Lin Y, Du K, Gau MR, Dmochowski IJ. Turn-on fluorescent capsule for selective fluoride detection and water purification.
Chem Sci 2023;
14:291-297. [PMID:
36687344 PMCID:
PMC9811533 DOI:
10.1039/d2sc05352g]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 11/29/2022] [Indexed: 12/03/2022] Open
Abstract
It has been a long-standing challenge to develop organic molecular capsules for selective anion binding in water. Here, selective recognition of aqueous fluoride was achieved through triple protonation of a hemicryptophane (L), which is composed of a fluorescent cyclotriveratrylene (CTV) cap and tris(2-aminoethyl)amine (tren) as the anion binding site. Fluoride encapsulation by [3H-L]3+ was evidenced by 1H NMR, 19F NMR, LC-MS, and X-ray crystallography. In addition, [3H-L]3+ exhibited a 'turn-on' fluorescence signal (λ em = 324 nm) upon fluoride addition. An apparent association constant K A = (7.5 ± 0.4) × 104 M-1 and a detection limit of 570 nM fluoride were extracted from the fluorescence titration experiments in citrate buffer at pH 4.1. To the best of our knowledge, [3H-L]3+ is the first example of a metal-free molecular capsule that reports on fluoride binding in purely aqueous solutions with a fluorescence response. Finally, the protonated capsule was supported on silica gel, which enabled adsorptive removal of stoichiometric fluoride from water and highlights real-world applications of this organic host-guest chemistry.
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