Mossbauer spectroscopy sample preparation

In an attempt to assess the biological relevance of the cluster conversion observed in the purified FNR transcription factor and the oxygen sensing properties of this protein in vivo, we have studied by Mossbauer spectroscopy several preparations of . coli maintained in anaerobic media and then submitted to controlled aerobic conditions. Our strategy was to study pairs of whole cell samples in which FNR is either over-expressed or is lacking which would enable us to recognize the contri-... 

The precursor of ° Ru is ° Rh (tip, = 3 years). It is prepared by irradiating natural ruthenium metal with 20 MeV deuterons, " Ru (d, n) Rh. The target is then allowed to decay for several months to diminish the accompanying Rh activity. In a report on ° Ru Mossbauer spectroscopy [111], the authors reported on spectra of Ru metal, RuOa, and [Ru(NH3)4(HS03)2] at liquid helium temperature in standard transmission geometry using a Ge(Li) diode to detect the 127 keV y-rays. The absorber samples contained 1 g of ruthenium per cm. ... 

Properties of FeCr,o solid samples have been studied by X-ray diffraction, 57Fe Mossbauer spectroscopy and magnetic measurements to stimulate the interaction of Fe with fullerene. FeCr,o samples have been prepared by decomposition of the 1,3-dipolar cycloadduct of the fullerene and ferrocene nitrile oxide. The components exhibit super paramagnetic properties originating from an interaction between FeCr,o complexes within the nano-particles. Each nano-particle consists of hundreds to thousands complexes (546). 

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

As described above, the combination of EPR and Mossbauer spectroscopies, when applied to carefully prepared parallel samples, enables a detailed characterization of all the redox states of the clusters present in the enzyme. Once the characteristic spectroscopic properties of each cluster are identified, the determination of their midpoint redox potentials is an easy task. Plots of relative amounts of each species (or some characteristic intensive property) as a function of the potential can be fitted to Nernst equations. In the case of the D. gigas hydrogenase it was determined that those midpoint redox potentials (at pFi 7.0) were —70 mV for the [3Fe-4S] [3Fe-4S]° and —290 and —340mV for each of the [4Fe-4S]> [4Fe-4S] transitions. 

The state of tin in Pt/Sn/alumina catalysts was investigated bv Li and Shia (25) via Mossbauer spectroscopy (i/9Sn enriched isotopes) and XPS. The former technique indicated the presence of Sn+, Sn+2 and Sn, in proportions that depended on the method of preparation, but in all cases the Sn+4 component dominated. These conclusions were confirmed by the XPS experiments. Additional TPR tests on the reduced catalyst and on samples exposed to air showed that reoxidation of Pt/Sn/alumina reduced preparations was rather slow, confirming our EXAFS observations. The presence of zero valent tin in similar preparations, using the acetone complexation procedure, was recently confirmed by Li, Stencel and Davis (12) in an extended XPS investigation. For reduced samples, with a Pt Sn ratio 1 5, these authors estimated that approximately 68% of the tin was in the metallic state. However, they observed that exposure of the sample to air for 10 minutes entirely eliminated the XPS detectable Sn°. Their data also indicated that upon reduction, chlorine migrated from the surface to the alumina. Thus, XPS which measures surface composition indicates a higher sensitivity to oxidation than was demonstrated by our EXAFS experiments, which is a bulk diagnostic. 

Sample purity is a key concern. The NRVS experiment is a bulk technique sampling all Fe nuclei, and impurities that also contain the probe nucleus may confound quantitative data interpretation. Impurities may be introduced during sample preparation or may result from sample instability during measurement. Because of this, care must be taken to ensure purity and reproducibility as judged by Mossbauer (see Mdssbauer Spectroscopy), single-crystal X-ray diffraction, electronic absorption spectroscopy (see Electronic Spectroscopy), Raman spectroscopy or other qnalitative techniqnes. 

Because Raman spectmm stems from the bonds vibrations, it provides an intrinsic nano-probing and offers a bottom-up approach of nanostmctured materials that comes as a good complement to other techniques such as transmission electron microscopy. X-ray diffraction, and infrared, and Mossbauer spectroscopy. Since almost no sample preparation is needed, Raman technique [12, 13] is commonly used to investigate nanomaterials. This could provide the phase identification and, possibly, size estimation [14]. 

Einally, europium oxide nanorods have been prepared by the sonication of an aqueous solution of europium nitrate in the presence of ammonia [85]. The particle sizes measured from transmission electron micrographs and HRSEM are about 50 X 500 nm (W x L). Sonication of an aqueous solution of europium nitrate in the presence of ammonia results in the precipitation of europium hydroxide The as-prepared material is europium hydroxide, as confirmed by TGA, DSC, XPS, and Mossbauer spectroscopy measurements, as well as by PXRD of the as-prepared sample assisted by microwave irradiation... 

A series of ultrastable zeolite Y samples containing Fe(III) ions were prepared by solid-state ion exchange of the ammonium forms of zeolite Y under deep-bed conditions at various temperatures [19]. The properties of these materials were compared with those of FeY samples prepared by conventional solid-state ion exchange using Mossbauer spectroscopy. 

According to X-ray powder data by Mayer et al. (1973) and Mayer and Cohen (1972) EuAgjSij is tetragonal with the ordered ThCr2Si2-type [I4/mmm, a = 4.309(5), c = 10.49(5)] for sample preparation, see LaAg2Si2. From the large unit cell dimensions as well as from Mossbauer spectroscopy Mayer and Cohen... 

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