Spectrophotometric determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction

A simple method for the determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction is described. The procedure is based on the extraction of mercury in the form of a complex and its subsequent determination by spectrophotometry. The complex is formed between Hg(II) and 2-(2-benzothiazolylazo)-p-cresol. The detection at 650 nm is performed directly in the metal-rich phase, which is spread on a triacetylcellulose membrane. The method eliminates the need to use a cuvet or large quantities of samples and reagents. The parameters that influence the preconcentration were studied, and the analytical characteristics were determined. The enrichment factor and the consumptive index for this method were 64 and 0.16 mL, respectively. The LOD (3.3 microg/L) and LOQ (11.1 microg/L) were also determined. The accuracy of the method was tested by the determination of mercury in certified reference materials BCR 397 (Human Hair) and SRM 2781 (Domestic Sludge). The method was applied to the determination of mercury in samples of drinking water, sea water, and river water.     

Mixing and Matching Siderophore Clusters: Structure and Biosynthesis of Serratiochelins from Serratia sp. V4

Interrogation of the evolutionary history underlying the remarkable structures and biological activities of natural products has been complicated by not knowing the functions they have evolved to fulfill. Siderophores-soluble, low molecular weight compounds-have an easily understood and measured function: acquiring iron from the environment. Bacteria engage in a fierce competition to acquire iron, which rewards the production of siderophores that bind iron tightly and cannot be used or pirated by competitors. The structures and biosyntheses of "odd" siderophores can reveal the evolutionary strategy that led to their creation. We report a new Serratia strain that produces serratiochelin and an analog of serratiochelin. A genetic approach located the serratiochelin gene cluster, and targeted mutations in several genes implicated in serratiochelin biosynthesis were generated. Bioinformatic analyses and mutagenesis results demonstrate that genes from two well-known siderophore clusters, the Escherichia coli enterobactin cluster and the Vibrio cholera vibriobactin cluster, were shuffled to produce a new siderophore biosynthetic pathway. These results highlight how modular siderophore gene clusters can be mixed and matched during evolution to generate structural diversity in siderophores.     

¹H and ¹³C-NMR data of the simplest plumeran indole alkaloids isolated from Aspidosperma species

Indole alkaloids are the chemotaxonomic markers of the Aspidosperma genera. Those that have the simplest plumeran skeleton are classified as the precursors of biosynthetic routes and the intermediates for several synthetic reactions. This work aims to review the 1H and 13C-NMR data, up to 2011, describing the skeleton of 35 different plumeran indole alkaloids, from a group of 46 of them, and highlight the main spectral differences amongst them.     

Multicriteria optimization with a multiobjective golden section line search

This work presents an algorithm for multiobjective optimization that is structured as: (i) a descent direction is calculated, within the cone of descent and feasible directions, and (ii) a multiobjective line search is conducted over such direction, with a new multiobjective golden section segment partitioning scheme that directly finds line-constrained efficient points that dominate the current one. This multiobjective line search procedure exploits the structure of the line-constrained efficient set, presenting a faster compression rate of the search segment than single-objective golden section line search. The proposed multiobjective optimization algorithm converges to points that satisfy the Kuhn-Tucker first-order necessary conditions for efficiency (the Pareto-critical points). Numerical results on two antenna design problems support the conclusion that the proposed method can solve robustly difficult nonlinear multiobjective problems defined in terms of computationally expensive black-box objective functions.     

SrSnO<Subscript>3</Subscript>:Nd obtained by the polymeric precursor method

In this work, the synthesis of Nd-doped SrSnO₃ by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO₃ and SrSn_0.99Nd_0.01O₃. For Sr_0.99Nd_0.01SnO₃, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.     

Temperature‐dependent Raman spectroscopy study in MoO3 nanoribbons

This paper reports a study of vibrational, structural and morphological properties of molybdenum oxide nanoribbons. Temperature‐dependent Raman spectroscopy measurements in MoO₃ nanoribbons revealed morphological changes in the 150–350 °C temperature range. No structural phase transitions were observed, thus showing that the orthorhombic phase is stable from room temperature (nanoribbons) up to 650 °C (bulk‐like phase) where large plates have been formed by the coalescence of the nanoribbons. The interpretation of temperature‐dependent Raman data (wavenumber and linewidths) is supported by scanning electron microscopy that is used to directly probe the morphological changes in MoO₃ samples. The observed phenomena in the Raman data for MoO₃ nanoribbons can be applied to other nanomaterials. Copyright © 2012 John Wiley & Sons, Ltd.     

Magnetic and superconducting phase diagrams in ErNi2B2C

We present measurements of the superconducting upper critical field H_c2(T) and the magnetic phase diagram of the superconductor ErNi₂B₂C made with a scanning tunneling microscope (STM). The magnetic field was applied in the basal plane of the tetragonal crystal structure. We have found large gapless regions in the superconducting phase diagram of ErNi₂B₂C, extending between different magnetic transitions. A close correlation between magnetic transitions and H_c2(T) is found, showing that superconductivity is strongly linked to magnetism.     

Abrupt change in radiation-width distribution for 147Sm neutron resonances

We obtained the total radiation widths of s-wave resonances through an R-matrix analysis of (147)Sm(n,γ) cross sections. Distributions of these widths differ markedly for resonances below and above E(n)=300 eV, which is in stark contrast to long-established theory. We show that this change, as well as a similar change in the neutron-width distribution reported previously, is reflected in abrupt increases in both the average (147)Sm(n,γ) cross section and fluctuations about the average near 300 eV. Such effects could have important consequences for applications such as nuclear astrophysics and nuclear criticality safety.     

Lexicographic optimization for the multi-container loading problem with open dimensions for a shoe manufacturer

4OR - Motivated by a real-world application, we present a multi-container loading problem with 3-open dimensions. We formulate it as a biobjective mixed-integer nonlinear program with lexicographic...     

β-Cyclodextrin PAMAM Dendrimer Surface Doped with Silver and Hexacyanoferrate (III) and its Applications for Dopamine Detection in Synthetic Samples

A synthesis of β-cyclodextrin (β-Cd) functionalized with polyamide dendrimer PAMAM G.0 complexed with silver and potassium hexacyanoferrate (III) forming a mixed-valence complex (β-Cd-PAMAM-Ag/Fe) was proposed. This material was characterized by scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), X-Ray diffraction (XRD), Energy Dispersion Spectroscopy (EDS) and Electron Paramagnetic Resonance (EPR). The hybrid complex was electrochemically investigated using cyclic voltammetry and some parameters (electrolyte, concentration of electrolyte, pH and scan rate) were evaluate in order to obtain optimum analytical responses. The β-Cd-PAMAM-Ag/Fe material was successfully applied in the electrocatalytic oxidation of dopamine (DOP) using Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV).