Photosensitization of hypomycin B - A novel perylenequinonoid pigment withonly one intramolecular hydrogen bond

Electron spin resonance technique and spin-trapping methods were used to de termine the photoproduction of O-1(2) and O-2(.-) by hypomycin B (HMB), a n ovel perylene-quinonoid pigment (PQP) possessing only one hydroxyl group. I t was found that the yields of O-1(2) and O-2(.-) for HMB were comparable t o those for hypocrellin A, a typical natural PQP with good photosensitivity . In addition, the absorption and fluorescence spectra for HMB were investi gated. The pKa values in the ground and excited states of HMB were determin ed to be 8.94 and 5.54, respectively. Thus, the photodynamic mechanisms of HMB may involve not only the photogeneration of O-1(2) and O-2(.-) but also the light-induced acidification. Consequently, HMB is proposed to be a goo d photodynamic therapeutic agent.