CHEMILUMINESCENCE OF BENZOIC AND CINNAMIC-ACIDS, AND FLAVONOIDS IN THE PRESENCE OF ALDEHYDE AND HYDROGEN-PEROXIDE OR HYDROXYL RADICAL BY FENTON REACTION

Light emission (chemiluminescence; CL) was observed by exciting phenolic compounds with hydrogen peroxide (H2O2) or hydroxyl radical (HO .), formed from H2O2 and FeCl2 by the Fenton reaction. The intensity of the CL of benzoic acid derivatives in the presence of H2O2 was in the order of gallic acid > caffeic acid > 3,5-dimethoxy-4-hydroxycinnamic acid > isovanillic acid = syringic acid. The CL intensity of flavonoids and related compounds, measured in the presence of HO . was in the following order; rutin > myricetin is-approximately-equal-to isoquercitrin > quercetin > kaempferol > isorhamnetin, for the major flavonols; nasunin > rubrobrassicin > delphinidin > cyanidin = malvin > malvidin, for anthocyanins. These results indicated that CL increased with increasing number of vicinal hydroxyl groups to that at C-4 of benzoic acid or its derivatives, and at C'-4 of flavonoids. The data further indicated that glycosylation at C-3 of quercetin enhanced the CL of flavonoids, and that this was dependent on the nature of the sugar moiety, rhamnosylglucose being more effective than glucose. The order of the CL intensity of flavonoids agreed well with that of the radical scavenging activities of these compounds, as determined by ESR and by using a linoleic acid-beta-carotene-lipoxygenase system.