Blockwise approach to fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a: convergent Synthesis of a decasaccharide representative of a dimer of the branched repeating unit

The D'A'B'(E')C'DAB(E)C decasaccharide representative of a dimer of a frame-shifted pentasaccharide repeating unit of the O-specific polysaccharide of Shigella flexneri 2a was synthesized as its methyl glycoside by condensing a pentasaccharide donor (D'A'B'(E')C') and a pentasaccharide acceptor (DAB(E)C-OMe). Several convergent routes to these two building blocks, involving either the AB linkage or the BC linkage as the disconnection site, were evaluated in comparison to the linear strategy. The latter was preferred. It is based on the use of the trichloroacetimidate chemistry. The target branched oligosaccharide was designed to probe the recognition at the molecular level of the natural polysaccharide by protective monoclonal antibodies.     

Combination of nitroxide‐mediated polymerization and SET‐LRP for the synthesis of high molar mass branched and star‐branched poly(n‐butyl acrylate) characterized by size exclusion chromatography and rheology

Branched and star‐branched polymers were successfully synthesized by the combination of two successive controlled radical polymerization methods. A series of linear and star poly(n‐butyl acrylate)‐co‐poly(2‐(2‐bromoisobutyryloxy) ethyl acrylate) statistical copolymers, P(nBA‐co‐BIEA)_x, were first synthesized by nitroxide‐mediated polymerization (NMP at T > 100 °C). The subsequent polymerization of n‐butyl acrylate by single electron transfer‐living radical polymerization (SET‐LRP at T = 25 °C), initiated from the brominated sites of the P(nBA‐co‐BIEA)_x copolymer, produced branched or star‐branched poly(n‐butyl acrylate) (PnBA). Both types of polymerizations (NMP and SET‐LRP) exhibited features of a controlled polymerization with linear evolutions of logarithmic conversion versus time and number‐average molar masses versus conversion for final M_n superior to 80,000 g mol^?1. The branched and star‐branched architectures with high molar mass and low number of branches were fully characterized by size exclusion chromatography. The Mark–Houwink Sakurada relationship and the analysis of the contraction factor (g′ = ([η]_branched/[η]_linear)_M) confirmed the elaboration of complex PnBA. The zero‐shear viscosities of the linear, star‐shaped, branched, and star‐branched polymers were compared. The modeling of the rheological properties confirmed the synthesis of the branched architectures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Approximation of the distribution of excesses using a generalized probability weighted moment method

The POT (Peaks-Over-Threshold) approach consists of using the generalized Pareto distribution (GPD) to approximate the distribution of excesses over a threshold. In this Note, we consider this approximation using a generalized probability weighted moment (GPWM) method. We study the asymptotic behaviour of our new estimators and also the functional bias of the GPD as an estimate of the distribution function of the excesses. To cite this article: J. Diebolt et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Organocatalysis with dendrimers

This review gives an overview of the use of dendrimers and dendrons as organocatalysts, i.e. as catalysts in the absence of any metal. A large variety of dendrimeric structures have already been used for such a purpose, varying in size (generation), type and location (core or surface) of the organocatalytic entities, and overall chemical composition. The main types of reactions catalyzed concern bond formation (in particular C-C bonds), bond cleavage (in particular of esters), reductions and oxidations. In many cases, good to excellent enantioselectivities have been observed, in some cases associated with a positive dendritic effect (better properties when the generation of the dendrimer increases). Due to their large size compared to products, the dendrimeric organocatalysts can be often recovered and reused several times.     

Modeling basic components of solid oxide fuel cells using density functional theory: Bulk and surface properties of CeO2

In this paper, the structural and electronic properties of CeO₂ are studied using conventional and hybrid density functional theory. A computational protocol, based on the parameter-free hybrid functional PBE0 coupled with a 4f in-valence basis set for Ce atoms based on a 28 electrons small core pseudopotential is able to reasonably reproduce both structural and electronic experimental data. Such a protocol is then applied to the modeling of true 2-D periodic CeO₂ slabs of non polar low-index surfaces. The obtained results show that the (111) surface is more stable than the (110) one (0.73 vs 0.81 J/m²), with a substantial rumbling in the outermost planes of this latter. Finally, as a first step toward reactivity at CeO₂ surfaces involved in solid oxide fuel cells, the importance of electrostatic effects in the adsorption of chemical species such as CO is presented. These results will allow for a detailed study of catalytic reactions at ceria surface.     

Two-dimensional electrophoresis investigation of short-term response of flax seedlings to a cold shock

The flax, Linum usitatissimum L., is particularly suitable for studying the transduction and long-term signal storage of environmental signals. To investigate the underlying molecular mechanisms, we have focused on the initial changes in the proteome since these offer the possibility of reflecting the plant's history of exposure to stress. In principle, this 'proteome signature' might be revealed by two-dimensional electrophoresis (2-DE). We have therefore determined the potential of 2-DE to study the kinetics of changes to the proteome of flax induced by a 1 min cold shock. Protein identification is difficult with flax because of the lack of knowledge of gene sequences. Nevertheless, 2-DE analysis can be informative providing the significance of changes can be evaluated. We have developed a stringent threshold method to determine the significance of changes in gels obtained with proteins extracted from hypocotyls at different times after cold shock. This allowed us to reliably detect and characterize the kinetics of a set of seven spots that responded to cold shock and that constitute candidates for a proteome signature of long-term signal storage.     

Some effects of protonation on the electronic structure of pyridine and cytosine

The effects of protonation on the charge distributions of pyridine and cytosine are investigated with the help of the Iterative Extended Hückel technique. The polarization of the -electrons is then included explicitly in a Pariser-Parr-Pople computation of the - ^* transition energies of the pyridinium and cytosinium ions.

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Zusammenfassung Mit Hilfe der IEH-Methode wird die Auswirkung der Protonierung auf die Ladungsverteilung bei Pyridin und Cytosin untersucht. Die Polarisierung der -Elektronen wird dann in eine PPP-Rechnung der - ^*-übergangsenergie beim Pyridinium- und Cytosiniumion übernommen.

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Résumé On étudie, à l'aide de la méthode de Hückel étendue iterative, les effets de la protonation sur la répartition des électrons dans les molécules de pyridine et de cytosine. On introduit ensuite explicitement la polarisation des électrons dans le calcul des énergies de transition - ^* des ions pyridinium et cytosinium par la méthode de Pariser, Parr et Pople.

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This work was supported by grant n GM-12229 of the U.S. Public Health Service (National Institute of General Medical Sciences).     

Nitric oxide release during evoked neuronal activity in cerebellum slices: detection with platinized carbon-fiber microelectrodes.

Nitric oxide is an important biological messenger that particularly induces the relaxation of smooth muscle cells surrounding vessels, and, hence, controls the flow of blood. This mechanism is essential for brain function, and its fine control, termed functional hyperemia, is supposed to be realized by certain neurons that may release bursts of NO*. The aim of the present study is to examine the advantages of platinized carbon-fiber microelectrodes (5-7 microm tip diameter) for the direct and in situ electrochemical detection of NO* released by neurons into ex vivo cerebellum slices. After establishing the different analytical properties of the platinized carbon-fiber microelectrodes in vitro on NO* solutions at 50 nM to 1 mM concentration, they were characterized using DEA-NONOate solutions that chemically decompose into NO*, and therefore mimic the measurement of transient variations of NO* concentration in biological samples. This validated the present approach, so that direct, in situ ex vivo measurements of nitric oxide released by neurons in a rat cerebellar slice are presented and discussed.     

Assets management on electrical grid using Faster-RCNN

Electrical utility companies around the world are keeping track of all equipment on their distribution grid, because it will help them improve the management and the quality of the services they offer to their customers. Asset management of the electric grid is usually conducted manually, which is expensive, time consuming and the results obtained are often not accurate. In this article an automated asset management system for electricity, transport infrastructures is proposed, it is based on images taken by drones and analysed by Faster Region proposal Convolutional Neural Networks (Faster-RCNN) to generate the inventory. The designs of CNN are inspired from the human brain structures, they have been applied to many fields such as object recognition and crowed counting with promising results that are proven to be better than human observer. In order to evaluate the proposed asset management approach, a sample of images was randomly selected from a given dataset, the inventory results generated by the CNN based model are accurate, faster and cheaper than the previous approach based on human observers and helicopters.