Fe protoporphyrin

Hemoproteins, such as hemoglobin and the cytochromes, contain heme. Heme is an iron-porphyrin compound (Fe -protoporphyrin IX) in... 

The FePcY-PDMS supramolecular catalyst resembles the architecture of natural enzymes. In this system the PDMS membrane takes over the role of the phospholipid double layer likewise, the zeolite imitates the protein and the FePc complex the Fe-protoporphyrin. Zeolite-encaged Cu-histidine complexes were also studied as mimics of natural Cu-enzyme complexes.173... 

The mimetic biosensor for ELD described in Section ni.B.4.b, incorporating polymerized Fe-protoporphyrin IX (75c) and Os(II) ions, can be used for determination of diacyl peroxides in organic solution. The electrode was tested for determination of BzOOBz extracted from a pharmaceutical geP. ... 

Fig. 5.8. H NMR spectra of high spin Fe(lII) porphyrins. (A) Fe TPP-C1 (no substituent at the pyrrole positions). Signal a refers to pyrrole protons signals b, c and d refer to the meta, ortho and para phenyl protons respectively [19]. (B) Fe (protoporphyrin IX)-C1 (see Fig. 5.7A for the ligand). Signals a belong to the methyl groups, signals b and g to the 13,17 a-CH2 and the 3,8 a-CH signals d to the COOH signals e to the 13,17 P-CH2 signals h and i to the 3,8 P-CH cis and p-CH trans respectively [20].

In D4h (tetragonal) symmetry there is only one unpaired electron in two degenerate orbitals of correct symmetry to give rise to n bonds with a n orbital of the porphyrin moiety [34]. The H NMR spectrum of Fe(protoporphyrin IX)-imidazole-cyanide is reported in Fig. 5.17 [35]. The free rotation of the imidazole ring about the metal-nitrogen bond, which is fast on the NMR timescale, simulates a tetragonal symmetry as far as the chemical shifts are concerned [36]. The four methyls are all downfield, though to a quite smaller value than in the case of... 

Fig. 5.17. H NMR spectrum of Fe(protoporphyrin IX)-imidazole-cyanide (adapted from [35, 60]) (labeling as in Fig. 5.7B).

Not only has binding of imidazoles and pyridines to Fe protoporphyrin IX been studied, as discussed in Section 4.1.2, but also photodissociation of axial ligands such as pyridines, imidazoles, or piperidines from six-coordinate, low-spin Fe porphyrins, in which the porphyrin is derived from protoporphyrin IX, or proto- or deuteroporphyrin IX dimethyl ester, has been investigated in nonaqueous solvents using picosecond transient absorption spectroscopy (see Photochemistry of Transition Metal Complexes). It has been shown that photodissociation leads to the formation of five-coordinate complexes, that is, only one ligand appears to be released upon excitation of the six-coordinate complex. ... 

Most known multiheme cytochromes and enzymes belong to the family of cytochromes c (see Iron Heme Proteins Electron Transport), which contain Fe-protoporphyrin IX covalently attached to the polypeptide chain by two thioether bonds, formed by addition of two cysteinyl residues to the vinyl side-chains of the porphyrin ring. The two cysteines form a characteristic amino acid sequence motif CXXCH, usually indicative of heme c ligation, and where the histidine is the axial fifth ligand to the iron. For some cytochromes (see Section 2), the number of residues between the two cysteines can be three or four. The heme redox potentials in cytochromes c cover a wide range and are tuned by several factors, usually dominated by the type of axial ligation and the extent of solvent exposure of the heme. ... 

An inverse task is given when there is demand for a macromolecule that specifically binds a small ligand. This question has only recently been addressed by peptide chemistry. For example, antiparallel bundles of four a-helices, which were assembled on a cyclic peptide structure as template, have been used to create hydro-phobic cavities for heme as a low-molecular-weight compound [3]. The specific complexation of Fe " protoporphyrin IX was facilitated by the proper positioning of liganding His residues. While this approach could be interesting from the perspective of rational protein design, it may be limited to special applications, and detailed structural information about the complex is not yet available. 

As discussed in the first section of this chapter, the P450 cytochromes, NOS, HOs, and cytochrome oxidases are all heme enzymes which are able to activate molecular oxygen. Related heme enzymes, such as the peroxidases and catalases, work with partially reduced dioxygen species. It has always been intriguing that each of these enzymes uses the same cofactor, heme or Fe-protoporphyrin IX, but performs a distinct physiological function. 

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