The electrochemical oxidation mechanisms of rosmarinic acid (RA) and verbascoside (VB), both caffeic acid
esters with two catechol moieties, were investigated. The redox mechanism is associated with the oxidation of the
catechol groups, and was studied over a wide pH range by cyclic, differential pulse and square wave voltammetry, using a
glassy carbon electrode. The voltammetric study revealed that both molecules, RA and VB, are reversibly oxidized in two
successive pH-dependent steps each with the transfer of two electrons and two protons. Moreover, it was found that the
first oxidation step is associated with the caffeic acid moiety, whereas the second oxidation step corresponds to the
oxidation in VB of the hydroxytyrosol group and in RA of the 3,4-dihydroxyphenyl lactic acid residue.
Keywords: Acteoside, caffeic acid, cinnamic acid derivatives, electrochemical characterization, hydroxytyrosol,
phenylpropanoid glycosides, voltammetry, erbascoside, rosmarinic acid, hydroxytyrosol, caffeic acid.
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