Synthetic studies toward C-glucosidic ellagitannins: a biomimetic total synthesis of 5-O-desgalloylepipunicacortein A

C-glucosidic ellagitannins constitute a subclass of bioactive polyphenolic natural products with strong antioxidant properties, as well as promising antitumoral and antiviral activities that are related to their capacity to interact with both functional and structural proteins. To date, most synthetic efforts toward ellagitannins have concerned glucopyranosic species. The development of a synthetic strategy to access C-glucosidic ellagitannins, whose characteristic structural feature includes an atropoisomeric hexahydroxydiphenoyl (HHDP) or a nonahydroxyterphenoyl (NHTP) unit that is linked to an open-chain glucose core by a C-aryl glucosidic bond, is described herein. The total synthesis of the biarylic HHDP-containing 5-O-desgalloylepipunicacortein?A (1?β) was achieved by either using the natural ellagic acid bis-lactone as a precursor of the requested HHDP unit or by implementing an atroposelective intramolecular oxidative biarylic coupling to forge this HHDP unit. Both routes converged in the penultimate step of this synthesis to enable a biomimetic formation of the key C-aryl glucosidic bond in the title compound.     

Determination of trehalose-6-phosphate in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> seedlings by hydrophilic-interaction liquid chromatography–mass spectrometry

A hydrophilic-interaction chromatography (HILIC) method coupled to electrospray ionization mass spectrometry (ESI-MS) was developed for the determination of trehalose-6-phophate (Tre6P) in Arabidopsis thaliana seedlings. The method was optimized for MS detection and separation of Tre6P from its isomers, such as sucrose-6-phosphate, by testing eluent pH, type of organic solvent and alkalinizer, and gradient conditions. Tre6P could be resolved from matrix components within 28 min by using a water–acetonitrile gradient (0.2 ml/min) at pH 12 with piperidine as alkalinizer. The method was validated for concentrations between 25 and 4,000 nM Tre6P in A. thaliana seedling extracts. Seedlings were extracted with consecutive liquid-liquid and solid-phase extractions, and analyzed with HILIC-MS. Obtained accuracy (80–120 %) and precision (<24 %) demonstrated the suitability of HILIC-MS for determining Tre6P level variations in plants. The limit of detection (LOD) was 3.5 nM Tre6P in extracts corresponding to 4.1 pmol.g⁻¹ fresh plant weight (FW). This is a considerable improvement with respect to anion-exchange chromatography (AEC)-MS (40 nM) and capillary electrophoresis-MS (80 nM). Furthermore, HILIC-MS analysis times were shorter than with AEC-MS (30 and 60 min, respectively). The applicability of the HILIC-MS method was demonstrated by the analysis of extracts from seedlings grown on medium containing 100 mM sorbitol or trehalose, resulting in mean Tre6P concentrations of 0.2 and 1.9 nmol.g⁻¹ FW, respectively. Similar concentrations were found with AEC-MS. HILIC-MS was also evaluated at a high flow rate (2.0 ml/min). This high-speed method resolved the Suc6P and Tre6P peaks within 3 min yielding a detection limit of 1.3 nM Tre6P.     

Three-dimensional direct femtosecond laser writing of second-order nonlinearities in glass

We demonstrate that direct femtosecond laser writing in silver-containing zinc and gallium phosphate glass enables generation of three-dimensional (3D) optical second-order nonlinear microstructures having an χ(2) value about 2.5 times that of quartz. The proposed physical model involves photo-reduction, photo-dissociation, and migration of silver species within the glass matrix. 3D laser-written second-order nonlinear structures could become a new class of nonlinear optical components.     

Shallow water analogue of the standing accretion shock instability: experimental demonstration and a two-dimensional model

Despite the sphericity of the collapsing stellar core, the birth conditions of neutron stars can be highly nonspherical due to a hydrodynamical instability of the shocked accretion flow. Here we report the first laboratory experiment of a shallow water analogue, based on the physics of hydraulic jumps. Both the experiment and its shallow water modeling demonstrate a robust linear instability and nonlinear properties of symmetry breaking, in a system which is one million times smaller and about one hundred times slower than its astrophysical analogue.     

Finite Size Scaling of the Dynamical Free-Energy in a Kinetically Constrained Model

We determine the finite size corrections to the large deviation function of the activity in a kinetically constrained model (the Fredrickson-Andersen model in one dimension), in the regime of dynamical phase coexistence. Numerical results agree with an effective model where the boundary between active and inactive regions is described by a Brownian interface.     

Management of the risk of backorders in a MTO–ATO/MTS context under imperfect requirements

Production systems are often classified according to the way production is released, e.g. make-to-stock (MTS), make-to-order (MTO), assembly-to-order (ATO) or engineer-to-order (ETO). The choice of a type of production depends on the decoupling point between customer and supplier. In some supply chains, like in the aeronautical sector, a customer may work according to a MTO process (since his product is highly specific) while his supplier works with a MTS process (since he delivers variants of standards components). This situation sets specific problems that are seldom considered in the literature, especially when collaboration between actors is required for an efficient management of the supply chain, which is the case when uncertainties are present. In this paper, we propose a method based on fuzzy modelling allowing a customer to choose a plan taking into account the uncertainty on his requirements when he works in MTO–ATO while his supplier is in MTS.     

Evolution of glass properties during a substitution of S by Se in Ge28Sb12S60 −xSex glass network

In this paper, a detailed study to examine the influence of chalcogen S/Se mole % in the Ge₂₈Sb₁₂S_60 ?xSe_x glass system, with x = 0, 15, 30, 45 and 60, is presented that provides insight into the effect of chalcogen content on the glass network and properties. Specifically, we report results of a systematic study to evaluate the relationship between compositional variation, glass properties and dominant bonding configurations. These materials are important to applications in optics manufacturing where correlation of physical and optical properties is required to predict fabrication behavior and ultimate material performance. It has been found that the dominant bonds in the glass system change upon reaching a specific molar ratio (percentage, %) of chalcogen substitution, between 30 < x < 45 mol%, changing from Ge―Se to Sb―Se bonds as the dominant bond type. This singularity has been observed using micro-Raman spectroscopy and X-ray photoelectron spectroscopy. This effect of the dominant bond configurational change was also shown to impart changes in important physical properties including micro-hardness, thermal properties, and the glass' viscometric behavior. Results indicate that the observed dominant bond change was responsible for a constant value in the evolution of both the micro-hardness and calorimetric glass transition temperature. The viscosity was also affected by the change in dominant bond type, breaking the monotony of the viscosity evolution during the S substitution, due to the total strength of the vitreous system which does not linearly increase.     

Boron-mediated polymerization of ylides derived from allylic arsonium salts: influence of the double bond substitution on the outcome

New oligomers or polymers are prepared by polymerization of arsonium ylides in the presence of boron compounds.