Singlet oxygen production abilities of oxidated aromatic compounds in natural water.

Singlet oxygen (O) is well known to be formed through energy transfer from excited state organic matters to O, playing an important role in the transformations of contaminants. However, the contribution of small oxidated aromatic compounds (OACs) to the production of O in surface water is unclear. In this study, 28 OACs were selected to investigate the correlations between their photochemical production abilities of O and molecular structures. Our results showed that the steady-state concentrations and quantum yields of O (Φ) generated by OACs were in the range of 7.0 × 10-1.4 × 10 M and 2.2 × 10-4.7 × 10, respectively, indicating that the photochemical production abilities of O by OACs varied greatly with types and positions of functional groups on the molecule. More importantly, the observed photochemical production of O was most notable in cases of molecules containing -OCH group and benzoquinone. A good quantitative structure-property relationship model was established between O producing ability, energy of the lowest unoccupied molecular orbitals (E) and the most positive net charge of hydrogen atoms (qH) of OACs. In addition, the role of O produced by 2, 6-dimethoxy-1, 4-benzoquinone, the OAC with the highest Φ, in the photodegradation of organic contaminants was validated by the enhanced degradation of atorvastatin under simulated sunlight, suggesting that OACs ubiquitously existed in surface water may greatly affect the fate and ecological risks of organic contaminants.