Ferrous dioxygen complex structure

Oxygen Binding and the Structure of the Ferrous Dioxygen Complex... 

E° = —196 mV) to the ferric P450CAM heme iron to produce the ferrous state of the protein, 3. Dioxygen binds to the ferrous heme iron to form the ferrous oxy complex, 4a/4b, whose valence structure can be presented either as the ferrous-02, 4a, or as the ferric superoxide, 4b, complex. Addition of carbon monoxide to 3 yields a ferrous carbon monoxide adduct, 5, with its characteristic absorbance peak at 450 nm [37],... 

A comparison of available X-ray structures of oxy-ferrous complexes in CYPlOl, CYP107, and CYP158 reveals very similar structural arrangements of the heme iron and axial figand with major differences concerning the detailed stereochemistry of the amino acid side chains and water molecules in the immediate vicinity of the bound dioxygen (14, 15). The main... 

Fig. 3. Catalytic cycle of cytochrome P-450 and the postulated partial structures of the intermediates. The dianionic porphyrin macrocycle is abbreviated as a parallelogram with nitrogens at the comers, in this and subsequent figures. Oxy-P-450 (4) is shown as a complex of ferric porphyrin and superoxide anion, but could also be describe as an adduct of neutral dioxygen and ferrous porphyrin. States 6 and 7 are hypothetical intermediates whose structures have not been established. Structures /, 2, and 7 are neutral (the dot and the positive charge on 7 indicate the radical state and electron deficiency of the n electron system of the porphyrin ring), while the overall charge on structures 3, 4, and 5 is minus one and on structure 6 is minus two. Adapted from Ref. [22]...

Thus, one atom from dioxygen is introduced into the substrate and the other into the resulting carboxylic acid. As a model for the enzymes, an iron(II) complex coordinated with a-keto acid has been synthesized. The complex Fe(TLA)(BF) (BF = benzoyl-formate) was prepared and its X-ray structure was determined [88, 89]. That complex is six-coordinate with a bidentate coordination of a-keto acid via the carboxylate oxygen and the carbonyl oxygen). When the complex was treated with dioxygen, decarbonylation does occur to give a carboxylate complex quantitatively. While the detailed mechanism remains to be elucidated, the addition of 2,4-di-/-butylphenol results in the formation of 0.75 mol of the corresponding biphenol per mole of the ferrous complex. 

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