Diazoluminomelanin: a synthetic luminescent biopolymer

The purpose of this work was to synthesize a water-soluble derivative of 5-amino-2, 3-dihydro-1, 4-phthalazinedione (luminol) that generated sustained high level luminescence under physiologic conditions without the necessity of a catalyst. The derivative was made by a diazotization reaction with luminol and 3-amino-L-tyrosine. The resulting orange-brown anionic polymer has been given the trivial name of diazoluminomelanin (DALM). It was water soluble above and insoluble at or below pH 5.0. DALM luminesced when treated with hydrogen peroxide without the presence of a catalyst at pHs ranging from 6.5 to 12.0. Microgram quantities produced high levels of chemiluminescence for longer than 52 hr. Dried polymer generated a long-term stable electron spin resonance spectrum. The long-term chemiluminescence of DALM at pH 6.8-7.4 makes it a potentially useful reagent for detecting free radicals and peroxides in cellular and biochemical preparations.