TEAC antioxidant activity of 4-hydroxybenzoates |
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Authors: | Tyrakowska B Soffers A E Szymusiak H Boeren S Boersma M G Lemańska K Vervoort J Rietjens I M |
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Affiliation: | Faculty of Commodity Science, Poznań University of Economics, Poland. btyrak@novci1.ae.poznan.pl |
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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. |
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Keywords: | 4-Hydroxybenzoates Antioxidant activity TEAC value pH dependency Mechanism Computer calculations Quantitative structure activity relationship Free radicals |
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