77331-80-7Relevant academic research and scientific papers
Singlet Oxygen-mediated Hydroxyl Radical Production in the Presence of Phenols: Whether DMPO-.OH Formation Really Indicates Production of .OH?
Ueda, Jun-Ichi,Takeshita, Keizo,Matsumoto, Shigenobu,Yazaki, Kinya,Kawaguchi, Mitsuru,Ozawa, Toshihiko
, p. 165 - 170 (2003)
The reaction of singlet oxygen (1O2) generated by ultraviolet-A (UVA)-visible light (λ > 330 nm) irradiation of air-saturated solutions of hematoporphyrin with phenolic compounds in the presence of a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), gave an electron spin resonance (ESR) spectrum characteristic of the DMPO-hydroxyl radical spin adduct (DMPO-.OH). In contrast, the ESR signal of 5,5-dimethyl-2-pyrrolidone-N-oxyl, an oxidative product of DMPO, was observed in the absence of phenolic compounds. The ESR signal of DMPO-.OH decreased in the presence of either a .OH scavenger or a quencher of 1O2 and under anaerobic conditions, whereas it increased depending on the concentration of DMPO. These results indicate both 1O2- and DMPO-mediated formation of free .OH during the reaction. When DMPO was replaced with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO), no DEPMPO adduct of oxygen radical species was obtained. This suggests that 1O 2, as an oxidizing agent, reacts little with DEPMPO, in which a strong electron-withdrawing phosphoryl group increases the oxidation potential of DEPMPO compared with DMPO. A linear correlation between the amounts of DMPO-.OH generated and the oxidation potentials of phenolic compounds was observed, suggesting that the electron-donating properties of phenolic compounds contribute to the appearance of .OH. These observations indicate that 1O2 reacts first with DMPO, and the resulting DMPO-1O2 intermediate is immediately decomposed/reduced to give .OH. Phenolic compounds would participate in this reaction as electron donors but would not more, DEPMPO did not cause the spin-trapping agent-mediated generation of .OH like DMPO did.
