Photodynamic action of hypocrellin A in liposomes

Hypocrellin A (HA), a perylenequinone derivative, is an efficient phototherapeutic agent. When HA is incorporated into small unilamellar liposomes of egg phosphatidylcholine, it generates 1O2 as demonstrated by 9,10-diphenylanthracene (9,10-DPA) photobleaching and detection of nitroxide radicals with ESR. The 1O2 quantum yield measured is 0.80±0.02. On irradiation of oxygen-saturated solution of HA-liposomes, hydroxyl radical OH is detected using DMPO as the ESR spin trapping agent. Hydroxyl radical is derived from superoxide radical anion O2-. The electron transfer reaction is also studied in deaerated solution. The results suggest that the photodynamic action of HA in lipid membranes proceeds via both Type I and Type II reactions.