Kinetic Study of the Quenching Reaction of Singlet Oxygen by Pyrroloquinolinequinol (PQQH2, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

A kinetic study of the quenching reaction of singlet oxygen (1O2) with pyrroloquinolinequinol (PQQH2, a reduced form of pyrroloquinolinequinone (PQQ)), PQQNa2 (disodium salt of PQQ), and seven kinds of natural antioxidants (vitamin C (Vit C), uric acid (UA), epicatechin (EC), epigallocatechin (EGC), α-tocopherol (α-Toc), ubiquinol-10 (UQ10H2), and β-carotene (β-Car)) has been performed. The second-order rate constants kQ (kQ = kq + kr, physical quenching and chemical reaction) for the reaction of 1O2 with PQQH2, PQQNa2, and seven kinds of antioxidants were measured in 5.0 wt % Triton X-100 micellar solution (pH 7.4), using UV−visible spectrophotometry. The kQ values decreased in the order of β-Car > PQQH2 > α-Toc > UA > UQ10H2 > Vit C ∼ EGC > EC ≫ PQQNa2. PQQH2 is a water-soluble antioxidant. The singlet oxygen-quenching activity of PQQH2 was found to be 6.3, 2.2, 6.1, and 22 times as large as the corresponding those of water-soluble antioxidants (Vit C, UA, EGC, and EC). Further, the activity of PQQH2 wa...