of the highest binding affinities for nitrate anions reported so far in polar media. Receptor 5 represents a unique example of a neutral receptor for the recognition of nitrate anions in polar solvent media by its zwitterionic form. The possible mechanism of proton-induced preorganization of these flexible, acyclic receptors in a convergent cone conformation followed by nitrate complexation has been proposed to rationalize the effective nitrate recognition.