Radical Scavenging Potential of Phenolic Compounds Encountered in O. europaea Products as Indicated by Calculation of Bond Dissociation Enthalpy and Ionization Potential Values

The radical scavenging potential of phenolic compounds occurring in Olea europaea and of recently identified hydroxytyrosol metabolites was evaluated by means of quantum chemical calculations. The bond dissociation enthalpy (BDE) of phenolic hydroxyl groups and the ionization potential (IP) were calculated as descriptors to predict the H-atom-donating and electron-donating abilities of antioxidants, respectively. Catechol derivatives had the lowest BDE values (77.7−80.1 kcal/mol) whereas the lignans, pinoresinol and 1-acetoxypinoresinol, and other monophenols had much higher BDE values (85.1−88.0 kcal/mol), which suggested a lower potential for radical scavenging. Side chain characteristics were not found to affect the size of BDE values although differences in lipophilicity (on the basis of calculated Log P values) indicate variability in the activity in real systems. Conclusions for the antioxidant potential could not be drawn based on the IP values. Lack of experimental data for most of the studied compounds due to oxidative instability and difficulties in synthesis or isolation supports the usefulness of a computational approach for those interested in the antioxidant potential of phenolics encountered in O. europaea products. Keywords: Bond dissociation enthalpy; density functional theory; ionization potential; lignans; O. europaea products; oleuropein; hydroxytyrosol metabolites