New Reactions with Thioaldehydes and Thienium Cations

Abstract

i) When generated under FVT conditions α-imino-thioaldehydes undergo a cyclization to dihydro-1,3-thiazoles. ii) Thienium cations, generated during a Pummerer reaction, can be trapped with dienes.     

Experimental implementation of reverse time migration for nondestructive evaluation applications

Reverse time migration (RTM) is a commonly employed imaging technique in seismic applications (e.g., to image reservoirs of oil). Its standard implementation cannot account for multiple scattering/reverberation. For this reason it has not yet found application in nondestructive evaluation (NDE). This paper applies RTM imaging to NDE applications in bounded samples, where reverberation is always present. This paper presents a fully experimental implementation of RTM, whereas in seismic applications, only part of the procedure is done experimentally. A modified RTM imaging condition is able to localize scatterers and locations of disbonding. Experiments are conducted on aluminum samples with controlled scatterers.     

Thermodynamics, structure and properties of polynuclear lanthanide complexes with a tripodal ligand: insight into their self-assembly

Self-assembly processes between a tripodal ligand and Ln(III) cations have been investigated by means of supramolecular analytical methods. At an equimolar ratio of components, tetranuclear tetrahedral complexes are readily formed in acetonitrile. The structural analysis of the crystallographic data shows a helical wrapping of binding strands around metallic cations. The properties of this series of highly charged 3D compounds were examined by using NMR spectroscopy and optical methods in solution and in the solid state. In the presence of excess metal, a new trinuclear complex was identified. The X-ray crystal structure elucidated the coordination of metallic cations with two ligands of different conformations. By varying the metal/ligand ratio, a global speciation of this supramolecular system has been evidenced with different spectroscopic methods. In addition, these rather complicated equilibria were successfully characterised with the thermodynamic stability constants. A rational analysis of the self-assembly processes was attempted by using the thermodynamic free energy model and the impact of the ligand structure on the effective concentration is discussed.     

The effects of filtration on the injection of cement-based grouts in sand columns

This article presents injection experiments and modeling of cement based grout in sand. In particular, it focuses on the role of filtration during the sand impregnation by the grout. One-dimensional injection tests in sand columns are performed. In these, the mass intake of the sample and the injection pressure are measured to quantify the effects of filtration during grouting. The cement-to-water ratio of the grout and the initial density of the soil are also studied. The modeling of these tests is achieved by incorporating the filtration and the damage coefficients in the classical transport in porous media equations. A method is proposed to determine these coefficients. The method simultaneously relies on both analytical analysis and experimental measurements. Density and viscosity effects are also considered in the model equations which are solved using the finite element method. The simulation of an injection test proves that the model is suitable to recover the injection pressure obtained experimentally. Finally, both experimental and numerical results reveal the importance of including filtration when analyzing one-dimensional injections of cement based grouts in sand.     

Electroactive self-assembled monolayers: Laviron's interaction model extended to non-random distribution of redox centers

The Laviron's interaction model, dedicated to randomly distributed electroactive adsorbed species, was extended to a non-random distribution in order to extract the current–voltage characteristics from any surface distribution of electroactive centers on self-assembled monolayer (SAM). Confronted to electrochemical behaviour of nitroxyl radical SAMs, the agreement observed between theory and experiments provides evidence of a distribution independence of the interaction parameters.     

All-optical generation of 40 Gb/s single sideband signals using a fiber Bragg grating

In this work, we demonstrate a reliable all-optical technique for performing optical double sideband (ODSB) to single sideband (OSSB) format conversion of a 40 Gb/s non-return-to-zero signal. It is based on the optimization of a detuned optical filter, which was implemented on a fiber Bragg grating (FBG) with a complex apodization profile. An OSSB signal with negligible distortion was obtained, as the FBG presented a nearly ideal frequency response. Higher tolerance to chromatic dispersion enabled by the OSSB signal in comparison to the ODSB signal was demonstrated on both simulation and experimental results.     

Multiresidue method for the detection of tranquillisers, xylazine, and a beta-blocker in animal production by liquid chromatography-tandem mass spectrometry

Tranquillisers are often used in animal production, especially in pigs to calm them before transport to the slaughterhouse. The use of certain substances (derived from phenothiazine) is totally prohibited, whilst other compounds (butyrophenone and beta-blockers) are regulated through the establishment of MRLs. A physico-chemical detection method based on liquid chromatography-tandem mass spectrometry is described. Validation was carried out according to the criteria laid down in Directive 2002/657/EC. The method was also used to detect and quantify these substances in treated animals.     

Integrated nanoreactor systems: triggering the release and mixing of compounds inside single vesicles

We present a method that allows the on-demand release and mixing of zepto- to femtoliter volumes of solutions in the interior of vesicular nanoreactors. The reactors comprise a nested system of lipid vesicles, part of which release their cargo in the interior of the others during a thermotropic phase transition. The performance of individual reactors immobilized on glass is characterized using confocal microscopy and a fluorescent dye that reports dilution during the release. The results confirm the predicted temperature-induced response and reveal a release transition width of 3 degrees C with a half time of approximately 1 min.     

Trimethylsilyl halide-promoted Michaelis-Arbuzov rearrangement

[reaction: see text] We describe a new, straightforward, and easy-to-handle method for achieving an unprecedented trimethylsilyl halide-catalyzed Michaelis-Arbuzov-like rearrangement. This rearrangement occurs at temperatures from room temperature to 80 degrees C and does not require addition of any alkyl halide. The scope and limitations of this new reaction are explored, as well as its mechanism.     

Total synthesis of the ramoplanin A2 and ramoplanose aglycon

Full details of a convergent total synthesis of the ramoplanin A2 and ramoplanose aglycon are disclosed. Three key subunits composed of residues 3-9 (heptapeptide 15), pentadepsipeptide 26 (residues 1, 2 and 15-17), and pentapeptide 34 (residues 10-14) were prepared, sequentially coupled, and cyclized to provide the 49-membered depsipeptide core of the aglycon. Key to the preparation of the pentadepsipeptide 26 incorporating the backbone ester was the asymmetric synthesis of an orthogonally protected l-threo-beta-hydroxyasparagine and the development of effective and near-racemization free conditions for esterification of its hindered alcohol (EDCI, DMAP, 0 degrees C). The coupling sites were chosen to maximize the convergency of the synthesis including that of the three subunits, to prevent late stage racemization of carboxylate-activated phenylglycine-derived residues, and to enlist beta-sheet preorganization of an acyclic macrocyclization substrate for 49-membered ring closure. By altering the order of final couplings, two macrocyclization sites, Phe(9)-d-Orn(10) and Gly(14)-Leu(15), were examined. Macrocyclization at the highly successful Phe(9)-d-Orn(10) site (89%) may benefit from both beta-sheet preorganization as well as closure at a d-amine terminus within the confines of a beta-turn at the end of the H-bonded antiparallel beta-strands. A more modest, but acceptable macrocyclization reaction at the Gly(14)-Leu(15) site (40-50%) found at the other end of the H-bonded antiparallel beta-strands within a small flexible loop may also benefit from preorganization of the cyclization substrate, is conducted on a substrate incapable of competitive racemization, and accommodates the convergent preparation of analogues bearing depsipeptide modifications. Deliberate late-stage incorporation of the subunit bearing the labile depsipeptide ester and a final stage Asn(1) side-chain introduction provides future access to analogues of the aglycons which themselves are equally potent or more potent than the natural products in antimicrobial assays.