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4283421 
Journal Article 
Comparative antioxidant potency and solvent polarity effects on HAT mechanisms of tocopherols 
Bakhouche, K; Dhaouadi, Z; Jaidane, N; Hammoutene, D 
2015 
1 
Computational and Theoretical Chemistry
ISSN: 2210-271X
EISSN: 2210-2728 
1060 
58-65 
WOS:000353745400009 
The antioxidant activity of the four forms of tocopherol has been investigated in gas phase and in different solvents using PBE0/6-31+G(d) level of theory. The three main working mechanisms, homolytic hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) have been considered. The O-H bond dissociation free energy (BDFE), ionization potential (IP), proton dissociation free energy (PDFE), proton affinity (PA) and electron transfer free energy (ETFE) parameters have been calculated in gas phase and solvents. The theoretical results show the effect of the substituent position with respect to the phenolic O-H group on the reactivity. The methyl group, in ortho position, lends additional inductive and steric stability to the tocopheroxyl radical and therefore, increases antioxidant activity. cc-tocopherol is shown to be the most reactive form in gas phase with the lowest BDFE, IP, and PA values, whereas in all solvents, gamma-tocopherol has the lowest PA and PDFE values.



The solvent effects are evaluated using an implicit salvation model (IEF-PCM). We have used a good model to calculate the salvation free energy of proton and electron in different media, where proton or electron was attached to one molecule of solvent and the obtained species were optimized using IEF-PCM approach in the same solvent. In gas phase, and non-polar solvents like benzene and toluene, BDFE value is lower than PA and IP, this suggested that HAT would be the most favorable mechanism for explaining the antioxidant activity of tocopherols, whereas SPLET mechanism is thermodynamically preferred in polar solvents like water, DMSO and methanol, where PA value of all forms of tocopherol is considerably lower than BDFE and IP. (C) 2015 Elsevier B.V. All rights reserved. 
Tocopherols; Antioxidant activity; Inductive effect; Solvent effect; Free energy