二氟沙星在中性水溶液中的光化学性质

摘要

对二氟沙星在中性水溶液中的光化学性质进行了研究.在pH值为7.17的水溶液中二氟沙星的紫外吸收峰位于273 nm (摩尔消光系数ε=33000 dm3∙mol-1∙cm-1),323 nm (ε=15500 dm3∙mol-1∙cm-1),335 nm (ε=15500 dm3∙mol-1∙cm-1)处.荧光吸收和发射光谱均显示二氟沙星具有pH效应,其pKa(电离平衡常数)测定分别为5.9和9.8.二氟沙星的荧光量子产额较低,在pH=3.00时达到最大值,为0.06.同时对二氟沙星在中性水溶液中的激光光解和脉冲辐解进行详细研究.激光光解研究发现在水溶液中二氟沙星的三重激发态位于620 nm,其摩尔消光系数为7900 dm3∙mol-1∙cm-1.通过能量转移的方法得到其三重激发态的能量为263.5 kJ∙mol-1,三重激发态的量子产额为0.21.在激光激发下,二氟沙星进行单光子电离其量子产额为0.02.脉冲辐解研究表明二氟沙星可以与水合电子(e-aq)及羟基自由基(∙OH)快速反应,其二级反应动力学常数分别为1.72×1010和1.0×1010 dm3∙mol-1∙s-1.本文对二氟沙星光化学性质的研究有助于确定其光敏毒性的产生机理.%The photochemical properties of difloxacin (DFX) were investigated in neutral aqueous solution. DFX aqueous solution showed intense absorption with one peak at 273 nm (molar absorption coefficientε=33000 dm3∙mol-1∙cm-1) and two other peaks at 323 and 335 nm (ε=15500 dm3∙mol-1∙cm-1) with the same molar absorption coefficient. Both the absorption and emission properties of DFX were pH-dependent. The acid dissociation constant (pKa) for the protonation equilibria of the ground state (5.9 and 9.8) were determined spectroscopical y. DFX fluoresces weakly, and its maximum quantum yield for fluorescence emission was 0.06 at pH 3. Laser flash photolysis and pulse radiolysis studies were carried out to characterize the transient species of DFX aqueous solution. Triplet-triplet absorption reached a maximum at 620 nm with a molar absorption coefficient of 7900 dm3∙mol-1∙cm-1. The energy transfer method was used to estimate the triplet energy of DFX, which was 263.5 kJ∙mol-1. The quantum yield of triplet formation was determined to be 0.21. Furthermore, DFX showed monophotonic photoionization with a quantum yield of 0.02. Pulse radiolysis indicated that DFX could react with e-aq and∙OH, and the bimolecular rate constants for these reactions were 1.72×1010 and 1.0×1010 dm3∙mol-1∙s-1, respectively. It is expected that this research may be helpful in determining the phototoxicity mechanism of DFX.