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

Abstract

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.

Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation

“…This is in agreement with the works of Song et al [52] . and Zhou et al., [56,57] which reported that the electronic spectra showed a gradual red shift upon increasing the degree of distortion. However, Cramariuc et al [51] .…”

Formation of π‐Cation Radicals in Highly Deformed Copper(II) Porphyrins: Implications for the Distortion of Natural Tetrapyrrole Macrocycles

“…Our recent studies have shown that the 3d electronic structure of the metal center can be tuned by macrocyclic deformations and the resulting change in the core size, and this tuning is related to the specific properties of the distorted heme . It has been proven indirectly that the activation of oxygen in heme and the reaction of the activated oxygen are two independent processes . In hemoprotein, the heme component is encapsulated in a distal pocket composed of amino acids, which can prevent electron removal from the metal atom , .…”

Optimal Size Matching and Minimal Distortion Energy: Implications for Natural Selection by the Macrocycle of the Iron Species in Heme

“…Figure shows that only the curve for the iron series crosses that of the metal‐free one, and the other two slightly cross or drift away from it; even the largest core, containing nickel(II), is just close to the lowest limiting free‐metal core value. The results also imply that porphyrin distortion can be affected by the size of the central ion as well as stretching of alkyl bridges and crowding of peripheral groups in synthetic nonplanar porphyrins. In the current model series, the small nickel(II) [or cobalt(II)] ion slightly increases the degree of distortion, as shown by the fact that the L N1N3 values are shorter in the metal‐containing series than in the metal‐free one and the A mC values are larger in the former than in the latter (Table ).…”

“…Macrocyclic distortion can induce changes in the electronic, magnetic, and binding properties of the central iron ion and in the nonbinding interactions of the meso ‐aryl groups . In recent studies, a relationship between macrocyclic distortion and the electronic activities of metals was established for several series of ruffle‐, saddle‐, and dome‐type porphyrins (Figure , a–d) . We found that macrocyclic distortion ( A mC ) directly affects the core size (Figure , a–b), which induces changes in the electronic configuration of the central metal ions (Figure , b–c) such as iron(III),, cobalt(II),, copper(II), and zinc(II) .…”

“…In recent studies, a relationship between macrocyclic distortion and the electronic activities of metals was established for several series of ruffle‐, saddle‐, and dome‐type porphyrins (Figure , a–d) . We found that macrocyclic distortion ( A mC ) directly affects the core size (Figure , a–b), which induces changes in the electronic configuration of the central metal ions (Figure , b–c) such as iron(III),, cobalt(II),, copper(II), and zinc(II) . In the conversion process, an electron (or electron pair) in a 3d orbital is activated (Figure , c–d), which guarantees the potential catalytic abilities of these metal complexes (Figure , d–e).…”