A large kinetic isotope effect in the reaction of ascorbic acid with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO˙) in aqueous buffer solutions

Ikuo Nakanishi, Yoshimi Shoji, Kei Ohkubo, Toshihiko Ozawa, Ken Ichiro Matsumoto, Shunichi Fukuzumi

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Abstract

A large kinetic isotope effect (KIE,kH/kD) of 12.8 was observed for the hydrogen-transfer reaction from ascorbic acid to 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO˙) in a phosphate buffer solution (0.05 M, pH/pD 7.0) at 298 K. The isotopic difference in the activation energies (6.8 kJ mol−1) determined from the temperature dependence of the KIE suggests that quantum mechanical tunneling may partly play a role in the reaction, although the isotopic ratio of the Arrhenius prefactor (AH/AD= 0.86) is within the semiclassical limits.

Original languageEnglish
Pages (from-to)11505-11507
Number of pages3
JournalChemical Communications
Volume56
Issue number77
DOIs
StatePublished - 4 Oct 2020

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© The Royal Society of Chemistry 2020.

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