H‐atom acceptor capacity of free radicals used in antioxidant measurements

Abstract

AbstractAntioxidants 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•), and indirectly to labile H‐atoms of the R•‐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• and LOO• 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. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011