Chelation of hypocrellin B with zinc ions with electron paramagnetic resonance (EPR) evidence of the photodynamic activity of the resulting chelate

Hypocrellin B (HB), a perylenequinone derivative, is an efficient photother apeutic agent. The chelation of HB with Zinc ions (Zn2+) results in a metal chelate (Zn-HB) which exhibits considerable absorption (lambda (max) = 612 nm) in the phototherapeutic window. The structure of this chelate has been characterized by U-V-Vis, IR and mass spectra. The redox potentials of the Zn-HB chelate were E-ox = + 1.1V (vs. SCE) and E-re = -0.7V (vs. SCE) as m easured using the circle volt curve. The quantum yield of singlet oxygen ge nerated by the Zn-HB chelate was 0.86, which both the electron spin trap (E PR) method and the chemical trap method show to be about 0.1 higher than th at of its parent compound HB. In irradiated oxygen-saturated solutions of Z n-HB chelate, superoxide radical anions and hydroxyl radicals were detected by EPR spectroscopy using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the s pin-trapping agent.