Transient intermediates in the reduction of Fe(III) myoglobin-ligand complexes by electrons at low temperature

Abstract

1. 1.|The reductions of a number of sperm-whale Fe(III) myoglobin-ligand complexes by electrons generated by γ-irradiation in ethylene glycol/water glass, have been investigated by using low-temperature spectrophotometry. The ligands are azide, fluoride, imidazole and water. 2. 2.|The reduction of the Fe(III) myoglobin-ligand complexes at 77 K leads to the formation of low-spin liganded Fe(II) myoglobin, in the case of the azide, imidazole and water derivatives, while the reduction of the fluoride derivative proceeds both by a pathway involving prior dissociation of the ligand and with the ligand in position. 3. 3.|Investigation of the effect of temperature on the stability of the Fe(II) myoglobin-ligand complexes indicates that more than one bound states exists in dissociation of the ligand molecule from the ferrous heme iron of the reduced azide and imidazole derivatives. 4. 4.|The results are discussed in terms of the possible structure of the Fe(II) myoglobin complexes and it is suggested that the low-spin state is created by a strained configuration of the heme center with the iron atom in an intermediate position relative to the heme plane.