DFT study of the antiradical properties of some aromatic compounds derived from antioxidant essential oils: C–H bond vs. O–H bond

This paper describes a theoretical comparative study of the antiradical properties of six aromatic compounds namely eugenol (EUG), safrole (SAF), myristicin (MYR), carvacrol (CAR), cinnamaldehyde (CIN), and isoeugenol (ISO) found in antioxidant essential oils. Using density functional theory (DFT) calculations, some structural characteristics such as molecular descriptors, frontier molecular orbitals, and molecular electrostatic potential have been studied. Three main antiradical mechanisms, hydrogen atom transfer (HAT), single electron transfer proton transfer (SETPT, and sequential proton loss electron transfer (SPLET) have been also investigated. In addition, the Gibbs free energies related to the reactions of the studied compounds with two reactive oxidant species (HO^• and HOO^•) have been computed. Throughout the study, the implicitly of polar and nonpolar solvents (water and benzene) has been taken into account. It was found that EUG, SAF, CIN, and ISO scavenge free radicals by means of a CH bond, while CAR and ISO by means of an OH bond. In the gas and benzene phases, all the studied compounds prefer to undergo HAT mechanism, while in water, SPLET is more favoured for CIN, CAR, and ISO and both HAT and SPLET are possible for EUG, SAF, and MYR. In all the studied mediums, the sequence of the antiradical potential is: MYR ≈ SAF ≈ ISO ≈ EUG > CAR > CIN. This order is in line with the available experimental results.