title: Temperature-dependent free radical reaction in water.
abstract: Temperature-dependent free radical reactions were investigated using nitroxyl radicals as redox probes. Reactions of two types of nitroxyl radicals, TEMPOL (4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl) and carbamoyl-PROXYL (3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl), were tested in this paper. Heating a solution containing a nitroxyl radical and a reduced form of glutathione (GSH) caused temperature-dependent decay of electron paramagnetic resonance (EPR) signal of the nitroxyl radical. Heating a solution of the corresponding hydroxylamine form of the nitroxyl radical showed EPR signal recovery. The GSH-dependent reduction of nitroxyl radicals at 70°C was suppressed by antioxidants, spin trapping agents, and/or bubbling N(2) gas, although heating carbamoyl-PROXYL with GSH showed temporarily enhanced signal decay by bubbling N(2) gas. Since SOD could restrict the GSH-dependent EPR signal decay of TEMPOL, O(2) (•-) is related with this reaction. O(2) (•-) was probably generated from dissolved oxygen in the reaction mixture. Oxidation of the hydroxylamines at 70°C was also suppressed by bubbling N(2) gas. Heating a solution of spin trapping agent, DMPO (5,5-dimethyl-1-pyrroline-N-oxide) showed a temperature-dependent increase of the EPR signal of the hydroxyl radical adduct of DMPO. Synthesis of hydroxyl radical adduct of DMPO at 70°C was suppressed by antioxidants and/or bubbling N(2) gas. The results suggested that heating an aqueous solution containing oxygen can generate O(2) (•-).
authors.affiliation: Radiation Modifier Research Team, Heavy-Ion Radiobiology Research Group, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Minako
authors.initials: M
authors.lastname: Nyui
authors.forename: Masato
authors.initials: M
authors.lastname: Kamibayashi
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ozawa
authors.forename: Ikuo
authors.initials: I
authors.lastname: Nakanishi
authors.forename: Kazunori
authors.initials: K
authors.lastname: Anzai