A myoglobin functional model composed of a ferrous porphyrin and a cyclodextrin dimer with an imidazole linker

A 1:1 inclusion complex (Fe(II)PImCD) of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(II) (Fe(II)P) and an O-methylated beta-cyclodextrin dimer with an imidazole linker (ImCD) was found to bind dioxygen in aqueous solution. The half-saturation pressure of dioxygen (P(1/2) (O2)) is 1.7 torr at 25 degrees C, which is 10 times lower than that for a previous myoglobin functional model (hemoCD) with a pyridine linker. Meanwhile, the half-life of oxygenated Fe(II)PImCD is 3 h, which is 10 times shorter than that of oxygenated hemoCD. The covering of the iron(II) center by a microscopic environment is essential for preventing autoxidation of oxygenated ferrous porphyrin, which is promoted by nucleophilic attack of H(2)O and/or nucleophiles such as inorganic anions. Due to structural requirements, covering of the Fell center of Fe(II)PImCD is insufficient compared with the case of hemoCD. As a result, water molecules can penetrate more easily the cleft of the O(2)-Fe(II)PImCD complex and act as an autoxidation inducer. This structure also causes poorer selectivity against carbon monoxide (M=1040). In contrast, the dioxygen affinity of Fe(II)PImCD is much higher than that of hemoCD because the imidazole moiety is a stronger electron donor than pyridine.