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Issue 4, 2012
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Xanthones as antioxidants: A theoretical study on the thermodynamics and kinetics of the single electron transfer mechanism

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Abstract

Mangosteen (Garcinia mangostana) is considered the queen of the tropical fruits. It has a dark red pericarp that is rich in bioactive compounds including xanthones, which have been classified as very good antioxidants from several experimental results. In this work, the antioxidant properties of twenty xanthones isolated from the pericarp of Garcinia mangostana are studied considering the single electron transfer mechanism (SET). According to their most acidic pKa value, under physiological conditions the monoanionic form is present in significant amounts. For this reason, eight deprotonated xanthones are also considered in this study. Quantum chemical calculations were performed in order to assess their free radical scavenging capacity in terms of vertical ionization energies and vertical electron affinities. With these two chemical descriptors it is possible to construct a map that allows a straightforward comparison of the electron transfer viability between any pair of reactants. Such a map for the studied xanthones and the free radicals ˙OH and O2˙, in aqueous solution, indicates that xanthones can either donate or accept electrons in order to deactivate free radicals. A new relationship between the ionization potential and the electron affinity is proposed to predict the thermochemical viability of the SET processes. The electron transfer reactions between xanthones and ˙OH or O2˙ are endergonic and, therefore, thermodynamically unfeasible. However, the reaction of deprotonated xanthones with ˙OH is exergonic. Thus, the deprotonated xanthones are more reactive than the neutral species through the SET mechanism. The monoanions of xanthones, which are present under physiological conditions were found to react with ˙OH at diffusion-limited rates.

Graphical abstract: Xanthones as antioxidants: A theoretical study on the thermodynamics and kinetics of the single electron transfer mechanism

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Publication details

The article was received on 19 Oct 2011, accepted on 09 Jan 2012 and first published on 13 Feb 2012


Article type: Paper
DOI: 10.1039/C2FO10229C
Citation: Food Funct., 2012,3, 442-450
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    Xanthones as antioxidants: A theoretical study on the thermodynamics and kinetics of the single electron transfer mechanism

    A. Martínez, E. Hernández-Marin and A. Galano, Food Funct., 2012, 3, 442
    DOI: 10.1039/C2FO10229C

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