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Iron structural models

Despite several decades of studies devoted to the characterization of Fe-ZSM-5 zeolite materials, the nature of the active sites in N20 direct decomposition (Fe species nuclearity, coordination, etc.) is still a matter of debate [1], The difficulty in understanding the Fe-ZSM-5 reactivity justifies a quantum chemical approach. Apart from mononuclear models which have been extensively investigated [2-5], there are very few results on binuclear iron sites in Fe-ZSM-5 [6-8], These DFT studies are essentially devoted to the investigation of oxygen-bridged binuclear iron structures [Fe-0-Fe]2+, while [FeII(p-0)(p-0H)FeII]+ di-iron core species have been proposed to be the active species from spectroscopic results [9]. We thus performed DFT based calculations to study the reactivity of these species exchanged in ZSM-5 zeolite and considered the whole nitrous oxide catalytic decomposition cycle [10],... [Pg.369]

Kim, J. and D.C. Rees. Structural models for the metal centers in the nitrogenase molybdenum-iron protein. Science 257,1677-1682 (1992). [Pg.116]

This emphasizes that iron(II) complexes bearing more bulky bis(pyrazol-l-yl)acetate ligands should be good structural models to mimic mononuclear non-heme iron dependent enzymes. [Pg.111]

Structural models, which are synthesized to imitate features of the proposed structure of the active site. These may be used to demonstrate the chemical conditions, which allow such structures to exist, to investigate their chemical properties and to give a better understanding of the spectroscopic characteristics of the native proteins. Examples of these include the mixed carbonyl/cyano complexes of iron, used to verify the infrared spectra to the hydrogenases (Fig 7.4) (Lai et al. 1998) and the nickel-thiolate complexes which have low redox potentials like the hydrogenases (Franolic et al. 1992). [Pg.170]

In conclusion, the presented dinuclear iron structure is the first example of a bio-mimetic iron compound, which can be regarded as a first generation model for the class of [Fe]-only hydrogenases. The complex incorporates both relevant carbon monoxide ligands, as well as three bridging thiolato ligands, which could be possibly present in the active site of these enzymes. [Pg.197]

The electrochemistry of dinitrogen bridging two porphyrin ligated ruthenium centers has been studied as a possible route to fixed nitrogen [45 -47]. Diazene stabilized by bonding to two iron centers in a FeS system has been advanced as a structural model of a plausible intermediate in biological nitrogen fixation [48-50]. [Pg.239]

The defect structure of Fei O with the NaCl-type structure had been estimated to be a random distribution of iron vacancies. In 1960, Roth confirmed, by powder X-ray diffraction, that the defect structure of wiistite quenched from high temperatures consists of iron vacancies (Vp ) and interstitial iron (Fcj) (there are about half as many FCj as Vpe). This was a remarkable discovery in the sense that it showed that different types of crystal defects with comparable concentrations are able to exist simultaneously in a substance, Roth also proposed a structure model, named a Roth cluster, shown in Fig. 1.84. Later this model (defect complex = vacancy -F interstitial) was verified by X-ray diffraction on a single crystal and also by in-situ neutron diffraction experiments. Moreover, it has been shown that the defect complex arranges regularly and results in a kind of super-structure, the model structure of which (called a Koch-Cohen model) is shown in Fig. 1.85 together with the basic structures (a) and (b). [Pg.108]

This account will deal in turn with structural features of the one-iron, two-iron, four-iron and three-iron proteins, and also with the most important topic of interconversion between the three-iron and four-iron clusters. Model compounds will be described briefly. Finally, kinetic studies and the role of iron-sulfur proteins in complex enzymes will be discussed. [Pg.626]

The thermodynamic stability of the binuclear site has been demonstrated by the spontaneous assembly of [Fe20(02CR)2L2] (13) from ferric salts in the presence of water, an alkyl carboxylate salt, and a tridentate nitrogen donor ligand L that can cap an octahedral face on iron (8). Suitable ligands include tris(pyrazolyl)borates and 1,4,7-triazacyclononanes. Structure (13) is in essence a portion of the basic ferric acetate structure. The complexes are excellent physical and structural models of the diiron sites and model some aspects of reactivity including redox activity and interconversion of the oxo and hydroxo bridge. [Pg.442]

An elegant and efficient approach for the synthesis of structural models of carboxylate-rich non-heme dinuclear iron proteins involves the use of bulky ligands of the terphenyl carboxylate family [47, 48]. The resulting dinuclear iron(II) complexes can adopt two conformations, called the windmill and the paddlewheel motif (Scheme 2.9). [Pg.43]

Figure 12.9 Structural model for deoxymyoglobin based on the formation of a five-coordinate iron complex of tetraphenylporphyrin (12.23, R = Ph), stabilised by 2-methyl imidazole. Figure 12.9 Structural model for deoxymyoglobin based on the formation of a five-coordinate iron complex of tetraphenylporphyrin (12.23, R = Ph), stabilised by 2-methyl imidazole.
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(III) resting state have been prepared using open iron (III) porphyrins with alkyl or aryl thiolates, however. [Pg.835]

These correspond to the S Is — M d7t(e) and Sis > M d<7(t2) transitions split in energy by 10Dq (in the d6 final state). The resolved intensities provide the n and cr covalencies (i.e., thiolate S character) in the d-orbitals of this site. In a comparison of the S K-edge data for the iron-sulfur model complexes of Holm and collaborators58 to the proteins with structurally congruent sites, the intensity is generally decreased... [Pg.33]


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See also in sourсe #XX -- [ Pg.8 ]




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