Theoretical Studies on the Radical Scavenging Activity of Bergenin and Gallic acid Isolated from the Roots of Shorea beccariana Burck

This study aims to compare the antioxidant activities of gallic acid and bergenin from the roots of Shorea beccarian using both experimental and computational approaches. Isolation and structural characterization of the compounds were performed using UV-Vis, IR, and NMR spectroscopy, while antioxidant activity was assessed in vitro using the DPPH method. The results showed that gallic acid exhibited very strong antioxidant activity (IC₅₀ = ۴۸.۳۱ ppm), whereas bergenin displayed moderate activity (IC₅₀ = ۱۴۸.۰۰ ppm). Computational studies were conducted to evaluate antioxidant mechanisms through hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) pathways against DPPH• and HOO• radicals. Gallic acid demonstrated lower bond dissociation energy (BDE) and Gibbs free energy (ΔG), particularly via the HAT mechanism, indicating a higher radical-scavenging ability. Kinetic analysis revealed that gallic acid TS(a) had the lowest activation energy (ΔG‡ ۵,۵۳ kcal/mol) and the highest rate constant (k = ۲.۶۰×۱۰۹ s⁻¹), while bergenin TS(b) showed a high reaction rate but formed less stable products. Quantum parameters (Egap, η, ω) further supported that gallic acid is more electrophilic and electronically reactive than bergenin. Overall, gallic acid was found to be superior as an antioxidant both thermodynamically and kinetically, predominantly acting through the HAT mechanism, providing valuable insights for the design of more effective antioxidant compounds.

کلیدواژه ها:

Antioxidant activity ، bergenin ، Gallic acid ، Shorea beccariana