STUDIES ON THE CHELATION OF HYPOCRELLIN-A WITH ALUMINUM ION AND THE PHOTODYNAMIC-ACTION OF THE RESULTING COMPLEX

Hypocrellin A (HA), a perylenoquinone derivative, is an efficient phot otherapeutic agent. The chelation of HA with aluminium ion (Al3+) resu lts in the formation of a 1:1 complex (Al3+-HA). The probable structur e for this complex has been proposed. Compared with HA, this complex h as a much higher solubility in water. In addition, Al3+-HA preserves t he O-1(2)-generating function of HA as demonstrated by diphenylanthrac ene photobleaching experiments. In irradiated oxygen-saturated solutio ns of Al3+-HA superoxide radical anion and hydroxyl radical are formed as verified using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the elec tron spin resonance (ESR) spin trapping agent. The production of super oxide radical anion is enhanced significantly in the presence of elect ron donors such as 1-benzyl-1,4-dihydronicotinamide (BNAH). These resu lts suggest that the photodynamic action of Al3+-HA proceeds via both type 1 and type 2 reactions.