H-bonded oxyhemoglobin models with substituted picket-fence porphyrins: The model compound equivalent of site-directed mutagenesis

Iron(II) complexes of picket-fence-type porphyrins having one of the four pivalamide pickets replaced by a substituent capable of H-bonding have been synthesized as models for oxyhemoglobin. This synthetic approach is analogous to site-directed mutagenesis of the distal residues in oxygen-binding hemoproteins. Rate and equilibrium data for dioxygen binding have been determined to evaluate the effect of the H-bonding substituent and to make comparisons with more passive substituents.