离子液体可以有效地萃取水相中的喹诺酮类药物, 为了探讨其萃取机理, 通过荧光、 紫外和红外光谱法等手段研究了离子液体1-己基-3-甲基咪唑六氟磷酸盐(［C6mim］PF6)与喹诺酮药物氟罗沙星(fleroxacin, FLX)间的相互作用。 由荧光发射谱图可知, 随［C6mim］PF6加入量的增大, FLX体系的荧光强度发生有规律的猝灭。 Stern-Volmer猝灭常数随温度的升高而降低。 另外, 相同条件时FLX的紫外吸收光谱随着［C6mim］PF6的加入逐渐降低并发生红移, 表明两者在基态时形成了不发射荧光的复合物, 确定猝灭类型为静态猝灭。 15, 25和35 ℃时, ［C6mim］PF6与FLX相互作用的表观结合常数Ka分别为130.0, 198.3和170.6 L·mol-1。 计算热力学参数, ΔG<0, 表明萃取是自发过程, 而ΔS和ΔH均大于零, 推测萃取的主要驱动力可能为疏水作用。 ［C6mim］PF6在水中可较为有序地排布, 亲水性咪唑环指向外部水相, 疏水性的烷基链一起构成疏水内腔。 在疏水内腔中, 咪唑环中的—CH与电负性大的N原子相邻, C更强烈地吸引H原子上的电子, 使H成为潜在的氢键供体。 而FLX上的π电子比较密集, 使得其整体电负性较大, 可作为氢键的受体, 咪唑环中的—CH与FLX上的π电子形成 —CH…π键, FLX可进入疏水内腔, 从而被包接萃取。 另外, 红外谱图分析表明, FLX分子中的—COOH基团可能取代了原本与PF-6结合的水分子而发生了氢键缔合的疏水相互作用。

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.