Development of a stereoselective co-mediated dihydropyran ring contraction

A highly stereoselective approach for the synthesis of trans-1,2-disubstituted cyclobutanes through an Al-promoted cobalt-mediated O-->C ring contraction of dihydropyrans is described. [reaction: see text].     

Crossed characterisation of polymer-layered silicate (PLS) nanocomposite morphology: TEM, X-ray diffraction, rheology and solid-state nuclear magnetic resonance measurements

As the nanocomposite properties dramatically depend on the dispersion state of the filler in the matrix, it is essential to develop technical methods to characterise the nanodispersion both qualitatively and quantitatively. In this study, complete characterisations of the nanodispersion of organomodified clays in polyamide 6, polypropylene and poly(butylene terephtalate) are presented and discussed using different analytical tools. All four characterisation methods have been evaluated experimentally. TEM has been used to qualitatively characterise the dispersion. As TEM picture might be not fully representative of the whole sample, many pictures have to be analysed to mirror the global repartition. XRD is particularly adapted to the study of intercalated morphology of nanocomposite since the distance between two platelets can be calculated but needs TEM to provide more complete conclusions. Melt rheology and solid-state NMR are bulk analyses. During the measurement the sample is representative of the material. Rheology is relatively simple to make measurements and to get semi-quantitative data. In connection with NMR, we can get quantitative measurements on the degree of nanodispersion in the nanocomposite.     

Digital correlation of grainy shadow images for surface profile measurement

An optical method, combining the projection of a structured light pattern with the digital correlation technique, is discussed in this paper. This method allows measurement of full-field profile on object surface of about 20 mm square size. Tests on a rotated plane surface have been performed in order to quantify the method capabilities. It is shown that this technique leads to an accuracy of about 1 μm for a spatial resolution of around half a millimeter. Profile measurements of a micro-engraved object and at the crack tip of a polymer sample are also presented. Results give proof that this technique remains efficient even in presence of important height slope.     

Design of a Gd‐DOTA‐Phthalocyanine Conjugate Combining MRI Contrast Imaging and Photosensitization Properties as a Potential Molecular Theranostic

The design and synthesis of a phthalocyanine – Gd‐DOTA conjugate is presented to open the way to novel molecular theranostics, combining the properties of MRI contrast imaging with photodynamic therapy. The rational design of the conjugate integrates isomeric purity of the phthalocyanine core substitution, suitable biocompatibility with the use of polyoxo water‐solubilizing substituents, and a convergent synthetic strategy ended by the use of click chemistry to graft the Gd‐DOTA moiety to the phthalocyanine. Photophysical and photochemical properties, contrast imaging experiments and preliminary in vitro investigations proved that such a combination is relevant and lead to a new type of potential theranostic agent.     

Enantioselective Synthesis and Physicochemical Properties of Libraries of 3‐Amino‐ and 3‐Amidofluoropiperidines

The enantioselective syntheses of 3‐amino‐5‐fluoropiperidines and 3‐amino‐5,5‐difluoropiperidines were developed using the ring enlargement of prolinols to access libraries of 3‐amino‐ and 3‐amidofluoropiperidines. The study of the physicochemical properties revealed that fluorine atom(s) decrease(s) the pK_a and modulate(s) the lipophilicity of 3‐aminopiperidines. The relative stereochemistry of the fluorine atoms with the amino groups at C3 on the piperidine core has a small effect on the pK_a due to conformationnal modifications induced by fluorine atom(s). In the protonated forms, the C?F bond is in an axial position due to a dipole–dipole interaction between the N?H⁺ and C?F bonds. Predictions of the physicochemical properties using common software appeared to be limited to determine correct values of pK_a and/or differences of pK_a between cis‐ and trans‐3‐amino‐5‐fluoropiperidines.     

An analytical workflow for the molecular dissection of irreversibly modified fluorescent proteins

Owing to their ability to be genetically expressed in live cells, fluorescent proteins have become indispensable markers in cellular and biochemical studies. These proteins can undergo a number of covalent chemical modifications that may affect their photophysical properties. Among other mechanisms, such covalent modifications may be induced by reactive oxygen species (ROS), as generated along a variety of biological pathways or through the action of ionizing radiations. In a previous report [1], we showed that the exposure of cyan fluorescent protein (ECFP) to amounts of ^?OH that mimic the conditions of intracellular oxidative bursts (associated with intense ROS production) leads to observable changes in its photophysical properties in the absence of any direct oxidation of the ECFP chromophore. In the present work, we analyzed the associated structural modifications of the protein in depth. Following the quantified production of ^?OH, we devised a complete analytical workflow based on chromatography and mass spectrometry that allowed us to fully characterize the oxidation events. While methionine, tyrosine, and phenylalanine were the only amino acids that were found to be oxidized, semi-quantitative assessment of their oxidation levels showed that the protein is preferentially oxidized at eight residue positions. To account for the preferred oxidation of a few, poorly accessible methionine residues, we propose a multi-step reaction pathway supported by data from pulsed radiolysis experiments. The described experimental workflow is widely generalizable to other fluorescent proteins, and opens the door to the identification of crucial covalent modifications that affect their photophysics.

Laser-induced breakdown spectroscopy applications in the steel industry: Rapid analysis of segregation and decarburization

Rapid chemical analysis is increasingly a prerequisite in the steel making industry, either to check that a steel product complies with customers' specifications, or to investigate the presence of defects that may lead to mechanical property failure of the product. Methods conventionally used for assessment, such as the monitoring of decarburization and segregation, performed by chemical etching of a polished surface followed by optical observation, tend to be relatively fast, simple and applicable to large sample areas; however, the information obtained is limited to the spatial extent of the defect. Other techniques, such as electron probe microscopy and scanning electron microscopy — energy dispersive X-ray, can be used for providing detailed chemical composition at the micro-scale, for a better understanding of the mechanisms involved; however, their use is limited to analyzing comparatively very small sample areas (typically a few mm²).     

One-step synthesis of metallic and metal oxide nanoparticles using amino-PEG oligomers as multi-purpose ligands: size and shape control, and quasi-universal solvent dispersibility

A one-step and room temperature synthesis toward metallic and metal oxide nanoparticles soluble both in water and organic solvent is reported. This was achieved using amino-PEG oligomers that make it possible to control the size and shape of the nanoparticles.     

Stochastic Arithmetic in Multiprecision

Floating-point arithmetic precision is limited in length the IEEE single (respectively double) precision format is 32-bit (respectively 64-bit) long. Extended precision formats can be up to 128-bit long. However some problems require a longer floating-point format, because of round-off errors. Such problems are usually solved in arbitrary precision, but round-off errors still occur and must be controlled. Interval arithmetic has been implemented in arbitrary precision, for instance in the MPFI library. Interval arithmetic provides guaranteed results, but it is not well suited for the validation of huge applications. The CADNA library estimates round-off error propagation using stochastic arithmetic. CADNA has enabled the numerical validation of real-life applications, but it can be used in single precision or in double precision only. In this paper, we present a library called SAM (Stochastic Arithmetic in Multiprecision). It is a multiprecision extension of the classic CADNA library. In SAM (as in CADNA), the arithmetic and relational operators are overloaded in order to be able to deal with stochastic numbers. As a consequence, the use of SAM in a scientific code needs only few modifications. This new library SAM makes it possible to dynamically control the numerical methods used and more particularly to determine the optimal number of iterations in an iterative process. We present some applications of SAM in the numerical validation of chaotic systems modeled by the logistic map.