Antioxidative properties of hydroxycinnamic acid derivatives and a phenylpropanoid glycoside. A pulse radiolysis study

Spectral and redox properties of the phenoxyl radicals from hydroxycinnamic acid derivatives and one selected component of phenylpropanoid glycosides, verbascoside, were studied using pulse radiolysis techniques. On the basis of the pH dependence of phenoxyl radical absorptions, the p K a values for deprotonation of sinapic acid radical and ferulic acid radical are 4.9 and 5.2. The rate constants of one electron oxidation of those antioxidants by azide radical and bromide radical ion were determined at pH 7. The redox potentials of those antioxidants were determined as 0.59–0.71 V vs NHE at pH 7 with reference standard 4-methoxyphenol and resorcinol.