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 H2O 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 O2-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.
Kano
Koji
K
Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan. kkano@mail.doshisha.ac.jp
Kitagishi
Hiroaki
H
Mabuchi
Takahiro
T
Kodera
Masahito
M
Hirota
Shun
S
D000818:Animals; D002244:Carbon / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry; D002626:Chemistry, Pharmaceutical / Q000379:methods; D003505:Cyclodextrins / Q000737:chemistry*; D019281:Dimerization; D006420:Hemeproteins / Q000737:chemistry*; D006801:Humans; D007093:Imidazoles / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D009211:Myoglobin / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011725:Pyridines / Q000737:chemistry; D013696:Temperature
D003505:Cyclodextrins; D006420:Hemeproteins; D007093:Imidazoles; D008665:Metalloporphyrins; D009211:Myoglobin; D011725:Pyridines; C035807:ferroporphyrin; D002244:Carbon; C029899:imidazole; D002248:Carbon Monoxide; C023666:pyridine; D010100:Oxygen