title: Investigating the mechanism of phenol photooxidation by humic substances.
abstract: To probe the mechanism of the photosensitized loss of phenols by humic substances (HS), the dependence of the initial rate of 2,4,6-trimethylphenol (TMP) loss (R(TMP)) on dioxygen concentration was examined both for a variety of untreated as well as borohydride-reduced HS and C(18) extracts from the Delaware Bay and Mid-Atlantic Bight. R(TMP) was inversely proportional to dioxygen concentration at [O(2)] > 50 μM, a dependence consistent with reaction with triplet excited states, but not with (1)O(2) or RO(2). Modeling the dependence of R(TMP) on [O(2)] provided rate constants for TMP reaction, O(2) quenching, and lifetimes compatible with a triplet intermediate. Borohydride reduction significantly reduced TMP loss, supporting the role of aromatic ketone triplets in this process. However, for most samples, the incomplete loss of sensitization following borohydride reduction, as well as the inverse dependence of R(TMP) on [O(2)] for these samples, suggests that there remains another class of oxidizing triplet sensitizer, perhaps quinones.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States.
authors.forename: Kelli S
authors.initials: KS
authors.lastname: Golanoski
authors.forename: Shuo
authors.initials: S
authors.lastname: Fang
authors.forename: Rossana
authors.initials: R
authors.lastname: Del Vecchio
authors.forename: Neil V
authors.initials: NV
authors.lastname: Blough
mesh_terms: D000042:Absorption / Q000528:radiation effects; D001578:Benzopyrans / Q000737:chemistry; D001894:Borohydrides; D003408:Cresols / Q000737:chemistry* / Q000528:radiation effects*; D006812:Humic Substances / Q000032:analysis*; D007700:Kinetics; D008027:Light; D008031:Lignin / Q000737:chemistry; D008956:Models, Chemical; D010084:Oxidation-Reduction / Q000528:radiation effects; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry / Q000379:methods*; D045483:Rivers / Q000737:chemistry; D013057:Spectrum Analysis
chemical_list: D001578:Benzopyrans; D001894:Borohydrides; D003408:Cresols; D006812:Humic Substances; D008031:Lignin; C505148:2,4,6-trimethylphenol; D010100:Oxygen; C005023:fulvic acid