Synthesis of Carbohydrate Derived α-Methylene-γ-lactones by Diasterecseldctive,Low Temperature Reformatsky-Type Reactions

Hexopyranoside- and hexofuranose uloses with either ethyl 2-(branamethyl)acrylate in the presence of laminar Zn/Ag-graphite or ethyl 2-(trimethylsilylinethyl)acrylate/tetra-n-butylanrnonium fluoride undergo stereoselective branching, mainly with formation of spiro α-methylene-γ-lactones.     

Poly(lactic acid) composites with poly(lactic acid)‐modified carbon nanotubes

This work reports the study of the effect of chemical functionalization of carbon nanotubes on their dispersion in poly(lactic acid). The nanotubes were functionalized by the 1,3‐dipolar cycloaddition reaction, generating pyrrolidine groups at the nanotube surface. Further reaction of the pyrrolidine groups with poly(lactic acid) was studied in solution and in the polymer melt. The former involved refluxing the nanotubes in a dimethylformamide/polymer solution; the latter was carried out by direct melt mixing in a microcompounder. The carbon nanotubes collected after each process were characterized by thermogravimetry and by X‐ray photoelectron spectroscopy, showing evidence of polymer bonded to the nanotube surface only when the reaction was carried out in the polymer melt. The composites with polymer modified nanotubes present smaller average agglomerate area and a narrower agglomerate area distribution. In addition, they show improved tensile properties at low CNT concentration and present lower electrical resistivity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3740–3750     

Bulk universality for Wigner matrices

We consider N × N Hermitian Wigner random matrices H where the probability density for each matrix element is given by the density ν(x) = e^?U(x). We prove that the eigenvalue statistics in the bulk are given by the Dyson sine kernel provided that U ∈ C⁶( \input amssym $\Bbb R$ ) with at most polynomially growing derivatives and ν(x) ≥ Ce^?C|x| for x large. The proof is based upon an approximate time reversal of the Dyson Brownian motion combined with the convergence of the eigenvalue density to the Wigner semicircle law on short scales. © 2010 Wiley Periodicals, Inc.     

Determination of glyphosate and its metabolites in plant material by reversed‐polarity CE with indirect absorptiometric detection

A simple CE method for simultaneous determination of glyphosate and its metabolites (i.e. aminomethylphosphonic acid, glyoxylate, sarcosine and formaldehyde) in plants is reported here. A BGE of pH 7.5, 10% ACN, 7.5 mM phthalate, containing 0.75 mM hexadecyltrimethylammonium bromide as an electro‐osmotic flow modifier, an applied voltage of –20 kV and absorptiometric monitoring at 220 nm were the optimal chemical and instrumental parameters. The method, with development time 20 min, shows linear calibrations within the range 5–500 μg/mL (for all target analytes) with correlation coefficients between 0.999 and 0.998. It has been validated by application to samples of Lolium spp. The electroinjection mode hinders most interferents to enter the capillary, thus providing a clean electropherogram and making unnecessary long sample‐preparation steps.     

A comparative study of the non-isothermal degradation of natural rubber from Mangabeira (Hancornia speciosa Gomes) and Seringueira (Hevea brasiliensis)

Due to the increasing search for alternative sources of natural rubber (NR) whose properties are similar to Hevea brasiliesis, several sources have been studied in the past few years. Among them, Mangabeira (Hancornia speciosa Gomes), which is native to Amazon rainforest and other regions of Brazil, has a potential as another viable rubber source. As a continuation of a series of comparative studies between Hancornia and Hevea (clone RRIM 600) these two species by our research team, their thermal behavior was analyzed by thermogravimetry (TG) using Flynn–Wall–Ozawa’s approach in order to obtain kinetic parameters (reaction order, pre-exponential factor and activation energy) of the decomposition process. Results indicated that the thermal behavior of NR from Hancornia was comparable to Hevea with some differences observed as follows: reaction order for Hancornia was higher than for Hevea at the beginning of degradation and very close for temperatures over 350 °C; activation energy and pre-exponential factor had the same trend, i.e., increased with increasing degree of conversion remaining almost constant between 20 and 70% and then increasing for higher degrees, although Hevea was slightly more thermally stable than Hancornia. These major influences in the degradation process in the early stage are attributed to differences in non-rubber constituents present in these two species.     

Energetic Silver Salts with 5-Aminotetrazole Ligands

Methylation of 5-amino-1H-tetrazole ( 1 ) gives 1-methyl-5-amino-1H-tetrazole ( 2 ) and 2-methyl-5-amino-1H-tetrazole ( 3 ). A new family of energetic silver complexes based on ligands 1 , 2 and 3 with perchlorate and nitrate anions ( 10 – 15 ) were synthesized and characterized by using IR, Raman, and NMR (¹H, ¹³C, ¹⁴N, and ³⁵Cl NMR) spectroscopy, elemental analysis, and mass spectrometry. The crystal structures of the compounds were determined where possible and reveal interesting structural details that are discussed herein. Additionally, differential scanning calorimetry was used to assess the thermal stability of the new salts, which showed excellent thermal stabilities at temperatures up to and above 225 °C. Standard tests were also used to assess the sensitivity of the materials towards impact and friction. All the silver complexes showed increased sensitivity values in comparison with analogous protonated 5-amino-1H-tetrazolium perchlorate and nitrate salts. Some of these materials have sensitivity values that are comparable to commonly used primary explosives and all of them either deflagrate ( 12 – 14 ) or detonate loudly ( 10 and 11 ) on contact with an open flame. Lastly, nitrate salt 11 is easily initiated by thermal shock. It shows reasonably low sensitivity in comparison with other silver salts (e.g., silver azide or silver fulminate), which makes handling it much less hazardous. Compound 11 also has good thermal stability, decomposing at ≈300 °C, and shows interesting properties as a more environmentally benign alternative to lead(II) diazide in initiation devices for civil and military applications.