H. Drechsel et al., Spectroscopic studies on iron complexes of different anthracyclines in aprotic solvent systems, INORG CHEM, 40(21), 2001, pp. 5324-5333
Iron complexes of daunorubicin, idarubicin, pirarubicin, and doxorubicin in
anhydrous DMF were studied by UV/vis, CD, fluorescence, Mossbauer, and EPR
spectroscopy. Titration studies of the metal-free anthracyclines showed on
e (UV-detectable) deprotonation step requiring 2 equiv of base, compared to
1 equiv for quinizarine. Metal complexation was studied at three different
metal/ligand ratios, and with increasing amounts of base. The results obta
ined from optical spectroscopy show the existence of two different complex
species and give clear indications for the requirements of metal complexati
on. Complex species I, formed at a low iron-to-ligand ratio, is less depend
ent on base addition than complex species II formed with equimolar ferric i
on. EPR and Mossbauer experiments provide further insight into the structur
es of both complex species. Lack of spin density of the Mossbauer samples i
n EPR indicates spin coupling between the metal centers. Mossbauer spectra
consist of single quadrupole doublets with values typical for high-spin fer
ric ion in an octahedral arrangement. The Mossbauer spectroscopic features
at 7 T exclude the presence of S = 0 dimers. Complex I represents a monomer
ic ferric iron complex whereas complex H is consistent with a more or less
aggregrated oligomeric Fe-anthracycline system.