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Abstract: Energy-dispersive X-ray absorption spectroscopy is an increasingly powerful tool for the investigation of kinetic processes in chemical systems as an element-specific local structure and electronic-state probe. Advances in synchrotron radiation sources and detector technology are pushing the time resolution of the method to ever shorter periods, currently milliseconds to microseconds, while also providing a concomitant improvement in data quality that now makes feasible the identification of structural and electronic motifs characteristic of intermediate states in chemical processes. To maximize the value of the newly available high-quality time-resolved data, techniques for consistent data normalization and structural component analysis have been developed and here are illustrated in a model study of the electron-transfer reaction between [IrCl6]2- with [Co(CN)5]3-.
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Aug 2005
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Abstract: Time resolved energy dispersive X-ray absorption spectroscopy has been used to follow the structural evolution of the inner-sphere electron transfer reaction between [IrCl6]2? and [Co(CN)5]3?, and to characterise the local structure of the iridium metal centre in the bridged activated complex formed during the reaction.
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Sep 2005
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Abstract: A new high-pressure phase of pure nitric acid (HNO(3)) has been characterised at 1.6 GPa at room temperature by high-pressure neutron powder and X-ray single-crystal diffraction techniques. This is the first crystalline phase obtained upon compression of liquid nitric acid at room temperature and appears to be the stable phase up to pressures of at least 4 GPa. The crystal structure of this new phase shows some similarities to that of the low-temperature phase of nitric acid at ambient pressure, which has been redetermined as part of this study. Both structures share a herringbone packing of hydrogen-bonded molecular catemers, although the presence of disorder within the hydrogen bonds within one of the catemers of the low-temperature phase makes its structure comparatively more complex.
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Jan 2010
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Jun 2008
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Abstract: Subtleties in the electronic structure of complex materials can be directly observed, in great detail, by means of the Bragg diffraction of x-rays whose energy matches an atomic resonance. Strange atomic multipoles can be encountered in the interpretation of measured Bragg intensities, e.g., chirality and magnetic charge. Additionally, the x-ray technique allows the direct observation of the enantiomorphic screw-axis in chiral crystals, such as tellurium, low quartz and berlinite.
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Nov 2009
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Abstract: The oxidation of sulfur in marine archaeological timbers under museum storage conditions is a recently identified problem, particularly for major artefacts such as historic ships excavated from the seabed. Recent work on the Vasa has stressed the role of iron in catalysing the oxidative degradation of the wood cellulose and the polyethylene glycols used to restore mechanical integrity to the timbers. In developing new treatment protocols for the long term preservation of Henry VIII of England's flagship, the Mary Rose, we are investigating the potential of chelating agents to neutralise and remove the iron products from the ships timbers. We have explored the use of aqueous solutions of chelating agents of calcium phytate, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and ammonium citrate to extract the iron compounds. All of these solutions exhibit some level of iron removal; however the key is to find the most effective concentration at pH of around 7 of the reagent solution, to minimise the treatment time and find the most cost-effective treatment for the whole of the Mary Rose hull. Fe K-edge XAFS data from samples of Mary Rose timbers, before and after treatment by the chelating agents mentioned has been collected. The data collected provide valuable insights into the effectiveness of the treatment solutions.
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Oct 2009
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Jan 2010
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Abstract: We have examined alkaline sulfidic (0.5–0.003 M Na2S), aqueous solutions of Hg(II)-S complexes (4–370 ppm Hg(II)) by Hg LIII edge EXAFS spectroscopy at 296, 348 and 423 K. Data were collected using the ID26 High Brilliance X-ray Spectroscopy beamline at the ESRF. Analysis of these EXAFS spectra shows Hg coordinated by two S atoms at 2.30 Å; multiple scattering analyses reveal a linear [–S–Hg–S–] arrangement in the solution complex. These results are in agreement with earlier results on more concentrated solutions of these complexes. There is also evidence in the data for polynuclear sulfide complexes at 296 K and 348 K for samples with the lowest sulfide concentrations although this is complicated by multiple scattering effects.
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Aug 2007
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Abstract: Core/shell nanoparticles of M–B (M = Fe, Co) with amorphous and mixed amorphous + bcc-Fe core have been synthesized by chemical reduction of metallic salts by sodium borohydride. The XANES spectra show the existence of a surface layer consisting of metallic hydroxides in a percentage around 15 at.%. The EXAFS reveals the existence of short-range order in the amorphous core with a contribution from the M–O pairs of the shell and a variation of the coordination numbers with respect to bulk alloys. The existence of Fe-bcc in the mixed alloys is observed in the Fourier transform of the EXAFS data.
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Apr 2007
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Abstract: This study investigated proton adsorption to an extracellular polymeric substance (EPS) producing bacterial strain, Bacillus licheniformis S-86, in order to characterise and quantify the contribution made by EPS to cell surface reactivity. Potentiometric titrations were conducted using both untreated cells and cells from which the EPS layer had been extracted. Surface-complexation modelling indicated the presence of four different functional groups in both untreated and EPS-free cells. These sites are assigned to phosphodiester, (pKa 3.3–3.4), carboxylic (pKa 5.3–5.4), phosphoryl/ (pKa 7.4–7.5) and hydroxyl/amine (pKa 9.9–10.1) type groups. The pKa values for the four groups were very similar for untreated and EPS-free cells, indicating no qualitative difference in composition, but site concentrations in the untreated cells were statistically found to be significantly higher than those in the EPS-free cells for the pKa 3.3–3.4 and pKa 9.9–10.1 sites. Infrared analysis provided supporting evidence that site 2 is carboxylic in nature but did not reveal any difference in IR absorption between the native and EPS-free cells. Dissolved organic carbon (DOC) analysis conducted during this study indicated that DOC release by cells is significant, and that the EPS layer is the major contributor.
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Jan 2008
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