Metrological aspects of a gas-phase DFT/B3LYP quantum-chemical approach to prioritize radical scavenging activity among a group of olive oil phenols

Abstract

Aim: A protocol relying on quantum chemical calculations to assist prioritization of phenolic compounds as antioxidants in terms of hydrogen atom donation efficiency is presented. The use of reference compounds, an important metrological issue for a future harmonization and standardization of computational approaches in research is also considered. Methods: A density functional theory (DFT) approach, namely B3LYP/6-311G++(2d,2p)//B3LYP/6-31G in the gas-phase was used for structure optimization, frequency calculation and single point energy (SPE) calculation to obtain the bond dissociation enthalpy (BDE) value of the most active O-H of olive oil phenols. For some of them used as a test set and for comparison, BDE values were calculated using three more approaches, M05-2X in the gas-phase, Becke three-parameter Lee-Yang-Parr (B3LYP) and implicit solvent effects (n-heptane to model bulk oils) with the integral equation formalism version of the polarizable continuum model (IEF-PCM), Minnesota 05 functional with double nonlocal exchange (M05-2X) at a single step using 6-31G+(d) basis set and solvation model density (SMD) as solvation model. Phenol and Trolox were used as reference compounds for ΔBDE calculation. Results: The proposed protocol was faster by 1.35-, 1.6-, and 8.3-fold respectively than the other three and provided almost the same activity trend application to other type of olive oil phenols indicated that prioritization based on ΔBDE values was in accordance with the limited existing experimental findings in bulk oils, and the order of activity was generally in agreement with the structure-antioxidant activity criteria. Conclusions: Present findings highlighted the usefulness of quantum chemical calculations as a tool to screen/prioritize molecules with an established structure saving experimental effort and waste production. The expression of results relatively to phenol and Trolox BDE values, may assist comparisons among research findings and facilitate standardization. Based on the findings hydroxytyrosol and related compounds should be efficient hydrogen atom donors compared to other potent virgin olive oil phenols.