Group Mossbauer spectroscopy

R3Sn(IV)]4H2TPPS, (R = Me, Bu, Ph), respectively, in the solid state, are maintained in solution. Pentacoordination, in a Tbp configuration, eq-Rs, has been proposed for RsSnflV) derivatives of L-homocysteic acid on the basis of IR and Mossbauer spectroscopy The SO3 and NH3 groups of L-homocysteic acid are not involved in the coordination. 

With trifluoromethanesulfonic acid, all four vinyl groups are displaced at - 78°, to give a compound that was shown by Mossbauer spectroscopy to contain both Sn(II) and Sn(IV), and that was assigned the formula Sn [Sn (S03CF3)6]. Trivinyltin carboxylates have also been prepared from the reaction between tet avinyltin and mercury(I) carboxylates, which may be generated electrochemically in situ (185). 

Until then, the purification of the Fepr protein had been a laborous job as a 240-L batch yielded only as little as 5 mg of protein. With the overexpression clones of the Fepr proteins, the range of proteinconsuming studies such as Mossbauer spectroscopy, EXAFS, and, last but not least, crystallization experiments was greatly extended. Thus, several groups set off to systematically investigate the spectroscopic properties of both Fepr proteins, poised at all four (proposed) redox states. 

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... 

The magnetic properties of the new solid solution series SrFe Rui 3 3, (0 < X < 0.5) with distorted perovskite structure, where iron substitutes exclusively as Fe(in) thereby causing oxygen deficiency, has also been studied by Greenwood s group [147] using both u and Fe Mossbauer spectroscopy. Iron substitution was found to have little effect on the magnetic behavior of Ru(IV) provided that X remains small (x < 0.2). 

The reader is also referred to the CD-ROM enclosed at the end of this book, where we have collected a large variety of examples of applications of Mossbauer spectroscopy in many disciplines. The first part of the CD-ROM presents a lecture series on Mossbauer spectroscopy (Principles and typical applications), which has been arranged particularly for teaching purposes. The second part comprises a large number of special applications contributed by various research groups specialized on Mossbauer spectroscopy. 

The results of Mossbauer spectroscopy investigations of Fe(C0)5 decomposition on Ti02 samples pretreated in three different fashions are given in Table I. These three samples were pretreated in a manner intended to produce different populations of Ti + ions and hydroxyl groups on the surface of the support. This is explained in the discussion section. 

The [Fe =0(TMP+ )]+ complex exhibited a characteristic bright green color and corresponding visible absorbance in its UV-vis spectrum. In its NMR spectrum, the meta-proton doublet of the porphyrin mesityl groups were shifted more than 70 ppm downfield from tetramethylsilane (TMS) because they were in the presence of the cation radical, while the methyl protons shift between 10 and 20ppm downfield. In Mossbauer spectroscopy, the isomer shift, 5 of 0.06 mm/s, and A q value of 1.62mm/s were similar to those for other known Fe(IV) complexes. Electron paramagnetic resonance (EPR), resonance Raman (RR), and EXAFS spectroscopies provided additional indications of an Fe =0 n-cation radical intermediate. For instance,... 

The rapid progress in the understanding of the active site of aconitase in the 1980 s has primarily originated from the work of H. Beinert and his collaborators. Three essential factors contributed to the success of this work 1) a ready and consistent source of enzyme (gram quantities), 2) a solid chemical and biochemical understanding of aconitase, and 3) close interactions with outstanding collaborators (most notably E. Munck s group for Mossbauer spectroscopy and B. M. 

Spectroscopic studies on the Fe-Mo protein by EPR and Mossbauer spectroscopy have shown six iron atoms each in a distinctive magnetic environment coupled to an overall S=3/2 spin system (6,7,8) and electron nuclear double resonance (ENDOR) studies suggest one molybdenum per spin system (8). The 5 Fe signals (five or six doublets) observed in the ENDOR spectra (8) indicate a rather asymmetric structure for the Fe/Mo/S aggregate in which the iron atoms roughly can be grouped into two sets of trios, each set having very similar hyperfme parameters. 

In a recent study, Fernandez-Bertran et al. used mechanochemical reactions to prepare a number of hemin complexes with amino acids such as arginine, histidine, lysine, methionine and tryptophan. The basic amino acids react with the hemin peripheral propionic acid groups, while arginine is also able to form a pentacoordinated complex at the Fe(III) centre. The reactions were followed by IR and Mossbauer spectroscopies [77a]. The solid-state reaction of hemin with KCN, Na2S and various substituted imidazoles has also been investigated [77b]. 

Mossbauer spectroscopy Oxidation and spin states of the metal in the prosthetic group. Electronic structure and spatial arrangement of the active centre 124,125)... 

The discussion of activity from X-ray data in conjunction with kinetic data is also difficult because, apart from considerations of dynamics, these techniques do not provide the essential knowledge about the energy states of given atoms or groups. It is necessary to inspect the electronic structure of at least certain regions of the protein. Methods exist for this inspection, and these include electron paramagnetic resonance, ultraviolet, circular dichroism, Raman and Mossbauer spectroscopies. The full understanding of activity can only come when the information derived from all available methods is assimilated and rationalized. 

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