Hydration Mossbauer spectroscopy

Three series of Au nanoparticles on oxidic iron catalysts were prepared by coprecipitation, characterized by Au Mossbauer spectroscopy, and tested for their catalytic activity in the room-temperature oxidation of CO. Evidence was found that the most active catalyst comprises a combination of a noncrys-taUine and possibly hydrated gold oxyhydroxide, AUOOH XH2O, and poorly crystalhzed ferrihydrate, FeH0g-4H20 [421]. This work represents the first study to positively identify gold oxyhydroxide as an active phase for CO oxidation. Later, it was confirmed that the activity in CO2 production is related with the presence of-OH species on the support [422]. 

Cytochromes from bacterial, yeast, and mammalian sources have been investigated by Mossbauer spectroscopy (114—117). Horseheart cytochrome c and the c-type cytochrome from T. utilis show spectra characteristic of low-spin Fe(III) in the oxidized form of the protein and low-spin Fe(II) for the reduced form of the protein. Lang et al. (115) have analyzed the Mossbauer data in terms of a low-spin Hamiltonian in some detail. Cooke and Debrunner (116) present quadrupole data on dehydrated forms of oxidized and reduced cytochrome c the quadrupole splittings for hydrated and dehydrated forms of the reduced protein are quite similar in contrast to a difference of the oxidized form. No spin-state change is reported for either form of cytochrome c. 

Several investigators have noted that the Al/Fe ratio in the product phases tends to be higher than that of the starting material, and have concluded that an iron(III) oxide or hydroxide is also formed. Teoreanu et al. (T33), using Mossbauer spectroscopy and XRD, concluded that the hydration products formed from C2F or C4AF at ordinary temperatures included FH3. With C2F above 75°C, this was replaced by hematite. Fukuhara et al. (F29)... 

Full internal motions of protein Dynamic and thermodynamic coupling between hydration water and protein, seen in Mossbauer spectroscopy and computer simulations... 

Studies using high-resolution transmission electron microscopy coupled with Mossbauer spectroscopy on experimental systems (Tamaura et al., 1981, 1983) and on flocculants, the precipitates associated with bacterial activity (Schwertmann and Fitzpatrick, 1992), often detect the presence of other iron minerals such as the more hydrated iron... 

Pinerii and coworkers, and a few other groups, have used ESR and Mossbauer spectroscopy as well as SANS, extended x-ray absorption fine structure (EX.AFS), and magnetization and susceptibility data to analyze local. struct.ure in perfluorinated ionomer membranes and the distribution of water within them isee, for inst,ance, (61-65) 1. The application of the KNDOR (electron nuclear double resonance) technique to deuteriated methanol-swollen Scunples of these membranes has been reportesd i-ecentiy (66). Photophysical methods have also tef n applied in hydration. si.udies of these membranes (67-69). Finally, some NMR results on the same hydrated perfluorinat,ed ionomer.s well as on hydrated... 

On the other hand, the spectroscopic techniques probe individual ionic species which build up the ionic aggregates. These techniques permit the investigation of the immediate chemical environments, the mobility of cations and water-ions Interactions. Metal nuclear magnetic resonance and Mossbauer spectroscopy are sensitive probes of counter cations and provide valuable information on the cations and their environment. Infrared spectroscopy is complementary to the above methods and addresses itself to the bound SO3" anions or water and the interaction of water molecules with the various species with which it is in contact. A common conclusion that is reached in the above mentioned studies is that four or five water molecules are needed to complete the hydration process. Reducing the level of moisture content (which surrounds the ionic species) below four water molecules per unit SOj site enhances the Coulombic interaction between the ionic species. This eventually leads to the formation of ion pairs in the dry membranes. These ion pairs do not necessarily disperse homogeneously in the fluorocarbon matrix but tend to form aggregates, phase separated from the matrix materials as demonstrated in the scattering studies. 

Until recently, all ferritin cores were thought to be microcrystalline and to be the same. However, x-ray absorption spectroscopy, Mossbauer spectroscopy, and high-resolution electron microscopy of ferritin from different sources have revealed variations in the degree of structural and magnetic ordering and/or the level of hydration. Structural differences in the iron core have been associated with variations in the anions present, e.g., phosphate or sulfate, and with the electrochemical properties of iron. Anion concentrations in turn could reflect both the solvent composition and the properties of the protein coat. To understand iron storage, we need to define in more detail the relationship of the ferritin protein coat and the environment to the redox properties of iron in the ferritin core. 

The fact that iron(ll) was clearly detected by Mossbauer spectroscopy gives a direct evidence for the iron uptake mechanism of strategy I. As the time of the iron treatment increased, the reductive capacity was decreasing because of the increased amount of iron already taken up by the root [73]. According to the Mossbauer parameters of the Fe(ll), one can see that it formed a hexaaquo complex [52] that might be the primary hydrated product of the ferric chelate reductase enzyme, accumulated in the apoplast and not attached to any of the cell wall components. At the same time, the increase in the Fe(lll)A component, representing iron both attached to the apoplast and taken up inside the cell, could be observed. The ferritin-like component (denoted by Fe(lll)B) was absolutely not detectable, which means this duration of... 

The main methods of investigating the effect of supplementary materials and other additions on cement hydration include XRD, SEM, NMR, Mossbauer spectroscopy, IR, and thermal analysis. Poorly crystallized products that form in these materials are advantageously investigated by TG, DTG, DTA, DSC, and conduction calorimetry. Thermal methods have also been suggested for characterization of the supplementary and other materials. 

Internal dynamics of biomolecules is practically frozen without water. Upon increasing hydration level, it develops in a stepwise fashion [508]. At h K 0.15 g/g, internal protein motion, monitored by hydrogen exchange, achieves its solution rate [509]. Full internal dynamics of lysozyme is restored at /t 0.38 g/g [510]. Mossbauer spectroscopy studies evidence restoration of the internal dynamics of lysozyme... 

The verification of the presence of hydrogen in the film has proved more controversial, primarily because many of the structural investigations have been carried out after the film has been dried in vacuo. An example of the problems here is the fact that electron diffraction, which has to be carried out in vacuo, reveals a relatively well-crystallised spinel lattice whose origin may be the comparatively high sample heating encountered in the electron beam. Moreover, the use of in situ techniques, such as Mossbauer and X-ray absorption spectroscopy, clearly reveals marked differences between the spectra of the films in situ and the spectra of the same films ex situ as well as the spectra of y-Fe203 and y-FeOOH standards. These differences are most naturally ascribed to hydration of the spinel forms. 

Protein rate processes are strongly affected by hydration. The dry protein shows greatly reduced internal motions, measured by Moss-liauer spectroscopy, neutron scattering, fluorescence spectroscopy, and other methods. Surface motions, monitored by spin probes or spin or Mossbauer labels, are similarly frozen in the dry protein. The following paragraphs comment on the appearance of motion characteristic of the hydrated protein and on the coupling between protein and solvent motions. 

Spectroscopic methods for hydration of ions were reviewed for structural aspects and dynamic aspects of ionic hydration by Ohtaki and Radnai (150). They discussed X-ray diffraction, neutron diffraction, electron diffraction, small-angle X-ray (SAXS) and neutron-scattering (SANS), quasi-elastic neutron-scattering (QENS) methods, extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) spectroscopies, nuclear magnetic resonance (NMR), Mossbauer, infrared (IR), Raman, and Raleigh-Brillouin spectroscopies. The clay interlayer molecular modeling where clay surface is interfaced with aqueous solution also includes ions that are also solvated by interlayer water. 

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