| Abstract
| - Observations on the applicability of the ABTS•+ assay to define structure−activity relationships (SARs)among phenols (AH) were based on experimental data and theoretical calculations. All AH examined(hydroxycinnamic derivatives, simple polyphenols, polyhydroxybenzoates, and flavonoids) were foundto be active toward ABTS•+. Moreover, known weak radical scavengers (i.e., coumaric and isoferulicacids) were found to be efficient or comparatively active to caffeic or rosmarinic acids in contradictionto the AH classification based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) data or the bond dissociationenthalpy values. This behavior was observed both in ethanol and in buffered (pH 7.4) environment.Resorcinol and phloroglucin were found to be more active than catechol and hydroquinone, whereas,among polyhydroxybenzoates, 2,4-dihydroxybenzoic acid was the least active, in line with the DPPHand theoretical data. Therefore, it can be argued that the ABTS•+ assay may give an indication forthe presence of antioxidants in a certain system but SARs cannot be readily inferred. Keywords: ABTS•+ assay; DPPH assay; DFT calculations; structure−activity relationship; phenolicantioxidants
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