Selective Potassium Ion Recognition by Benzo-15-crown-5 Fluoroionophore/γ-Cyclodextrin Complex Sensors in Water

• Published in: Analytical chemistry (Washington) Vol. 72; no. 23; pp. 5841 - 5846
• Main Authors: Yamauchi, Akiyo, Hayashita, Takashi, Kato, Ayako, Nishizawa, Seiichi, Watanabe, Masatoshi, Teramae, Norio
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.12.2000
• Subjects: Analytical chemistry; Chemistry; Exact sciences and technology; General, instrumentation; Ions; Molecules; Potassium; Water; Equilibrium constant; Fluorescence detector; Molecular structure; Oligoholoside; Association constant; Organic ligand; Crown compound; Pattern recognition; Chemical sensor; Radiative lifetimes; Potassium Complexes; Cyclodextrin; Concentration effect; Alkali metal Complexes; Chemical properties; Aqueous solution
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac000741i

Three fluoroionophores Cn (n = 1, 3, 5), in which the crown ether unit and pyrenyl moiety are connected by a −(CH2) n − spacer, have been used to construct supramolecular Cn/γ-cyclodextrin (γ-CyD) complexes for alkali metal ion sensing in water. The Cn (n = 3, 5) are found to selectively form 2:1 complexes with K+ in the presence of γ-CyD and exhibit the pyrene dimer emission in water. Equilibrium analysis of the C3/γ-CyD complex reveals that the observed dimer emission arises from a 2:1:1 complex of C3 with K+ and γ-CyD. In the absence of K+, the fluorescence lifetimes for the dimer species ((C3)2CyD and (C3)2(CyD)2) and the monomer species (C3CyD and C3(CyD)2) are 13−18 and 130−180 ns, respectively. Upon addition of 0.10 M KCl, a rising component corresponding to pyrene excimer formation is observed at the dimer emission region. For the C3/γ-CyD complex, the apparent association constant for K+ of (3.8 ± 1.3) × 109 M-2 is only slightly affected by the presence of Na+. Although the C5/γ-CyD complex shows high sensitivity for K+, the selectivity for K+ over Na+ is lower than that of the C3/γ-CyD complex. In contrast, fluoroionophore C1 with the shortest methylene spacer exhibits no response for alkali metal cations in the presence of γ-CyD. These results demonstrate that the response function of supramolecular Cn/γ-CyD complexes is strongly affected by the methylene spacer length of Cn. The highest K+ selectivity is obtained for the C3/γ-CyD complexes in water.