Aqueous on/off fluorescent switches based on systems of quinoline / quinoline-macrocycle

Abstract

The changes in the spectrophotometric and the spectrofluorimetric properties of Quinoline (QUI) by the addition of water soluble macrocycles with different characteristics such as cyclodextrins (CD; α, β, hydroxypropyl-β, methyl-β and γ) and sulfonate calixarenes (SCAn, n = 6 and 8) were analyzed at acidic and neutral pH at 25.0 °C. Spectral changes were observed for the basic form of QUI. Small decreases of absorbance were indicative of interactions between QUI and the macrocycles. The association constants were determined in the cases of QUI-βCD and QUI-γCD. In all cases, the fluorescence of QUI was quenched in the presence of the macrocycles. The values of the Stern-Volmer constants (KQ/M−1) were (54.030 ± 0.001) and (57.050 ± 0.001) for βCD and γCD and (3.8 ± 0.1) x 104 and (2.40 ± 0.06) x 104 for SCA6 and SCA8. These values were interpreted as the association constants (KA) of the non fluorescent complexes formed in the ground state since the fluorescence quenching was evaluated as static. The unusual quenching of fluorescence produced by the CD macrocycles and the high differences in the values of the KA for CD and SCA were interpreted by the different types of specific interactions operating in the systems studied acting as switches on/off.