PHOTODYNAMIC-ACTION OF HYPOCRELLIN-A IN LIPOSOMES

Hypocrellin A (HA), a perylenequinone derivative, is an efficient phot otherapeutic agent. When HA is incorporated into small unilamellar lip osomes of egg phosphatidylcholine, it generates O-1(2) as demonstrated by 9,10-diphenylanthracene (9,10 DPA) photobleaching and detection of nitroxide radicals with ESR. The O-1(2) quantum yield measured is 0.8 0+/-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 O-2( .-). The electron transfer reaction is also studied in deaerated solut ion. The results suggest that the photodynamic action of HA in lipid m embranes proceeds via both Type I and Type II reactions.