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Abstract: Rh-Containing artificial metalloenzymes based on two mutants of sterol carrier protein_2L (SCP_2L) have been shown to act as hydroformylases, exhibiting significant activity and unexpectedly high selectivity in the hydroformylation of a range of alkenes. Here we report modifications of the catalyst performance by site directed mutagenesis, and studies of the biophysical properties of these catalysts. Catalysts were prepared based on single methionine mutants of SCP_2L for hydroformylation studies. Multinuclear (1H, & 13C), multi-dimensional (2D) solution NMR spectroscopy, EXAFS and XANES were employed to probe the structure. Biophysical studies using 2D [1H 13C] HSQC NMR spectroscopy of 13C-methyl methionine labeled catalysts were used to investigate changes in protein conformation. Hydroformylation studies employing the methionine mutants as catalysts revealed the significant effects of mutation on hydroformylation activity. Among the methionine mutant catalysts M1A of V83C and A100C, and M112A of V83C exhibited significantly higher activity than their parent proteins with improved selectivity. A metal binding role for methionine was suggested by EXAFS and XANES data on selenomethionine variants.

Open Access

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Abstract: The electrochemical generation of hydrogen is a key enabling technology for the production of sustainable fuels. Transition metal chalcogenides show considerable promise as catalysts for this reaction, but to date there are very few reports of tellurides in this context, and none of these transition metal telluride catalysts are especially active. Here, we show that the catalytic performance of metallic 1T′-MoTe2 is improved dramatically when the electrode is held at cathodic bias. As a result, the overpotential required to maintain a current density of 10 mA cm−2 decreases from 320 mV to just 178 mV. We show that this rapid and reversible activation process has its origins in adsorption of H onto Te sites on the surface of 1T′-MoTe2. This activation process highlights the importance of subtle changes in the electronic structure of an electrode material and how these can influence the subsequent electrocatalytic activity that is displayed.

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Abstract: Understanding interactions between iron (oxyhydr)oxide nanoparticles and plutonium is essential to underpin technology to treat radioactive effluents, in clean-up of land contaminated with radionuclides, and to ensure the safe disposal of radioactive wastes. These interactions include a range of adsorption, precipitation and incorporation processes. Here, we explore the mechanisms of plutonium sequestration during ferrihydrite precipitation from an acidic solution. The initial 1 M HNO3 solution with Fe(III)(aq) and 242Pu(IV)(aq) underwent controlled hydrolysis via the addition of NaOH to pH 9. The majority of Fe(III)(aq) and Pu(IV)(aq) was removed from solution between pH 2 and 3 during ferrihydrite formation. Analysis of Pu-ferrihydrite by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy showed that Pu(IV) formed an inner sphere tetradentate complex on the ferrihydrite surface, with minor amounts of PuO2 present. Best fits to the EXAFS data collected from Pu-ferrihydrite samples aged for two- and six- months showed no statistically significant change in the Pu(IV)-Fe oxyhydroxide surface complex despite the ferrihydrite undergoing extensive recrystallisation to hematite. This suggests the Pu remains strongly sorbed to the iron (oxyhydr)oxide surface and could be retained over extended time periods.

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Abstract: The formation of mixed-metal cobalt oxides, representing potential metal–support compounds for cobalt-based catalysts, has been observed at high conversion levels in the Fischer–Tropsch synthesis over metal oxide-supported cobalt catalysts. An often observed increase in the carbon dioxide selectivity at Fischer–Tropsch conversion levels above 80% has been suggested to be associated to the formation of water–gas shift active oxidic cobalt species. Mixed-metal cobalt oxides, namely cobalt aluminate and cobalt titanate, were therefore synthesised and tested for potential catalytic activity in the water–gas shift reaction. We present a preparation route for amorphous mixed-metal oxides via thermal treatment of metal precursors in benzyl alcohol. Calcination of the as prepared nanoparticles results in highly crystalline phases. The nano-particulate mixed-metal cobalt oxides were thoroughly analysed by means of X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, X-ray absorption near edge structure spectroscopy, extended X-ray absorption fine structure, and high-resolution scanning transmission electron microscopy. This complementary characterisation of the synthesised materials allows for a distinct identification of the phases and their properties. The cobalt aluminate prepared has a cobalt-rich composition (Co1+xAl2−xO4) with a homogeneous atomic distribution throughout the nano-particulate structures, while the perovskite-type cobalt titanate (CoTiO3) features cobalt-lean smaller particles associated with larger ones with an increased concentration of cobalt. The cobalt aluminate prepared showed no water–gas shift activity in the medium-shift temperature range, while the cobalt titanate sample catalysed the conversion of water and carbon monoxide to hydrogen and carbon dioxide after an extended activation period. However, this perovskite underwent vast restructuring forming metallic cobalt, a known catalyst for the water–gas shift reaction at temperatures exceeding typical conditions for the cobalt-based Fischer–Tropsch synthesis, and anatase-TiO2. The partial reduction of the mixed-metal oxide and segregation was identified by means of post-run characterisation using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy energy-dispersive spectrometry.

Open Access

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Abstract: We have tested the application of a novel, non-destructive XRD technique to the crystallographic analysis of the pigments in artistic paint samples as a forerunner to the investigation of paintings. Back-reflection energy-dispersive XRD is a powder technique that is not sensitive to the shape of the sample and can therefore be applied without sample preparation. A panel of oil-based paints commonly used by 20th century artists, previously prepared to test hyperspectral imaging capabilities, was used as a test-bed. This panel was taken to the Diamond Light Source synchrotron in the UK and the diffraction patterns of individual paints were recorded. For example, an analysis of the diffraction pattern of ‘Flake White’ (Michael Harding paints) shows clearly the presence of zincite (ZnO), cerrussite (PbCO3) and hydrocerrussite (2PbCO3.Pb(OH)2). In addition to simple phase identification, the technique also furnishes precise unit cell dimensions and information about particle size and morphology via the analysis of peak widths. These additional parameters have the potential to distinguish pigment production methods and dates, crucial information for art historical research and authentication purposes. In this presentation, we will review the data derived using the test panel and discuss the implications for the scientific analysis of paintings and other painted objects.