Electrochemical study of the increased antioxidant capacity of flavonoids through complexation with iron(II) ions

• Metal-Flavonoid complexes exhibit greater antioxidant capacity than the free flavonoid;.
• Voltammetric profile is an additional information for determining antioxidant capacity;.
• Pyrogallol group is a stronger complex-forming group than the catechol;.
• Morin, quercetin and fisetin increased their antioxidant capacity in 15%, 32% and 28%, respectively.

Flavonoids are polyphenolic compounds that act as natural antioxidants in the human body through various mechanisms, with an emphasis on suppressing reactive oxygen species (ROS) formation by inhibiting enzymes, the direct capture of ROS, and the regulation/protection of antioxidant defenses. Additionally, flavonoids can coordinate with transition metals to catalyze electron transport and promote free radical capture. Recently, metal ion chelation mechanisms have generated considerable interest, as experimental data show that flavonoids in metal complexes exhibit greater antioxidant activity than free flavonoids. However, few studies have correlated the complexing properties of flavonoids with their antioxidant capacity. Thus, the aim of this study was to use the CRAC (Ceric Reducing Antioxidant Capacity) electrochemical assay to measure the antioxidant capacity of five free flavonoids and Fe2+-flavonoid complexes. In addition, the interactions between the flavonoids and Fe2+ were analyzed based on the oxidation peaks formed in their cyclic voltammograms