Hydroxyl radical attack on dopamine. 
Hydroxyl radicals were generated in the presence of 1 mM dopamine (3,4-dihydroxyphenylethylamine) at pH 7.2 (50 mM phosphate buffer) by the following two mechanisms: 1) a classic Fenton-type reaction between hydrogen peroxide and a ferrous chelate (ferrous diethylenetriaminepentaacetate) and 2) the cyclical redox reactions of iron-EDTA/ascorbate.  Three ring-monohydroxylated products of dopamine were detected by high performance liquid chromatography with electrochemical detection: 2-hydroxydopamine, 5-hydroxydopamine, and 6-hydroxydopamine in an approximate ratio of 3:2:1.  Scavengers of hydroxyl radicals (dimethyl sulfoxide, mannitol, ethanol) suppressed the yields of products in a concentration-dependent manner.  The formation of nonphysiologic hydroxylated forms of dopamine can provide a probe for the formation of hydroxyl radicals in dopamine neurons.