Energy‐dispersive X‐ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxides

An energy‐dispersive X‐ray absorption spectroscopy beamline mainly dedicated to X‐ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending‐magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set‐up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr‐doped manganites and the structural deformation in nickel perovskites under high applied pressure.     

Multimodal imaging: an evaluation of univariate and multivariate methods for simultaneous EEG/fMRI

The combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has been proposed as a tool to study brain dynamics with both high temporal and high spatial resolution. Multimodal imaging techniques rely on the assumption of a common neuronal source for the different recorded signals. In order to maximally exploit the combination of these techniques, one needs to understand the coupling (i.e., the relation) between electroencephalographic (EEG) and fMRI blood oxygen level-dependent (BOLD) signals.     

Effects of Impregnated Amidophosphonate Ligand Concentration on the Uranium Extraction Behavior of Mesoporous Silica

A series of solid-phase uranium extractants were prepared by post-synthesis impregnation of a mesoporous silica support previously functionalized with octyl chains by direct silanization. Five materials were synthesized with 0, 0.2, 0.3, 0.4 and 0.5 mmol of the amidophosphonate ligand DEHCEBP per gram of functionalized solid, and the effect of the ligand concentration on the uranium extraction efficiency and selectivity of the materials was investigated. Nitrogen adsorption–desorption data show that with increasing ligand loadings, the specific surface area and average pore volume decrease as the amidophosphonate ligand fills first the micropores and then the mesopores of the support. Acidic uranium solutions with a high sulfate content were used to replicate the conditions in ore treatment leaching solutions. Considering the extraction kinetics, the equilibration time was found to increase with the ligand concentration, which can be explained by the clogging of micropores and the multilayer arrangement of the DEHCEBP molecules in the materials with their highest ligand contents. The fact that the equilibrium ligand/uranium ratio is about 2 mol/mol regardless of the ligand concentration in the material suggests that all the ligand molecules remain accessible for extraction. The maximum uranium extraction capacities ranged from 30 mg∙g⁻¹ at 0.2 mmol∙g⁻¹ DEHCEBP to 54 mg∙g⁻¹ in the material with 0.5 mmol∙g⁻¹ DEHCEBP. These materials could therefore potentially be used as solid-phase uranium extractants in acidic solutions with high sulfate concentrations.     

β-Alkylation through Dehydrogenative Coupling of Primary Alcohols and Secondary Alcohols Catalyzed by Thioether-Functionalized N-Heterocyclic Carbene Ruthenium Complexes

A catalytic system for the direct β-alkylation of secondary alcohol with primary alcohol has been investigated. In this work, a series of cationic Ru(II)(η⁶-p-cymene) complexes with thioether-functionalized N-heterocyclic carbene ligands (imidazole-based 1 a – l and benzimidazole-based 2 a – e ) have been successfully synthesized and evaluated as catalysts. This investigation shows that modifications in the ligand moiety (thioether group and/or NHC core) have a strong effect on both selectivity and reactivity. Imidazole-based complex 1 c , with only 1 mol % of catalyst loading, displayed the best catalytic activity as well as the highest selectivity for the β-alcohol up to 98 : 2 for this tandem borrowing hydrogen/aldol methodology. Applied to a wide range of substrates, β-alkylated secondary alcohols have been obtained in moderate yields, but generally with complete conversion and very high selectivity.