@article{oai:repo.qst.go.jp:00079617,
 author = {Nakanishi, Ikuo and Shoji, Yoshimi and Ohkubo, Kei and Ozawa, Toshihiko and Ken-ichiro, Matsumoto and Nakanishi, Ikuo and Shoji, Yoshimi and Ohkubo, Kei and Ozawa, Toshihiko and Matsumoto, Kenichiro},
 issue = {Suppl.1},
 journal = {Free Radical Biology & Medicine},
 month = {Nov},
 note = {The radical-scavenging activity and mechanism of antioxidants are of considerable importance to develop drugs for oxidative stress-associated diseases.  2,2-Dipheny-1-picrylhydrazyl (DPPH) radical has been frequently used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen radicals.  However, the insolubility of the DPPH radical in water has precluded the its use in aqueous solutions without cosolvents.  Recently, we have succeeded in solubilizing the DPPH radical in using β-cyclodextrin (β-CD).  This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous solutions.  We report herein the kinetic isotope effect in the reaction of three water-soluble antioxidants, which are ascorbic acid (AscH(2)), Trolox, and (+)-catechin, with the β-CD-solubilized DPPH radical in aqueous buffer solutions.
Upon mixing of the β-CD-solubilized DPPH radical in water (Milli-Q) with a phosphate buffer solution (0.1 M, pH 7.0) of AscH(2) at a volumetric ratio of 1:1 on a UNISOKU RSP-1000-02NM stopped-flow spectrophotometer at 298 K, the absorption band at 527 nm due to the DPPH radical immediately decreased.  From the kinetic analysis for the decay of the absorbance at 527 nm, the second-order rate constant (k(H)) was in phosphate buffer (0.05 M, pH 7.0) determined to be 7.9 x 10(3) M(-1) s(-1).  When H(2)O was replaced by D(2)O to prepare the phosphate buffer solutions, the second-order rate constant (k(D)) for the reaction between AscH(2) and the β-CD-solubilized DPPH radical was significantly smaller than the corresponding k(H) value (k(D) = 1.5 x 10(3) M(-1) s(-1)).  Thus, the kinetic isotope effect (k(H)/k(D)) was calculated to be 5.2.  The k(H)/k(D) values for Trolox and (+)-catechin were also determined in the same manner to be 7.3 and 6.5, respectively.  Based on these results, the scavenging mechanism of the DPPH radical by these antioxidants will be discussed.},
 title = {Kinetic Isotope Effect in the Reaction of Water-Soluble Antioxidants with Water-Solubilized 2,2-Diphenyl-1-picrylhydrazyl Radical in Aqueous Buffer Solutions},
 volume = {145},
 year = {2019}
}