Preparation of thin-sections of painting fragments: Classical and innovative strategies

For more than a century, the analyses of painting fragments have been carried out mainly through the preparation of thick resin-embedded cross-sections. Taking into account the development of innovative micro-analytical imaging techniques, alternatives to this standard preparation method are considered. Consequently, dedicated efforts are required to develop preparation protocols limiting the risks of chemical interferences (solubilisation, reduction/oxidation or other reactions) which modify the sample during its preparation, as well as the risks of analytical interferences (overlap of detected signals coming from the sample and from materials used in the preparation). This study focuses particularly on the preparation of thin-sections (1–20 μm) for single or combined fourier transform infrared (FTIR) spectroscopy and X-ray 2D micro-analysis. A few strategies specially developed for the μFTIR analysis of painting cross-sections have already been reported and their potential extrapolation to the preparation of thin-sections is discussed. In addition, we propose two new specific methods: (i) the first is based on a free-embedding approach, ensuring a complete chemical and analytical neutrality. It is illustrated through application on polymeric design objects corpus; (ii) the second is based on a barrier coating approach which strengthens the sample and avoids the penetration of the resin into the sample. The barrier coating investigated is a silver chloride salt, an infrared transparent material, which remains malleable and soft after pellet compression, enabling microtoming. This last method was successfully applied to the preparation of a fragment from a gilded Chinese sculpture (15th C.) and was used to unravel a unique complex stratigraphy when combining μFTIR and μXRF.     

Importance of temporal-envelope speech cues in different spectral regions

This study investigated the ability to use temporal-envelope (E) cues in a consonant identification task when presented within one or two frequency bands. Syllables were split into five bands spanning the range 70-7300 Hz with each band processed to preserve E cues and degrade temporal fine-structure cues. Identification scores were measured for normal-hearing listeners in quiet for individual processed bands and for pairs of bands. Consistent patterns of results were obtained in both the single- and dual-band conditions: identification scores increased systematically with band center frequency, showing that E cues in the higher bands (1.8-7.3 kHz) convey greater information.     

Structure of a Complex Formed by a Protein and a Helical Aromatic Oligoamide Foldamer at 2.1 Å Resolution

In the search of molecules that could recognize sizeable areas of protein surfaces, a series of ten helical aromatic oligoamide foldamers was synthesized on solid phase. The foldamers comprise three to five monomers carrying various proteinogenic side chains, and exist as racemic mixtures of interconverting right‐handed and left‐handed helices. Functionalization of the foldamers by a nanomolar ligand of human carbonic anhydrase II (HCA) ensured that they would be held in close proximity to the protein surface. Foldamer–protein interactions were screened by circular dichroism (CD). One foldamer displayed intense CD bands indicating that a preferred helix handedness is induced upon interacting with the protein surface. The crystal structure of the complex between this foldamer and HCA could be resolved at 2.1 Å resolution and revealed a number of unanticipated protein–foldamer, foldamer–foldamer, and protein–protein interactions.     

Comparative Analysis of Conjugated Alkynyl Chromophore–Triazacyclononane Ligands for Sensitized Emission of Europium and Terbium

A series of europium and terbium complexes based on a functionalized triazacyclononane carboxylate or phosphinate macrocyclic ligand is described. The influence of the anionic group, that is, carboxylate, methylphosphinate, or phenylphosphinate, on the photophysical properties was studied and rationalized on the basis of DFT calculated structures. The nature, number, and position of electron‐donating or electron‐withdrawing aryl substituents were varied systematically within the same phenylethynyl scaffold in order to optimize the brightness of the corresponding europium complexes and investigate their two‐photon absorption properties. Finally, the europium complexes were examined in cell‐imaging applications, and selected terbium complexes were studied as potential oxygen sensors.     

Comparison between the behaviour of native and denatured DNA at mercury and gold electrodes by capacity measurements and cyclic voltammetry

The effect of the double-layer structure on the adsorption of DNA has been studied by comparing its behaviour at Hg and Au interfaces. Some features of the adsorbing behaviour are studied by the use of combined cyclic voltammetry and capacity measurement. The results illustrate the common characteristics at both interfaces as regards the lowering of the capacity in the vicinity of the pzc, although the kinetics of the process is different on the two metals. The adsorption behaviour at larger values of the charge cannot be compared directly because on Hg this is masked by a reduction at negative charges which does not occur in the accessible range on Au, while an oxidation occurs at positive charges on Au.     

Organosoluble star polymers from a cyclodextrin core

Well‐defined star polymers were synthesized with a combination of the core‐first method and atom transfer radical polymerization. The control of the architecture of the macroinitiator based on β‐cyclodextrin bearing functional bromide groups was determined by ¹³C NMR, fast atom bombardment mass spectrometry, and elemental analysis. In a second step, the polymerization of the tert‐butyl acrylate monomer was optimized to avoid a star–star coupling reaction and allowed the synthesis of a well‐defined organosoluble polymer star. The determination of the macromolecular dimensions of these new star polymers by size exclusion chromatography/light scattering was in agreement with the structure of armed star polymers in a large range of predicted molecular weights. This article describes a new approach to polyelectrolyte star polymers by postmodification of poly(tert‐butyl acrylate) by acrylic arm hydrolysis in a water‐soluble system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5186–5194, 2005     

Electrochemical investigations of amino acids at solid electrodes: Part II. Amino acids containing no sulfur atoms: Tryptophan,tyrosine, histidine and derivatives

The electrochemical properties of amino acids containing no sulfur atoms have been investigated using stationary or rotating solid electrodes such as Au and vitreous carbon. Among the 20 amino acids present in the proteins only tryptophan and tyrosine are specifically oxidizable at a gold, platinum or carbon electrode. Histidine is oxidizable only at a carbon electrode. In the case of tryptophan and tyrosine the oxidation phenomena are very similar whatever the nature of the electrode. Oxidation can be performed on a smooth surface electrode, and at the level of metal oxide formation it leads to a mixture of monomeric species (oxindolalanyl with tryptophan and hexacyclodienone alanyl with tyrosine) and polymeric species (filming effect: polytryptophan with tryptophan, polyphenylene oxide alanyl with tyrosine). According to experimental features (pH, concentrations, electrode angular velocity, etc.) either the first of the second electrochemical oxidation pathway can be favored.     

Deflection profiles of a monoenergetic atomic beam crossing a standing light wave

We calculate the shape of the deflection profile of a monoenergetic atomic beam crossing a laser standing wave, in a situation where many spontaneous emission processes occur during the interaction time. We predict that double peaked structures appear when the laser is detuned from resonance.