Abstract：Ionic liquid can effectively extract quinolones medicines from aqueous phase. In order to explore the extraction mechanism, the interaction between ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim]PF6) and fleroxacin (FLX) were studied by using fluorescence, UV-VIS absorption and infrared spectrometry. With the increasing addition of [C6mim]PF6, inerratic fluorescence quenching of FLX solution could be observed from fluorescence spectra. Stern-Volmer constant had negative correlation with temperature. Besides, the addition of [C6mim]PF6 caused a decrease and red-shift of absorption peak in UV-VIS absorption spectra of FLX, which indicated the fluorescence quenching of FLX by [C6mim]PF6 was due to the formation of [C6mim]PF6-FLX complex in the ground state through static quenching procedure. Apparent affinity binding constants Ka of interaction between [C6mim]PF6 and FLX were 130.0，198.3，170.6 L·mol-1 at 15，25，35 ℃, respectively. Calculating of thermodynamics parameters, ΔG<0, ΔS＞0，ΔH＞0, demonstrated extraction was a spontaneous process，and hydrophobic interaction probably was the major driving force of extraction. [C6mim]PF6 could orderly distribute in water with the hydrophilic imidazole ring pointing out to the aqueous phase and the hydrophobic alkyl chains together arranging into hydrophobic cavities. In these hydrophobic cavities, the H of —CH— adjacent to N of imidazole rings is a potential H-bond donor, and intensive π electrons in FLX could act as H-bond acceptor, so the FLX entered the hydrophobic cavities of [C6mim]PF6 due to the interaction of —CH…π type bonds between —CH of [C6mim]+ and π electrons included in FLX. Furthermore, based on infrared spectra, it suggested that the hydrophobic interaction might be the result of FLX replacing the H2O molecular combined with PF-6 through the hydrogen bonding interaction between PF-6 and —COOH groups of FLX.
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