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.     

Expanding the chemical space in practice: diversity-oriented synthesis

Diversity-Oriented Synthesis (DOS) aims to broaden the frontier of accessible collections of complex and diverse small molecules. This review endeavours to dissect the DOS concept through three elements of diversity: building block, stereochemistry, and skeleton. Recent examples in the literature that emphasize the efficient combinations of these elements to generate diversity are reported.     

Triazole-linked analogue of deoxyribonucleic acid ((TL)DNA): design, synthesis, and double-strand formation with natural DNA

A new triazole-linked analogue of DNA ((TL)DNA) has been designed and synthesized using click chemistry. The chain elongation reaction using copper-catalyzed Huisgen cycloaddition was successful and gave the artificial oligonucleotide that formed a stable double strand with the complementary strand of natural DNA.     

Effect of liposome composition on β-blocker interactions studied by capillary electrokinetic chromatography

Liposome capillary electrokinetic chromatography was used to investigate the interactions between three β-blockers of different hydrophobicity and various liposome solutions. The studied β-blockers comprised alprenolol, propranolol, and carvedilol. The composition of the liposome solutions, containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phos-phoethanolamine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l -serine, and cholesterol in various molar ratios, was designed by a response surface methodology-central composite design approach. Subsequently, after conducting the liposome capillary electrokinetic chromatography experiments and determining the retention factors from the electrophoretic mobilities of the compounds, and further calculating the distribution coefficients, an analysis of variance was performed. After extracting the statistical models, optimal operational conditions were obtained based on the developed models. To further investigate the interactions between the β-blockers and the liposomes, nanoplasmonic sensing experiments were carried out on two different liposome systems. The overall results demonstrate the strong influence of cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l -serine on the distribution coefficients.     

Total synthesis of norbadione A

A short, convergent synthesis of the mushroom pigment norbadione A is described. The construction of an appropriately substituted naphtholactone intermediate involved a regioselective Diels-Alder reaction between a bis(triisopropylsilyloxy)diene and 2,6-dichlorobenzo-1,4-quinone. A double Suzuki-Miyaura cross-coupling between a diboronate and two identical enol triflates was another key feature of the synthesis.     

Dioxygenase-catalysed cis-dihydroxylation of meta-substituted phenols to yield cyclohexenone cis-diol and derived enantiopure cis-triol metabolites

cis-Dihydroxylation of meta-substituted phenol (m-phenol) substrates, to yield the corresponding cyclohexenone cis-diol metabolites, was catalysed by arene dioxygenases present in mutant and recombinant bacterial strains. The presence of cyclohexenone cis-diol metabolites and several of their cyclohexene and cyclohexane cis-triol derivatives was detected by LC-TOFMS analysis and confirmed by NMR spectroscopy. Structural and stereochemical analyses of chiral ketodiol bioproducts, was carried out using NMR and CD spectroscopy and stereochemical correlation methods. The formation of enantiopure cyclohexenone cis-diol metabolites is discussed in the context of postulated binding interactions of the m-phenol substrates at the active site of toluene dioxygenase (TDO).     

Development and trends in synchrotron studies of ancient and historical materials

Synchrotron photon-based methods are increasingly being used for the physico-chemical study of ancient and historical materials (archaeology, palaeontology, conservation sciences, palaeo-environments). In particular, parameters such as the high photon flux, the small source size and the low divergence attained at the synchrotron make it a very efficient source for a range of advanced spectroscopy and imaging techniques, adapted to the heterogeneity and great complexity of the materials under study. The continuous tunability of the source — its very extended energy distribution over wide energy domains (meV to keV) with a high intensity — is an essential parameter for techniques based on a very fine tuning of the probing energy to reach high chemical sensitivity such as XANES, EXAFS, STXM, UV/VIS spectrometry, etc. The small source size attained (a few micrometres) at least in the vertical plane leads to spatial coherence of the photon beams, giving rise in turn to a series of imaging methods already crucial to the field. This review of the existing literature shows that microfocused hard X-ray spectroscopy (absorption, fluorescence, diffraction), full-field X-ray tomography and infrared spectroscopy are the leading synchrotron techniques in the field, and presents illustrative examples of the study of ancient and historical materials for the various methods. Fast developing analytical modalities in scanning spectroscopy (STXM, macro-XRF scanning) and novel analytical strategies regarding optics, detectors and other instrumental developments are expected to provide major contributions in the years to come. Other energy domains are increasingly being used or considered such as far-infrared and ultraviolet/visible for spectroscopy and imaging. We discuss the main instrumental developments and perspectives, and their impact for the science being made on ancient materials using synchrotron techniques.