Food Antioxidants: Chemical Insights at the Molecular Level

Abstract

In this review, we briefly summarize the reliability of the density functional theory (DFT)-based methods to accurately predict the main antioxidant properties and the reaction mechanisms involved in the free radical-scavenging reactions of chemical compounds present in food. The analyzed properties are the bond dissociation energies, in particular those involving OH bonds, electron transfer enthalpies, adiabatic ionization potentials, and proton affinities. The reaction mechanisms are hydrogen-atom transfer, proton-coupled electron transfer, radical adduct formation, single electron transfer, sequential electron proton transfer, proton-loss electron transfer, and proton-loss hydrogen-atom transfer. Furthermore, the chelating ability of these compounds and its role in decreasing or inhibiting the oxidative stress induced by Fe(III) and Cu(II) are considered. Comparisons between theoretical and experimental data confirm that modern theoretical tools are not only able to explain controversial experimental facts but also to predict chemical behavior.

Carboxyl Group as a Radical Scavenging Moiety: Thermodynamics of 2H+/2e– Processes of Phloretic Acid

“…[31] Among them, chemical nature of scavenged radicals particularly influences scavenging processes. [24,32] To investigate radical scavenging potential of phloretic acid we used the same set of radicals as in our recent papers. [29,30] It embraces oxygen-derived radicals with very different characteristics:…”

“…[35] The density functional theory (DFT)-based methods are able to accurately predict antioxidant potencies and reaction mechanisms involved in radical scavenging reactions of (poly)phenolic compounds. [24] Geometry optimizations and frequency calculations for phloretic acid and its radical cation, radicals, anions, radical anions, as well as for ten selected radicals and their species involved in radical scavenging pathways were carried out using the M06-2X functional [36] and the 6-311++G(d,p) basis set. Among the suite of density functionals, M05-2X, M06-2X and M-11L Minnesota functionals are particularly suitable for systems where main-group thermochemistry, kinetics, and noncovalent interactions are important.…”

“…These and some other possible mechanisms (such as proton-coupled electron transfer (PCET) and sequential proton-loss hydrogen-atom transfer (SPLHAT)) have been recently reviewed. [24] Already published studies dealing with radical scavenging mechanisms of natural (poly)phenols have mostly been based on single, 1H + /1e -processes. [25] However, depending on a number and position of radical scavenging moieties such as phenolic O-H and imino N-H groups, they may also proceed as double (multiple) sequential 1H + /1e -mechanisms.…”

Theoretical Study of Primary Antioxidant Action Thermodynamics

“…The reaction enthalpy of the second step has been denoted as electron transfer enthalpy, ETE (Klein and Lukeš, 2006a). Flavonoids may also act as secondary antioxidants via chelation of copper and iron cations (Craft et al 2012, Gülçin 2012, Galano et al 2016, Dimitrić Marković et al 2011, Leopoldini et al 2011. These cations can significantly contribute to the acceleration of the oxidation.…”

Quantum Chemical Investigation on the Antioxidant Activity of Neutral and Anionic Forms of Juglone: Metal Chelation and Its Effect on Radical Scavenging Activity

“…The usual thermodynamic descriptors of antioxidant activity (AOA) were used to evaluate the effect of the metal ions on the radical scavenging activity of neutral juglone. These descriptors are [17] as follows:…”