Theoretical studies on the antioxidant activity of pinobanksin and its ester derivatives: Effects of the chain length and solvent

- Replacing the 3-hydroxyl by ester group with different alkyl chains does not change much of the antioxidant activity of pinobanksin.
- Solvent effects can alter the thermodynamically preferred mechanisms.
- The 7-hydroxyl contributes mainly to the antioxidant activities of the investigated compounds.

The effects of the ester group and solvent on the structure and antioxidant activity of pinobanksin were carried out using DFT calculation. First, the properties of the intramolecular hydrogen-bonds in the investigated compounds were studied. Second, the antioxidant capacities of the investigated compounds were analyzed by HAT, SET-PT and SPLET mechanisms from thermodynamic point. The conclusions are: (1) HAT mechanism is most favorable in the gas and CCl4 phases, while SPLET mechanism is more favored in the CH3CN and H2O phases. In the CHCl3 phase, the thermodynamically preferred mechanism is HAT for the 3−OH and 5−OH groups. While, HAT and SPLET mechanisms may run simultaneously for the 7−OH group. (2) Replacing the 3−OH group by ester group with different alkyl chains does not change much of the antioxidant activity of pinobanksin. (3) Besides, the 7−OH group contributes mainly to the antioxidant activities of the investigated compounds.