Mechanisms Associated with Superoxide Radical Scavenging Reactions Involving Phenolic Compounds Deduced Based on the Correlation between Oxidation Peak Potentials and Second-Order Rate Constants Determined Using Flow-Injection Spin-Trapping EPR Methods
{"title":"Mechanisms Associated with Superoxide Radical Scavenging Reactions Involving Phenolic Compounds Deduced Based on the Correlation between Oxidation Peak Potentials and Second-Order Rate Constants Determined Using Flow-Injection Spin-Trapping EPR Methods","authors":"Yasuhiro Sakurai*, Shuhei Yamaguchi, Tomoyuki Yamashita, Yao Lu, Keiko Kuwabara, Tomoko Yamaguchi, Yusuke Miyake, Kenji Kanaori, Seiya Watanabe and Kunihiko Tajima, ","doi":"10.1021/acs.jafc.4c02873","DOIUrl":null,"url":null,"abstract":"<p >Flow-injection spin-trapping electron paramagnetic resonance (FI-EPR) methods that involve the use of 5,5-dimethyl-pyrroline-<i>N</i>-oxide (DMPO) as a spin-trapping reagent have been developed for the kinetic study of the O<sub>2</sub><sup>•–</sup> radical scavenging reactions occurring in the presence of various plant-derived and synthetic phenolic antioxidants (Aox), such as flavonoid, pyrogallol, catechol, hydroquinone, resorcinol, and phenol derivatives in aqueous media (pH 7.4 at 25 °C). The systematically estimated second-order rate constants (<i>k</i><sub>s</sub>) of these phenolic compounds span a wide range (from 4.5 × 10 to 1.0 × 10<sup>6</sup> M<sup>–1</sup> s<sup>–1</sup>). The semilogarithm plots presenting the relationship between <i>k</i><sub>s</sub> values and oxidation peak potential (<i>E</i><sub>p</sub>) values of phenolic Aox are divided into three groups (A1, A2, and B). The <i>k</i><sub>s</sub>–<i>E</i><sub>p</sub> plots of phenolic Aox bearing two or three OH moieties, such as pyrogallol, catechol, and hydroquinone derivatives, belonged to Groups A1 and A2. These molecules are potent O<sub>2</sub><sup>•–</sup> radical scavengers with <i>k</i><sub>s</sub> values above 3.8 × 10<sup>4</sup> (M<sup>–1</sup> s<sup>–1</sup>). The <i>k</i><sub>s</sub>–<i>E</i><sub>p</sub> plots of all phenol and resorcinol derivatives, and a few catechol and hydroquinone derivatives containing carboxyl groups adjacent to the OH groups, were categorized into the group poor scavengers (<i>k</i><sub>s</sub> < 1.6 × 10<sup>3</sup> M<sup>–1</sup> s<sup>–1</sup>). The <i>k</i><sub>s</sub> values of each group correlated negatively with <i>E</i><sub>p</sub> values, supporting the hypothesis that the O<sub>2</sub><sup>•–</sup> radical scavenging reaction proceeds via one-electron and two-proton processes. The processes were accompanied by the production of hydrogen peroxide at pH 7.4. Furthermore, the correlation between the plots of <i>k</i><sub>s</sub> and the OH proton dissociation constant (p<i>K</i><sub>a</sub><sup>•</sup>) of the intermediate aroxyl radicals (<i>k</i><sub>s</sub>–p<i>K</i><sub>a</sub><sup>•</sup> plots) revealed that the second proton transfer process could potentially be the rate-determining step of the O<sub>2</sub><sup>•–</sup> radical scavenging reaction of phenolic compounds. The <i>k</i><sub>s</sub>–<i>E</i><sub>p</sub> plots provide practical information to predict the O<sub>2</sub><sup>•–</sup> radical scavenging activity of plant-derived phenolic compounds based on those molecular structures.</p>","PeriodicalId":41,"journal":{"name":"Journal of Agricultural and Food Chemistry","volume":null,"pages":null},"PeriodicalIF":5.7000,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Agricultural and Food Chemistry","FirstCategoryId":"97","ListUrlMain":"https://pubs.acs.org/doi/10.1021/acs.jafc.4c02873","RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"AGRICULTURE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Flow-injection spin-trapping electron paramagnetic resonance (FI-EPR) methods that involve the use of 5,5-dimethyl-pyrroline-N-oxide (DMPO) as a spin-trapping reagent have been developed for the kinetic study of the O2•– radical scavenging reactions occurring in the presence of various plant-derived and synthetic phenolic antioxidants (Aox), such as flavonoid, pyrogallol, catechol, hydroquinone, resorcinol, and phenol derivatives in aqueous media (pH 7.4 at 25 °C). The systematically estimated second-order rate constants (ks) of these phenolic compounds span a wide range (from 4.5 × 10 to 1.0 × 106 M–1 s–1). The semilogarithm plots presenting the relationship between ks values and oxidation peak potential (Ep) values of phenolic Aox are divided into three groups (A1, A2, and B). The ks–Ep plots of phenolic Aox bearing two or three OH moieties, such as pyrogallol, catechol, and hydroquinone derivatives, belonged to Groups A1 and A2. These molecules are potent O2•– radical scavengers with ks values above 3.8 × 104 (M–1 s–1). The ks–Ep plots of all phenol and resorcinol derivatives, and a few catechol and hydroquinone derivatives containing carboxyl groups adjacent to the OH groups, were categorized into the group poor scavengers (ks < 1.6 × 103 M–1 s–1). The ks values of each group correlated negatively with Ep values, supporting the hypothesis that the O2•– radical scavenging reaction proceeds via one-electron and two-proton processes. The processes were accompanied by the production of hydrogen peroxide at pH 7.4. Furthermore, the correlation between the plots of ks and the OH proton dissociation constant (pKa•) of the intermediate aroxyl radicals (ks–pKa• plots) revealed that the second proton transfer process could potentially be the rate-determining step of the O2•– radical scavenging reaction of phenolic compounds. The ks–Ep plots provide practical information to predict the O2•– radical scavenging activity of plant-derived phenolic compounds based on those molecular structures.
期刊介绍:
The Journal of Agricultural and Food Chemistry publishes high-quality, cutting edge original research representing complete studies and research advances dealing with the chemistry and biochemistry of agriculture and food. The Journal also encourages papers with chemistry and/or biochemistry as a major component combined with biological/sensory/nutritional/toxicological evaluation related to agriculture and/or food.