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Evaluation of the Radical-Scavenging Activity of Antioxidants in Water Using a Water-Solubilized 2,2-Dipheny-1-picrylhydrazyl Radical
https://repo.qst.go.jp/records/72904
https://repo.qst.go.jp/records/729047b7c4ace-0ddb-444b-90fd-359affc70ea7
| Item type | 会議発表用資料 / Presentation(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2018-08-27 | |||||
| タイトル | ||||||
| タイトル | Evaluation of the Radical-Scavenging Activity of Antioxidants in Water Using a Water-Solubilized 2,2-Dipheny-1-picrylhydrazyl Radical | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_c94f | |||||
| 資源タイプ | conference object | |||||
| アクセス権 | ||||||
| アクセス権 | metadata only access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||
| 著者 |
Nakanishi, Ikuo
× Nakanishi, Ikuo× Ohkubo, Kei× Ozawa, Toshihiko× Matsumoto, Ken-ichiro× 中西 郁夫× 大久保 敬× 小澤 俊彦× 松本 謙一郎 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | 2,2-Diphenyl-1-picrylhydrazyl radical (DPPH•), a relatively stable radical, has been used to evaluate the activity of antioxidants as a reactivity model of reactive oxygen species (ROS) for 60 years [1]. However, the insolubility of DPPH• in water has precluded its use in aqueous media without cosolvents such as, ethanol. The pH of the reaction media of antioxidants is of great importance, because antioxidant molecules have one or more ionizable OH groups and their ionization state largely influence the reactivity of antioxidants. However, the pH of the reaction media is not precisely controlled in the presence of the cosolvents. Recently, we have reported that DPPH• is successfully solubilized in water using β-cyclodextrin (β-CD) [2,3]. In this study, we introduce a novel technique to evaluate the kinetic radical-scavenging activity of antioxidants using the β-CD-solubilized DPPH• in physiological concentrations of buffer solutions. 25 mL of boiling water (Milli-Q) was added to the solid mixture of DPPH• (0.15 mmol) and β-CD (0.70 mmol). The suspension was stirred until it reached room temperature and filtered with a membrane filter (pore size: 0.22 µm). The as-obtained filtrate showed an absorption band at 527 nm, which is diagnostic of DPPH•. The concentration of DPPH• was estimated by using the ε value of 11000 M–1 cm–1 determined for DPPH• in a 1:1 ethanol–buffer solution [4]. Upon mixing of Trolox, a water-soluble analog of α-tocopherol (vitamin E), with the β-CD-solubilized DPPH• in phosphate buffer solution (0.1 M, pH 7.4) at 298 K, the absorption band at 527 nm decreased immediately. The decay of the absorbance at 527 nm monitored by a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer obeyed pseudo-first-order kinetics, when the concentration of Trolox was maintained at more than a 10-fold excess of DPPH• concentration. The pseudo-first-order rate constants (kobs) linearly increased with increasing the Trolox concentration. From the slope of the linear plot, the second-order rate constant (k) for the scavenging of DPPH• by Trolox was determined to be 1.8 × 104 M–1 s–1. The k value of the reaction between Trolox and DPPH• in methanol at 298 K was determined in the same manner to be 2.3 × 102 M–1 s–1, which is about 80-fold smaller than that in phosphate buffer solution (0.1 M, pH 7.4). Ascorbic acid (AscH2) scavenged the β-CD-solubilized DPPH• with the k value of 7.2 × 103 M–1 s–1 in phosphate buffer solution (0.1 M, pH 7.4) at 298 K. Because the pKa value of AscH2 is known to be 4.1, AscH2 undergoes deprotonation and exists in its anionic form, AscH– in phosphate buffer solution (0.1 M, pH 7.4). Thus, the actual species that scavenged DPPH• is AscH–. On the other hand, in methanol, the kobs value for the DPPH•-scavenging reaction by AscH2 was much smaller than that in phosphate buffer solution (0.1 M, pH 7.4) and constant with the change in the AscH2 concentration used in excess. This suggests that little AscH– was produced by the deprotonation of AscH2 in methanol. Thus, the radical-scavenging activity of antioxidants is largely affected by the nature of solvents. The solubilization of DPPH• in water by β-CD enables us to evaluate the radical-scavenging activity of antioxidants with use of the same probe, DPPH•, as that has been used in organic solvents for 60 years. \nREFERENCES [1] M.S. Blois, Nature 181 (1958) 1199 [2] I. Nakanishi, K. Ohkubo, K. Imai, M. Kamibayashi, Y. Yoshihashi, K. Matsumoto, K. Fukuhara, K. Terada, S. Itoh, T. Ozawa, S. Fukuzumi, Chem. Commun. 51 (2015) 8311 [3] I. Nakanishi, K. Ohkubo, M. Kamibayashi, Y. Ogawa, T. Ozawa, K. Matsumoto, S. Fukuzumi, ChemistrySelect 1 (2016) 3367 [4] O. Friaa, D. Brault, Org. Biomol. Chem. 4 (2006) 2417 |
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| 会議概要（会議名, 開催地, 会期, 主催者等） | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | International Conference 2018 Modern Trends in Natural Sciences and Advanced Technologies in Science Education | |||||
| 発表年月日 | ||||||
| 日付 | 2018-08-21 | |||||
| 日付タイプ | Issued | |||||
