Determination of hydrogen peroxide scavenging activity of cinnamic and benzoic acids employing a highly sensitive peroxyoxalate chemiluminescence-based assay: structure-activity relationships.

A series of cinnamic acids along with their corresponding benzoate analogues were tested for their ability to scavenge hydrogen peroxide (H(2)O(2)), by using a highly sensitive, peroxyoxalate chemiluminescence assay. Among benzoic acid derivatives, vanillic acid (3-hydroxy-4-methoxybenzoic acid) was found to be the most efficient H(2)O(2) scavenger with its hydrogen peroxide scavenging activity (SA(HP)) being 170.20 microM(-1), whereas protocatechuic acid (3,4-dihydroxybenzoic acid) exhibited the weakest activity (5.90 microM(-1)). Caffeic acid (3,4-dihydroxycinnamic acid) was the strongest antioxidant amongst cinnamate derivatives with a SA(HP) = 8.2 microM(-1), as opposed to m-coumaric acid (2-hydroxycinnamic acid), which was found to be a poor hydrogen peroxide scavenger (SA(HP) = 0.18 microM(-1)). Comparison between the two groups revealed that benzoate derivatives are much stronger hydrogen peroxide quenchers in relation with their cinnamate analogues, and this finding was discussed on a basis of structure-activity relationships and comparative assessment of other antioxidant characteristics.