Hydroxyl and hydroperoxyl radicals scavenging by isoliquiritigenin and liquiritigenin: a quantum chemical study

Scavenging activities of isoliquiritigenin (ISO) and liquiritigenin (LIQ) toward hydroxyl (•OH) and hydroperoxyl (•OOH) radicals were studied using the density functional theory (DFT). Two representative reaction mechanisms, hydrogen atom transfer (HAT) and radical adduct formation (RAF), were investigated. In order to identify the scavenging activity of each active site of ISO and LIQ, the thermodynamic and kinetic parameters of all channels involved in two mechanisms were calculated in both gas and water phases. We found that RAF is the major mechanism of ISO scavenging •OH and •OOH. In the whole reaction of LIQ with •OH/•OOH, B′4-OH group in LIQ is always the most active site, meaning that HAT is the main mechanism of LIQ scavenging •OH/•OOH. For scavenging both radicals, ISO has a much higher activity than LIQ, which is probably due to the nearly planar conjugated conformation of ISO. The calculation results are valuable for designing high-activity scavengers against radicals.