Journal of the American Chemical Society, Vol.117, No.16, 4545-4561, 1995
Spectroscopic Definition of the Geometric and Electronic-Structure of the Nonheme Iron Active-Site in Iron(II) Bleomycin - Correlation with Oxygen Reactivity
The geometric and electronic structure of high-spin ferrous complexes of bleomycin (Fe(II)BLM) and the structural analog PMAH ([Fe(II)PMA](+), 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. From the excited state ligand field transition energies in the low-temperature MCD spectra, the XAS pre-edge shapes and intensities, and EXAFS analysis, solid [Fe(II)PMA](+) has been determined to have a five-coordinate, square-pyramidal geometry (E(dx2-y2) - E(dz2) = 6100 cm(-1)) with a short Fe-N bond (1.93 Angstrom), while in solution [Fe(II)PMA](+) binds a solvent molecule at the sixth position to form a distorted octahedral complex (E(dx2-y2) - E(dz2) = 2110 cm(-1)) with an expanded coordination sphere which still maintains one short Fe-N bond (2.00 Angstrom).
Keywords:X-RAY ABSORPTION;MAGNETIC-CIRCULAR-DICHROISM;SYNTHETIC ANALOG APPROACH;AROMATIC NITROGEN-HETEROCYCLES;CARBON-MONOXIDE COMPLEX;CHARGE-TRANSFER;METAL-BINDING;THEORETICAL INVESTIGATIONS;RESONANCE SPECTROSCOPY;DEOXYRIBONUCLEIC-ACID