PHOTOCHEMISTRY OF AQUEOUS ADRIAMYCIN AND DAUNOMYCIN. A SPIN TRAPPING STUDY WITH 17O ENRICHED OXYGEN AND WATER

Abstract— Photolyses at 485 or 490 nm of air saturated, H₂^I7O enriched, aqueous solutions of adriamycin (ADR) in the presence of 5,5-dimethyl-l-pyrroline-l-oxide (DMPO) produce a mixture of hydroxyl radical spin-adducts, i.e. DMPO-¹⁶OH- and DMPO-¹⁷OH-, as detected by electron spin resonance (ESR). DMPO-¹⁷OH- was also observed during the irradiation at these same wavelengths of aqueous solutions of ADR or daunomycin (DA) containing DMPO and ¹⁷O enriched oxygen. Therefore, the observed hydroxyl radical spin-adducts derive from both water and gaseous oxygen. It is concluded from the measured relative spin-adduct concentrations and from the enrichment fractions that most of the DMPO-OH adducts originate from water. However, if anaerobic diluted solutions of ADR (200 μ M ) or DA (600 μM) in the presence of DMPO (13 mM and 27 m M respectively) are irradiated at these same wavelengths no spin adduct is detected, indicating that oxygen is needed for the adduct formation, at these drug and spin trap concentrations. DMPO-OH- is always observed if relatively high concentrations of either the drug (1.1–2.9 mM) or the spin trap(100–150 m M ) are used in argon saturated solutions. A water photooxidation mediated mechanism is proposed in order to account for these results, analogous to previous observations in the photochemistry of other water soluble anthraquinone derivatives.