Application of a Stopped-Flow EPR Method for the Detection of Short-Lived Flavonoid Semiquinone Radicals Produced by Oxidation Using 15N-Labeled Nitrosodisulfonate Radical (Fremy’s Salt)
- 作者: Kuwabara K.1, Sakurai Y.1, Sanuki H.1, Morimoto C.2, Li Y.3, Miyake Y.1, Kanaori K.1, Tajima K.1
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隶属关系:
- Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
- Department of Food and Nutrition, Matsuyama Shinonome Junior College
- Department of Chemistry, Tsinghua University
- 期: 卷 49, 编号 8 (2018)
- 页面: 911-924
- 栏目: Original Paper
- URL: https://journals.rcsi.science/0937-9347/article/view/248091
- DOI: https://doi.org/10.1007/s00723-018-1012-3
- ID: 248091
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详细
A stopped-flow-electron paramagnetic resonance (EPR) method was applied for the detection of short-lived radicals of flavonoids bearing a catechol moiety as the B-ring, such as flavonols (quercetin, fisetin, and rutin), flavanones (eriodictyol and taxifolin), flavanols (catechin and epicatechin), and flavone (luteolin). 15N-labeled sodium salt of nitrosodisulfonate (15NDS) was employed to obtain the highly resolved EPR hyperfine structure (hfs) of flavonoid-derived semiquinone radicals under stoichiometrically regulated reaction conditions in aqueous media (pH 10). The EPR hfs of these flavonoids radicals, except catechin and epicatechin, were recorded. Based on the g value and the proton hyperfine coupling constants (hfcc), these flavonoid-derived radicals were assigned to be semiquinone radicals of the catechol moiety (B-ring). For example, the observed EPR hyperfine structure (hfs) of the luteolin radical (Lut−·) was composed of four sets of doublet splitting, which could be ascribed to the three protons of the B-ring (a2′ = 0.136, a5′ = 0.102, and a6′ = 0.272 mT) and a vinyl proton of the C-ring (a3 = 0.099 mT). In addition, the characteristically small doublet splitting resolved for the fisetin anion radical (Fis−·, 0.028 mT) was assigned to the aromatic proton at the C5 carbon of the A-ring, indicating that the unpaired electron of the radials was partially delocalized onto the A-ring through the π bonds involved in the vinyl-carbonyl moiety of the C-ring. The hfcc of the methine protons at the C2 carbon of taxifolin and eriodictyol-derived radicals (Tax−· and Eri−·) was, respectively, evaluated to be 0.102 and 0.230 mT. The assignment of the proton hfcc of flavonoid-derived semiquinone radicals will be discussed in relation with the molecular structure of the C-ring.
作者简介
Keiko Kuwabara
Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
Email: tajima@kit.ac.jp
日本, Matsugasaki, Sakyo-ku, Kyoto, 606-8585
Yasuhiro Sakurai
Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
Email: tajima@kit.ac.jp
日本, Matsugasaki, Sakyo-ku, Kyoto, 606-8585
Hodaka Sanuki
Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
Email: tajima@kit.ac.jp
日本, Matsugasaki, Sakyo-ku, Kyoto, 606-8585
Chie Morimoto
Department of Food and Nutrition, Matsuyama Shinonome Junior College
Email: tajima@kit.ac.jp
日本, Matsuyama, Ehime, 790-8531
Yong Li
Department of Chemistry, Tsinghua University
Email: tajima@kit.ac.jp
中国, Beijing, 100084
Yusuke Miyake
Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
Email: tajima@kit.ac.jp
日本, Matsugasaki, Sakyo-ku, Kyoto, 606-8585
Kenji Kanaori
Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
Email: tajima@kit.ac.jp
日本, Matsugasaki, Sakyo-ku, Kyoto, 606-8585
Kunihiko Tajima
Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
编辑信件的主要联系方式.
Email: tajima@kit.ac.jp
日本, Matsugasaki, Sakyo-ku, Kyoto, 606-8585