ESR-spin trapping study on the sonochemistry of liquids in the presence ofoxygen. Evidence for the superoxide radical anion formation

The sonolysis of water and some organic liquids such as ethylene glycol, me thanol and chloroform in the presence of oxygen, at 20 and 475 kHz ultrasou nd frequencies has been investigated by the ESR-spin trapping technique. 5, 5-Dimethyl-1-pyrroline-N-oxide (DMPO), 3,3,5,5-tetramethylpyrroline-N-oxide (TMPO) and N-tert-butyl-alpha -phenyl nitrone (PBN) were able to trap supe roxide radical anion, generated as the result of the sonication of the orga nic media. The addition of superoxide dismutase (SOD) resulted in a dramati c decrease of the ESR signal intensity of the superoxide radical adduct. In addition, the thermolysis of the liquids under ultrasound was shown by ESR detection of the spin adducts of the radicals formed by homolytic fragment ation. Occasionally, the nature of the detected spin adduct was dependent o n the sonication time or on the frequency of the ultrasonic radiation. Expe riments carried out in the presence of 2-methyl-2-nitrosopropane (MNP) resu lted in the detection of radicals originating from thermal decomposition of the spin trap, showing its lability under ultrasonic radiation. (C) 2001 E lsevier Science B.V. All rights reserved.