Fig. 1. Molecular structures of EC, ECG, EGC, EGCG, MG, MC, MR, rutin, sodium ascorbate (Na⁺AsH^-), vitamin C, ubiquinol-10, and 5,7-diisopropyltocopheroxyl (Toc).

Fig. 2. (a) Change in absorbance of tocopheroxyl radical (Toc) at 420 nm during reaction of Toc with epicatechin (EC) in ethanol solution at 25.0°C. [Toc] _{t = 0} = 0.20 mM and [Epicatechin] _{t = 0} = 3.87 mM. (b) Dependence of pseudo-first-order rate constant (k_obsd) on concentration of epicatechin in ethanol.

Fig. 3. (a) Plots of second-order rate constant (k_r) for epicatechin (open circle) versus pH and of mole fraction (f) of three epicatechin species (EC-H₂, EC-H⁻, and EC²⁻) versus pH (solid line). Dotted line is a simulation curve. (b) Plots of second-order rate constant (k_r) for epicatechin gallate (open circle) versus pH and of mole fraction (f) of five ECG species (ECG-H₅, ECG-H₄⁻, ECG-H₃²⁻, ECG-H₂³⁻, and ECG-H⁴⁻) versus pH (solid line). Dotted line is a simulation curve.

Fig. 4. Plots of second-order rate constant (k_r) for the reaction of EC (closed square), ECG (open square), EGC (closed circle), and EGCG (open circle) with 5,7-diisopropyltocopheroxyl (Toc) versus pH.

Fig. 5. (a) Plots of second-order rate constant (k_r) for methyl gallate (open circle) versus pH and of mole fraction (f) of three MG species (MG-H₃, MG-H₂⁻, and MG-H ²⁻) versus pH (solid line). Dotted line is a simulation curve. (b) Plots of second-order rate constant (k_r) for 4-methylcatechol (open circle) versus pH and of mole fraction (f) of three MC species (MC-H₂, MC-H⁻, and MC ²⁻) versus pH (solid line). Dotted line is a simulation curve.

Fig. 6. Three different molecular forms of (a) 4-methylcatechol (MC-H₂, MC-H⁻, MC²⁻), (b) 5-methoxyresorcinol (MR-H₂, MR-H⁻, MR²⁻), and (c) methyl gallate (MG-H₃, MG-H₂⁻, MG-H²⁻) in aqueous solution and their reaction rates, k_ri.

Fig. 7. (a) Three different molecular forms of epicatechin (EC-H₂, EC-H⁻, EC²⁻) in aqueous solution and their reaction rates, k_ri. (b) Five different molecular forms of epicatechin gallate (ECG-H₅, ECG-H₄⁻, ECG-H₃²⁻, ECG-H₂³⁻, ECG-H⁴⁻) in aqueous solution and their reaction rates, k_ri.

Fig. 8. Plots of log k_r vs E_P for catechins (EC, ECG, EGC, and EGCG) and related compounds (MC and MG).

Fig. 9. (a) pH dependence of the rate constant (k_r) for ECG (open circle), the sum of those for EC and MG (closed circle), and that for ascorbic acid (open square). (b) pH dependence of the rate constant (k_r) for EGCG (open circle), the sum of those for EGC and MG (closed circle), and that for ascorbic acid (open square).

Second-order rate constants (k_r) for the reaction of tocopheroxyl (Toc) with catechins (epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate) and related antioxidants in ethanol, 2-propanol/water (5/1, v/v), and Triton X-100 micellar solution (5.0 wt%) at pH 4.0 and 7.0 at 25.0°C, and peak oxidation potentials (E_P)

pH dependence of the second-order rate constants (k_r) for the reaction of catechins (epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate) with 5,7-diisopropyltocopheroxyl (Toc) in 5.0 wt% Triton X-100 micellar solution

pH dependence of the second-order rate constants (k_r) for the reaction of methyl gallate, 4-methylcatechol, 5-methoxyresorcinol, and vitamin C with tocopheroxyl (Toc) in 5.0 wt% Triton X-100 micellar solution

The reaction rates (k_ri, i = 1 – 5) for undissociated, monoanion, dianion, trianion, and tetraanion forms of catechins (EC, ECG, EGC, and EGCG) and related antioxidants in 5.0 wt% Triton X-100 micellar solution