Study on the structure-activity relationship of derivative antioxidants of cinnamic acid

Chlorogenic acid, forsythiaside and other derivatives of cinnamic acid are active components of Chinese herbs. In this paper, their scavenging effects on HO are studied by the o-phenathroline chemiluminescent system. The experimental results were elucidated by the quantum chemistry calculation (3-21G, B3LYP). The relationships of structure-activity indicate that DeltaE value, the difference of the energy between the mother molecule and its free radical, is a better parameter to represent the activity of phenolic antioxidants to scavenge free radicals. Forming of intramolecular hydrogen bonding or ortho bezoquinone structure through resonance between the serniquinonoid free radical and ortho group can stabilize the semiquinonoid free radical. The semiquinonoid free radical can be further stabilized by the electron-providing substitutive group in the para position of the H-abstraction hydroxyl.