Porphyrins reactions with oxygen

Fig. 3. Diagrammatic sketch showing the change in tertiary structure of a hemoglobin a chain on reaction with oxygen. Movement of the iron atom into the plane of the porphyrin ring causes a movement of helix F toward helix H, which expels tyrosine in position 140 from its pocket between the two helices. From (PIO), M. F. Perutz, Stereochemistry of cooperative effects in haemoglobin. Nature (London) 228, 726 (1970) with permission of the author and publisher.

Figures 23 and 24, there is no obvious steric restraint in achieving a conformation of the C17 chain in which the C12-C13 bond is adjacent to the iron and parallel to the porphyrin plane. Clearly, the Ci2-Ci3 bond could readily take part in reactions with oxygen or other ligands at iron or with iron itself. Such reactions could obviously function in processes of electron transfer or coupling with phosphorylation. Since there are...

The synthesis and turnover of porphyrins that are precursors of heme are important hecanse of the central role of heme proteins, hemoglobin, and the cytochromes in reactions with oxygen and in electron transfer. Qnantitatively, hemoglobin synthesis is a major part of the nitrogen economy in hitmans. 

Alkyliron(lll) porphyrin complexes are air. sensitive, and when exposed to oxygen under ambient conditions the products are the very stable iron(IIl) /t-oxo dimers, [Fe(Por)]20. A more careful investigation revealed that the reaction of the alkyl complexes with oxygen proceeds via insertion of O2 into the Fe—C bond. " When a solution of Fe(Por)R (R = Me, Et, i-Pr) is exposed to O2 at —70 C, the characteristic H NMR spectrum of the low spin iron alkyl complex disappears and is replaced by a new, high spin species. The same species can be generated from the reaction of an alkyl hydroperoxide with Fe(Por)OH, and is formulated as... 

These results produce an ordering of the one-electron reduction potentials as shown in Figure 14.9. This order is consistent with results on the reactions of oxygen and porphyrins with carotenoids (McVie at al. 1979, Conn et al. 1992), for example, p-CAR - reacts much more efficiently with oxygen than LYC - and DECA -. Comparative studies have been made in benzene due to the decreased solubility of XANs in hexane and Table 14.8 gives the corresponding bimolecular rate constants for electron transfer. Overall, the one-electron reduction potentials increase in the order ZEA < P-CAR LUT < LYC < APO - CAN < ASTA. 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

The reaction of solid porphyrin films with light in the presence of oxygen by producing MgTPP must affect electrical properties, in particular semi conduct on, photoconduction, and photovoltaic properties. We have provided evidence for "photodoping" by light and oxygen, a phenomenon that must be clearly understood if these materials are to have device applications. 

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