Tunneling in the hydrogen-transfer reaction from a vitamin e analog to an inclusion complex of 2,2-diphenyl-1-picrylhydrazyl radical with β-cyclodextrin in an aqueous buffer solution at ambient temperature

Ikuo Nakanishi, Yoshimi Shoji, Kei Ohkubo, Shunichi Fukuzumi

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Recently, increasing attention has been paid to quantum mechanical behavior in biology. In this study, we investigated the involvement of quantum mechanical tunneling in the hydrogen-transfer reaction from Trolox, a water-soluble analog of vitamin E (α-tocopherol), to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) in a phosphate buffer solution (0.05 M, pH 7.0). DPPH was used as a reactivity model of reactive oxygen species and solubilized in water using β-cyclodextrin (β-CD). The second-order rate constants, kH and kD, in 0.05 M phosphate buffer solutions prepared with H2O (pH 7.0) and D2O (pD 7.0), respectively, were determined for the reaction between Trolox and DPPH, using a stopped-flow technique at various temperatures (283–303 K). Large kinetic isotope effects (KIE, kH/kD) were observed for the hydrogen-transfer reaction from Trolox to the β-CD-solubilized DPPH in the whole temperature range. The isotopic ratio of the Arrhenius prefactor (AH/AD = 0.003), as well as the isotopic difference in the activation energies (19 kJ mol−1), indicated that quantum mechanical tunneling plays a role in the reaction.

Original languageEnglish
Article number1966
JournalAntioxidants
Volume10
Issue number12
DOIs
StatePublished - Dec 2021

Bibliographical note

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

  • Antioxidant
  • Hydrogen transfer
  • Kinetic isotope effect
  • Tunneling

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