Enantioselective synthesis of indolizidine alkaloid trans-209D

(S)-N-Boc-baikiain, readily accessible from enantiomerically enriched 2,3-epoxy-5-hexen-1-ol 4 (prepared by Sharpless asymmetric epoxidation), was used as the starting material in the synthesis of indolizidine alkaloid trans-209D , which was obtained in 13 steps and 14% yield from 1 (5% from 4).     

Influence of substrate heating on the evaporation dynamics of pinned water droplets

The dynamics of evaporating water droplets deposited on a heated substrate is investigated numerically. Droplets are pinned with a contact line radius of R = 1 mm. Evaporative mass flow and convection occurring inside the droplets are studied for different heating substrate sizes L S and heating temperatures T S. A simplified model neglecting hydrodynamics in air and evaporative cooling and assuming droplets to be spherical caps is simulated with a finite element method. A toruslike convective cell appears inside the droplets as evaporation takes place. For L S/ R > 1, the contact line is warmer than the apex of the droplets, and convection generates a downstream flow in the vicinity of the symmetry axis of the droplets. For L S/ R < 1, it is the apex that is warmer. Convection then generates an upstream flow. The overall evaporation time is described. It slows when L S/ R > 1.     

Full structure of the carbohydrate chain of the lipopolysaccharide of Providencia rustigianii O34

A lipopolysaccharide isolated from an opportunistic pathogen of the Enterobacteriaceae family Providencia rustigianii O34 was found to be a mixture of R-, SR-, and S-forms consisting of a lipid moiety (lipid A) that bears a core oligosaccharide, a core with one O-polysaccharide repeating unit attached, and a long-chain O-polysaccharide, respectively. The corresponding carbohydrate moieties were released from the lipopolysaccharide by mild acid hydrolysis and studied by sugar and methylation analyses along with one- and two-dimensional NMR spectroscopy and high-resolution electrospray ionization mass spectrometry. As a result, the structures of the core and the O-polysaccharide were established, including the structure of the biological repeating unit (an oligosaccharide that is preassembled and polymerized in biosynthesis of the O-polysaccharide), as well as the mode of the linkage between the O-polysaccharide and the core. Combining the structure of the carbohydrate moiety thus determined and the known structure of lipid A enabled determination of the full lipopolysaccharide structure of P. rustigianii O34.     

Assessing the stable carbon isotopic composition of intercellular CO2 in a CAM plant using gas chromatography-combustion-isotope ratio mass spectrometry

Most of the literature focused on internal CO(2) (Ci) determinations in plants has used indirect methods based on gas-exchange estimations. We have developed a new method based on the capture of internal air gas samples and their analysis by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). This method provided a direct measure of intercellular CO(2) concentrations combined with stable carbon isotopic composition in O. ficus-indica plants. Plants were grown at both ambient and elevated CO(2) concentration. During the day period, when the stomata are closed, the Ci was high and was very (13)C-enriched in both ambient and elevated CO(2)-grown plants, reflecting Rubisco's fractionation (this plant enzyme has been shown to discriminate by 29 per thousand, in vitro, against (13)CO(2)). Other enzyme fractionations involved in C metabolism in plants, such as carbonic anhydrase, could also be playing an important role in the diurnal delta(13)C enrichment of the Ci. During the night, when stomata are open, Ci concentrations were higher in elevated (and the corresponding delta(13)C values were more (13)C-depleted) than in ambient CO(2)-grown plants.     

Room-Temperature-Stable Diazoalkenes by Diazo Transfer from Azides: Pyridine-Derived Diazoalkenes

Recently, stable diazoalkenes have received significant attention as a new substance class in organic chemistry. While their previous synthetic access was exclusively limited to the activation of nitrous oxide, we here establish a much more general synthetic approach utilizing a Regitz-type diazo transfer with azides. Importantly, this approach is also applicable to weakly polarized olefins such as 2-pyridine olefins. The new pyridine diazoalkenes are not accessible by the activation of nitrous oxide, allowing for a considerable extension of the scope of this only recently accessed functional group. The new diazoalkene class has properties distinct from the previously reported classes, such as photochemically triggered loss of dinitrogen affording cumulenes and not C−H insertion products. Pyridine-derived diazoalkenes represent the so far least polarized stable diazoalkene class reported.     

Controlled synthesis of graphene oxide/alumina nanocomposites using a new dry sol–gel method of synthesis

The present paper gives new insight into the problem of controlling the morphology of reduced graphene oxide/alumina (RGO/Al₂O₃) nanocomposites. The dry and simplified sol–gel methods of RGO/Al₂O₃ nanocomposite synthesis were compared and the influence of six key synthesis parameters on the morphology of the resulting nanocomposite powders was investigated to optimize the morphology of RGO/Al₂O₃ nanocomposites in terms of reducing the undesired agglomeration of RGO/Al₂O₃ nanocomposite flakes to a significant minority and obtaining the uniform coverage of RGO surface with Al₂O₃ nanoparticles. Our investigations indicate that, despite the high excess of Al₂O₃ used (95 wt%), the lowest RGO/Al₂O₃ flake agglomeration and the formation of a uniform layer composed of Al₂O₃ nanoparticles with the average size of 58 nm occurred only when 5 wt% of graphene oxide was used as a substrate for the deposition of Al₂O₃ nanoparticles together with triethyl aluminium as an Al₂O₃ precursor and dry hexane as the reaction environment. The resulting organic precursor was thermally decomposed at 280 °C for 3 h in air atmosphere (R4 reaction pathway). This was confirmed by the high BET-specific surface area (242.4 m²/g) and the high open porosity (0.7 cm³/g) of the obtained RGO(5 wt%)/Al₂O₃ nanocomposite. This is also the first study with a detailed discussion of the reactions expected to occur during the synthesis of an RGO/Al₂O₃ nanocomposite.     

Electrostatic Fluxes and Plasma Rotation in the Edge Region of EXTRAP-T2R

The EXTRAP-T2 reversed field pinch has undergone a significant reconstruction into the new T2R device. This paper reports the first measurements performed with Langmuir probes in the edge region of EXTRAP-T2R. The radial profiles of plasma parameters like electron density and temperature, plasma potential, electrical fields and electrostatic turbulence-driven particle flux are presented. These profiles are interpreted in a momentum balance model where finite Larmor radius losses occur over a distance of about two Larmor radii from the limiter position. The double shear layer of the E×B drift velocity is discussed in terms of the Biglari-Diamond-Terry theory of turbulence decorrelation.     

A thermo-mechanical modelling of the Tribological Transformations of Surface

The Tribological Transformations of Surface (TTS) are observed on samples of certain steels undergoing repeated compressive loadings. They correspond to a permanent, solid–solid phase transformation localized on the surfaces of the sample on which the loading is applied. The main hypothesis of the study is that TTS are not only due to the mechanical loading but also to the thermal loading which is associated to. Thus, a thermo-mechanical model is first proposed in the present Note, which is inspired by previous works on TRansformation Induced Plasticity (TRIP). The potentialities of the model are also briefly illustrated by a simple 1D example. To cite this article: G. Antoni et al., C. R. Mecanique 337 (2009).