Special Articles on Coordination Chemistry of Biologically Important SubstancesNote Complex Formation of a Model Compound of Anthracycline Antibiotics to Fe(lll) Ion and Its Dissociation along with Reduction

1, 8-Dihydroxyanthraquinone (1, 8-DHAQ), one of model compounds for the anthraquinone moiety of some anthracycline antibiotics, forms coordination compounds with iron(Ill) ion in various metal/ligand ratios of 1/1 to 1/3. The EPR spectra show that 1, 8-DHAQ dissociates to give a metal-free semiquinone radical upon electrochemical reduction, though weak interaction with the metal ion still remains. The result suggests possible switching of coordination-dissociation between anthracyclines and metal ions which may be triggered by oxidation-reduction in the processes of redox cycles involved in anthracycline-dependent lipid peroxidation in biological systems where the presence of metal ions is considered to be essential.