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

Abstract

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 and HB*-) and singlet oxygen (1O2) generated via photosensitization of the preparation in aqueous solution were detected by using electron paramagnetic resonance (EPR) and spectrophotometric methods. It was observed that 1O2 was formed with a quantum yield of 0.72, similar to that for HB in organic solvents, further, hydroxyl radicals (*OH) 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 or 1O2 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, O2*- and HB*-) but also the type II mechanism by singlet oxygen (1O2). It can be concluded further that the new preparation basically maintains the inherent photodynamic activity of HB, or even higher.