A Quantum Chemical Investigation on the Antioxidant Activity of Licoisoflavone Derivatives

In this paper,21 substituents with various electron donating and electron withdrawing characters were placed in the available positions of Licoisoflavone in order to study their effect on the three O-H bond dissociation enthalpies and ionisation potential via DFT/B3LYP method.Results show that the B-ring is more important than the A-ring from the BDE and IP point of view because the radical structure formed after hydrogen atom abstraction from the 4-OH group can be stabilized by the resonance between the three rings.The results show that intramolecular hydrogen bonding effects are able to considerably stabilize the parents and radicals.The NBO analysis results also confirmed the intramolecular hydrogen bond stabilization.The formation of strong intramolecular hydrogen bonds and suitable spin density distributions in several radicals result in low BDE and IP values.The calculated BDE and IP values have been correlated with Hammett constants.The found dependencies are suitably linear,which can be important for the synthesis of novel antioxidants based on Licoisoflavone.