title: Kinetic study of aroxyl radical scavenging and α-tocopheroxyl regeneration rates of pyrroloquinolinequinol (PQQH2, a reduced form of pyrroloquinolinequinone) in dimethyl sulfoxide solution: finding of synergistic effect on the reaction rate due to the coexistence of α-tocopherol and PQQH2.
abstract: Measurements of aroxyl radical (ArO•)-scavenging rate constants (ks AOH) of antioxidants (AOHs: pyrroloquinolinequinol (PQQH2), α-tocopherol (α-TocH), ubiquinol-10 (UQ10H2), epicatechin, epigallocatechin, epigallocatechin gallate, and caffeic acid) were performed in dimethyl sulfoxide (DMSO) solution, using stopped-flow spectrophotometry. The ks AOH values were measured not only for each AOH but also for the mixtures of two AOHs ((i) α-TocH and PQQH2 and (ii) α-TocH and UQ10H2). A notable synergistic effect that the ks AOH values increase 1.72, 2.42, and 2.50 times for α-TocH, PQQH2, and UQ10H2, respectively, was observed for the solutions including two kinds of AOHs. Measurements of the regeneration rates of α-tocopheroxyl radical (α-Toc•) to α-TocH by PQQH2 and UQ10H2 were performed in DMSO, using double-mixing stopped-flow spectrophotometry. Second-order rate constants (kr) obtained for PQQH2 and UQ10H2 were 1.08 × 105 and 3.57 × 104 M−1 s−1, respectively, indicating that the kr value of PQQH2 is 3.0 times larger than that of UQ10H2. It has been clarified that PQQH2 and UQ10H2 having two HO groups within a molecule may rapidly regenerate two molecules of α-Toc• to α-TocH. The result indicates that the prooxidant effect of α-Toc• is suppressed by the coexistence of PQQH2 or UQ10H2.
authors.affiliation: Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Ouchi
authors.forename: Kazuto
authors.initials: K
authors.lastname: Ikemoto
authors.forename: Masahiko
authors.initials: M
authors.lastname: Nakano
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Nagaoka
authors.forename: Kazuo
authors.initials: K
authors.lastname: Mukai
mesh_terms: D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D016166:Free Radical Scavengers / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D010084:Oxidation-Reduction; D045542:PQQ Cofactor / Q000737:chemistry*; D024502:alpha-Tocopherol / Q000737:chemistry*
chemical_list: D016166:Free Radical Scavengers; D045542:PQQ Cofactor; D024502:alpha-Tocopherol; D004121:Dimethyl Sulfoxide