Effects of Gold Nanoparticles on the Antioxidant Power of Gallic Acid: A Computational Investigation Using a Cluster Model

Computational approaches within the framework of density functional theory (DFT) are used to probe the effects of gold nanoparticles (AuNPs) on the antioxidant potency of gallic acid (H₄GA), which is a prototypical polyphenolic acid. Four small gold clusters, Au _<i>n</i> with <i>n</i> = 2, 3, 6, and 11, are employed as simple models to simulate the surface of AuNPs. The antioxidant capacity is evaluated through the ability to donate a hydrogen atom and to transfer an electron, which are characterized by the bond dissociation enthalpy (BDE) and ionization energy (IE) of the antioxidant, respectively. The reactions of both H₄GA and its anionic conjugate H₃GA^- toward the hydroperoxyl radical (HOO^•) are examined following the formal hydrogen atom transfer (HAT) mechanism. The assembly of either H₄GA or H₃GA^- on nanostructured Au surfaces can be used as an effective strategy to greatly improve the antioxidant activity, instead of modifying the chemical structure of the antioxidant. Molecular docking computations reveal some key interactions between GA-Au₁₁ clusters and lipoxygenases, highlighting their antioxidant potential. These findings emphasize the importance of specific molecular features in enhancing antioxidant activity and offering insights for the development of more effective antioxidants.