Nanoscale Platelet Formation by Monounsaturated and Saturated Sophorolipids under Basic pH Conditions

The self‐assembly behavior of the yeast‐derived bolaamphiphile sophorolipid (SL) is generally studied under acidic/neutral pH conditions, at which micellar and fibrillar aggregates are commonly found, according to the (un)saturation of the aliphatic chain: the cis form, which corresponds to the oleic acid form of SL, spontaneously forms micelles, whereas the saturated form, which corresponds to the stearic acid form of SL, preferentially forms chiral fibers. By using small‐angle light and X‐ray scattering (SLS, SAXS) combined with high‐sensitivity transmission electron microscopy imaging under cryogenic conditions (cryo‐TEM), the nature of the self‐assembled structures formed by these two compounds above pH 10, which is the pH at which they are negatively charged due to the presence of a carboxylate group, has been explored. Under these conditions, these compounds self‐assemble into nanoscale platelets, despite the different molecular structures. This work shows that the electrostatic repulsion forces generated by COO^? mainly drive the self‐assembly process at basic pH, in contrast with that found at pH below neutrality, at which self‐assembly is driven by van der Waals forces and hydrogen bonding, and thus, is in agreement with previous findings on carbohydrate‐based gemini surfactants.     

Identification of the scatter in high cycle fatigue from temperature measurementsIdentification de la dispersion des limites d'endurance à l'aide d'un essai d'échauffement.

It is proposed to determine the scatter in a Wöhler diagram by analyzing temperature changes induced by microplasticity. A unified framework is introduced to study both phenomena. The identification procedure is applied to a dual-phase steel. To cite this article: C. Doudard et al., C. R. Mecanique 332 (2004).     

New techniques of characterisation

During the last decade, amazing advances in microelectronics have led to the development of large infrared focal plane arrays (IRFPAs) with a high density of pixels per square centimetre. Bispectral and soon multispectral detectors are now under development. In order to follow or even anticipate this race for spatial and spectral resolution, new techniques of characterisation have been developed in our laboratory, allowing the measurement of the spatial and spectral responses of a hundred of thousands pixels forming the IRFPA. Thus, a test bench for the measurement of hyperspectral cartographies has been realised. The principle of measurement and experimental results will be presented. For the measurement of spatial responses, the projection of targets that illuminate the entire surface of the IRFPA and contain sub-pixel details is required in order to extract the line (or spot) spread function of every pixel. For this, non-imaging techniques of projection based on the self-imaging property of periodic targets have been elaborated. The first results and the potential of this original approach will be discussed. To cite this article: N. Guérineau et al., C. R. Physique 4 (2003).     

State of the Art and Perspectives of Biomedical Imaging at the ESRF

Over the last decade, synchrotron radiation sources have seen a significant increase in brilliance, and the advent of free electron lasers has made entire new research fields accessible to investigations with X-rays. These advances in light source capabilities have resulted not only in a host of scientific advances and discoveries, but also in a need for a new generation of X-ray imaging detectors that can match the sources' capabilities in terms of frame rate and image dynamic range while recording image information with fine granularity over a large – preferably uninterrupted – (multi)megapixel area with single-photon sensitivity. Developing such next-generation imagers is both costly and time-consuming, and the requirements at many photon science facilities are similar enough to invite a collaborative effort. The Percival (“Pixellated Energy Resolving CMOS Imager, Versatile And Large”) imager is being developed by a collaboration of DESY, Rutherford Appleton Laboratory (RAL), Elettra, and Diamond Light Source (DLS) to answer this need for the soft X-ray regime.     

An experimental correction proposed for an accurate determination of mass diffusivity of wood in steady regime

This paper presents an experimental study of the mass diffusion in the hygroscopic region of four temperate species and three tropical ones. In order to simplify the interpretation of the phenomena, a dimensionless parameter called reduced diffusivity is defined. This parameter varies from 0 to 1. The method used is firstly based on the determination of that parameter from results of the measurement of the mass flux which takes into account the conditions of operating standard device (tightness, dimensional variations and easy installation of samples of wood, good stability of temperature and humidity). Secondly the reasons why that parameter has to be corrected are presented. An abacus for this correction of mass diffusivity of wood in steady regime has been plotted. This work constitutes an advanced deal nowadays for characterising forest species.     

Crystal structure of trans(3R,2aS)-(-)-3-phenyl-hexahydro-oxazolo[3,2-a]pyridin-5-one.

Chiral, non-racemic hexahydro-oxazolo[3,2-a]pyridin-5-ones are strategic starting materials for the asymmetric synthesis of alkaloids, via the stereoselective C-C bond formation at the position a to the nitrogen atom. The stereoselectivity of this key step is mainly driven by the geometry of the fused rings of the oxazolopyridine moiety. In this work, the synthesis and X-ray structure of trans(3R,2aS)-(-)-3-phenyl-hexahydro-oxazolo[3,2-a]pyridin-5-one is reported.     

A novel nucleophilic attack to N-enoyl oxazolidinethiones

The oxazolidinethione synthon can act as a chiral auxiliary and nucleophile (S⁻) carrier molecule simultaneously. Surprisingly, the thiolate attacks N-enoyl oxazolidinethiones producing a new heterocycle, as established by X-ray analysis.     

Viscoelastic dewetting of constrained polymer thin films

Thin films of fluids are playing a leading role in countless natural and industrial processes. Here we study the stability and dewetting dynamics of viscoelastic polymer thin films. The dewetting of polystyrene close to the glass transition reveals unexpected features: asymmetric rims collecting the dewetted liquid and logarithmic growth laws that we explain by considering the nonlinear velocity dependence of friction at the fluid/solid interface and by evoking residual stresses within the film. Systematically varying the time so that films were stored below the glass-transition temperature, we studied simultaneously the probability for film rupture and the dewetting dynamics at early stages. Both approaches proved independently the significance of residual stresses arising from the fast solvent evaporation associated with the spin-coating process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3022–3030, 2006     

A short synthesis of lennoxamine via ynamides

Lennoxamine was synthesized in eight steps from 2,3-dimethoxybenzoic acid via an intermediate ynamide by using palladium-catalyzed Heck-Suzuki-Miyaura domino reactions.