Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
 
Kinetics and Mechanism for the Scavenging Reaction of the 2,2-Diphenyl-1-picrylhydrazyl Radical by Synthetic Artepillin C Analogues
Tomonori KawashimaSushma MandaYoshihiro UtoKei OhkuboHitoshi HoriKen-ichiro MatsumotoKiyoshi FukuharaNobuo IkotaShunichi FukuzumiToshihiko OzawaKazunori AnzaiIkuo Nakanishi
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JOURNALS OPEN ACCESS

2012 Volume 85 Issue 8 Pages 877-883

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Abstract

The kinetics for the reaction of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) with artepillin C, a prenylated phenylpropanoid found specifically in Brazilian propolis, and its analogues was examined in deaerated acetonitrile (MeCN) to shed light on the mechanism for the radical-scavenging reaction of phenolic antioxidants as well as on the structure–activity relationship. Among the examined analogues, a compound having a catechol moiety is found to have the largest second-order rate constant (k) for the DPPH-scavenging reaction. The deuterium kinetic isotope effect of 1.6 was observed for the DPPH-scavenging reaction of artepillin C in the presence of 0.13 M CD3OD or CH3OH in deaerated MeCN at 298 K. The log k values were found to be linearly correlated with calculated energy difference values (DHT, HT: hydrogen transfer) between the artepillin C analogues and the corresponding phenoxyl radicals, while such a linear correlation cannot be observed between the log k values and calculated ionization potentials (IP), DHT − IP, or experimental one-electron-oxidation potentials of the artepillin C analogues. These results together with a calculated structure of the transition state for the reaction between the artepillin C analogue and DPPH suggest that the DPPH-scavenging reaction of the artepillin C analogues in deaerated MeCN proceeds via a one-step hydrogen-atom transfer from the phenolic OH group to DPPH rather than an electron transfer followed by proton transfer.

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© 2012 The Chemical Society of Japan
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