The aluminium(III) complex of hypocrellin B as a PDT photosensitizer

The complex of hypocrellin B (HB) with aluminium was synthesized to improve the water solubility and red absorption of the parent pigment. The complex ation of HB with Al3+ resulted in the formation of a complex with 1:1 Al(ii i):HB stoichiometry (Al3+-HB) measured by molar ratio and continuous variat ion methods, respectively. The structure of this complex has been character ized by UV-Vis, IR, H-1 NMR and elemental analysis data. Compared with HB, the complex possesses excellent solubility in water; in addition, the absor ption wavelength of Al3+-HB shifts bathochromically into the phototherapeut ic window (600-900 nm). The generation of active oxygen species, including the superoxide radical anion (O-2(.-)) and singlet oxygen (O-1(2)), by Al3-HB photosensitization was observed. The efficiency of O-2(.-) generation b y Al3+-HB was twice as much as that of HB. Under our experimental condition s, the rate of O-2(.-) generation by Al3+-HB was about 2.3 muM min(-1) meas ured by the cytochrome c reduction method using 578 nm light. The quantum y ield of singlet oxygen (O-1(2)) was 0.23 in DMSO determined by the 9,10-DPA (diphenylanthracene) photobleaching experiments. These results suggest tha t the new complex possesses an enhanced type I process but a decreased type II process as compared with hypocrellin B.