Absolute configuration determination of 2-(2-oxo-3-indolyl)acetamide derivatives

We describe a reliable method for determining the absolute configuration of 2-(2-oxo-3-indolyl)acetamides based on analysis of the ¹H NMR spectra of their phenylethylamide diastereomers. The conformational preferences for two diastereomeric amides were calculated by DFT, which matched well with the experimental results. X-ray diffraction analysis allowed us to validate the method.     

On the spectra of certain rooted trees

Let T be an unweighted tree with vertex root v which is the union of two trees T₁=(V₁,E₁), T₂=(V₂,E₂) such that V₁ ∩ V₂ = {v} and T₁ and T₂ have the property that the vertices in each of their levels have equal degree. We characterize completely the eigenvalues of the adjacency matrix and of the Laplacian matrix of T. They are the eigenvalues of symmetric tridiagonal matrices whose entries are given in terms of the vertex degrees. Moreover, we give some results about the multiplicity of the eigenvalues. Applications to some particular trees are developed.     

Spectra of generalized Bethe trees attached to a path

A generalized Bethe tree is a rooted tree in which vertices at the same distance from the root have the same degree. Let P_m be a path of m vertices. Let {B_i:1?i?m} be a set of generalized Bethe trees. Let P_m{B_i:1?i?m} be the tree obtained from P_m and the trees B₁,B₂,…,B_m by identifying the root vertex of B_i with the i-th vertex of P_m. We give a complete characterization of the eigenvalues of the Laplacian and adjacency matrices of P_m{B_i:1?i?m}. In particular, we characterize their spectral radii and the algebraic conectivity. Moreover, we derive results concerning their multiplicities. Finally, we apply the results to the case B₁=B₂=…=B_m.     

Multielemental analysis of dried residue from metal-bearing waters by wavelength dispersive X-ray fluorescence spectrometry

The purpose of this work was evaluation of instrumental sensitivity and detection limits for determination of elemental composition (20 different elements ranging from Na to Pb) of liquid mining samples by using conventional Wavelength Dispersive X-Ray Fluorescence (WDXRF) instrumentation. Preconcentration of elements from liquid samples was performed by means of a simple dried residue process, and spectral evaluation was carried out by integration of the peak area (using WinQXAS/AXIL package software, International Atomic Energy Agency (IAEA)) instead of the common net peak line intensity traditionally used in conventional WDXRF systems. With the proposed methodology, the calculated detection limits were in the µg L^− 1 range (from 0.005 to 0.1 mg L^− 1 level depending on the element) in all cases, which is suitable for element determination in most liquid samples involved in environmental studies such as metal mining liquid effluents. The detection limits are also below the established limits of the TCLP 1311 (United States Environmental Protection Agency (US-EPA)) and DIN 38414-S4 (German Standard legislation) procedures, which are commonly used to evaluate the leaching of metals from landfill disposal.     

On certain curves of genus three in characteristic two

We study curves of genus 3 over algebraically closed fields of characteristic 2 with the canonical theta characteristic totally supported in one point. We compute the moduli dimension of such curves and focus on some of them which have two Weierstrass points with Weierstrass directions towards the support of the theta characteristic. We answer questions related to order sequence and Weierstrass weight of Weierstrass points and the existence of other Weierstrass points with similar properties. – Dedicated to the treasured memory of our coauthor, Paulo Henrique Viana     

Ionic liquid: an efficient and reusable media for seleno- and thioester synthesis promoted by indium

A series of thio and selenoesters were efficiently obtained employing stable diorganyl chalcogenides, acyl chlorides, and In as reducing agent in BMIM·PF₆. Recycling of the ionic liquid was also performed, which was reused three times.     

Relaxation time spectra from short frequency range small-angle dynamic rheometry

In this work, the influence of the experimental frequency range over the relaxation time spectrum is studied. The relaxation time spectra were calculated from dynamic moduli, a well-known ill-posed problem, using a regularization method. The method solves the ill-posed problem by simultaneous minimization of the regularized standard deviation and a restriction function. The solution was validated using a simulated spectrum. Truncated moduli data generated from simulated spectra were used to evaluate the method for smaller frequency range data. Finally, experimental data of a wormlike micellar system mixed in aqueous solution with a zwitterionic copolymer were used to validate the method. It was possible to obtain relaxation time spectra from short frequency range data if the relaxation time range is allowed to be higher than the inverse of the highest and lowest experimental frequencies. These spectra can be used qualitatively to describe complex systems when no time-temperature superposition experiments are feasible.     

(N‐Heterocyclic carbene)Pd(triethylamine)Cl2 as precatalyst for the synthesis of Poly(triarylamine)s

The use of a highly active, air‐, and moisture‐stable N‐heterocyclic carbene‐palladium(II) complex for the polymerization of anilines and aryl dibromides or dichlorides by Buchwald‐Hartwig coupling is presented. In comparison to previous catalytic systems, higher molecular weight polymers with improved yields were obtained in shorter reaction times. The first examples of fabrication of OFETs with polytriarylamines synthesized with aryl dichlorides and anilines are also presented. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4904–4911