Mdssbauer spectroscopy, iron

Characterization of Supported Iron Oxide Particles Using Mdssbauer Spectroscopy and Magnetic Susceptibility... 

Fe(OH), using Mdssbauer spectroscopy, optical spectroscopy and transmission electron microscopy. Phy. Chem. Min. 22 11-20 McCreadie, H. Blowes, D.W. (2000) Influence of reduction reactions and solid-phase composition on porewater concentrations of arsenic. Environ. Sd. Tedm. 34 3159-3166 McFadden, L.D. Hendricks, D.M. (1985) Changes in the content and composition of pedogenic iron oxyhydroxides in a chronose-quence of soils in Southern Cahfomia. Quart. Res. 23 189-204... 

G.L. Grandjean, E. (eds.) Mdssbauer spectroscopy applied to inorganic chemistry. Plenum Publ. Corp., 3 417-444 Webb, J. Macey, D.J. Mann, S. (1989) Biomineralization of iron in molluscan teeth. In Mann, S. Webb, J. Williams, R.J.P. (eds.) Biomineralization Chemical and biochemical perspectives. VCH Weinheim, 345-387 Webster, J.G. Swedlund, P.J. Webster, K.S. (1998) Trace metal adsorption onto an acid mine drainage iron(lll) oxy hydroxy sulfate. Environ. Sci.Techn. 32 1361-1368 Wedepohl, K.H. (1969) Composition and abundance of common igneous rocks. In Wedepohl, K.H. (ed.) Handbook of geochemistry. Springer, Berlin, 1 227-249 Wedepohl, K.H. (1969a) Composition and abundance of common sedimentary rocks. 

One type of the constituent metallocenters in the MoFe protein has the properties of a somewhat independent structural entity. This component, referred to as the FeMo cofactor (FeMo-co), was first identified by Shah and Brill (1977) as the stable metallocluster extracted from acid-denatured MoFe protein. The FeMo-co was able to fully activate a defective protein in the extracts of mutant strain UW45, a protein which subsequently was shown to contain the P clusters but not the EPR-active center. The isolated cofactor accounted for the total S = t system observed by EPR and Mdssbauer spectroscopies of the holo-MoFe protein (Rawlings et al., 1978). Elemental analysis indicated a composition of Mo Fee-8 Se-g for the cofactor, which, if there are two FeMo-co s per a2 2> accounts for all the molybdenum and approximately half the iron in active enzyme (Nelson etai, 1983). Although FeMo-co has been extensively studied [reviewed in Burgess (1990)] the structure remains enigmatic. To date, all attempts to crystallize the cofactor have failed. This is possibly due to the instability and resultant heterogeneity of the cofactor when removed from the protein. Also, there is a paucity of appropriate models for spectral comparison (see Coucouvanis, 1991, for a recent discussion). Final resolution of this elusive structure may require its determination as a component of the holoprotein. 

Maeda, Takashima, and Nishida 149> have prepared iron(H) complexes of pyri-dincarbaldehyde and quinolinecarbaldehyde ligands. Only complexes of the type [Fe((2-pym>R)2 (NCS)2], with 2-pym being 2-pyridylmethylene, and R = isoproyla-mine, p-anisidine, p-toluidine, aniline, p-chloroaniline, o-toluidine ( 1/2 CHC13), o-chloroaniline, were found by Mdssbauer spectroscopy and magnetic susceptibility... 

The Mossbauer spectra of iron in numerous minerals have been studied, but a few examples will serve to illustrate this technique. In the rockforming silicate minerals, Mdssbauer spectroscopy has been used to study the oxidation state, spin state and coordination of iron, and its distribution between different sites in a structure. Thus, Fig. 2.46 (after Williams et al., 1971) shows the spectrum of an augite [essentially (Ca,Mg,Fe)2Si20J, the structure of which contains two kinds of sixfold-coordinate sites that may be occupied by iron (the Ml and M2 sites). The Mdssbauer spectrum can be fitted to three quadrupole doublets peaks 1 and 1 have parameter characteristic of Fe (in both Ml and M2 sites), peaks A and A have parameters characteristic of Fe in Ml, and peaks C and C of Fe + in the M2 sites. These assignments, based chiefly on comparisons with endmember compositions and related species, also enable estimates of site populations to be made on the basis of the areas under the peaks. Studies of the variation in site populations as a function of composition and thermal treatment have led to important advances in understanding intercrystalline order-disorder equilibria, as pioneered in the work of Virgo and Hafner (1970). 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

The static and dynamic Janh-Teller effects in copper(II) [Cu(diAMHsar)](N03)4 H20 sarcophaginate and the dynamic one in analogous iron(II) complex were detected by variable temperature EPR, optical, and magnetic studies, and by Fe Mdssbauer spectroscopy, respectively [245, 246], and calculated using a density functional approach [247]. 

The presence of iron ions in various coordination states was evidenced in Na-Mont by Mdssbauer spectroscopy. Ion-exchange and subsequent treatment in N2 or H2 resulted in the formation of polynuclear iron moieties in the form of iron hydrous oxides, containing iron in octahedral positions. Upon pillaring very similar species were formed as well. 

Because the synthetic iron oxides whose synthesis is described in this book consist of very small crystals ranging in size from ca. 3 nm to several Lim, they are characterized and checked for purity by the techniques commonly used for submicroscopic to nano-sized particles. The most important of these techniques are X-ray powder diffraction and electron microscopy. In addition, Mdssbauer spectroscopy, infra red absorption spectroscopy and themial analysis provide useful information (Wilson, 1987). 

This concept was consistent with the results of other investigations. First, reaction-center preparations free of iron or in which iron is replaced by another metal ion such as manganese, remain photochemi-cally active in other words, the presence of iron for electron transfer is not obligatory. Second, examination of T e-enriched reaction-center preparations by Mdssbauer spectroscopy showed that the iron remains in the high-spin state irrespective of whether ubiquinone is oxidized or reduced. On the other hand, ifubiquinone is removed, the reaction center loses its photochemical activity but when the ubiquinone is restored, the original level of photochemical activity is also restored. 

Since 1980, newer physical techniques such as Mdssbauer spectroscopy, X-ray absorption spectroscopy and iron-sulfur-core extrusion have been used to address the question of the structure of FeS-X. The initial Mossbauer spectroscopic study by (EH) Evans, Rush, Johnson and (MC W) Evans2o indicated... 

J. R. DeBord, W. M. Reiff, R. Haushalter, and J. Zuhieta, J. 3-D Organically templated mixed valence (Fe /Fe ) iron phosphate with oxide-centered Fe40(P04)4 cubes Hydrothermal synthesis, crystal strnctnre, magnetic susceptibility, and mdssbauer spectroscopy of [H3NCH2CH2NH3]2[Fe40(P04)4] H20 Chemistry of Materials, 9 1994( 1997). 

Mineeva RM (1978) Relationship between Mdssbauer spectra and defect structure in biotites from electric field gradient calculations. Phys Chem Minerals 2 267-277 Mizutani T, Fukushima Y, Kobayashi T (1991) Synthesis of 1 1 and 2 1 iron phyllosihcates and characterization of their iron state by Mdssbauer spectroscopy. Clays Clay Minerals 39 381-386 Moon N, Coffin CT, Steinke DC, Sands RH, Dnnham WR (1996) A high-sensitivity Mdssbaner spectrometer facilitates the study of iron proteins at natural abundance. Nncl Instr Meth Phys Res B 119 555-564... 

The Mdssbauer effect on the Fe nuclei in biotite.] Kristallografiya 17 328-331 PopperP (1951) Transmission of natural and synthetic mica in the ultra-violet. Nature 168 1119-1120 Raclavasky K, Sitek J, Lipka J (1975) Mdssbauer spectroscopy of iron in clay minerals. 5th IntT Conf Mdssbauer Spectroscopy, Proc Part II, p 368-371... 

Mossbauer Spectroscopy. Mdssbauer spectroscopy has been used as a powerful technique to probe the electronic structure of the five- and six-coordinate ferrous nitrosyl porphyrins. The isomer shifts of both types of complexes (5 0.35 mm s ) are similar and show temperature dependences that are consistent with a second-order Doppler effect, but are slightly smaller than those of most other iron(II) porphyrin complexes (5 0.45 mm Unlike the isomer... 

Proper understanding of the process of DCL in the presence of catalysts needs an understanding of the electronic changes a catalyst goes through during a DCL process. Huffman et al. have reviewed the use of Mdssbauer spectroscopy, magnetization, and x-ray absorption studies to determine the chemical status of the iron-based catalysts before... 

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