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

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.

Intrinsic Iron‐Containing Multiwalled Carbon Nanotubes as Electro‐Fenton Catalyst for the Conversion of Benzene to Redox‐Active Surface‐Confined Quinones

“…These observations confirm the involvement of the electro‐Fenton reaction in the BZ oxidation in this work. Extended characterization experiments with UV/Vis spectroscopy (ethanolic extract of the GCE/MWCNT‐Fe*@BZO) showed a specific broad absorbance peak at λ max =600 nm (Figure C, curve b), which may be attributed to the presence of a quinone–Fe 3+ complex system, (Fe 3+ obtained after the electro‐Fenton reaction with BZ) that had formed at the interface. Figure A shows the LC–MS spectrum of the ethanolic extract of the MWCNT‐Fe*@BZO.…”

Industrial bioprocessing perspectives on managing therapeutic protein charge variant profiles

“…This is partially due to the complex interactions in the cell culture environment. For example, antioxidants in combination with transition metals may create higher levels of ROS by recycling the ROS producing metals (Kärkönen & Fry, 2006;Nkhili, Loonis, Mihai, El Hajji, & Dangles, 2014;Ueda, Takai, Shimazu, & Ozawa, 1998). In addition, many species that control ROS may impact both intracellular and extracellular processes.…”

Deutscher Lebensmittelchemikertag 2014 in Gießen

“…Im Vergleich mit der in der Literatur ebenfalls als prooxidativ beschriebenen Gallussäure [41,42] konnten hier für L-Ascorbinsäure und GLUC, nicht jedoch für D-Glucose, Strangbruch-induzierende Effekte nachgewiesen werden, die mit dem prooxidativen Charakter von Reduktonen in Verbindung stehen dürften. Dosisabhängig war nach Inkubation mit 0-100 µM L-Ascorbinsäure eine Abnahme an intakten Nukleinsäuremolekülen zu verzeichnen.…”