Fe III Hemin Compounds

Iron-Porphyrin Model Compounds A. Fe(III) Hemin Compounds 

There have been two additional experiments which verified this basic picture of the nuclear hyperfine interaction in hemins. Johnson (78) increased the spin-lattice relaxation time by performing the Mossbauer experiment under field and temperature conditions which provide a large value of H/T. At 1.6 °K and in an applied field of 30 kG, a magnetic hyperfine interaction corresponding to that expected for high spin Fe(III) and for the g-values is measured experimentally. Recently, Lang et al. have found that a portion of hemin chloride dissolved in tetrahydro-furan at 1 mM concentration displays a hyperfine interaction at 4 °K in zero applied magnetic field. Their conclusion is that a portion of the hemin is present in a monomeric form in this solvent, a situation which is not apparent to any extent in water, acetic acid, chloroform, or dimethyl sulfoxide (77) at any concentrations used. 

Chloroprotohemin in pyridine solution shows a different behavior two quadrupole fine pairs replace the single quadrupole fine pair for chloroprotohemin in aqueous solution. The wide quadrupole splitting (1.8 mm/S) of the new line pair is more characteristic of Mossbauer spectra obtained for methemoglobin these spectra will be discussed in the next section, but it suffices to point out here that the pyridine coordination produces an environment more nearly like the hexacoordinated environment of the iron in the hemoproteins (78). 

Mossbauer data for 2,4 diacetyl deuteroporphyrin IX dimethyl ester and Fe(II) protoporphyrin IX obtained at 77 °K show isomer shifts 

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