Analytical Sciences

Application of Electrochemiluminescence for the Evaluation of the Antioxidant Capacity of Some Phenolic Compounds Against Superoxide Anion Radicals

Masanori MATSUOKA and Jiye JIN

Department of Chemistry, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan

This paper for the first time reports on novel and non-enzymatic method for studying the free radical-scavenging properties of phenolic compounds against superoxide anion radicals (O₂·⁻) by using the cathodic electrochemiluminescence (ECL) of lucigenin (Luc²⁺). The ECL of Luc²⁺ at a glassy carbon (GC) electrode is observed in an aeration electrolytic solution (pH 7), which is believed to be due to the reaction of a one-electron reduced form of Luc²⁺ (i.e. a radical cation, Luc·⁺) with in situ electrogenerated O₂·⁻. The ECL intensity is dependent on the concentration of dissolved oxygen, and is suppressed dramatically by superoxide dismutase (SOD), a typical O₂·⁻ scavenger. Since the coexisting hydrogen peroxide (H₂O₂) has no influence on the cathodic ECL of Luc²⁺, it is thus suggested that the ECL signal specifically reflected the O₂·⁻ concentration level generated at the electrode surface. When phenolic compounds were added into the solution, this resulted in the inhibition of ECL signals due to the elimination of O₂·⁻. The ECL inhibition rate measured at each concentration was compared against the SOD equivalent (U mL⁻¹), and the relative antioxidant efficiency, K_ao (U mmol⁻¹ equivalent SOD), was used to evaluate the antioxidant activity of some phenolic compounds, including flavonoids, in this study. Structurally different water-soluble phenols were compared, and those compounds containing to catechol skeletal structure are found to present the higher antioxidant capacity.

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