Probing the antioxidant activity of polyphenols by CIDNP: from model compounds to green tea and red wine.
Polyphenols occur naturally in a vast variety of plants. One of their predominant properties is their antioxidant activity. To provide a deeper understanding of the antioxidant mechanism, (1)H CIDNP spectroscopy (CIDNP=chemically induced dynamic nuclear polarization) is used to study model hydrogen abstraction reactions with four catechin-based polyphenols: catechin (CA), gallocatechin (GC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). The experiments involve photoinduced hydrogen-atom transfer to a hydrogen abstractor (e.g., excited isopropylthioxanthone) followed under steady-state conditions and in a time-resolved fashion (resolution 500 ns-1 ms). It is found that hydrogen abstraction is an essentially stochastic process with a slight preference for the B rings in the catechin-based polyphenols. Remarkably, analogous reactivity patterns could be followed in the "real systems", green tea and red wine. We also show that CIDNP can be used as a semiquantitative tool to assess chemical reactivity.
Neshchadin
Dmytro
D
Institute of Physical and Theoretical Chemistry, Graz University of Technology, Technikerstrasse 4/I, 8010 Graz, Austria.
Levinn
Rebecca
R
Gescheidt
Georg
G
Batchelor
Stephen N
SN
D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology*; D002392:Catechin / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry* / Q000494:pharmacology*; D005419:Flavonoids / Q000737:chemistry* / Q000494:pharmacology*; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry* / Q000494:pharmacology*; D059808:Polyphenols; D013057:Spectrum Analysis; D013662:Tea / Q000737:chemistry*; D014920:Wine / Q000032:analysis*
D000975:Antioxidants; D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols; D013662:Tea; D002392:Catechin; C045651:epigallocatechin gallate