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 phenol ic compounds with hydrogen peroxide (H2O2) or hydroxyl radical (HO .), formed from H2O2 and FeCl2 by the Fenton reaction. The intensity of t he CL of benzoic acid derivatives in the presence of H2O2 was in the o rder of gallic acid > caffeic acid > 3,5-dimethoxy-4-hydroxycinnamic a cid > isovanillic acid = syringic acid. The CL intensity of flavonoids and related compounds, measured in the presence of HO . was in the fo llowing order; rutin > myricetin is-approximately-equal-to isoquercitr in > quercetin > kaempferol > isorhamnetin, for the major flavonols; n asunin > rubrobrassicin > delphinidin > cyanidin = malvin > malvidin, for anthocyanins. These results indicated that CL increased with incre asing 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 indic ated that glycosylation at C-3 of quercetin enhanced the CL of flavono ids, and that this was dependent on the nature of the sugar moiety, rh amnosylglucose being more effective than glucose. The order of the CL intensity of flavonoids agreed well with that of the radical scavengin g activities of these compounds, as determined by ESR and by using a l inoleic acid-beta-carotene-lipoxygenase system.