Coupled column liquid chromatography for the rapid determination of N-methylcarbamates and some of their main metabolites in water

Summary A sensitive and selective coupled-column liquid chromatography (LC-LC) method was developed for the trace level determination of some N-methylcarbamates and some of their main metabolites as aldicarb, aldicarb-sulphoxide, aldicarb-sulphone, carbofuran and 3-hydroxicarbofuran in drinking and ground waters. The limit of determination can be reduced to 0.1 μg.L⁻¹ by solid phase extraction with a subsequent evaporation step. Environmental samples spiked at 0.1 μg.L⁻¹ were preconcentrated off-line with graphite carbon and then analyzed by LC-LC with UV detection yielding average recoveries between 81–109% (n=5) with RSD between 5–9%. The overall procedure allowed a sample throughput of up to 30 samples per day.     

Syntheses and Crystal Structures of Polynuclear Cu(I) Complexes Containing the 1,1′-Bis-(diphenylphosphino)-ferrocene Ligand

 The reaction between [Cu(NCMe)₄][PF₆] and 1,1′-bis-(diphenylphosphino)-ferrocene (dppf) in several ratios, solvents, and conditions led to the synthesis and structural characterization of the Cu(I) complexes [Cu(dppf)(Odppf)][PF₆] (1), [(dppf)Cu(μ-dppf)Cu(dppf)][PF₆]₂ (2), and [(dppf)Cu(μ-Cl)₂Cu(dppf)] (3). Although 1 and the cation in 2 were known, the first was structurally characterized for the first time, exhibiting a significant asymmetry in the coordination sphere of Cu(I) owing to the presence of oxygen. In 2, the PF₆ ⁻ anion led to an interesting crystal packing with large open channels containing water. Finally, DFT calculations on a model of 3 showed that its HOMO exhibits, besides Fe, a significant Cu and Cl character, which is reflected in its electrochemical properties.     

Controlled ring‐opening polymerization of trimethylene carbonate and access to PTMC‐PLA block copolymers mediated by well‐defined N‐heterocyclic carbene zinc alkoxides

Four novel Zinc–NHC alkyl/alkoxide/chloride complexes ( 4 , 5 , 9 and 9′ ) were readily prepared and fully characterized, including X‐ray diffraction crystallography for 5 and 9′ . The reaction of N‐methyl‐N′‐butyl imidazolium chloride ( 3.HCl ) with ZnEt₂ (2 equiv.) afforded the corresponding [(C_NHC)ZnCl(Et)] complex ( 4 ) via a protonolysis reaction, as deduced from NMR data. The alcoholysis of 4 with BnOH led to quantitative formation of the dinuclear Zn(II) alkoxide species [(C_NHC)ZnCl(OBn)]₂ ( 5 ), as confirmed by X‐ray diffraction analysis. The NMR data are in agreement with species 5 retaining its dimeric structure in solution at room temperature. The protonolysis reaction of N‐(2,6‐diisopropylphenyl)‐N′‐ethyl methyl ether imidazolium chloride ( 8.HCl ) with ZnEt₂ (2 equiv.) yielded the [(C_NHC)ZnCl(Et)] species 9 . The latter was found to be reactive with CH₂Cl₂ in solution and to cleanly convert to the corresponding Zn(II) dichloride [(C_NHC)ZnCl₂]₂ ( 9′ ), whose molecular structure was also elucidated using X‐ray diffractometry. Unlike Zn(II)–NHC alkoxide species 1 and 2 , which contain a NHC flanked with an additional N‐functional group (i.e. thioether and ether, respectively), the Zn(II) alkoxide species 5 incorporates a monodentate NHC ligand. The Zn(II) complexes 1 , 2 and 5 were tested in the ring‐opening polymerization (ROP) of trimethylene carbonate (TMC). All three species are effective initiators for the controlled ROP of trimethylene carbonate, resulting in the production of narrow disperse PTMC material. Initiator 1 (incorporating a thioether moiety) was found to perform best in the ROP of TMC. Notably, the latter also readily undergoes the sequential ROP of TMC and rac‐LA in the presence of a chain‐transfer agent, leading to well‐defined and high‐molecular‐weight PTMC/PLA block copolymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Poly (acrylic acid) microchannel modification for the enhanced resolution of catecholamines microchip electrophoresis with electrochemical detection

A new modification of glass electrophoresis microchips based on poly (acrylic) acid immobilization has been performed. It is based on the reaction of PAA with an amine functionalized surface, obtained through the bifunctional reagent 3-aminopropyl triethoxysilane. Parameters affecting all the three steps involved: surface activation, silanization and polymer immobilization were optimized employing soda-lime glass plates. Characterization by SEM and XPS was carried out. Application of the modified microchips to the separation of a model system: dopamine (D), epinephrine (E) and norepinephrine (NE), that on the other hand are of high clinical relevance was performed employing amperometric detection. Modification is necessary for obtaining partial resolution of all the three analytes in a microchip with an effective separation length of 30 mm. Situation changes from no resolution (Rs) at all (only one peak was achieved for the mixture) to a partial resolution (Rs D–NE and Rs NE–E are 0.25 and 0.24 respectively). Microchips with 60 mm of separation channel were also modified, implying this procedure a resolution enhancement (Rs of 0.49 and 0.28 for D–NE and NE–E respectively), even when methanol is employed as organic modifier (Rs values of 0.70 (D–NE) and 0.66 (NE–E) for a 3% MeOH).     

Methyl dynamics studied by ENDOR spectroscopy: a new method

A new method for the investigation of methyl group rotation dynamics in free radicals in solids is described, based on the temperature dependence of the methyl protons ENDOR enhancement. The method is shown to work for hindering barriers of any height, and for both radicals trapped in single crystals and in powdered samples. As specific examples, the Arrhenius parameters for the methyl rotation in free radicals produced by γ-irradiation of 1-alanine and 4-methyl-2, 6 di-t-butyl-phenol are determined.     

Measuring the impacts of production risk on technical efficiency: A state-contingent conditional order-m approach

This article studies the influence of risk on farms’ technical efficiency levels. The analysis extends the order-m efficiency scores approach proposed by Daraio and Simar (2005) to the state-contingent framework. The empirical application focuses on cross section data of Catalan specialized crop farms from the year 2011. Results suggest that accounting for production risks increases the technical performance. A 10% increase in output risk will result in a 2.5% increase in average firm technical performance.     

A GRASP metaheuristic for humanitarian aid distribution

Large scale disasters, natural or human-made, have huge consequences on people and infrastructures. After a disaster strikes, the distribution of humanitarian aid to the population affected is one of the main operations to be carried out, and several crucial decisions must be made in a short time. This paper addresses a last-mile distribution problem in disaster relief operations, under insecure and uncertain conditions. A model is presented that takes into account the cost and time of operation, the security and reliability of the routes, and the equity of aid handed out. The output of the model consists of a detailed set of itineraries that can be used to build an implementable distribution plan. Given its high complexity, the resulting problem is solved using a multi-criteria metaheuristic approach. In particular, a constructive algorithm and a GRASP based metaheuristic are developed, which are tested in a case study based on the 2010 Haiti earthquake.