title: Dimer formation during UV photolysis of diclofenac.
abstract: Dimer formation was observed during ultraviolet (UV) photolysis of the anti-inflammatory drug diclofenac, and confirmed with mass spectrometry, NMR and fluorescence analysis. The dimers were combinations of the two parent molecules or of the parent and the product of photolysis, and had visible color. Radical formation during UV exposure and dissolved oxygen photosensitized reactions played a role in dimer formation. Singlet oxygen formed via photosensitization by photolysis products of diclofenac. It reacted with diclofenac to form an epoxide which is an intermediate in some dimer formation pathways. Quantum yield of photolysis for diclofenac was 0.21±0.02 and 0.19±0.02 for UV irradiation from medium pressure and low pressure mercury vapor lamps, respectively. Band pass filter experiments revealed that the quantum yield is constant at wavelengths >200 nm. The same dimers formed in laboratory grade water when either of the two UV sources was used. Dimers did not form in wastewater effluent matrix, and diclofenac epoxide molecules may have formed bonds with organic matter rather than each other Implications for the importance of dimer formation in NOM are discussed.
authors.affiliation: Department of Civil, Environmental and Architectural Engineering, University of Colorado, UCB 428, Boulder, CO 80309, United States; Department of Civil and Environmental Engineering, University of North Carolina, 9201 University City Blvd, Charlotte, NC 28223, United States.
authors.forename: Olya S
authors.initials: OS
authors.lastname: Keen
authors.forename: E Michael
authors.initials: EM
authors.lastname: Thurman
authors.forename: Imma
authors.initials: I
authors.lastname: Ferrer
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Dotson
authors.forename: Karl G
authors.initials: KG
authors.lastname: Linden
mesh_terms: D004008:Diclofenac / Q000032:analysis / Q000737:chemistry*; D010782:Photolysis; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D004008:Diclofenac; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Pharmaceuticals; Photopolymerization; Photosensitized reactions; Quantum yield; Singlet oxygen; Ultraviolet photolysis