Abstract
Antioxidants are well-known for their beneficial effects on human health. Their capacity to scavenge free radicals mainly depends on their capacity to transfer H atoms to free radicals (R-center dot), and indirectly to labile H-atoms of the R-center dot-parent molecule (R-H). The aim of this study was to select an accurate method to estimate bond dissociation enthalpies (BDEs) of ROO-H, LOO-H and DPPH-H. ROO center dot and LOO center dot are radicals involved in lipid peroxidation and DPPH is a free radical used to measure antioxidant activities. BDE(ROO-H) was systematically calculated with more than 20 different methods (HF, post-HF and DFT). This methodology was performed on three ROO-H prototypes (HOO-H, CH3OO-H, and CH3CH2OO-H) for which theoretical BDEs were compared to experimental BDEs. B3P86 and BHandH/6-31+G(d,p) appeared as the best compromises. The influence of R chain length and conjugation degree on BDEs was studied with DFT. Both parameters did not significantly change BDE(ROO-H), except when intra H bonding was formed. The DPPH-H BDE was accurately calculated with B3P86. This functional could definitely be considered as a good compromise since it also gave a reliable estimation of O-H BDE for polyphenols. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1131-1142, 2011