Spectroscopic definition of the geometric and electronic structure of the non-heme iron active site in iron(II) bleomycin. Correlation with oxygen reactivity

Journal Article · Wed Apr 26 04:00:00 EDT 1995 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00121a013· OSTI ID:45026

Loeb, K E; Zaleski, J M; Westre, T E; Hedman, B; Hodgson, K O; Solomon, E I ^[1]; Guajardo, R J; Mascharak, P K ^[2]

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1. Stanford Univ., CA (United States)
2. Univ. of California, Santa Cruz, CA (United States)

The geometric and electronic structure of high-spin ferrous complexes of bleomycin (Fe{sup II}BLM) and the structural analog PMAH ([Fe{sup II}PMA]{sup +}, where PMAH is a macrocyclic ligand with pyrimidine, imidazole, deprotonated amide, and secondary and primary amine functionalities) have been investigated by optical (Abs) and X-ray (XAS) absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopies. The lability of high-spin iron combined with steric constraints of the BLM ligand framework and its weaker axial interaction with solvent support a dissociative mechanism for O{sub 2} reactivity. Our spectroscopic studies of solid [Fe{sup II}PMA]{sup +} have defined the nature of such a five-coordinate intermediate as square pyramidal which provides an open coordination position for reaction with O{sub 2}. A major electronic structure difference between Fe{sup II}BLM (and [Fe{sup II}PMA]{sup +}) and other non-heme ferrous sites is the presence of low-energy CT transitions which reflect strong iron(II) {yields} pyrimidine backbonding. Despite generally being considered a non-heme iron system due to the absence of an extensive delocalized {pi} network, the existence of low-energy MLCT transitions with reasonable intensity, hence the presence of some backbonding, identifies BLM as an important link bridging the chemistry of non-heme and heme active sites. 113 refs., 17 figs., 4 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 45026
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 16 Vol. 117; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ABSORPTION SPECTRA
BLEOMYCIN
ELECTRONIC STRUCTURE
EXCITED STATES
GROUND STATES
IRON COMPLEXES
LIGANDS
MAGNETIC CIRCULAR DICHROISM
MOLECULAR STRUCTURE
RAMAN SPECTRA
STRUCTURAL CHEMICAL ANALYSIS
X-RAY SPECTRA