Haggi Ernesto, Bertolotti Sonia, García Norman A
Unidad Académica Río Gallegos, Universidad Nacional de la Patagonia Austral, 9400 Río Gallegos, Argentina.
Chemosphere. 2004 Jun;55(11):1501-7. doi: 10.1016/j.chemosphere.2004.01.016.
The aerobic visible-light-photosensitised irradiation of methanolic solutions of either of the phenolic-type contaminants model compounds (ArOH) p-phenylphenol (PP), p-nitrophenol (NP) and phenol (Ph), and for two additional phenolic derivatives, namely p-chlorophenol (ClP) and p-methoxyphenol (MeOP), used in some experiments, was carried out. Employing the natural pigment riboflavin (Rf) as a sensitiser, the degradation of both the ArOH and the very sensitiser was observed. A complex mechanism, common for all the ArOH studied, operates. It involves superoxide radical anion (O2-) and singlet molecular oxygen (O2(1delta(g)) reactions. Maintaining Rf in sensitising concentrations levels (approximately 0.02 mM), the mechanism is highly dependent on the concentration of the ArOH. Kinetic experiments of oxygen and substrate consumption, static fluorescence, laser flash photolysis and time-resolved phosophorescence detection of O2(1delta(g)) demonstrate that at ArOH concentrations in the order of 10 mM, no chemical transformation occurs due to the complete quenching of Rf singlet excited state. When ArOH is present in concentrations in the order of mM or lower, O2- is generated from the corresponding Rf radical anion, which is produced by electron transfer reaction from the ArOH to triplet excited Rf. The determined reaction rate constants for this step show a fairly good correlation with the electron-donor capabilities for Ph, PP, NP, ClP and MeOP. In this context, the main oxidative species is O2-, since O2(1delta(g)) is quenched in an exclusive physical fashion by the ArOH. The production of O2- regenerates Rf impeding the total degradation of the sensitiser. This kinetic scheme could partially model the fate of ArOH in aquatic media containing natural photosensitisers, under environmental conditions.
对两种酚类污染物模型化合物（ArOH），即对苯基苯酚（PP）、对硝基苯酚（NP）和苯酚（Ph），以及另外两种酚类衍生物，即对氯苯酚（ClP）和对甲氧基苯酚（MeOP）的甲醇溶液进行了有氧可见光光敏辐照实验。以天然色素核黄素（Rf）作为敏化剂，观察到ArOH和敏化剂自身均发生了降解。所有研究的ArOH都遵循一种共同的复杂机制，该机制涉及超氧自由基阴离子（O2-）和单线态分子氧（O2(1Δg)）反应。当Rf保持在敏化浓度水平（约0.02 mM）时，该机制高度依赖于ArOH的浓度。氧气和底物消耗的动力学实验、静态荧光、激光闪光光解以及O2(1Δg)的时间分辨磷光检测表明，当ArOH浓度约为10 mM时，由于Rf单重激发态的完全猝灭，未发生化学转化。当ArOH浓度为mM级或更低时，由ArOH向三重激发态Rf的电子转移反应产生相应的Rf自由基阴离子，进而生成O2-。该步骤的反应速率常数与Ph、PP、NP、ClP和MeOP的给电子能力呈现出较好的相关性。在此情况下，主要的氧化物种是O2-*，因为O2(1Δg)被ArOH以排他的物理方式猝灭。O2-*的产生使Rf再生，从而阻碍了敏化剂的完全降解。该动力学方案可以部分模拟环境条件下含有天然光敏剂的水生介质中ArOH的归宿。
