Method Mossbauer spectroscopy

On the basis of a number of physico-chemical methods (Mossbauer spectroscopy, electron diffraction, EXAFS) the iron cores of naturally occurring haemosiderins isolated from various iron-loaded animals and man (horse, reindeer, birds and human old age) were consistently shown to have ferrihydrite-like iron cores similar to those of ferritin (Ward et ah, 1992, 2000). In marked contrast, in the tissues of patients with two pathogenic iron-loading syndromes, genetic haemochromatosis and thalassaemia, the haemosiderins isolated had predominantly amorphous ferric oxide and goethite cores, respectively (Dickson etah, 1988 Mann etah, 1988 ... 

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. 

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]. 

Miinck, E. Aspekts of Fe Mossbauer spectroscopy. In Que, L. (ed.) Physical Methods in Bioinorganic Chemistry, p. 287. University Science Books, Sausalito (2000)... 

The miniaturized Mossbauer spectrometer MIMOS II has been used already in several terrestrial applications which would not have been possible before. A number of other possible terrestrial applications, for example, in the field, in industry, and fundamental research, are under consideration. With the new generation of the Mossbauer spectrometer MIMOS 11, the method itself can be applied to numerous new fields in research, environmental science, planetary science, and many other fields. Because of this reason, Mossbauer spectroscopy may become a more widely used method than it is today. 

Gonser, U., Fischer, H. In Gonser, U. (ed.) Topics in Current Physics, Mossbauer Spectroscopy II The Exotic Side of the Method. Springer, Berlin (1981)... 

A CD-ROM is attached containing a teaching course of Mossbauer spectroscopy (ca. 300 ppt frames), a selection of examples of applications of Mossbauer spectroscopy in various fields (ca. 500 ppt frames), review articles on computation and interpretation of Mossbauer parameters using modem quantum-mechanical methods, list of properties of isotopes relevant to Mossbauer spectroscopy, appendices refering to book chapters, and the first edition of this book which appeared in 1978. In subsequent printmns files are available via springer.extra.com (see imprint page). 

The nuclear transitions are very sensitive to the local environment of the atom, and Mossbauer spectroscopy is a sensitive probe of the different environments an atom occupies in a solid material. By analyzing the chemical shifts and quadrupole splitting in Mossbauer spectra of samples containing Mossbauer-ac-tive nuclei, information on the state of oxidation and the local structure can be obtained. Only a few nuclei can be used for this purpose, so this method has limited but powerful applications. 

Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of Fischer-Tropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mossbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hagg or s-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the a-value of the product distribution and the carburization rate. 

TABLE 7. Structural determination of organometallic compounds containing tin(II) atoms by NMR and Mossbauer spectroscopy methods... 

The Mossbauer effect as a spectroscopic method probes transitions within an atom s nucleus and therefore requires a nucleus with low-lying excited states. The effect has been observed for 43 elements. For applications in bioinorganic chemistry, the 57Fe nucleus has the greatest relevance and the focus will be exclusively on this nucleus here. Mossbauer spectroscopy requires (a) the emission of y rays from... 

Introduce instrumental techniques used in analysis of the bioinorganic systems I will lecture on (Chapter 3 Instrumental and Computer-Based Methods). Typically, these would be electron paramagnetic resonance (EPR) and Mossbauer spectroscopies not often covered in undergraduate instrumental analysis courses plus X-ray diffraction and NMR techniques used for structural analyses of metalloproteins and their small molecule model compounds. 

Previous attempts to distinguish between the different kinds of pairs by applying microscopic methods such as conventional Mossbauer spectroscopy were unsatisfactory, since the Mossbauer spectra corresponding to the HS state of the iron(II) atoms in the [HS-LS] and [HS-HS] spin pairs are indistinguishable. Zero-field Mossbauer spectroscopy applied to the bpym-bridged iron(II) dinuclear compounds only gives access to the total fraction... 

Alternative ways to study the kinetics of bulk transformations would be to monitor changes in weight or in magnetization. Such methods, however, are less specific about the initial and final state of the catalyst than Mossbauer spectroscopy is. 

The most direct information on the state of cobalt has come from Mossbauer spectroscopy, applied in the emission mode. As explained in Chapter 5, such experiments are done with catalysts that contain the radioactive isotope 57Co as the source and a moving single-line absorber. Great advantages of this method are that the Co-Mo catalyst can be investigated under in situ conditions and the spectrum of cobalt can be correlated to the activity of the catalyst. One needs to be careful, however, because the Mossbauer spectrum one obtains is strictly speaking not that of cobalt, but that of its decay product, iron. The safest way to go is therefore to compare the spectra of the Co-Mo catalysts with those of model compounds for which the state of cobalt is known. This was the approach taken... 

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