Effects of reaction environments on radical-scavenging mechanisms of ascorbic acid

Ikuo Nakanishi, Yoshimi Shoji, Kei Ohkubo, Kiyoshi Fukuhara, Toshihiko Ozawa, Kenichiro Matsumoto, Shunichi Fukuzumi

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

The effects of reaction environments on the radical-scavenging mechanisms of ascorbic acid (AscH2) were investigated using 2,2 diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by β-cyclodextrin (β-CD) in water. The DPPHscavenging rate of AscH2 in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0). An organic soluble 5,6-isopropylidene-L- ascorbic acid (iAscH2) scavenged DPPH much slower in acetonitrile (MeCN) than in MeOH. In MeOH, Mg(ClO4)2 significantly decelerated the DPPH•-scavenging reaction by AscH2 and iAscH2, while no effect of Mg(ClO4)2 was observed in MeCN. On the other hand, Mg(ClO4)2 significantly accelerated the reaction between AscH2 and β-CD-solubilized DPPH (DPPH/β-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO4)2 to the AscH2-DPPH/β-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, the DPPH•-scavenging reaction by iAscH2 in MeCN may proceed via a one-step hydrogen-atom transfer, while an electron- transfer pathway is involved in the reaction between AscH2 and DPPH•/β-CD in phosphate buffer solution. These results demonstrate that the DPPH•-scavenging mechanism of AscH2 are affected by the reaction environments.

Original languageEnglish
Pages (from-to)116-122
Number of pages7
JournalJournal of Clinical Biochemistry and Nutrition
Volume68
Issue number2
DOIs
StatePublished - 1 Mar 2021

Bibliographical note

Funding Information:
This work was partially supported by Grant-in-Aid (No. 18K06620 to IN, 20H02779, 20H04819, 18H04650, 17H03010, and 16H02268 to KO) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Publisher Copyright:
© 2021 JCBN

Keywords

  • Antioxidant
  • Ascorbic acid
  • Hydrogen transfer
  • Radical
  • Reaction mechanism

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