Synthesis and dioxygen-binding properties of double-sided porphyrinatoiron(II) complexes bearing covalently bound axial imidazole

Double-sided porphyrinatoiron(II) complexes bearing covalently bound axial imidazole, 5-[2-(5-imidazolylvaleryloxy)-6-(pivaloyloxy)phenyl]-10,15,20-tris[2,6- bis(pivaloyloxy)phenyl]porphyrinatoiron(II) and 5-[2-(3,3-dimethylbutyryloxy)-6-(5-imidazolylvaleryloxy)phenyl]-10,15,20-tris[2, 6-bis(3,3-dimethylbutyryloxy)phenyl]porphyrinatoiron(II), have been synthesized. On the basis of their absorption and ¹H NMR spectra, the axial imidazole group is co-ordinated. The complexes reversibly form stable dioxygen adducts in toluene at 25 °C, and the kinetics of binding of O₂ and CO has been investigated. When embedded in phospholipid unilamellar vesicles, the complexes possess the ability to transport dioxygen in an aqueous medium. The binding affinity of the pivaloyloxy derivative [P_1/2(O₂) = 27 Torr] is equal to that of a red blood cell suspension and the half-life of the dioxygen adduct formed was 1.5 d under physiological conditions (pH 7.4, 37 °C).