Photosensitization mechanism of active species by the complex of hypocrellin B with aluminum ion

To improve the water solubility and red absorption of the parent hypocrelli n B (HB), the complex of HB with aluminum ion has been first synthesized in high yield. The photodynamic action of Al3+-HB, especially the generation mechanism of active species, ([Al3+-HB](.-), O-2(.-) and O-1(2)) was studie d using electron paramagnetic resonance (EPR) and spectrophotometric method s. In the deoxygenated DMSO solution of Al3+-HB, the semiquinone anion radi cal of Al3+-HB is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significa ntly promotes the reduction of Al3+-HB. When oxygen is present, superoxide anion radical (O-2(.-)) is formed via the electron transfer from [Al3+-HB]( .-) to the ground state molecular oxygen. Singlet oxygen (O-1(2)) can be pr oduced via the energy transfer from triplet Al3+-HB to ground state oxygen molecules. Furthermore, it is very significant that the accumulation of [Al 3+-HB](.-) would replace that of O-2(.-) or O-1(2) with the consumption of oxygen in the sealed system.