Abstract
The interaction of the uranyl(VI) ion (UO22+) with two anthracyclines, adriamycin (Adr) and daunorubicin (Dnr), has been studied by absorption, circular dichroism, fluorescence and NMR spectroscopy. We have shown that both drugs can form two complexes with UO22+, a process strongly dependent on the dielectric constant of the solvent, the metal-to-ligand ratio (R), and the pH. The first complex (I) involves coordination of the metal ion to the [C(11)−O−, C(12)=O] chelating site, while the second complex (II) involves coordination to the [C(6)−O−, C(5)=O] site. In aqueous solutions at pH 6.5, the formation of complex I takes place with two drug molecules per UO22+ ion. At higher pH or R values, complex II forms, and probably has a polymeric structure with one uranyl ion bridging two drug chromophores through both the keto-phenolate sites. In methanolic solutions the simultaneous formation of both complexes I and II is demonstrated by both CD and NMR spectroscopy. Dissociation of the complexes occurs upon interaction of the drug complexes with native DNA, with the free anthracyclines intercalating between the base pairs of the nucleotide.
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