Transformation of quercetin by singlet oxygen generated by a photosensitized reaction

Quercetin suppressed singlet molecular oxygen-dependent photobleaching of crocin in the presence of rose bengal as a photosensitizer. The suppression by quercetin concurred the transformation of quercetin to a compound which had an absorption maximum at about 330 nm. The rate of the transformation was slowed down by a singlet molecular oxygen quencher, azide. The transformation was suppressed by ascorbate, too. Half of the transformed product was reduced to quercetin by ascorbate. These results suggest that quercetin is converted to a compound which is reducible by ascorbate by a reaction with singlet molecular oxygen.