Theoretical investigation on the antioxidative activity of anthocyanidins: A DFT/B3LYP study

• Anthocyanidins.
• Antioxidative activities.
• DFT theoretical study.
• Structure–activity relationship.

Anthocyanidins are an important class of plant pigment, in the present work the antioxidative properties of anthocyanidins have been explored by density functional theory calculations, three main antioxidative mechanisms, which include H atom transfer (HAT), single electron transfer (SET) and sequential proton loss electron transfer (SPLET), have been investigated at B3LYP/6-311G(d,p) level of theory. The O–H bond dissociation enthalpies (BDEs), ionization potentials (IPs), electron affinities (EAs), proton affinities (PAs) and electron transfer enthalpies (ETEs) are investigated in gas phase and aqueous solution. Results show 3-OH and 4′-OH posses lower BDE as compared to other OH groups, the substituents in B-ring influence 4′-OH BDE, but exhibit negligible influence on other OH BDEs. Among all investigated anthocyanidins, pelargonidin has the highest IP and EA in gas phase, substituent in ortho position of 4′-OH leads to remarkable decrease in IP and EA. OH substituent in B-ring almost show no influence on PAs and ETEs of 3-, 5-, and 7-phenolate anions, but OCH3 substituent influence them significantly. For PAs and ETEs of 4′-phenolate anion, two types of substituents both exhibit remarkable influence. Base on the simplest anthocyanidins, pelargonidin, molecular simplification has been performed to explore the necessary pharmacophores responsible for the antioxidative activity of anthocyanidins.