Water-Induced Regeneration of a 2,2-Diphenyl-1-picrylhydrazyl Radical after Its Scandium Ion-Promoted Electron-Transfer Disproportionation in an Aprotic Medium

A neutral, stable radical, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH ), has been frequently used to estimate the activity of antioxidants for more than 60 years. However, the number of reports about the effect of metal ions on the reactivity of DPPH is quite limited. We have recently reported a un...

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Bibliographic Details
Published in:Molecules (Basel, Switzerland) Switzerland), 2023-06, Vol.28 (13), p.5002
Main Authors: Nakanishi, Ikuo, Shoji, Yoshimi, Ohkubo, Kei, Ito, Hiromu, Fukuzumi, Shunichi
Format: Article
Language:English
Subjects:
Absorption spectra
Acetonitrile
Anions
Cations
Communication
comproportionation
Disproportionation
Electron paramagnetic resonance
Electron spin resonance
electron transfer
Electron Transport
Electrons
Instrument industry
Ions
Ions - chemistry
Lewis acid
Metal ions
radical
Rare earth metals
Scandium
Scandium - chemistry
scandium ion
Spectroscopy
Spectrum analysis
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Summary:A neutral, stable radical, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH ), has been frequently used to estimate the activity of antioxidants for more than 60 years. However, the number of reports about the effect of metal ions on the reactivity of DPPH is quite limited. We have recently reported a unique electron-transfer disproportionation of DPPH to produce the DPPH cations (DPPH ) and anions (DPPH ) upon the addition of scandium triflate [Sc(OTf) (OTf = OSO CF )] to an acetonitrile (MeCN) solution of DPPH . The driving force of this reaction is suggested to be an interaction between DPPH and Sc . In this study, it is demonstrated that the addition of H O to the DPPH -Sc(OTf) system in MeCN resulted in an increase in the absorption band at 519 nm due to DPPH . This indicated that an electron-transfer comproportionation occurred to regenerate DPPH . The regeneration of DPPH was also confirmed by electron paramagnetic resonance (EPR) spectroscopy. The amount of DPPH increased with an increasing amount of added H O to reach a constant value. The detailed mechanism of regeneration of DPPH was proposed based on the detailed spectroscopic and kinetic analyses, in which the reaction of DPPH with [(DPPH) Sc(H O) ] generated upon the addition of H O to [(DPPH) Sc] is the rate-determining step.
ISSN:1420-3049
1420-3049
DOI:10.3390/molecules28135002