Is HOMO Energy Level a Good Parameter to Characterize Antioxidant Activity

Semiempirical quantum chemical method AM1 was employed to calculate the highest occupied molecular orbital (HOMO) energy levels (EHOMO) for various types of antioxidants. It was verified that the correlation between logarithm of free radical scavenging rate constants (lgks) and EHOMO substantially arises from the correlation between EHOMO and O-H bond dissociation energies (BDE) of antioxidants. Furthermore, EHOMO were poorly correlated with the logarithm of relative free radical scavenging rate constants (lgk3/k1) for various types of antioxidants that possess complex structures (r = 0.5602). So in a broad sense, EHOMO was not an appropriate parameter to characterize the free radical scavenging activity of antioxidants.