Electron-nuclear coupling in nitrosyl heme proteins and in nitrosyl ferrous and oxy cobaltous tetraphenylporphyrin complexes.
Electron spin echo envelope modulation (ESEEM) spectroscopy has been used to study electron-nuclear interactions in the following isoelectronic S = 1/2 complexes: NO-FeII(TPP) (TPP = tetraphenylporphyrin) with and without axial nitrogenous base, nitrosylhemoglobin in R and T states, and O2-CoII(TPP) with and without axial base. Only the porphyrin pyrrole nitrogens contribute to the ESEEM of the 6-coordinate nitrosyl FeII(TPP) complexes, nitrosylhemoglobin (R-state), and the nitrosyl complexes of alpha and beta chains. Pyrrole nitrogens in the 5-coordinate complex NO-FeII(TPP) are coupled too weakly to unpaired spin and therefore do not contribute to the ESEEM. A partially saturated T-state nitrosylhemoglobin does not exhibit echo envelope modulations characteristic of 6-coordinate nitrosyl species, which confirms that the proximal imidazole bond to heme iron is disrupted. Study of 6-coordinate O2-CoII(TPP)(L) complexes (L = nitrogenous base) using 14N- and 15N-labeled ligands and porphyrins enabled a detailed analysis of coupling parameters for both pyrrole and axial nitrogens. The pyrrole 14N coupling frequencies are similar to those in NO-FeII(TPP)(L). The Fermi contact couplings for axially bound nitrogen, calculated from simulation of ESEEM spectra for a series of O2-CoII(TPP)(L) complexes (L = pyridine, 4-picoline, 4-cyanopyridine, 4-carboxypyridine, and 1-, 2-, and 4-methylimidazole) illustrate a trend toward stronger hyperfine interactions with weaker bases.
Magliozzo
R S
RS
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
McCracken
J
J
Peisach
J
J
D004578:Electron Spin Resonance Spectroscopy; D005583:Fourier Analysis; D006441:Hemoglobin A; D006454:Hemoglobins; D006801:Humans; D007093:Imidazoles; D007202:Indicators and Reagents; D007501:Iron; D046911:Macromolecular Substances; D008665:Metalloporphyrins; D011725:Pyridines
D006454:Hemoglobins; D007093:Imidazoles; D007202:Indicators and Reagents; D046911:Macromolecular Substances; D008665:Metalloporphyrins; D011725:Pyridines; C008657:nitrosyl hemoglobin; D006441:Hemoglobin A; D007501:Iron