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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

1
Quantum RedOx Chemistry Group, Institute for Quantum Life Science (iQLS), Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan
2
Institute for Advanced Co-Creation Studies, Open and Transdisciplinary Research Initiatives, Osaka University, 2-8 Yamada-oka, Suita, Osaka 565-0871, Japan
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Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
4
Faculty of Science and Engineering, Meijo University, Nagoya 468-8502, Japan
*
Authors to whom correspondence should be addressed.
Academic Editor: Nino Russo
Antioxidants 2021, 10(12), 1966; https://doi.org/10.3390/antiox10121966
Received: 9 November 2021 / Revised: 3 December 2021 / Accepted: 6 December 2021 / Published: 8 December 2021
(This article belongs to the Section Natural and Synthetic Antioxidants)
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. View Full-Text
Keywords: antioxidant; hydrogen transfer; kinetic isotope effect; tunneling antioxidant; hydrogen transfer; kinetic isotope effect; tunneling
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MDPI and ACS Style

Nakanishi, I.; Shoji, Y.; Ohkubo, K.; Fukuzumi, S. 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. Antioxidants 2021, 10, 1966. https://doi.org/10.3390/antiox10121966

AMA Style

Nakanishi I, Shoji Y, Ohkubo K, Fukuzumi S. 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. Antioxidants. 2021; 10(12):1966. https://doi.org/10.3390/antiox10121966

Chicago/Turabian Style

Nakanishi, Ikuo, Yoshimi Shoji, Kei Ohkubo, and Shunichi Fukuzumi. 2021. "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" Antioxidants 10, no. 12: 1966. https://doi.org/10.3390/antiox10121966

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