Local structural analyses on molten terbium fluoride in lithium fluoride and lithium-calcium fluoride mixtures

X-ray absorption fine structure (XAFS) measurements on terbium fluoride in molten lithium fluoride and in molten lithium-calcium fluoride mixtures, (e.g. 0.20TbF₃-0.80LiF, 0.20TbF₃-0.62LiF-0.18CaF₂, 0.20TbF₃-0.48LiF-0.32CaF₂, 0.50TbF₃-0.50LiF, and 0.50TbF₃-0.38LiF-0.12CaF₂), have been carried out. In the solid state, coordination number of terbium (N_i) and inter ionic distances between terbium and fluorine in the first neighbor (r_i) are nearly constant in all mixtures. In 0.20TbF₃-0.80LiF, 0.20TbF₃-0.62LiF-0.18CaF₂ and 0.50TbF₃-0.50LiF mixtures, N_i's decrease from ca. 8 to 6 and r_i's also decrease from ca. 2.29 to 2.26 Å on melting. On the other hands, in molten 0.20TbF₃-0.48LiF-0.32CaF₂ and 0.50TbF₃-0.38LiF-0.12CaF₂ mixtures, N_i's are slightly larger than 6 and r_i's do not change. These facts correspond to the amount of F⁻ supplied by solvent melts, i.e. the effect of CaF₂ becomes predominant at bCaF₂ > 0.32 in ternary 0.20TbF₃-aLiF-bCaF₂ mixtures and at bCaF₂ > 0.12 in ternary 0.50TbF₃-aLiF-bCaF₂ mixtures.     

Functional silica nanoparticles synthesized by water-in-oil microemulsion processes

Water-in-oil (W/O) microemulsion is a well-suitable confined reacting medium for the synthesis of structured functional nanoparticles of controlled size and shape. During the last decade, it allowed the synthesis of multi-functional silica nanoparticles with morphologies as various as core–shell, homogenous dispersion or both together. The morphology and properties of the different intermediates and final materials obtained through this route are discussed in the light of UV–Vis–NIR spectroscopy, dynamic light scattering (DLS) and X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and magnetometer SQUID analysis.     

Coordination properties of zinc finger peptides revisited: ligand competition studies reveal higher affinities for zinc and cobalt

Zinc fingers are ubiquitous small protein domains which have a Zn(Cys)(4-x)(His)(x) site. They possess great diversity in their structure and amino acid composition. Using a family of six peptides, it was possible to assess the influence of hydrophobic amino acids on the metal-peptide affinities and on the rates of metal association and dissociation. A model of a treble-clef zinc finger, a model of the zinc finger site of a redox-switch protein, and four variants of the classical ββα zinc finger were used. They differ in their coordination set, their sequence length, and their hydrophobic amino acid content. The speciation, metal binding constants, and structure of these peptides have been investigated as a function of pH. The zinc binding constants of peptides, which adopt a well-defined structure, were found to be around 10(15) at pH 7.0. The rates of zinc exchange between EDTA and the peptides were also assessed. We evidenced that the packing of hydrophobic amino acids into a well-defined hydrophobic core can have a drastic influence on both the binding constant and the kinetics of metal exchange. Notably, well-packed hydrophobic amino acids can increase the stability constant by 4 orders of magnitude. The half-life of zinc exchange was also seen to vary significantly depending on the sequence of the zinc finger. The possible causes for this behavior are discussed. This work will help in understanding the dynamics of zinc exchange in zinc-containing proteins.     

Total syntheses of the bromotyrosine-derived natural products ianthelline, 5-bromoverongamine and JBIR-44

The total syntheses of the bromotyrosine-derived natural products ianthelline, 5-bromoverongamine and JBIR-44 are described and their cytotoxic activity in a cervical cancer (HeLa) cell line and human umbilical vein endothelial cells (HUVECs) are reported.     

Animal urine as painting materials in African rock art revealed by cluster ToF‐SIMS mass spectrometry imaging

The rock art site at the village of Songo in Mali is a very important Dogon ritual place where, since the end of the nineteenth century until today, takes place the ceremony of circumcision. During these ceremonies, paintings are performed on the walls of the shelter with mainly three colors: red, black and white. Ethnological literature mentions the use of animal urine of different species such as birds, lizards or snakes as a white pigment. Urine of these animals is mainly composed of uric acid or urate salts. In this article, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is used to compare uric acid, snake urine and a sample of a white pigment of a Dogon painting coming from the rock art site of Songo. ToF‐SIMS measurements in both positive and negative ion modes on reference compounds and snake urine proved useful for the study of uric acid and urate salts. This method enables to identify unambiguously these compounds owing to the detection in negative ion mode of the ion corresponding to the deprotonated molecule ([M ? H]^? at m/z 167.01) and its fragment ions. Moreover, the mass spectra obtained in positive ion mode permit to differentiate uric acid and urate salts on the basis of specific ions. Applying this method to the Dogon white pigments sample, we show that the sample is entirely composed of uric acid. This proves for the first time, that animal urine was used as a pigment by the Dogon. The presence of uric acid instead of urate salts as normally expected in animal urine could be explained by the preparation of the pigment for its application on the stone. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal stability of TiO2-anatase: Impact of nanoparticles morphology on kinetic phase transformation

TiO₂ is a material of great interest for many technological applications among which, as catalyst support. As this specific application requires a good thermal stability of the material, the phase transition between the two most commonly used titania polymorphs, anatase and rutile, has been extensively studied over the past decade. However not much importance has been given to the initial and final particles morphologies. In this study, anatase nanoparticles with an elongated shape were synthesized and their kinetic phase transformation was studied. The thermal treatments were conducted at temperatures ranging from 500 to 700 °C. The morphology evolution and the phase transition were characterized by X-ray diffraction and transmission electron microscopy. The phase transformation kinetics is best described by the interface nucleation models. The values of the measured kinetic parameters are significantly lower than those proposed in the literature for isotropic particles, with an activation energy of E_a = 345 kJ mol^?1. The influence of morphology and, as a consequence, the influence of exposed faces on anatase particles, are presented and discussed.     

Solid-state NMR study of Na versus K doping of para-phenylene oligomers

13C solid-state nuclear magnetic resonance (NMR) experiments were performed on p-terphenyl, p-quaterphenyl, and p-sexiphenyl either in their pristine or doped with alkali metals form. The 13C NMR spectra of doped materials show new resonances by comparison with pristine compounds. For the K-doped materials, these resonances appear in the 90-135 ppm range, while for Na-doped materials, they are observed in the larger 20-150 ppm range. It suggests that the interaction between the alkali ions and the oligomers depends on the nature of the alkali. It is corroborated by 13C NMR experiments after exposure to air that show different behaviors. As expected, air exposure of K-doped samples restores the pristine spectra. This is not the case for Na doping, where the signature of the doped material persists even after exposure to air. In the latter case, some 13C resonances can be assigned to sp3 hybridized carbons and to the quinoid group. It suggests that Na doping induces a polymerization of the oligophenylenes.     

An Energy Stable Monolithic Eulerian Fluid-Structure Numerical Scheme

The conservation laws of continuum mechanics, written in an Eulerian frame, do not distinguish fluids and solids, except in the expression of the stress tensors, usually with Newton’s hypothesis for the fluids and Helmholtz potentials of energy for hyperelastic solids. By taking the velocities as unknown monolithic methods for fluid structure interactions (FSI for short) are built. In this paper such a formulation is analysed when the solid is compressible and the fluid is incompressible. The idea is not new but the progress of mesh generators and numerical schemes like the Characteristics-Galerkin method render this approach feasible and reasonably robust. In this paper the method and its discretisation are presented, stability is discussed through an energy estimate. A numerical section discusses implementation issues and presents a few simple tests.     

Determination of cadmium in Bentonite clay mineral using a carbon paste electrode

Sodium activated Bentonite, a sodium modified Montmorillonite, was submitted to cadmium sorption from nitrate solutions in order to simulate a cadmium polluted clay mineral. The remaining cadmium concentration in solution was analyzed at equilibrium by means of Differential Pulse Polarography (DPP) in order to calculate the cadmium concentration sorbed by the clay. The cadmium distribution between clay mineral and solution was observed for different concentrations, showing a Freundlich sorption profile. The clay mineral, previously submitted to the cadmium sorption procedure, was included in a carbon paste in order to investigate the cadmium content by voltammetric determination. For cadmium detection in Bentonite, a linear response of the carbon paste electrode (CPE) was observed in the 5 · 10^–5– 1.8 · 10^–4 mol/g range with good reproducibility. Received: 23 July 1998 / Revised: 19 November 1998 / Accepted: 26 November 1998