Sonolysis of ubiquinone in aqueous solutions. An EPR spin-trapping study

Free radical formation in aqueous solutions of ubiquinone (coenzyme Q(0)) induced by ultrasound was studied by EPR and spin trapping with 3,5-dibromo-4-nitrosobenzene sulphonate. When aqueous solutions of ubiquinone were sonicated with 50-kHz ultrasound in the presence of argon or nitrogen, radicals formed by addition of (OH)-O-. or H-. to the double bonds of the ubiquinone ring and methyl radicals were observed as the major spin adducts. The methyl radicals were formed by pyrolysis of ubiquinone. These radicals led to the degradation of ubiquinone. The reduced from of ubiquinone, ubiquinol, was formed by sonication in the presence of argon, and its formation was prevented by addition of native but not of denatured superoxide dismutase. Sodium formate, which scavenges (OH)-O-. to form CO2-., enhanced ubiquinol formation but partially inhibited the degradation of the ubiquinone ring. No ubiquinol was formed in nitrogen- or oxygen-saturated solutions under our conditions. These results indicate that ubiquinol was formed by reduction of ubiquinone by O-2(-.), which was generated by the sonolysis of argon-saturated water.