FREE-RADICAL INTERMEDIATES AND STABLE PRODUCTS IN THE OXIDATION OF INDOLE-3-ACETIC-ACID

The free-radical intermediates and the stable products formed on one-e lectron oxidation of indole-3-acetic acid (IAA) in aqueous solution we re investigated. The dibromine radical anion generated radiolytically reacted with IAA to yield the IAA radical cation. In acid solution, th e latter decays by a first-order process (k = 1.8 x 10(4) s(-1)) to yi eld carbon dioxide and the skatole radical. At pH 7 it deprotonates (p K(a) = 5.09 +/- 0.02), giving the indolyl radical, which decays only b y a bimolecular process (rate constant of first-order reactions <100 s (-1)) which yields indole-3-carbinol as one of the products. Under ste ady-state irradiation at pH 7 the free radicals had a sufficient lifet ime to allow the small fraction of radical cation present in equilibri um to undergo decarboxylation, consistent with the observed formation of carbon dioxide. Glutathione reacted with the indolyl radical, regen erating IAA, and with the skatole radical to yield skatole. In the pre sence of oxygen the skatole radical is rapidly converted to a peroxyl radical, which appears to decay only by bimolecular reactions with ind ole-3-aldehyde as one of the products. No evidence was found for the r eaction of the peroxyl radical with glutathione or for elimination of superoxide.