Iron-57 Mossbauer spectroscopy

The third prominent interaction in iron Mossbauer spectroscopy is the magnetic hyperfine interaction of the Fe nucleus with a local magnetic field. As explained in detail in Chap. 4, it can be probed by performing the Mossbauer experiment in the presence of an applied external magnetic field. 

Feathers, J. K., M. Berhane, and L. May (1998), Firing analysis of South-Eastern Missouri Indian pottery using iron Mossbauer spectroscopy, Archaeometry 40, 59-70. 

MS Mossbauer Spectroscopy [233-236] Chemical shift of nuclear energy states, usually of iron Chemical state of atoms... 

A number of ferrites have been subjected to shock modification and studied with x-ray diffraction as well as static magnetization and Mossbauer spectroscopy [87V01], Studies were carried out on cobalt, nickel, and copper ferrites as well as magnetite (iron ferrite). 

Reinvestigation of iron porphyrins by Mossbauer spectroscopy using synchrotron radiation 98PAC917. 

Electrobalances suitable for thermogravimetry are readily adapted for measurements of magnetic susceptibility [333—336] by the Faraday method, with or without variable temperature [337] and data processing facilities [338]. This approach has been particularly valuable in determinations of the changes in oxidation states which occur during the decompositions of iron, cobalt and chromium oxides and hydroxides [339] and during the formation of ferrites [340]. The method requires higher concentrations of ions than those needed in Mossbauer spectroscopy, but the apparatus, techniques and interpretation of observations are often simpler. 

Iron electronic configurations in proteins studies by Mossbauer spectroscopy. A. J. Bearden and W. R. Dunham, Struct. Bonding (Berlin), 1970, 8, 2-52 (196). 

Tofield BC (1975) The Study of Covalency by Magnetic Neutron Scattering. 21 1-87 Trautwein AX, Bill E, Bominaar EL, Winkler H (1991) Iron-Containing Proteins and Related Analogs-Complementary Mossbauer, EPR and Magnetic Susceptibility Studies. 78 1-96 Trautwein AX (1974) Mossbauer-Spectroscopy on Heme Proteins. 20 101-167 Tressaud A, Dance J-M (1982) Relationships Between Structure and Low-Dimensional Magnetism in Fluorides. 52 87-146... 

First isolated from D. desulfuricans (28), desulfoferrodoxin (Dfe) was also isolated from D. vulgaris (29). D is a 28-kDa homodimer that contains two monomeric iron centers per protein. These iron centers were extensively characterized by UV/visible, EPR, resonance Raman, and Mossbauer spectroscopies (30). The data obtained were consistent with the presence of one Dx-like center (center I) and another monomeric iron center with higher coordination number (penta or hexacoordinate), with 0/N ligands and one or two cysteine residues (center II). Comparison of known Dfx sequences led to the conclusion that only five cysteines were conserved, and that only one of them could be a ligand of center II (31). 

Strongly supporting this spectroscopic data, Mossbauer spectroscopy of the as-isolated Rr shows the presence of two types of iron centers a magnetic component that can be well simulated by the parameters of Rd, and a diamagnetic component attributed to the diiron-oxo cluster and resulting from the antiferromagnetic coupling of the two irons. 

Mossbauer spectroscopy has been used to characterize the iron clusters in fuscoredoxin isolated from D. desulfuricans (133). The authors explained why the iron nuclearity was incorrectly determined, and studied the protein in three different oxidation states fully oxidized, one-electron reduced, and two-electron reduced. The error made in determining the iron cluster nuclearity was caused by the assumption that in the as-purified fuscoredoxin, cluster 2 is in a pure S = state. This assumption was proven to be false and unnecessary. In fact, the observation of four resolved, equal intensity (8% of total Fe absorption) spectral components associated with the S = i species in the as-purified protein is consistent with cluster 2 being a tetranuclear Fe cluster. The 4x8 = 32% Fe absorption for the four components indicates that only 64% of clusters 2 are in the S = state (the total Fe absorption for cluster 2 is 50% of the total Fe absorption). The remaining clusters 2 are in a different oxidation state, the spectrum of which is unresolved from that of cluster 1. 

This key enzyme of the dissimilatory sulfate reduction was isolated from all Desulfovibrio strains studied until now 135), and from some sulfur oxidizing bacteria and thermophilic Archaea 136, 137). The enzymes isolated from sulfate-reducing bacteria contain two [4Fe-4S] clusters and a flavin group (FAD) as demonstrated by visible, EPR, and Mossbauer spectroscopies. With a total molecular mass ranging from 150 to 220 kDa, APS reductases have a subunit composition of the type 012)32 or 02)3. The subunit molecular mass is approximately 70 and 20 kDa for the a and )3 subunits, respectively. Amino-acid sequence data suggest that both iron-sulfur clusters are located in the (3 subunit... 

Mossbauer spectroscopy confirmed the presence of four low-spin hemes. The iron-sulfur centers were identified as two different [4Fe-4g]2+,i+ centers. The [4Fe-4S] center II has an unusually small Fe hy-... 

Porphyrin is a multi-detectable molecule, that is, a number of its properties are detectable by many physical methods. Not only the most popular nuclear magnetic resonance and light absorption and emission spectroscopic methods, but also the electron spin resonance method for paramagnetic metallopor-phyrins and Mossbauer spectroscopy for iron and tin porphyrins are frequently used to estimate the electronic structure of porphyrins. By using these multi-detectable properties of the porphyrins of CPOs, a novel physical phenomenon is expected to be found. In particular, the topology of the cyclic shape is an ideal one-dimensional state of the materials used in quantum physics [ 16]. The concept of aromaticity found in fuUerenes, spherical aromaticity, will be revised using TT-conjugated CPOs [17]. 

Mossbauer spectroscopy is a specialist characterization tool in catalysis. Nevertheless, it has yielded essential information on a number of important catalysts, such as the iron catalyst for ammonia and Fischer-Tropsch synthesis, as well as the CoMoS hydrotreating catalyst. Mossbauer spectroscopy provides the oxidation state, the internal magnetic field, and the lattice symmetry of a limited number of elements such as iron, cobalt, tin, iridium, ruthenium, antimony, platinum and gold, and can be applied in situ. 

Figure 4.17 illustrates how Mossbauer spectroscopy reveals the identity of the major iron phases in a supported iron catalyst after different treatments. The top spectrum belongs to a fresh Fe/Ti02 catalyst, i.e. after impregnation and drying. 

The great advantage of Mossbauer spectroscopy is that it can be applied in situ. The major limitation of the technique is that it can only be applied to a couple of elements, among which iron and tin are the easiest to study. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

This study could be extended to the synthesis of iron nanoparticles. Using Fe[N(SiMe3)2]2 as precursor and a mixture of HDA and oleic acid, spherical nanoparticles are initially formed as in the case of cobalt. However, a thermal treatment at 150 °C in the presence of H2 leads to coalescence of the particles into cubic particles of 7 nm side length. Furthermore, these particles self-organize into cubic super-structures (cubes of cubes Fig. ) [79]. The nanoparticles are very air-sensitive but consist of zerovalent iron as evidenced by Mossbauer spectroscopy. The fact that the spherical particles present at the early stage of the reaction coalesce into rods in the case of cobalt and cubes in the case of iron is attributed to the crystal structure of the metal particles hep for cobalt, bcc for iron. 

Bearden, A. J., Dunham, W. R. Iron Electronic Configuration in Proteins Studies by Mossbauer Spectroscopy. Vol. 8, pp. 1-52. 

For a comparison of experimental Mossbauer isomer shifts, the values have to be referenced to a common standard. According to (4.23), the results of a measurement depend on the type of source material, for example, Co diffused into rhodium, palladium, platinum, or other metals. For Fe Mossbauer spectroscopy, the spectrometer is usually calibrated by using the known absorption spectrum of metallic iron (a-phase). Therefore, Fe isomer shifts are commonly reported relative to the centroid of the magnetically split spectrum of a-iron (Sect. 3.1.3). Conversion factors for sodium nitroprusside dihydrate, Na2[Fe(CN)5N0]-2H20, or sodium ferrocyanide, Na4[Fe(CN)]6, which have also been used as reference materials, are found in Table 3.1. Reference materials for other isotopes are given in Table 1.3 of [18] in Chap. 1. 

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