[Quenching of singlet molecular oxygen by screening pigments-- melanins and ommochromes]

Synthetic DOPA-melanin and natural screening pigments--sepiomelanin and ommochromes are shown to quench the luminescence of singlet molecular oxygen (1O2) in aqueous (D2O, pD = 7.5-8.1) solutions. The rate constants of 1O2 quenching are found to be equal to (1.2 +/- 0.6) 10(8) M-1 s-1 for monomeric units in DOPA-melanin and to (3 +/- 1) 10(6) M-1 s-1 for ommochromes. The data suggest that screening is not the only function of melanins, which may play a role of inhibitors of photodynamic damage in living tissues.