Indirect Photodegradation of Amine Drugs in Aqueous Solution under Simulated Sunlight

Abstract

The photodegradation of the widely used amine drugs including primary amine (mexiletine), secondary amine (propranolol, phenytoin), and tertiary amine (diphenhydramine, antipyrine) were investigated in the presence of nitrate and humic substances under simulated sunlight. All of the amine drugs were photodegraded by nitrate due to the attack of hydroxyl radicals ( • OH). The bimolecular rate constants for the reaction between each amine drug and • OH ranged from (2.1 ( 0.2) × 10 9 to (8.7 ( 0.3) × 10 9 M -1 s -1 . In contrast, only mexiletine, propranolol, and diphenhydramine were selectively photodegraded in the presence of humic substances (HS). Fulvic acid was a more efficient sensitizer than humic acid throughout. The HS triplet states were verified to be main reactive species in the photochemical reaction. Furthermore, an electron transfer mechanism for the reaction with the HS triplet states was proposed on the basis of all information obtained under a series of experiments. The electron transfer from the nonbonding electrons on nitrogen (N-electrons) of the amine drugs to the excited ketone of the HS occurred. The availability of N-electrons and presence of hydrogen on carbon R of amine (R-hydrogen) were two key factors for the electrontransfer interaction. Moreover, the photoproducts were identified by GC-MS and the degradation pathways were proposed. The results strongly suggest the impact of humic substances on the photochemical fate of amine drugs in the natural waters.

Photochemical degradation of PAHs in estuarine surface water: effects of DOM, salinity, and suspended particulate matter

“…(2) DOM can promote the production of 1 O 2 , ·OH, and the reactive triplet state of DOM ( 3 DOM*), which can promote the photodegradation of PAHs that degrade relatively slow by direct photolysis (Xia et al 2009;Chen et al 2009). (3) PAHs can be bound to DOM, which may restrain or accelerate the photodegradation rate of PAHs.…”

“…Therefore, it is important to understand the factors that affect the photochemical transformation processes of PAHs in the estuary surface water, especially under the changing estuarine conditions. It has been proposed in the literature that the photodegradation of PAHs consists of three main pathways: through radical cation intermediates, via reactions with singlet oxygen ( 1 O 2 ), and via reactions with hydroxyl radical (·OH) (Miller and Olejnik 2001;Fasnacht and Blough 2002;Chen et al 2009). PAHs in natural waters can degrade through direct photolysis (de Bruyn et al 2012) or indirect photosensitization processes with transient excited species such as singlet oxygen ( 1 O 2 ), hydroxyl radical (·OH), and other reactive species formed in sunlit natural waters (Fasnacht and Blough 2002;Jacobs et al 2008;Saeed et al 2011).…”

UV and visible light activated TiO2 photocatalysis of 6-hydroxymethyl uracil, a model compound for the potent cyanotoxin cylindrospermopsin

“…The influence of DOM on the solar photolysis of organic contaminants has been widely studied [31,32]. We used HA to assess the role of DOM* initiated degradation of 6-HOMU under 450 nm irradiation in the absence of NF-TiO 2 as a control experiment.…”

Transformation of 2,4,6-trimethylphenol and furfuryl alcohol, photosensitised by Aldrich humic acids subject to different filtration procedures

“…An alternative process is inter-system crossing to triplet states ( 3 HS*). 3 HS* are chemically reactive (by electron or hydrogen abstraction or energy transfer), and account for most of the photosensitising HS activity (Werner et al, 2005;Canonica, 2007;Chen et al, 2009). A major example of energy transfer is reaction with O 2 to yield 1 O 2 , which can be involved into the transformation of easily oxidised compounds (Aguer et al, 1999).…”