Antioxidant activities and free radical-mediated DNA strand breakages of five hydroxycinnamic acids were examined. Kinetic analysis of a stable galvinoxy (GO • )-scavenging reaction of hydroxycinnamic acids demonstrated that the molecular structure and the reaction medium were two important factors affecting the antioxidant mechanism and activity. In methanol, the kinetic process of the compounds, which have electron-donating groups (-OH, -OCH 3 ) in the ortho-or para-position of 4-OH, was primarily governed by the sequential proton loss electron transfer (SPLET mechanism). While, in ethyl acetate, the reaction mechanism is predominantly direct hydrogen atom transfer (HAT mechanism). But for the compounds having only one hydroxyl, both in ethyl acetate and methanol, the reaction mechanism is only HAT. At the same time, the compound bearing o-diphenoxyl is not the most active one in our tested environment.

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