Photogeneration of free radicals (•OH and HB•-) and singlet oxygen (1O2) by hypocrellin b in TX-100 micelles microsurroundings

To solve the problems faced in clinical use of hypocrellins, a water-soluble preparation of Hypocrellin B (HB), HB-Triton X-100 (TX-100) micelles, was prepared. To evaluate the photodynamic activity, the free radicals ((OH)-O-. and HB .macr ) and singlet oxygen (O-1(2)) generated via photosensitization of the preparation in aqueous solution were detected by using electron paramagnetic resonance (EPR) and spectrophotometric methods. It was observed that O-1(2) was formed with a quantum yield of 0.72, similar to that for HB in organic solvents, further, hydroxyl radicals ((OH)-O-.) could also be efficiently produced by the new preparation, which have never before been detected following HB photoactivities. In addition, the semiquinone anion radicals (HB.-) could also be generated via the self-electron transfer between an excited triplet state and a ground state molecule. The accumulation of HB.- would replace that of (OH)-O-. or O-1(2) with the depletion of oxygen in the system. All these findings suggested that the HB-TX-100 micelles could play the photodynamic action through not only the type I mechanism by free radicals ((OH)-O-., O-2(.-) and HB.-) but also the type II mechanism by singlet oxygen ((1) O-2). It can be concluded further that the new preparation basically maintains the inherent photodynamic activity of HB, or even higher.