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

Abstract

To improve the water solubility and red absorption of the parent hypocrellin 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 1O2) was studied using electron paramagnetic resonance (EPR) and spectrophotometric methods. In the deoxygenated DMSO solution of Al3+-HB, the semiquinone anion radical of Al3+-HB is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significantly 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 (1O2) can be produced via the energy transfer from triplet Al3+-HB to ground state oxygen molecules. Furthermore, it is very significant that the accumulation of [Al3+-HB]·- would replace that of O·-2 or 1O2 with the consumption of oxygen in the sealed system.