Pulse radiolysis, electron paramagnetic resonance spectroscopy and theoretical calculations of caffeic acid oligomer radicals

Seven representative compounds isolated from Salvia officinalis, among them caffeic acid, the dimer rosmarinic acid and oligomers of caffeic acid, were investigated with regard to their antioxidant potential both expressed by the radical scavenging activity and the stability and structure of the int...

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Bibliographic Details
Published in:Biochimica et biophysica acta 2003-03, Vol.1620 (1), p.97-107
Main Authors: Bors, Wolf, Michel, Christa, Stettmaier, Kurt, Lu, Yinrong, Foo, L.Yeap
Format: Article
Language:English
Subjects:
Azide radical
Benzoquinones - chemistry
Caffeic acid oligomer
Caffeic Acids - chemistry
Caffeic Acids - isolation & purification
Catechol semiquinone
Cinnamates - chemistry
Depsides
Electron paramagnetic resonance
Electron Spin Resonance Spectroscopy
Free Radical Scavengers - chemistry
Free Radical Scavengers - isolation & purification
Hybrid density-functional calculation
Hydroxyl radical
Hydroxyl Radical - chemistry
Kinetic modeling
Linear Models
Mathematics
Molecular Structure
Phenols - chemistry
Pulse Radiolysis
Rate constant
Rosmarinic Acid
Salvia officinalis
Salvia officinalis - chemistry
Transient spectrum
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Summary:Seven representative compounds isolated from Salvia officinalis, among them caffeic acid, the dimer rosmarinic acid and oligomers of caffeic acid, were investigated with regard to their antioxidant potential both expressed by the radical scavenging activity and the stability and structure of the intermediate radicals. Pulse-radiolytic investigation revealed very high rate constants with both hydroxyl and azide radicals. Evidence from kinetic modelling calculations suggested unusual complex behavior due to the presence of both O 4- and O 3-semiquinones and — in two cases — formation and decay of a hydroxyl radical adduct at the vinyl side chain. EPR spectroscopy studies, which included dihydrocaffeic acid as a model for the saturated side chains of the oligomers, confirmed that the radical structures after oxidation in slightly alkaline solutions are representing dissociated O 4-semiquinones. While according to calculations based on hybrid density-functional theory the other radical structures are valid intermediates, they cannot be observed except by pulse radiolysis due to their fast decay.
ISSN:0304-4165
0006-3002
1872-8006
DOI:10.1016/S0304-4165(02)00512-3