PHOTOCHEMISTRY OF AQUEOUS ADRIAMYCIN AND DAUNOMYCIN. A SPIN TRAPPING STUDY WITH17O ENRICHED OXYGEN AND WATER

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Abstract
Abstract—Photolyses at 485 or 490 nm of air saturated, H2I7O 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 and17O 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 (200μ M) or DA (600μM)in the presence of DMPO (13mMand 27 mMrespectively) 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 mM) 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.