Structure of the radical from one-electron oxidation of 4-hydroxycinnamate.
Radicals from one-electron oxidation of 4-hydroxycinnamate, ferulate and 3,4-dihydroxycinnamate have been formed by reaction with the oxidising triplet state of duroquinone. All three compounds react with triplet duroquinone with second order rate constants close to the diffusion-controlled limit. The identity of the resulting radicals is confirmed by observation of their characteristic visible absorption spectra. Time-resolved resonance Raman (TR3) spectra of the radical from 4-hydroxycinnamate were measured using a probe laser wavelength of 600 nm, to be in resonance with the long wavelength absorption band of the radical. The TR3 spectra contain prominent bands ascribed to the C-O and ring C-C stretching vibrations. The spectra are interpreted as indicating strong delocalisation of the radical site to the double bond in conjugation with the aromatic ring in 4-hydroxycinnamate. This contributes to the low reduction potential of the radical and the antioxidant properties of hydroxycinnamates.
Bisby
R H
RH
Division of Biological Sciences, School of Environmental and Life Sciences, University of Salford, Salford, M5 4WT, UK. r.h.bisby@salford.ac.uk
Parker
A W
AW
D016227:Benzoquinones / Q000494:pharmacology; D003373:Coumaric Acids / Q000737:chemistry*; D004583:Electrons; D005609:Free Radicals / Q000737:chemistry*; D007700:Kinetics; D007834:Lasers; D010084:Oxidation-Reduction; D010782:Photolysis; D011422:Propionates; D013059:Spectrum Analysis, Raman
D016227:Benzoquinones; D003373:Coumaric Acids; D005609:Free Radicals; D011422:Propionates; C495469:p-coumaric acid; C034257:duroquinone