Models of Oxygen Uptake and Transport

An obvious choice for the construction of artificial oxygen binding mimics is the use of oxidisible transition metal (particularly iron) complexes of porphyrin ligands such as 12.23, as in the natural system. In such cases, the O2 affinity is governed essentially by the reduction potential of the metal centre (Ej) as in the reaction + e = M +. Iron(ll) and cobalt(ll) are particularly favourable in 

In Fe(ll) model systems, protein tertiary structure is not present, and hence the issue of generating 

The more sophisticated pocket and picnic basket porphyrins are also capable of mimicking properties such as O2/CO binding selectivity in which the (normally high) CO affinity is reduced because of steric interactions between the CO molecule (which adopts a linear Fe C=0 conformation) and the capping or strapping moiety. Selectivity for small molecules such as O2 is also enhanced, relative to larger bases. 

9 Fetters, M. C., Rowan, A. E., Nolte, R. J. M., From simple to supramolecular cytochrome P450 mimics , Chem. Soc. Rev. 2000, 29, 375-384. 

Structural model systems are difficult to construct for cytochrome P-450 because thiolates do not bind strongly to Fe(III) porphyrin units, and oxidation of the thiolate to disulfides accompanied by reduction to Fe(II) is common (Equation 12.5). A range of models for the Fe(lll) resting state have been prepared using open iron(III) porphyrins with alkyl or aryl thiolates, however. 

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