ANTIOXIDATIVE PROPERTIES OF HYDROXYCINNAMIC ACID-DERIVATIVES AND A PHENYLPROPANOID GLYCOSIDE - A PULSE-RADIOLYSIS STUDY

Spectral and redox properties of the phenoxyl radicals from hydroxycin namic acid derivatives and one selected component of phenylpropanoid g lycosides, verbascoside, were studied using pulse radiolysis technique s. On the basis of the pH dependence of phenoxyl radical absorptions, the pK(a) values for deprotonation of sinapic acid radical and ferulic acid radical are 4.9 and 5.2. The rate constants of one electron oxid ation of those antioxidants by azide radical and bromide radical ion w ere determined at pH 7. The redox potentials of those antioxidants wer e determined as 0.59-0.71 V vs NHE at pH 7 with reference standard 4-m ethoxyphenol and resorcinol. (C) 1998 Elsevier Science Ltd. All rights reserved.