School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
J Hazard Mater. 2013 May 15;252-253:220-6. doi: 10.1016/j.jhazmat.2013.02.035. Epub 2013 Feb 28.
The photodegradation of β-blocker timolol in fulvic acid (FA) solution was investigated under simulated sunlight. The triplet excited state of FA ((3)FA()) and singlet oxygen ((1)O2) were the main reactive species responsible for the degradation of timolol in the aerated FA solutions. Both dissolved oxygen and iodide ions (I(-)) are the efficient quenchers of (3)FA(). The photodegradation was drastically accelerated after removing the dissolved oxygen. The presence of I(-) inhibited the photosensitized degradation of timolol in the deoxygenated FA solutions, whereas the role of I(-) in the reaction was concentration-dependent in the aerated solutions. The other halide ions such as chloride (Cl(-)) and bromide (Br(-)) exhibited less effect on the photodegradation of timolol in both aerated and deoxygenated solutions. By LC-DAD/ESI-MS/MS analysis, the photoproducts of timolol in both aerated and deoxygenated FA solutions were identified. Electron transfer interaction occurred between (3)FA(*) and amine moiety of timolol, leading to the cleavage of C-O bond in the side chain and oxidation of the hexatomic ring. These findings suggest the photosensitized degradation was a significant pathway for the elimination of timolol in natural waters.
富里酸（FA）溶液中β受体阻滞剂噻吗洛尔的光降解在模拟太阳光下进行了研究。FA 的三重态激发态（（3）FA（））和单线态氧（（1）O2）是导致充氧 FA 溶液中噻吗洛尔降解的主要反应性物质。溶解氧和碘化物离子（I(-)）都是（3）FA（）的有效猝灭剂。去除溶解氧后，光降解大大加速。在缺氧 FA 溶液中，I(-)的存在抑制了噻吗洛尔的光敏降解，而在充氧溶液中，I(-)的作用则取决于浓度。其他卤化物离子，如氯离子（Cl(-)）和溴离子（Br(-)），在充氧和缺氧溶液中对噻吗洛尔的光降解影响较小。通过 LC-DAD/ESI-MS/MS 分析，在充氧和缺氧 FA 溶液中鉴定了噻吗洛尔的光产物。（3）FA(*)与噻吗洛尔的胺基部分发生电子转移相互作用，导致侧链中 C-O 键的断裂和六元环的氧化。这些发现表明，光敏降解是天然水中噻吗洛尔消除的重要途径。
