Organocatalytic asymmetric synthesis of sulfoxides from sulfenic acid anions mediated by a Cinchona-derived phase-transfer reagent

Preliminary results concerning a conceptually novel route to chiral sulfoxides based on the asymmetric alkylation of sulfenate salts with alkyl halides mediated by a chiral phase-transfer catalyst are described. As a representative example, o-anisyl methyl sulfoxide was produced in 96% yield and with an enantiomeric excess of 58% using commercial cinchonidinium derivative 2a.     

Combustion response of an aluminum droplet burning in air

The combustion in air of a 100 μm-diameter aluminum droplet is studied by direct Navier–Stokes simulations. The model only considers the gas phase and includes a reduced Al/O₂ kinetic scheme with 8 species and 10 reactions. The model is validated against experimental burn time data and appears to be fairly correct despite its simplicity. The unsteady combustion is then investigated by superimposing an acoustic disturbance to the mean flow. The velocity-coupled response is computed for different frequencies and slip Reynolds numbers. A resonance peak is found to occur when the acoustic time scale matches the gas diffusion time scale. For lower frequencies however (typically below a few kHz), a quasi-steady regime seems to hold out which means that assuming quasi-steady combustion (e.g., given by a D² model) is valid in this case. In this regime, the computed response corresponds with a theoretical expression obtained by a linearization of the Ranz–Marshall correction term. This implies that unsteady aluminum combustion is strongly dependent on convection effects.     

Construction of spirolactones with concomitant formation of the fused quaternary centre--application to the synthesis of natural products

Polycyclic structures fused at a central carbon are of great interest due to their appealing conformational features and their structural implications in biological systems. Although progress in the development of synthetic methodologies towards such structures has been impressive, the stereoselective construction of such quaternary stereocentres remains a significant challenge in the total synthesis of natural products. This review highlights the progress in the formation of 1-oxaspiro[4.n]alkan-2-ones (2≤n≤7) with concomitant formation of the quaternary spiro centre.     

Investigation of uranium-colloid interactions in soil by dual field-flow fractionation/capillary electrophoresis hyphenated with inductively coupled plasma-mass spectrometry

This paper deals with the study of uranium-colloid interactions in a carbonated soil. The work is focused on the immediately available fraction obtained after a leaching process, according to a normalized batch method. In order to characterize the different colloidal carriers, Asymmetrical Flow Field-Flow Fractionation (As-Fl-FFF) coupled to different detectors (UV, Multi Angle Laser Light Scattering (MALLS) and Inductively coupled Plasma-Mass Spectrometry (ICP-MS)) was used. The colloidal carriers are mainly inorganic particles (carbonated particles and clays) mixed with organic substances. Furthermore, dissolved and colloidal uranium species in the leaching solutions were monitored by Capillary Electrophoresis (CE) coupled to ICP-MS, in order to investigate the uranium/colloids interactions. According to the first results, uranium fate in this specific soil is controlled by sorption/desorption phenomena, strongly pH dependent.     

Protein-triggered instant disassembly of biomimetic Layer-by-Layer films

Layer-by-Layer (LbL) coatings are promising tools for the biofunctionalization of biomaterials, as they allow stress-free immobilization of proteins. Here, we explore the possibility to immobilize phosvitin, a highly phosphorylated protein viewed as a model of bone phosphoproteins and, as such, a potential promotive agent of surface-directed biomineralization, into biomimetic LbL architectures. Two immobilization protocols are attempted, first, using phosvitin as the polyanionic component of phosvitin/poly-(L-lysine) films and, second, adsorbing it onto preformed chondroitin sulfate/poly-(L-lysine) films. Surprisingly, it is neither possible to embed phosvitin as the constitutive polyanion of the LbL architectures nor to adsorb it atop preformed films. Instead, phosvitin triggers instant massive film disassembly. This unexpected, incidentally detected behavior constitutes the first example of destructive interactions between LbL films and a third polyelectrolyte, a fortiori a protein, which might open a route toward new stimuli-responsive films for biosensing or drug delivery applications. Interestingly, additional preliminary results still indicate a promotive effect of phosvitin-containing remnant films on calcium phosphate deposition.     

The role of the counterion and of silicon chelation in the selective mono(trifluoromethylation) of tartaric acid derived 1,4-diketones

The addition of trifluoromethyl(trimethyl)silane (TFMTMS) to tartaric acid derived aromatic 1,4-diketones was reported to be highly stereoselective but also chemoselective towards a monoaddition product. This chemoselectivity remained unexplained. Complementary experiments and monitoring of the reaction by electrospray ionization mass spectrometry (ESI-MS) show that: i) the countercation (tetrabutylammonium (TBA(+)) or Cs(+)) associated to the initiator and the charged intermediates in the chain reaction plays a crucial role and ii) in the case of a tetrabutylammonium salt initiator, the second addition on the preformed monoadduct does occur but the resulting bis(trifluoromethyl)carbinolate is unable to evolve through the chain-transfer process and it exhibits an intramolecular Si-O interaction.     

Synthesis and fucosidase inhibitory study of unnatural pyrrolidine alkaloid 4-epi-(+)-codonopsinine

The total synthesis of enantiopure 4-epi-(+)-codonopsinine was achieved in 10 steps starting from D-ribose as a chiral building block. The key step involved a highly stereoselective nucleophilic addition of a Grignard reagent to a protected ribosylamine. Synthesis of the N-desmethyl derivative and its p-tolyl analogue was also accomplished, and the compounds were assayed against α-fucosidase.     

Locking the free-rotation of a prochiral star-shaped guest molecule inside a two-dimensional nanoporous network by introduction of chlorine atoms

Two star-shaped triazatrinaphthylene (TrisK) derivatives form highly-organized nanoporous honeycomb networks when adsorbed at the n-tetradecane/HOPG interface. STM reveals that replacing three H-atoms by three Cl-atoms in the chemical structure of the TrisK skeleton results in locking the free-rotation of the guest molecules inside the pore of the host network as a result of symmetry breaking.     

Coupling transfer matrix method to finite element method for analyzing the acoustics of complex hollow body networks

This paper exposes a procedure to couple multiport transfer matrices to finite elements for analyzing the acoustics of automotive hollow body networks with a minimum of memory requirements and computational time. Generally, hollow body networks are made up from a series of elongated fluid partitions similar to ducts or waveguides. These fluid partitions generally contain complex elements: junctions, noise control elements, and cavities. The location and type of these elements in the network, mainly the noise control elements (e.g., sealing parts), may impact the noise inside a car. In the proposed hybrid method, the elongated fluid partitions are modeled with fluid finite elements. All complexities are modeled with two-port or multiport transfer matrices. The coupling of these matrices to finite elements is naturally done at the weak integral formulation stage of the acoustical problem. The coupling does not add any degrees of freedom to, nor modify, the original finite element matrix system. Consequently, changing locations and types of noise control elements in the hollow body network is fast and does not require rebuilding the finite element system. This enables optimizing the acoustics of a complex network on a desktop computer. The hybrid method is compared to experimental results on a tee-shaped hollow body networks. Good correlations are obtained.