Interaction of flavonoids with ascorbate and determination of their univalent redox potentials: A pulse radiolysis study
Abstract
Concurrent pulse-radiolytic generation of flavonoid aroxyl radicals and ascorbyl radicals causes a complex kinetic interplay of competing and parallel reactions. Evaluation by "kinetic modelling," that is, taking into account all possible reactions by a set of differential equations, allowed us to determine equilibria constants for the univalent steps by a novel method. From these kinetic data we were able to calculate the redox potentials for dihydroquercetin, quercetin, rutin (a quercetin 3-glycoside), kaempferol, fisetin, and luteolin. Despite the limited number of substances, two structural criteria became apparent: all substances containing the B-ring catechol group and the 2,3-double bond have a higher redox potential than ascorbate and are consequently able to oxidize it to the ascorbyl radical. With fisetin and kaempferol having values very similar to ascorbate, only the flavanone dihydro-quercetin was capable of reducing the ascorbyl radical, thus fulfilling the so-called "ascorbate-protective" function, originally proposed by Szent-Györgyi. While flavonoids are effective radical scavengers, these rather high redox potentials for most flavonols may explain their occasional prooxidative behavior.
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Aryloxyl radicals are sometimes unstable showing a prooxidant behavior.
“However, it has been reported that the aryloxyl radicals are sometimes unstable showing a prooxidant behavior (Bors et al. 1995).”
From Reactive Oxygen Species, Toxicity, Oxidative Stress, and Antioxidants: Chronic Diseases and Aging (2023) · cites this paper as Bors et al. 1995
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- Authors
- Bors, W., Michel, C., & Schikora, S.
- Affiliations
- Helmholtz Munich (DE)
- Corresponding author
- Bors, Wolf
- Venue
- Free Radical Biology and Medicine
- Publisher
- Elsevier BV
- Published
- 1995-07
- Volume
- 19
- Issue
- 1
- Pages
- 45-52
- ISSN
- 0891-5849 (ISSN-L)
- OpenAlex
- W2033670414
- Cited by
- 187
- References
- 41
- Citations by year
- 2026: 1 · 2025: 3 · 2024: 5 · 2023: 2 · 2022: 2 · 2021: 3 · 2020: 6 · 2019: 4 · 2018: 2 · 2017: 1 · 2016: 3 · 2015: 4 · 2014: 4 · 2013: 5 · 2012: 10
- FWCI
- 7.59
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Free Radical Biology and Medicine (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Chemistry › Organic Chemistry › Free Radicals and Antioxidants
- Health Sciences › Medicine › Biochemistry › Phytochemicals and Antioxidant Activities
- Health Sciences › Medicine › Biochemistry › Antioxidant Activity and Oxidative Stress
- Keywords
- flavonoids, vitamin C, ascorbyl radical, kinetic modeling, taxifolin, quercetin, rutin, kaempferol, fisetin, luteolin, catechol groups, free radical scavenging, pro-oxidant activity
- MeSH terms
- Ascorbic Acid, Flavonoids, Hydrogen-Ion Concentration, Kinetics, Oxidation-Reduction, Pulse Radiolysis, Quercetin, Rutin, Molecular Structure, Flavonols, Kaempferols, Luteolin
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