Selection of theoretical parameter characterizing scavenging activity of antioxidants on free radicals

Semiempirical quantum chemistry method Austin Model 1 (AM1) was employed to calculate the theoretical parameters of 15 antioxidants. Such parameters as bond order, bond length, and the difference of heat of formation (Delta HOF) between the antioxidant and its phenolic free radicals were obtained. Through correlating with previous experimental results Delta HOF was proven to be a proper parameter (r = 0.9491) to characterize the free radical-scavenging activity of antioxidants, but bond order and bond length were not able to represent the antioxidant's ability to scavenge free radicals. By comparing the results calculated by different semiempirical methods, including AM1, Modified Neglect of Diatomic Overlap, and Parametric Method 3, AM1 was found to be the best for calculating Delta HOF.