Calix[4]arene with lower-rim β-amino α,β-unsaturated ketones containing bis-chelating sites as a highly selective fluorescence turn-on chemosensor for two copper(II) ions

I. Ting Ho, Jean Ho Chu, Wen-Sheng Chung*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

We report herein the synthesis of a fluorescence turn-on chemosensor, 25,27-bis{N-[1-(4-{[4-amino-4-(1-naphthyl)-2-oxo-3-butenyl]oxy}phenyl) aminocarbonyl]methoxy}-26,28-dihydroxycalix[4]arene (3b), which is highly selective toward Cu2+. The fluorescence intensity of 3b was enhanced upon adding [Cu(ClO4)2], which reached a maximum with approximately 4 equiv. of Cu2+ but then started to decrease in intensity at higher Cu2+ concentrations. Job plot experiments revealed a 1:2 binding stoichiometry of 3b with Cu2+. Based on 1H NMR titration results, we infer that there are two possible binding sites for Cu2+ in 3b: one at the lower-rim phenolic-OH and amide groups, and the second at the β-amino α,β-unsaturated ketone groups. It is important to note that during the complexation of 3b with [Cu(ClO4)2], the Cu2+ ions were reduced to Cu+ by both the phenolic OH and the amines of the β-amino α,β-unsaturated ketones. Furthermore, control compounds 6 and 9b were synthesized to clarify the possible binding sites of Cu2+ in 3b. By comparing the binding constants of 3b, 6, and 9b with Cu2+, we found that 3b exhibited a positive allosteric behavior toward the coordination of two Cu2+ ions. Calix[4]arene 3b shows high binding selectivity toward Cu2+ ions, which causes a dramatic enhancement of the fluorescence intensities at 341 and 452 nm by 4- and 40-fold, respectively. Chemosensor 3b can recognized two Cu2+ ions; both ions are reduced to Cu+ by both the phenolic-OH and the amines of the β-amino α,β- unsaturated ketones.

Original languageEnglish
Pages (from-to)1472-1481
Number of pages10
JournalEuropean Journal of Organic Chemistry
Issue number8
DOIs
StatePublished - 1 Mar 2011

Keywords

  • Copper
  • Fluorescence
  • Ionophores
  • Sensors
  • Supramolecular chemistry
  • UV/Vis spectroscopy

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