Oxygen Binding to Cobalt Porphyrins

The thermodynamic constants of oxygen binding to cobalt “picket fence” porphyrin complexes, meso-tetra(α,α,α,α-o-pivalamidophenyl)porphyrinatocobalt(II)-1-methylimidazole and 1,2-dimethylimidazole, are reported. In contrast to previously studied cobalt porphyrins, these complexes bind oxygen with the same affinity as cobalt substituted myoglobin and hemoglobin. Solvation effects are discussed as the source of this difference. The use of sterically hindered axial bases as models of T state hemoglobin is discussed.