F. Neese, J. Zaleski, A. Zaleski
Nov 10, 2000
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Journal
Journal of the American Chemical Society
Abstract
Bleomycin (BLM) is a glycopeptide antibiotic produced by the fungus Streptomyces verticillus which is used clinically for anticancer therapy. It is most active as an iron complex. A detailed spectroscopic and theoretical study of the ferric form of the drug, Fe(III)BLM, and its activated form, ABLM, is reported. ABLM, which has been shown to be a ferric hydroperoxide complex, is the last detectable intermediate in the reaction cycle of BLM that leads to a DNA radical and subsequent cleavage. Both forms of the drug are low-spin Fe(III) complexes and were studied with electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and absorption (ABS) spectroscopy. In addition, resonance Raman (rR) and circular dichroism (CD) spectra are reported for Fe(III)BLM. The g matrix was analyzed in detail, and Griffith's model for low-spin d5 complexes was experimentally evaluated. A ligand field analysis of the d−d region of the optical spectra resulted in a complete determination of the ligand field par...