ESR and UV-Vis studies of semiquinone radical anion and hydroquinone generated by irradiation of 15-Deacetyl-13-glycine substituted hypocrellin B

Abstract

15-Deacetyl-13-glycine substituted hypocrellin B (GDHB) is a new type of hypocrellin derivative with enhanced red absorption longer than 600 nm and water solubility. When an anaerobic DMSO or DMSO-buffer (pH 7.4) solution of GDHB was illuminated with > 470 nm light, a strong electron spin resonance (ESR) signal was formed. The ESR signal was assigned to the semiquinone anion radical of GDHB (GDHB^·-) based on a series of experiments. GDHB^·- was predominantly photoproducted via the self-electron transfer between the excited- and ground-state species. Decay of this species, both in the presence and absence of electron donor, was consistent with second-order kinetics. In aqueous solution, the TEMPO counterspin experiment indicated the formation of GDHB^·- that could not be detected by ESR method directly. The formation of GDHB^·- and hydroquinone of GDHB (GDHBH^·-) was also confirmed by spectrometric method. These findings suggested that GDHB was at least a favorable type I phototherapeutic agent.

Keywords:

• 15-Deacetyl-13-glycine substituted HB
• semiquinone anion radical
• hydroquinone
• ESR spectra
• spin counteraction
• spectrophotometric measurements