Scavenging of Hydrogen Peroxide by Allyl Methyl Sulfide and Diallyl Sulfide, Two Garlic Active Compounds: A Theoretical Study

Abstract

We study potential scavenging of hydrogen peroxide by Allyl Methyl Sulfide and Diallyl Sulfide, two garlic components. The antioxidant properties of garlic are attributed to organosulfide compounds, which react with reactive oxygen species preventing the oxidative stress. We used the B3LYP functional for structure analysis and M06-2X functional for the reactions employing gaseous, aqueous and non-polar environments. The conformational analysis and Fukui functions allowed the selection of the initial structures and the region of nucleophilic attack by hydrogen peroxide. The scavenging reactions analyzed are: 1) Sulfoxidation; 2) Epoxidation; and 3) Hydrogenation. Through the intrinsic reaction coordinate, the energy profile, the activation energies, the rate constant and its temperature-dependence were calculated. The results predict that reactions occur slowly and hydrogenation is not a feasible process. Finally, the sulfoxidation of Allyl Methyl Sulfide and Diallyl Sulfide resulted to be more thermodynamically and kinetically favorable than epoxidation (rate constant values, 10−10 s−1, in comparison with 10−18 s−1 from epoxidation), becoming the most probable pathway for hydrogen peroxide scavenging.