Molecular Mechanism Of Chemiluminescence Production By Halogenated Catechols And Cobalt-mediated Fenton-like System

Halogenated catechols are not only the metabolic intermediates of the environemtal pollutant chlorophenols, but also the important intermediates in organic synthesis and main byproducts of petrochemical industry, which widely exist in water and soil. The enrichment of chlorophenols has caused DNA damages in organisms, which brings about potential danger to human health. Recently, advanced oxidation processes(AOPs) have been increasingly used in degradation and treatment of organic pollutants, Fenton and Fenton-like reaction is one of the most economical, simple and effective method in AOPs. This thesis mainly studied chemiluminescence production during the degradation process of catechols by Co2+/H2O2 Fenton-like system, and discussed the detailed molecular mechanism and degradation mechanisms. The thesis consists of three major parts:1. We found recently that tetrachloro-1,4-benzoquinone(TCBQ) or tetrachlorohydroquinone and H2O2 could produce hydroxyl radicals(?OH)–dependent chemiluminescence, but its structural analogue tetrachlorocatechol(TCC) and H2O2 produced only extremely weak chemiluminescence. However, we found that a variety of transition metal ions enhanced chemiluminescence generation by TCC/H2O2, and among them Co2+ is most effective. Therefore we studied the unique molecular mechanism of the chemiluminescence generation by TCC/H2O2/Co2+. The results showed that Co2+-mediated Fenton-like system was different from the classical Fenton system, which can produced a variety of reactive oxygen species(ROS), such as ?OH, 1O2 and O2?-; The chemiluminescence produced by TCC/H2O2/Co2+ is likely to be due to the combined production of these different ROS, which is different from TCBQ/H2O2 system which is dependent on ?OH only.2. Co2+-mediated Fenton-like system can also significantly enhance chemiluminescence generation by other halogenatedcatechols other than TCC, and acorrelation was observed between the chemical structures and the chemiluminescence produced by CCs/H2O2/Co2+. The general trends are: halogen substituents facilitate chemiluminescence generation; the more halogen substitution, the stronger the chemiluminescence; chemiluminescence generation was greatly enhanced by halogen atoms subsituted at the ortho positions of the phenol hydroxyl group. Among all CCs tested, 3,4,6-Tr CC produced strongest chemiluminescence in the presence of Co2+/H2O2, which is even stronger than TCC/H2O2/Co2+ system.We found that the difference between CL generated by 3,4,6-Tr CC and TCC was not due to the formation of different products, but rather due to the formation of the same final product 2,5-dichloro-3,6-hydroxy-1,4-benzoquinone(DDBQ) with different rates and yields.3. Chlorinated benzoquinones(CBQs) are also a class of toxic metabolic intermediates generated by chlorophenols. Since CBQs and chlorinated catechols have similar chemical structures, their oxidative intermediates might be also similar. We found that when substituted with the same number of chlorine atoms, CBQs generated more types of hydroxylated products, including both mono- and dihydydroxylation products. However, chlorocatechols produced only single hydroxylated product due to the obvious directing effect of the hydroxy group on catechol.