Fixation of Zinc(II) Ion to Dioxygen in a Highly Deformed Porphyrin: Implications for the Oxygen Carrier Mechanism of Distorted Heme

Three saddle-type nonplanar zinc porphyrins strapped
by two short alkyl linkers have been synthesized. The deformation
induced by the linkers can cause a spectral red shift of >30 nm
compared
with the absorption maxima of regular porphyrins and can also regulate
the electronic structure of the central zinc­(II) ion. The zinc­(II)
ion then complexes and activates a free dioxygen to form a superoxide
group ligand by enlarging the splitting of energy levels of d orbitals
under strong core deformation. The fixation of dioxygen can be reasonably
explained by the Dewar–Chatt–Duncanson model. These
results indicate that this type of saddle porphyrin has the potential
to be used as a new model system of heme.