Porphyrin Model Compounds

We shall return to the discussion of the orientation and electronic structure of the dioxygen ligand during the next section which is primarily concerned with recent advances in the synthesis and physical characterization (particularly X-ray analysis) of oxygencarrying metal porphyrin model compounds. 

Table 3.4 lists values for A Eq and for some important oxidation and spin states found in bioinorganic molecules. Data are taken from reference 24 and from Table 1 of reference 25 for hemoglobin, myoglobin, and the picket-fence porphyrin model compound, FeTpivPP(l-Melm).25 The myoglobin and hemoglobin model compounds are discussed in Section 4.8.2. Reference 26 provides the Table 3.4 data on iron sulfur clusters found in many bioinorganic species.26 The unusual iron-sulfur and iron-molybdenum-sulfur clusters found in the enzyme nitrogenase are discussed more fully below and in Chapter 6. 

III. Iron-Porphyrin Model Compounds A. Fe(III) Hemin Compounds... 

Synchrotron-based nnclear resonance methods have revealed the vibrational dynamics of the iron atom in numerous systems, including alloys, amorphous materials, nanomaterials, and materials under high pressure. " The above-mentioned selectivity for the probe nucleus is particularly valuable for biological macromolecules, which may contain many thousands of atoms, bnt a locahzed active site is often the true center of interest. Since its availability, NRVS has been applied to study the vibrational dynamics of Fe in proteins, " porphyrin model compounds, and... 

The use of porphyrinic model compounds in reaction kinetics research is a convenient tool in screening and testing of different catalyst systems. 

P dyad 24 in toluene. The spectra have been normalized over the range 18,210-18,S20cm. The shape of the excitation spectrum is similar to that of a porphyrin model compound, and indicates that no significant singlet-singlet energy transfer from the carotenoid to the porphyrin has occurred. 

Vanadium deposition profiles in catalyst pellets have been determined by various researchers (14-30). For this purpose porphyrinic model compounds and industrial feedstocks are used. The used catalyst are mainly conventional hydrotreating catalysts with narrow pores. Therefore, metal deposition profiles show mainly deposition in the outer shells of the catalyst pellets (M- or U-shaped profiles), indicating that the metal deposition process is diffusion limited. 

Synchrotron-based nuclear resonance methods have revealed the vibrational dynamics of the iron atom in numerous systems, including alloys, amorphous materials, nanomaterials, and materials under high pressure. The above-mentioned selectivity for the probe nucleus is particularly valuable for biological macromolecules, which may contain many thousands of atoms, but a localized active site is often the true center of interest. Since its availability, NRVS has been applied to study the vibrational dynamics of Fe in proteins, porphyrin model compounds, " and iron-sulfur clusters. It is shown that NRVS can provide frequencies, amplitudes, and directions for Fe vibrations in the samples. It helps to clarify mode assignments in vibrational spectra and reveals many important vibrational modes of Fe that cannot be seen by other methods. In particular, NRVS reveals low-frequency motions of the Fe down to below 100 cm that control biological reactions. The applications presented here use Fe as the probe nucleus, but the principle applies to other Mossbauer isotopes such as " Sn, Kr, Ni, and Zn if appropriate sources are available. 

Early studies using porphyrin model compounds attempted to mimic reversible oxygen binding in myoglobin. This involved the synthesis of porphyrins with a variety of "straps", "caps", "tail bases", "picket fences" and "basket handles" that served to provide a degree of supramolecular control over the way oxygen bound to the iron cation. ... 

Fig. 29.9 The structure (determined by X-ray diffractirai) of a picket-fence porphyrin model compound with an azido ligand bound to the Fe(II) centre (a) a stick representation illustrating the protection of the [N3] ligand by the four fence-posts of the porphyrin ligand, and (b) a space-filling model looking down into the cavity. [Data I. Hachem e( al. (2009) Polyhedron, vol. 28, p. 954.] Coloin code Fe, gretai N, blue O, red C, grey H, white.

Araki K, Toma HE (2009) Supramolecular porphyrin model compounds for cytochrome p-450, cytochrome-c oxidase and photosynthetic systems. In Merce ALR, Felcman J, Recio MAE (eds) Molecular and supramolecular bioinorganic chemistry applications in medical sciences. Nova Science Publishers, New York, pp 83-136... 

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