Kinetic reaction mechanism of sinapic acid scavenging NO2 and OH Radicals: A theoretical study

The mechanism and kinetics underlying reactions between the naturally-occurring antioxidant sinapic acid (SA) and the very damaging NO2 and OH were investigated through the density functional theory (DFT). Two most possible reaction mechanisms were studied: hydrogen atom transfer (HAT) and radical adduct formation (RAF). Different reaction channels of neutral and anionic sinapic acid (SA- ) scavenging radicals in both atmosphere and water medium were traced independently, and the thermodynamic and kinetic parameters were calculated. We find the most active site of SA/SA- scavenging NO2 and OH is the -OH group in benzene ring by HAT mechanism, while the RAF mechanism for SA/SA-scavenging NO2 seems thermodynamically unfavorable. In water phase, at 298 K, the total rate constants of SA eliminating NO2 and OH are 1.30×108 and 9.20×109 M-1 S-1 respectively, indicating that sinapic acid is an efficient scavenger for both NO2 and OH.