Temperature-dependent free radical reaction in water

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 N2 gas, although heating carbamoyl-PROXYL with GSH showed temporarily enhanced signal decay by bubbling N2 gas. Since SOD could restrict the GSH-dependent EPR signal decay of TEMPOL, O2•− is related with this reaction. O2•− was probably generated from dissolved oxygen in the reaction mixture. Oxidation of the hydroxylamines at 70°C was also suppressed by bubbling N2 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 N2 gas. The results suggested that heating an aqueous solution containing oxygen can generate O2•−

EPR based Estimation of Radiation-Induced Reactive Oxygen Species

Generation of reactive oxygen species (ROS) is considered as essential trigger of biological effects of ionizing radiations, and may be deeply linked with the radiation quality.Amounts of total oxidation reactions (i.e. oxidative free radical species, •OH and HO2•), H2O2 generations, Oxygen consumptions, and •OH generations induced by X-ray, 20 keV/μm carbon beam, and 80 keV/μm carbon beam were estimated using EPR based techniques.Total oxidation reactions were estimated as 3, 1.3, and 0.66 μmol/L/Gy, amount of H2O2 generations were 0.2, 0.57, and 0.35 μmol/L/Gy, oxygen consumptions were 0.4, 0.39, and 0.15 μmol/L/Gy for X-ray, 20 keV/μm carbon beam, and 80 keV/μm carbon beam, respectively. The ratio of H2O2 generation per oxygen consumption were increased with LET, and were 0.5, 1.46, 2.33 for X-ray, 20 keV/μm carbon beam, and 80 keV/μm carbon beam, respectively. The •OH generations expected to be localized on the track/range of the radiation beam/ray, and both sparse (≈ 3.3 mM) and very dense (> 1.7 M) •OH generations were suggested. Percentage of sparse •OH generation decreased with LET becoming higher.The SFRBM\u27s 23rd Annual Meeting, a joint meeting with the Society for Free Radical Research International (SFRBM/SFRRI 2016

Generation of reactive oxygen species by heating aqueous solution containing oxygen

Interest for hyperthermia clinical cancer treatment has been increased recently, especially in combination use with existing treatments, i.e. chemotherapy, radiotherapy and immunotherapy to increase efficiency of those treatments. Mechanism for hyperthermal cell killing or sensitization to other stresses/treatments has been unclear. Relation of reactive oxygen species (ROS) to the effect of hyperthermia has been widely alleged and/or reported. Nitroxyl radicals have been conventionally used as chemical redox probe in vitro and in vivo experiments in fields of electron paramagnetic resonance (EPR) spectroscopy. In this presentation, temperature-dependent free radical reactions were investigated using nitroxyl radicals as redox probes. Gluthathione (GSH)-dependent EPR signal loss of nitroxyl radicals occurred temperature-dependently. Details of temperature-dependent reaction of nitroxyl radicals and GSH were investigated. Heating a solution of a hydroxylamine showed EPR signal recovery. Heating a spin trapping agent showed temperature-dependent increase of EPR signal due to the hydroxyl radical adduct. Most of reactions were suppressed by bubbling N2 gas. However, heating carbamoyl-PROXYL with GSH in the N2 gas atmosphere showed temporally enhanced signal decay. Results showed a possibility that heating an aqueous solution containing oxygen can generate O2•-.Oxygen Club of California 201

Temperature depending free radical reaction in water

Interest for hyperthermia clinical cancer treatment has been increased recently, especially in combination use with existing treatments, i.e. chemotherapy, radiotherapy and immunotherapy to increase efficiency of those treatments. Mechanism for hyperthermal cell killing or sensitization to other stresses/treatments has been unclear. Relation of reactive oxygen species (ROS) to the effect of hyperthermia has been widely alleged and/or reported. Nitroxyl radicals have been conventionally used as chemical redox probe in vitro and in vivo experiments in fields of electron paramagnetic resonance (EPR) spectroscopy. GSH-depending EPR signal loss of nitroxyl radicals was occurred temperature dependently. Details of temperature depending reaction of nitroxyl radicals and GSH were investigated. Some results in this study gave a suspicion of a temperature dependent induction of oxygen depending ROS formation in an aqueous solution. Possible mechanisms of the temperature depending free radical reactions in water was discussed.SFRBM\u27s 16th Annual Meetin

Comparison of Reactivity of Nitroxyl Free Radicals and Reactive Oxygen Species

Reactivity of nitroxyl free radicals and reactive oxygen species (ROS) were compared. In this presentation, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (carbamoyl-PROXYL) were tested as typical 6-memberd ring and 5-memberd ring nitroxyl compounds. Two free radical species of ROS, i.e. hydroxyl radical (•OH) and superoxide (O2•-), were also subjected to an examination. The •OH was observed by UV irradiation to a H2O2 aqueous solution. The O2•- was obtained by a hypoxanthine-xanthine oxidase (HX-XO) reactive system. The molecular amount of ROS generated was quantified by electron spin resonance (EPR) spin-trapping method using 5-(2,2-dimethyl-1,3-propoxycyclophosphoryl)-5-methyl-1-pyrroline-N-oxide (CYPMPO) as the spin-trapping agent. Amount of •OH generation by H2O2-UV reaction system and amount of O2•- generation by HX-XO system were adjusted to become the same amount. O2•- was react with TEMPOL relatively easier compared to carbamoyl-PROXYL. TEMPOL has more reactive with O2•- than •OH, while carbamoyl-PROXYL was much reactive with •OH than O2•-. TEMPOL-H, which is the hydroxyl amine form of TEMPOL, was slightly more reactive with •OH then O2•-. Carbamoyl-PROXYL-H, the hydroxyl amine form of carbamoyl-PROXYL, has the similar reactivity with O2•- or with •OH.1st QST International Symposium -Quantum Life Science

Reactivity of 2,2-Diphenyl-1-picrylhydrazyl Radical Solubilized in Water by beta-Cyclodextrin and Its Derivatives

Recently, we have reported the solubilization of 2,2-dizhenyl-1-picrylhydrazyl (DPPH) radical in water using beta-cyclodextrin (beta-CD). However, the yield of beta-CD-solubilized DPPH radical is less than 1% due to the poor solubility of beta-CD in water. In this study, the beta-CD derivatives, such as 2,6-di-O-methyl-beta-CD (DM-beta-CD), were used instead of beta-CD to improve the solubility of DPPH radical in water. The scavenging rate constants of DM-beta-CD-solubilized DPPH radical by the water-soluble antioxidants were about half as compared with those of beta-cd-solubilized DPPH.SFRBM\u27s 22nd Annual Meetin

Reactivity of 2,2-Diphenyl-1-picrylhydrazyl Solubilized in Water by β-Cyclodextrin and Its Methylated Derivative

A stable radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH), frequently used as a reactivity model of reactive oxygen species, was successfully solubilized in water by forming an inclusion complex with beta-cyclodextrin (b-CD), but the yield was less than 1%. When b-CD was replaced with 2,6-di-O-methyl-beta-cyclodextrin (DM-b-CD), the solubility of DPPH in water improved significantly. However, the reactivity of DM-b-CD-solubilized DPPH toward water-soluble antioxidants, such as ascorbate, Trolox, and caffeic acid, was significantly lower than that of b-CD-solubilized DPPH due to the steric hindrance of the methyl groups in DM-b-CD. Therefore, b-CD-solubilized DPPH is suitable for evaluating the innate activity of water-soluble antioxidants