**4. Conclusion**

A theoretical study on the antioxidant activity of natural pigment delphinidin and its derivative has been evaluated. The antiradical properties of all studied molecules are finalized through an antioxidant mechanism. All compounds follow the HAT mechanism in the gas phase and the SPLET mechanism in the aqueous medium. In gas-phase gallic acid, substituted compounds possess considerable enhancement in activities by providing more hydroxyl groups of near BDEs. In the water medium, **1c** posses a lower value of PA than other compounds. Frontier molecular orbital analysis also supports the radical scavenging activity of compounds. The HOMO-LUMO gap of each molecule increases when the medium

changes from the gas phase to the water medium. Hence all these are more stable in water especially gallic acid-based pigments, so the stability issue of bare pigments in the solvent can be solved by its gallates.
