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

Measurements of aroxyl radical (ArO•)-scavenging rate constants (k s 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) soluti...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 2013-11, Vol.61 (46), p.11048-11060
Main Authors: Ouchi, Aya, Ikemoto, Kazuto, Nakano, Masahiko, Nagaoka, Shin-ichi, Mukai, Kazuo
Format: Article
Language:English
Subjects:
alpha-tocopherol
alpha-Tocopherol - chemistry
antioxidants
Biological and medical sciences
caffeic acid
dimethyl sulfoxide
Dimethyl Sulfoxide - chemistry
epicatechin
epigallocatechin
Free Radical Scavengers - chemistry
Fundamental and applied biological sciences. Psychology
Kinetics
Molecular Structure
Oxidation-Reduction
PQQ Cofactor - chemistry
synergism
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Summary:Measurements of aroxyl radical (ArO•)-scavenging rate constants (k s 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 k s 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 k s 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 (k r) obtained for PQQH2 and UQ10H2 were 1.08 × 105 and 3.57 × 104 M–1 s–1, respectively, indicating that the k r 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.
ISSN:0021-8561
1520-5118
DOI:10.1021/jf4040496