Mossbauer spectroscopies Subject

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). 

About 1000 papers are published annually on organotin chemistry, and we have been able to include only 5% of these. We have deliberately avoided treating in depth those aspects of the subject that have been thoroughly reviewed recently, and, in particular, we have avoided duplicating the excellent surveys of the use of organotin compounds in organic synthesis (4), of " "Sn Mossbauer spectroscopy (5-9), and of Sn NMR spectroscopy (10-12) that are available. 

One large class of non-heme iron-containing biomolecules involves proteins and enzymes containing iron-sulfur clusters. Iron-sulfur clusters are described in Sections 1.7 (Bioorganometallic Chemistry) and 1.8 (Electron Transfer) as well as in Section 3.6 (Mossbauer Spectroscopy). See especially Table 3.2 and the descriptive examples discussed in Section 3.6.4. Iron-sulfur proteins include rubredoxins, ferrodoxins, and the enzymes aconitase and nitrogenase. The nitrogenase enzyme was the subject of Chapter 6 in the hrst edition of this text—see especially Section 6.3 for a discussion of iron-sulfur clusters. In this... 

The second class of iron-containing proteins which have been well-studied by Mossbauer spectroscopy, and by other resonance techniques, are the iron-sulfur proteins. These molecules are also known by the name, ferredoxins. Iron-sulfur proteins in several varieties serve as electron-transport agents for processes in plants, bacteria, and mammals. Perhaps the most-studied physiological process involving the iron-sulfur proteins is the study of their role in photosynthesis. This subject has been extensively reviewed by Arnon 126,135), Hind and Olson 127), Hall and... 

The application of Mossbauer spectroscopy to the investigation of catalysts began around 1970, and subsequently became quite popular, owing mainly to the importance of iron - with its rather rich chemistry - in many catalysts. By 1990 over 600 scientific reports had been published on the subject [19]. Most applications of Mossbauer spectroscopy to catalysts fall into one of the following categories ... 

The ion-exchange capability of various types of melanins allows binding of the Fe isotope, the most common probe used in Mossbauer spectroscopy. This method has proved to be a useful and accurate technique in the investigation of molecular and supramolecular structures of melanins. Both natural sepia and bovine eye melanins, as well as synthetic [Pg.300]

The macro-scale investigations showed that pretreatment of an iron surface with steam at 700°C itduces a dramatic increase in the catalytic activity for carbon deposition from hydrocarbons. Spectroscopic analysis (Auger and Mossbauer) combined with weight increase measurements prove that treatment of iron with steam at 700°C results in the conversion of the surface of the iron to FeO. At 800°C, this process is not just limited to the uppermost surface layers but penetrates to an appreciable depth of the material after a three hour treatment. Indeed Mossbauer spectroscopy data shows that nearly all of a 0.013 cm Fe foil is transformed to FeO in this time at 800°C. It should be mentioned that the reaction of steam with iron to produce FeO may be possible at temperatures above 570°C (3). The nonstoichiometric nature of FeO has been the subject of "a considerable number of papers. It is known, however, that the defects present in this material are vacant cation sites and trapped positive holes (26). 

We shall return to the theoretical discussion again in Chapter 3 to see how the spectrum can be influenced in detail by various properties of the resonant nucleus and by the extra-nuclear electrons. Before then, however, it will be convenient to outline the experimental techniques of Mossbauer spectroscopy and this forms the subject of the next chapter. 

Also included for convenience in this chapter is a small section on miscellaneous applications of Mossbauer spectroscopy to subjects such as surface states, chemical reactions, and diffusion in liquids, which are of chemical interest but do not as yet represent major areas of study. 

However, this model has been the subject of controversial discussions and some researchers argued against this remote control mechanism. Indeed, using emission Mossbauer spectroscopy (EMS), Wivel and co-workers (21) have shown that even when the CogSg phase is not detected, a promoter effect is observed by the addition of Co (Co/Mo < 0.4). Nevertheless, in any case, this model was very helpful in understanding metal sulfides activity and has clearly shown that the alumina support does not play any role in the promotion effect and that promotion resides uniquely at the interface of the two phases M0S2 and CogSg. 

Up to now, several thousand papers on various biological aspects of Mossbauer spectroscopy applications have been published (for some previous reviews see, for instance. Refs. 2-12), while only about 350—400 articles can be considered as biomedical from the narrower viewpoint (for reviews see Refs. 13-25). These studies were based mainly on Fe-containing subjects however, in a number of cases, Co, " Sn, l, Sm, Tb, and Au containing species were used. Various objects, from molecules to tissues and organs, were studied in normal physiological conditions and in the case of pathologies. 

Iron is one of the most abundant elements in solid and aqueous atmospheric samples and is usually introduced into the atmosphere as soil dust, fly ash from power plants, exhaust from combustion engines, and from industrial operations. The role of iron in important atmospheric chemical reactions is subject to numerous investigations. Mossbauer spectroscopy proves to be a useful analytical method to determine the iron containing species in the atmosphere. In Figure 16... 

Cycling studies at room temperature indicate that after an initial capacity decrease in the first 10-15 cycles the material was stable for the next several hundred cycles (the first 200 cycles are shown in Fig. 3.11). Interestingly, a conversion between Fe and FeFs was detected by Mossbauer spectroscopy, also at room temperature. The reason why only a part of the material seems to be active is not clear yet and will be subject of further investigations. It is likely that the materials transfer is prohibited for a part of the sample by the defect-free encapsulation of the iron nanoparticles. 

Two books which cover the majority of the methods described in this Chapter are Structural Methods in Inorganic Chemistry by E. A. V. Ebsworth, D. W. H. Rankin and S. Cradock, Blackwell, Oxford, 1987 and NMR, NQR, EPR and Mossbauer Spectroscopy in Inorganic Chemistry, R. V. Parish. Ellis Hor-wood, Hemel Hempstead, 1990. An older book, but one that covers a wider subject area, with some good chapters is Physical Methods in Advanced Inorganic Chemistry H. A. O. Hill and P. Day, eds.. Interscience, London, 1968. Readable insights into a limited number of particular areas can be found in Spectroscopy of Inorganic-Based Materials (Advances in Spectroscopy Vol 14). R. J. H. Clark and R. E. Hester, eds. John Wiley, Chichester, 1987. 

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