The TEAC antioxidant activity of 4-hydroxybenzoates

B. Tyrakowska, A.E.M.F. Soffers, H. Szymusiak, S. Boeren, M.G. Boersma, J. Lemanska, J. Vervoort, I.M.C.M. Rietjens

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Abstract

The influence of pH, intrinsic electron donating capacity, and intrinsic hydrogen atom donating capacity on the antioxidant potential of series of hydroxy and fluorine substituted 4-hydroxybenzoates was investigated experimentally and also on the basis of computer calculations. The pH-dependent behavior of the compounds in the TEAC assay revealed different antioxidant behavior of the nondissociated monoanionic form and the deprotonated dianionic form of the 4-hydroxybenzoates. Upon deprotonation the radical scavenging ability of the 4-hydroxybenzoates increases significantly. For mechanistic comparison a series of fluorobenzoates was synthesized and included in the studies. The fluorine substituents were shown to affect the proton and electron donating abilities of 4-hydroxybenzoate in the same way as hydroxyl substituents. In contrast, the fluorine substituents influenced the TEAC value and the hydrogen atom donating capacity of 4-hydroxybenzoate in a way different from the hydroxyl moieties. Comparison of these experimental data to computer-calculated characteristics indicates that the antioxidant behavior of the monoanionic forms of the 4-hydroxybenzoates is not determined by the tendency of the molecule to donate an electron, but by its ability to donate a hydrogen atom. Altogether, the results explain qualitatively and quantitatively how the number and position of OH moieties affect the antioxidant behavior of 4-hydroxybenzoates. Copyright (C) 1999 Elsevier Science Inc.
Original languageEnglish
Pages (from-to)1427-1436
JournalFree Radical Biology and Medicine
Volume27
Issue number11-12
DOIs
Publication statusPublished - 1999

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