DFT Investigation of the Solvent and Solute–Solvent Interactions Effects on Thermodynamics and Kinetics Reactivity of Free Radical Scavenging Activity by the Antioxidants Pelargonidin 3,5‐Diglucoside and Pelargonidin 3‐Glucoside Anthocyanins From Pomegranate Flowers

Anthocyanidins are natural compounds soluble in water and known for their various biological activities. They show potent antioxidant activity towards free radicals. Herein, we investigate the effects of different types of polar and nonpolar solvents on the antioxidant activity of pelargonidin 3‐glucoside. Density functional theory calculation has been performed using the hybrid functional M052X and the basis set 6‐31+G(d,p). The solvent effects were considered implicitly by using IEFPCM formalism where acetone, aniline, benzene, water, methanol, chloroform, and cyclohexane are the attested solvents. The antioxidant activity is evaluated by calculating bond dissociation enthalpies of different OH groups (BDEs) and ionization potentials (IP) of pelargonidin 3‐glucoside. In addition, the dipole moment and gap energy in different solvents were determined. The results show that the antioxidant activity of the pelargonidin 3‐glucoside increases with polarity and that water is the favored media for free radical scavenging. The results show that an exponential potential decays of ionization potential with the dielectric constant of the tilted solvent. The favorable mechanism involved in free radical scavenging of free radicals by anthocyanidin pelargonidin 3‐glucoside may depend on both the environment and the reactants. Herein, the effect of the solvent polarity on the stability of the transition state, activation, and the rate constant of the PC‐ET mechanism of OOCH3 free radical scavenging by the pelargonidin 3‐glucoside have been investigated. The obtained results showed that the free radical scavenging by 3‐glucoside may be strongly affected by the environmental media and the type of solvents, that is, polar or nonpolar solvents.