A Myoglobin Functional Model Composed of a Ferrous Porphyrin and a Cyclodextrin Dimer with an Imidazole Linker

Abstract 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 β‐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 °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 Fe II 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.