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Reactivity of food phenols with iron and copper ions: binding, dioxygen activation and oxidation mechanisms.

Authors
Type
Published Article
Journal
Food & Function
2042-650X
Publisher
The Royal Society of Chemistry
Publication Date
Volume
5
Issue
6
Pages
1186–1202
Identifiers
DOI: 10.1039/c4fo00007b
PMID: 24700074
Source
Medline
License
Unknown

Abstract

In this work, the affinity of common dietary phenols (gallic acid, caffeic acid, catechin, and rutin) for iron and copper ions was quantitatively investigated in neutral phosphate buffer as well as the reactivity of the complexes toward dioxygen. Contrasting behaviors were observed: because of the competing phosphate ions, Fe(III) binding is much slower than Fe(II) binding, which is rapidly followed by autoxidation of Fe(II) into Fe(III). With both ions, O2 consumption and H2O2 production are modest and the phenolic ligands are only slowly oxidized. By contrast, metal-phenol binding is fast with both Cu(I) and Cu(II). With Cu(I), O2 consumption and H2O2 production are very significant and the phenolic ligands are rapidly oxidized into a complex mixture of oligomers. The corresponding mechanism with Cu(II) is hampered by the preliminary rate-determining step of Cu(II) reduction by the phenols. The consequences of these findings for the stability and antioxidant activity of plant phenols are discussed.

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