Development of new DMAP-related organocatalysts for use in the Michael addition reaction of β-ketoesters in water

A general and efficient protocol for the Michael addition reactions of β-ketoesters in pure water has been developed. The reactions are successfully catalyzed by newly designed DMAP-related organocatalysts such as 4-(didecylamino)pyridine, and the desired Michael adducts are obtained in good to high yields     

Synthesis of saccharide precursors for preparation of potential inhibitors of glycosyltranferases

Ethyl 6-O-tert-butyldimethylsilyl-3,4-di-O-acetyl-2-thio-α-D-fructofuranoside (Va), its β-analog (Vb); as well as benzyl 6-O-tert-butyldimethylsilyl-3,4-di-O-acetyl-2-thio-α-D-fructofuranoside (Xa) and its β-analog (Xb), having an unprotected OH group at C-1, were prepared by sequential synthesis starting from commercially available D-fructose. These compounds represent suitable nucleophiles for the preparation of model carbohydrate mimetics of a glycosyltransferase inhibitor type in transition state. The structures of all compounds were confirmed by NMR spectral data and elemental analyses.     

Cover Picture: The Chemistry of Escapin: Identification and Quantification of the Components in the Complex Mixture Generated by an L‐Amino Acid Oxidase in the Defensive Secretion of the Sea Snail Aplysia californica (Chem. Eur. J. 7/2009)

Defensive chemicals such as the ink secretion of this marine gastropod mollusk—the sea hares Aplysia californica—are released following attacks from predators for protection. One might expect these secretions to be complex mixtures of products, given that they must work against a diversity of predators. In their Full Paper on page 1597 ff. , C. D. Derby et al. describe some of the chemical complexity of the ink of sea hares attributable to the enzyme “escapin”. Escapin is an L ‐amino acid oxidase that oxidatively deaminates its major substrate, L ‐lysine, to produce an equilibrium mixture of the molecules shown in this image. Photograph from Genny Anderson (Santa Barbara City College).

     

The Role of Intra-Yarn Shear in Integrated Multi-Scale Deformation Analyses of Woven Fabrics: A Critical Review

This article attempts to bring an enhanced insight into the analysis of in-plane shear behavior of woven fabrics. Two common methods have been used to characterize the shear behavior of woven preforms, namely the Bias Extension (BE) and Picture Frame (PF) tests. In spite of the identical macro-scale shear deformation of fabrics in these two characterization procedures, the current study demonstrates that their underlying micro- and meso-scale deformation mechanisms are quite distinct. The trellising mechanism, which is based on the well-known Pin-Joint Theory (PJT), has been regarded for a long time as the sole model to describe the meso-scale deformation of woven fabrics in both the BE and PF tests. Throughout this article, this mechanism is challenged for the PF test by undertaking a multi-scale analysis along with a critical review and integration of the previous experimental, analytical, and numerical studies. Intra-yarn shear, which has not been fully understood yet, is substantiated as a potential meso-level deformation mechanism occurring in the PF test. Accordingly, a new meso-level deformation model is proposed and compared with the trellising shear pattern in the BE setup. Afterward, the comparison is extended from meso-level to macro-level in order to provide more in-depth hypotheses for explaining differences reported in the literature between the shear characteristics of fabrics using BE and PF tests. Finally, some guidelines have been sought to select more reliable characterization method given a forming process.     

Dustiness test of nanopowders using a standard rotating drum with a modified sampling train

The standard rotating drum tester was used to determine the dustiness of two nanopowders, nano-TiO₂ and fine ZnO, in standard 1-min tests. Then, the sampling train was modified to determine the number and mass distributions of the generated particles in the respirable size range using a Scanning Mobility Particle Sizer (SMPS), an Aerodynamic Particle Sizer (APS) and a Multi-orifice Uniform Deposit Impactor (MOUDI) in the 30-min tests. It was found that very few particles below 100 nm were generated and the released rate of particles decreased with increasing rotation time for both nanopowders in the 30-min tests. Due to the fluffy structure of the released TiO₂ agglomerated particles, the mass distributions measured by the MOUDI showed large differences with those determined by the APS assuming the apparent bulk densities of the powders. The differences were small for the ZnO agglomerates, which were more compact than the TiO₂ agglomerates.     

Measurement of photo-fission yields and photo-neutron cross-sections in 209Bi with 50 and 65 MeV bremsstrahlung

The photo-fission yields and photo-neutron cross-sections of ( $ \gamma$ , 3n) and ( $ \gamma$ , 4n) on ²⁰⁹Bi induced by 50 and 65MeV bremsstrahlung have been measured by using a recoil catcher and an off-line $ \gamma$ -ray spectrometric technique. The mass-yield distribution of fission products in ²⁰⁹Bi induced by bremsstrahlung photons from the present work and literature data in the energy range 28-85MeV is symmetric around 103 mass units. However, the full width at half maximum of the yields distribution increases from 19 mass units at 28-40MeV to 23 mass units at 85MeV. The ( $ \gamma$ , 3n) reaction cross-section in the 50MeV and the ( $ \gamma$ , 4n) reaction cross-section in the 50 and 65MeV bremsstrahlung-induced reaction of ²⁰⁹Bi were determined for the first time.     

Photon radiation in $$e^+e^-\;\rightarrow \;$$hadrons at low energies with carlomat_3.1

We present a sample of results for the cross sections of several processes of low energetic \(e^+e^-\) annihilation into final states containing pions accompanied by one or two photons, or a light lepton pair. The results, which have been obtained with a new version of a multipurpose Monte Carlo program carlomat, labelled 3.1, demonstrate new capabilities of the program which, among others, include a possibility of taking into account either the initial or final state radiation separately, or both at a time, and a possibility of inclusion of the electromagnetic charged pion form factor for processes with charged pion pairs. We also discuss some problems related to the U(1) electromagnetic gauge invariance.     

Spatially localized current-induced crystallization of amorphous silicon films

Field-enhanced metal-induced solid phase crystallization (FE-MISPC) at room temperature is employed to create microscopic crystalline regions at predefined positions in hydrogen-rich amorphous silicon (a-Si:H) films. Electric field is applied locally using a sharp conductive tip in atomic force microscope (AFM) and nickel electrode below the a-Si:H film. The process is driven by a constant current of ?50 pA to ?500 pA while controlling the amount of transferred energy (1–300 nJ) as a function of time. Passing current leads to a formation of nanoscale pits in the a-Si:H films. Depending on the energy amount and rate the pits exhibit lower or orders of magnitude higher conductivity as detected by current-sensing AFM. High conductivity is attributed to a local crystallization of the films. This is confirmed by micro-Raman spectroscopy.     

Structural investigations of nitrided Nb2O5 and Nb2O5–SiO2 sol–gel derived films

Sol–gel derived xNb₂O₅–(100 ? x)SiO₂ films (where x = 100, 80, 60, 50, 40, 20, 0 mol%) were nitrided at various temperatures (800 °C, 900 °C, 1000 °C, 1100 °C and 1200 °C). The structural transformations occurring in the films as a result of ammonolysis were studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The XRD results have shown that the temperatures below 1100 °C were too low to obtain a pure NbN phase in the samples. The AFM observations indicate that the formation of the NbN phase and the size of NbN grains are related to the silica content in the layer. NbN grains become more regular and larger as the niobium content increases. The maximum grain size of about 100 nm was observed for x = 100. Preparation of the Nb₂O₅–SiO₂ sol–gel derived layers and the subsequent nitridation is a promising method of inducing crystalline NbN in amorphous matrices. It follows from the XPS results that a small amount of Nb₂O₅ remains in the films after nitridation at 1200 °C and that nitrogen reacted not only with Nb₂O₅ but also with SiO₂.