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 ubiqu inone were sonicated with 50-kHz ultrasound in the presence of argon o r nitrogen, radicals formed by addition of (OH)-O-. or H-. to the doub le bonds of the ubiquinone ring and methyl radicals were observed as t he 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 nat ive but not of denatured superoxide dismutase. Sodium formate, which s cavenges (OH)-O-. to form CO2-., enhanced ubiquinol formation but part ially inhibited the degradation of the ubiquinone ring. No ubiquinol w as formed in nitrogen- or oxygen-saturated solutions under our conditi ons. These results indicate that ubiquinol was formed by reduction of ubiquinone by O-2(-.), which was generated by the sonolysis of argon-s aturated water.