Thermal dependence of Raman descriptors of ceramides. Part II: effect of chains lengths and head group structures

The outermost layer of the mammalian skin, the stratum corneum (SC), represents the main skin barrier. The SC lipids have a very exceptional composition, as the main lipid classes are ceramides (CER), long-chain fatty acids and cholesterol. Information on the function of each CER subclass and on the relation between CER lipid organisation and composition is of great importance to unravel the mechanism controlling the skin barrier function. Raman spectroscopy has been increasingly used for the study of intra- and inter-molecular structures of long-chain lipid compounds. In this study, we employed Raman spectroscopy to evaluate the effect of (1) the chain length and (2) the polar head architecture on the conformational order and organisational behaviour of CERs. The relation between the structure and the stability of the organisation was studied by monitoring the thermotropic response of each CER in the temperature range between 25 and 95 °C. This work enabled the determination of a correlation between the gauche/trans ratio in the νCC region and the state of the lateral packing. Moreover, it was shown that –OH groups in the α position of the fatty acids reduce the stability while long alkyl chains reinforces the intra- and inter-chains order.     

A smart palladium catalyst in ionic liquid for tandem processes

New catalytic systems based on in situ and preformed palladium nanoparticles in ionic liquids (characterised by TEM) starting from palladium acetate or dipalladiumtris(dibenzylideneacetone) have been applied in the synthesis of 4-phenylbutan-2-one (II), a model compound for the preparation of fragrances. Imidazolium-based ionic liquid containing a methyl hydrogenophosphonate anion leads to an efficient Pd-catalyzed tandem coupling/reduction process, taking advantage of the multi-role of this solvent (nanoparticles stabiliser, base, hydrogen transfer agent). The influence of the mono-phosphine ligands (1-3) on the catalyst has been evaluated, showing that the ligand-free palladium system turns into the most appropriate for the formation of II using Pd(OAc)(2) as precursor. Fine-tuning conditions involved in this multi-parameter process have led us to propose a plausible mechanism based on the hydrogen transfer coming from the methyl hydrogenophosphonate anion.     

Synthesis and evaluation of a tri-tyrosine decorated dextran MR contrast agent for vulnerable plaque detection

This communication reports the synthesis, characterization and in vivo evaluation in mice of a new tri-tyrosine conjugated MR contrast agent, which may help to identify vulnerable plaques in atherosclerosis by targeting the lipid core.     

Structural investigation of LaAlO3 up to 63 GPa

We report a high-pressure synchrotron x-ray diffraction on a LaAlO(3) single crystal. The transition from rhombohedral to cubic at 14.8 GPa is confirmed by the loss of the superstructure reflections, whose intensity shows a linear pressure dependence, characteristic of a second-order transition. The crystal remains cubic up to 63 GPa, the highest pressure reached, which provides a confirmation over a very large pressure range of the general rules for the evolution of distortions of perovskites under pressure. We report the parameters of the Birch-Murnaghan equations of state in the low- and high-pressure phases and discuss the evolution of the bulk modulus.     

Use of isotope ratio mass spectrometry to differentiate between endogenous steroids and synthetic homologues in cattle: A review

Although substantial technical advances have been achieved during the past decades to extend and facilitate the analysis of growth promoters in cattle, the detection of abuse of synthetic analogs of naturally occurring hormones has remained a challenging issue. When it became clear that the exogenous origin of steroid hormones could be traced based on the ¹³C/¹²C isotope ratio of the substances, GC/C/IRMS has been successfully implemented to this aim since the end of the past century. However, due to the costly character of the instrumental setup, the susceptibility of the equipment to errors and the complex and time consuming sample preparation, this method is up until now only applied by a limited number of laboratories. In this review, the general principles as well as the practical application of GC/C/IRMS to differentiate between endogenous steroids and exogenously synthesized homologous compounds in cattle will be discussed in detail, and will be placed next to other existing and to be developed methods based on isotope ratio mass spectrometry. Finally, the link will be made with the field of sports doping, where GC/C/IRMS has been established within the World Anti-Doping Agency (WADA) approved methods as the official technique to differentiate between exogenous and endogenous steroids over the past few years.     

European analytical criteria: past, present, and future

In this paper, the past, present, and (possible) future of the European analytical criteria for residues are described. The elaboration of the revision of Commission Decision 9312561EC was a long process starting in 1996 and ending with the formation of a European Commission (EC) working group in 1998. This working group took account of developments in scientific and technical knowledge at that time and produced a draft version of the revision within 6 months. The revision, finally published in 2002 (2002/657/EC), includes new ideas on the identification of analytes and the criteria for performance assessment as well as validation procedures. Currently (2009), the evolution in analytical equipment and progress in scientific research, accompanied by recent European regulatory changes, demands an update or revision of the 2002/657/EC.     

Morphology of open films of discotic hexagonal columnar liquid crystals as probed by grazing incidence X-ray diffraction

The structure and the orientation of thermotropic hexagonal columnar liquid crystals are studied by grazing incidence X-ray diffraction (GIXD) for different discotic compounds in the geometry of open supported thin films. Whatever the film deposition mode (either spin-coating or vacuum evaporation) and the film thickness, a degenerate planar alignment with the liquid crystalline columns parallel to the substrate is found. However, if a specific thermal process is applied to the liquid crystal film, homeotropic anchoring (columns normal to the interface) can be stabilized in a metastable state.     

Post-Modification of Copolymers Obtained by ATRP for an Application in Heterogeneous Asymmetric Salen Catalysis

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity.     

eHydrogenation: Hydrogen-free Electrochemical Hydrogenation

Hydrogenation reactions are staple transformations commonly used across scientific fields to synthesise pharmaceuticals, natural products, and various functional materials. However, the vast majority of these reactions require the use of a toxic and costly catalyst leading to unpractical, hazardous and often functionally limited conditions. Herein, we report a new, general, practical, efficient, mild and high-yielding hydrogen-free electrochemical method for the reduction of alkene, alkyne, nitro and azido groups. Finally, this method has been applied to deuterium labelling.