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Mechanism of radiation-induced reactions in aqueous solution of coumarin-3-carboxylic acid; Effects of concentration, gas and additive on fluorescent product yield

Yamashita, Shinichi; Baldacchino, G.*; Maeyama, Takuya*; Taguchi, Mitsumasa; Muroya, Yusa*; Lin, M.*; Kimura, Atsushi; Murakami, Takeshi*; Katsumura, Yosuke

Radiation-induced reactions in aqueous solutions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated by pulse radiolysis with 35-MeV electron beam, final product analysis after $$^{60}$$Co $${gamma}$$-irradiations, and deterministic model simulations. It was found that C3CA reacts with the hydroxyl radical ($$^{bullet}$$OH) as well as the hydrated electron at nearly diffusion-controlled rate constants: 6.8$${times}$$10$$^{9}$$ and 2.1$${times}$$10$$^{10}$$ M$$^{-1}$$s$$^{-1}$$, respectively. Reactivity of C3CA toward O$$_{2}$$$$^{-}$$$$^{bullet}$$ was not confirmed. Production of a fluorescent molecule 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA) was detected by a fluorescence spectrometer coupled with high performance liquid chromatography. Production yields of 7OH-C3CA were in a range from 0.025 to 0.18 (100 eV)$$^{-1}$$, depending on irradiation conditions. A variety of the yield with saturating gas, additive, and C3CA concentration implied that there are at least two pathways from scavenging reaction of C3CA toward $$^{bullet}$$OH to 7OH-C3CA: peroxidation reaction followed by elimination of perhydroxyl radical and disproportionation reaction. A reaction mechanism involving the two pathways was proposed and incorporated into the simulations, showing good explanation of experimentally measured 7OH-C3CA yields with a constant conversion factor from $$^{bullet}$$OH scavenging to 7OH-C3CA production, 4.7%, unless $${t}$$-BuOH is not added.

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Category:Biochemistry & Molecular Biology

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