title: Mechanism of radiation-induced reactions in aqueous solution of coumarin-3-carboxylic acid: effects of concentration, gas and additive on fluorescent product yield.
abstract: The radiation-induced reactions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated in aqueous solutions by pulse radiolysis with a 35 MeV electron beam, final product analysis following (60)Co γ-irradiations and deterministic model simulations. Pulse radiolysis revealed that C3CA reacted with both hydroxyl radicals ((•)OH) and hydrated electrons (e(-) (aq)) with near diffusion-controlled rate constants of 6.8 × 10(9) and 2.1 × 10(10) M(-1) s(-1), respectively. The reactivity of C3CA towards O(2)(• -) was not confirmed by pulse radiolysis. Production of the fluorescent molecule, 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), was confirmed by final product analysis with a fluorescence spectrometer coupled to a high performance liquid chromatography (HPLC) system. Production yields of 7OH-C3CA following (60)Co γ-irradiations depended on the irradiation conditions and ranged from 0.025 to 0.18 (100 eV) (-1). Yield varied with saturating gas, additive and C3CA concentration, implying the presence of at least two pathways capable of providing 7OH-C3CA as a stable product following the scavenging reaction of C3CA with (•)OH, including a peroxidation/elimination sequence and a disproportionation pathway. A reaction mechanism for the two pathways was proposed and incorporated into a deterministic simulation, showing that the mechanism can explain experimentally measured 7OH-C3CA yields with a constant conversion factor of 4.7% from (•)OH scavenging to 7OH-C3CA production, unless t-BuOH was added.
authors.affiliation: Advanced Science Research Center (ASRC), Japan Atomic Energy Agency (JAEA), Shirakata-shirane 2-4, Tokai-mura, Naka-gun, Ibaraki, Japan. yamashita.shinichi@jaea.go.jp
authors.forename: Shinichi
authors.initials: S
authors.lastname: Yamashita
authors.forename: Gérard
authors.initials: G
authors.lastname: Baldacchino
authors.forename: Takuya
authors.initials: T
authors.lastname: Maeyama
authors.forename: Mitsumasa
authors.initials: M
authors.lastname: Taguchi
authors.forename: Yusa
authors.initials: Y
authors.lastname: Muroya
authors.forename: Mingzhang
authors.initials: M
authors.lastname: Lin
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kimura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Murakami
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Katsumura
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003374:Coumarins / Q000737:chemistry / Q000528:radiation effects*; D004058:Diffusion; D005453:Fluorescence; D005720:Gamma Rays; D005740:Gases; D017665:Hydroxyl Radical / Q000737:chemistry*; D007700:Kinetics; D011675:Pulse Radiolysis; D012996:Solutions; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry
chemical_list: D003374:Coumarins; D005740:Gases; D012996:Solutions; D014867:Water; D017665:Hydroxyl Radical; C104227:coumarin-3-carboxylic acid