XANES studies

X-ray absorption near edge structure (XANES) spectroscopy is a non-destructive and sensitive probe of the coordination number and geometry as well as of the effective charge of a chosen atom within a molecule and therefore also of the formal oxidation number. Recently, there have been a number of XANES studies at the sulfur K-edge demonstrating the sensitivity of... 

Evidence for the first reason was demonstrated in X-ray photoelectron spectroscopy (XPS) or X-Ray Absorption Near Edge Structure (XANES) studies, as well as by many voltammetric studies. ... 

X-ray Absorption Near Eldge Structure (XANES) Studies... 

Saib, A. M., Borgna, A., van de Loosdrecht, J., van Berge, P. J., and Niemantsverdriet, J. W. 2006. XANES study of the susceptibility of nano-sized cobalt crystallites to oxidation during realistic Fischer-Tropsch synthesis. Appl. Catal. A 312 12-19. 

NMR investigations [129, 132, 133], EXAFS and XANES studies [134-136], and theoretical calculations [127, 137, 138] performed on higher-order cyanocuprates strongly suggested that the cyanide anion was not bound to copper in these R2Cu(CN)Li2 species. Additional evidence was provided by the first X-ray crystal structure determinations of higher-order cyanocuprates ](C(5H4CH2NMe2-2)2 Cu(CN)Li2] [139] (Fig. 1.34) and [(tBu)2Cu(CN)Li2] [130] (Fig. 1.35). 

XPS spectra were collected for the same petroleum residua and asphaltene samples used in the XANES studies described above. For all samples the total amount of sulfur relative to carbon as measured by XPS was comparable to that determined by bulk elemental analysis. The spectra were deconvoluted by curve fitting, and the approximate quantifications thus derived are shown in Table 111. 

Spectroscopic properties of [Ru(bpy)3] " ", and the effects of varying the diimine ligands in [Ru(bpy)3 L ] + (L = diimine) on the electronic spectra and redox properties of these complexes have been reviewed. The properties of the optical emission and excitation spectra of [Ru(bpy)3] +, [Ru(bpy)2(bpy-d )] + and [Ru(bpy-d )3] " " and of related Os, Rh , and Pt and Os species have been analyzed and trends arising from changes in the metal d or MLCT character in the lowest triplet states have been discussed. A study of the interligand electron transfer and transition state dynamics in [Ru(bpy)3] " " has been carried out. The results of X-ray excited optical luminescence and XANES studies on a fine powder film of [Ru(bpy)3][C104]2 show that C and Ru localized excitation enhances the photoluminescence yield, but that of N does not. 

Research based on time-resolved XAS in an optical pump-x-ray probe scheme has first been implemented at synchrotron radiation sources. Mills et al. [2] used a 20 Hz repetition rate Nd YAG laser to photolyse carbonmonomyoglobin (MbCO) and monitor the photolysis product with time-resolved XAS around the K-edge of the iron atom. Other studies were carried out on different types of photolyzed systems in liquids, by Thiel et al. [3], Clozza et al. [4], Chance et al. [5,6] and Chen et al. [7,8,9]. All these studies were limited to the nanosecond or longer time domain. We recently reported on time-resolved XANES studies of a Ruthenium complex in water solution reaching the picosecond time scale [10]. This work allows us to evaluate the feasibility of future time-resolved XAS experiments, which we present below together with our new results. 

These are soluble, sarcoplasmic calcium-binding proteins found in vertebrates. Invertebrates contain different sarcoplasmic calcium-binding proteins.247 Parvalbumins are low molecular weight (10 000-12 000), acidic proteins which contain two binding sites for Ca2+. The structure of parvalbumin has been determined, and details of the calcium sites are given in Table 6. XANES studies indicate that the calcium sites are similar to those in calmodulin, but different from troponin C.244,248 The two parvalbumin sites have different coordination numbers, six and eight.249... 

Several reviews on gold therapy have appeared recently, with an emphasis on metabolism by Shaw,19 on ligand exchange reactions by Sadler and coworkers,20 on EXAFS and XANES studies by Elder et al.,21 and on studies of gold thiolate complexes in vivo and in vitro by Brown and Smith.22... 

Coethite An EXAFSd and XANES study of As(lll) adsorption to a synthetic goethite suggested bidentate inner-sphere binding. One plot of As(lll) and As(V) pH adsorption envelopes. As(lll) data fitted to constant capacitance SCMf Manning, Fendorf and Goldberg (1998)... 

Birnessite (8-Mn02) Condensation of glucose and glycine under soil ambient conditions (measurement of optical density) yields of humic substances XANES study of change in speciation of Mn ESR study of Mn speciation in solution 13C CPMAS NMR spectra of FA fraction resembling spectra of natural FAs Jokic et al. (2001b)... 

A XANES study of the Au/A1203 system has shown that Au3+ was reduced to Au° in helium at 623 K, and that sodium cyanide treatment dissolved some 80% of the gold the remaining Au + was however reduced by a second helium treatment.54... 

The reversible character of the Al transitions was recently confirmed by 27A1-MAS-NMR and Al K-edge XANES studies by van Bokhoven et al.. 2 Following heating and steaming up to 450°C the Al reverts completely to its tetrahedral lattice position upon ammonia treatment. At 550°C irreversible transitions of aluminum come to the fore. 

XANES studies of ruthenium-polystyrene hydrogenation catalysts (32) show strong multiple-scattering resonance due to carbon atoms in the first coordination shell which exhibit high backscattering at low kinetic energy of the photoelectron, in accordance with EXAFS results. 

Bianconi et al. have devoted XANES studies to the determination of the local structure of amorphous A1203 (15,29) and Si02 (29,31). In a review dedicated to problems in mineralogy and geochemistry, Waychunas and Brown (306) have considered crystalline and amorphous aluminosilicates. 

The effect of SO2 gas has been also examined in relation with the behavior of ceria as sorbent/catalyst for the removal/destniction of this pollutant [187]. An 0 K edge XANES study complemented XPS data (see above) showing that contact with SO2 produces sulfates which thermally decompose in the 390-670 K range, and that the presence of anion vacancies favors the formation of SO3 instead of SO4. The promotion of ceria with copper was shown to enhance the SO2 removal activity in all cases (reduced/oxidized state). 

Fig. 12.11 Structure and composition of three different ND powders with diamond contents ranging from <23 wt.% (UD50) to >80 wt.% (UD98) as determined by XANES studies [78]...

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