Iron-ligand bonding properties of synthetic iron-porphyrin complexes with oxygen transporting ability in aqueous media

Mössbauer spectra, i.r. spectra (Fe-CO stretching), and photodissociation quantum yields of the oxygen and CO adducts were measured for synthetic iron-porphyrin complexes with oxygen transporting ability in aqueous media: the 5,10,15,20-tetra{α-o-[2′,2′-dimethyl-20′-(2″- trimethyl-ammonioethylphosphonatoxy)eicosanamido]phenyl}porphyrinatoiron(II) (lipid-heme) complex of 1-laurylimidazole (lauryl = dodecyl) or 1-lauryl-2-methylimidazole embedded in the bilayer of phospholipid liposome (abbreviated as liposome-lipid-heme) and the tetradecyl-substituted copper-iron(II)-diporphyrin (diheme) complex of 1-laurylimidazole solubilized in a surfactant micelle (micelle-diheme). The quadrupole splitting (ΔE_Q) for the CO adduct of the diheme indicated a large electric-field gradient at the iron nucleus, probably due to steric hindrance of the diheme structure. Its CO-stretching vibration (ν_CO) and photodissociation quantum yield (Φ), obtained by flash photolysis, were similar to those of carboxy hemoproteins and suggested the distorted ligation of CO to Fe. Mössbauer parameters for the oxygen adducts of liposome-lipid-heme and micelle-diheme in aqueous media agreed with those for the oxy hemoproteins.