UV-VISIBLE AND ELECTRON-SPIN-RESONANCE STUDY OF MERCAPTO-SUBSTITUTED HYPOCRELLIN-B - PHOTOGENERATION OF SEMIQUINONE RADICAL-ANION AND SUPEROXIDE

Mercapto-substituted hypocrellin B derivatives (MHBDs), display, in th e absence of electron donors, a characteristic absorbance peak and ele ctron spin resonance (ESR) signal, which can be attributed to the semi quinone radical anion, formed by intermolecular electron transfer. In the presence of electron donors, the amplitude of the ESR signal incre ases significantly. irradiation of MHBDs in the presence of oxygen lea ds to the generation of superoxide radicals, which may be registered b y the spin trapping technique; the formation mechanism of superoxide i n the absence or presence of electron donors is discussed. The free ra dicals and superoxide radicals formed on photoirradiation of MHBDs may play a hitherto unrecognized role in biological processes. (C) 1997 E lsevier Science S.A.