Natural acridones and coumarins as free radical scavengers: Mechanistic and kinetic studies

[Display omitted] •Good radical scavenging activities are found for compounds in Paramignya trimera root.•5-hydroxynoracronycin is the most potential antioxidant against HOO radicals.•The H- atom transfer mechanism is found dominant in water and pentyl ethanoate. In this work, we combined density functional theory (i.e., the M05-2X/6–311++G(d,p)//M05-2X/6–31+G(d) level) and statistical rate models to investigate free-radical scavenging activities of natural compounds found in Paramignya trimera root: four coumarins (i.e., paratrimerins E, paratrimerins F, pandanusin A, xanthyletin) and three acridones (i.e., citrusinine-I, 5-hydroxynoracronycin, paratrimerin C). Reaction mechanisms, including hydrogen atom transfer (HAT), single electron transfer (SET), proton transfer (PT) and radical adduct formation (RAF), were studied thermodynamically and kinetically in different environments: gas-phase, water and pentyl ethanoate (PEA). 5-hydroxynoracronycin is found as the most potential antioxidant with the HAT as the most dominant mechanism in the considered media.