Investigation of the scavenging mechanism of tyrosyl radical by hydroxybenzohydroxamic acid derivatives: A DFT study

The free radical scavenging activity of a series of hydroxybenzohydroxamic acid derivatives have been studied in gas phase, water and benzene environments, using the density functional theory. Different mechanisms of reactions have been considered: single electron transfer (SET), hydrogen atom transfer (HAT). Rate constants were determined to know if the radical scavenging activity of these compounds proceeds via an H-atom or an electron-transfer mechanism. Calculations showed that the presence of the adjacent hydroxyl groups on phenyl ring increases the radical stability through intramolecular hydrogen bonds. The calculated bond dissociation enthalpy (BDE) values for hydroxyl groups on phenyl ring of studied compounds revealed the important role of resonance in stability of radical obtained from the hydrogen atom abstraction by free radical. Results show that the radical scavenging capacity of trimidox is more than the other molecules. The results demonstrate that the H-atom transfer mechanism for scavenging of free radical is more preferable than the single-electron transfer in considered environments.