Kinetic study of the formation of N‐chloro compounds using N‐chlorosuccinimide

Second‐order rate constants were determined for the chlorination reaction of 2,2,2‐trifluoethylamine and benzylamine with N‐chlorosuccinimide at 25 °C and an ionic strength of 0.5 M. These reactions were found to be of first order in both reagents. According to the experimental results, a mechanism reaction was proposed in which a chlorine atom is transferred between both nitrogenous compounds. Kinetics studies demonstrate that the hydrolysis process of the chlorinating agent does not interfere in the chlorination process, under the experimental conditions used in the present work. Free‐energy relationships were established using the results obtained in the present work and others available in the literature for chlorination reactions with N‐chlorosuccinimide, being the pK_a range included between 5.7 and 11.22. Copyright © 2014 John Wiley & Sons, Ltd.     

Real Valuations on Skew Polynomial Rings

Let D be a division ring, T be a variable over D, σ be an endomorphism of D, δ be a σ-derivation on D and R?=?D[T; σ, δ] the left skew polynomial ring over D. We show that the set \((Val_\nu(R),\preceq)\) of σ-compatible real valuations which extend to R a fixed proper real valuation ν on D has a natural structure of parameterized complete non-metric tree, where \(\preceq \) is the partial order given by \(\mu \preceq \widetilde{\mu}\) if and only if \(\mu (f)\leq \widetilde{\mu}(f)\) for all f?∈?R and \(\mu, \widetilde{\mu} \in Val_\nu (R)\) . Furthermore and as a consequence, we also prove a criterion of irreducibility for left skew polynomials that includes as a particular case an Eisenstein valuation criterion which generalizes a similar one of Churchill and Zhang (J Algebra 322:3797–3822, 2009).     

The one-dimensional cutting stock problem with usable leftovers – A survey

In this article, we review published studies that consider the solution of the one-dimensional cutting stock problem (1DCSP) with the possibility of using leftovers to meet future demands, if long enough. The one-dimensional cutting stock problem with usable leftovers (1DCSPUL) is a problem frequently encountered in practical settings but often, it is not dealt with in an explicit manner. For each work reviewed, we present the application, the mathematical model if one is proposed and comments on the computational results obtained. The approaches are organized into three classes: heuristics, item-oriented, or cutting pattern-oriented.     

Asymmetric logistic peak as a suitable function for the resolution of highly asymmetric voltammograms in non-bilinear systems

The asymmetric logistic peak is tested as a new function for the parametric signal fitting (PSF) of highly asymmetric electrochemical signals in non-bilinear datasets, such as those obtained in linear sweep voltammetry (LSV) or in the presence of irreversible electrochemical processes. This new multivariate curve resolution strategy (PSF-ALPA) is successfully applied to LS voltammograms measured for the Cd(II)-glutathione system with a hanging mercury drop electrode, where Cd(II) is reversibly reduced, and to differential pulse voltammograms (DPV) measured at a glassy carbon electrode, where Cd(II) reduction becomes irreversible. Matrix augmentation by using LS voltammograms measured at different scan rates provides good results and encourages the development of ALPA methodology for third order data.     

Pros and cons of analytical methods to quantify surrogate contaminants from the challenge test in recycled polyethylene terephthalate

Different analytical methods were optimized and applied to quantify certain surrogate contaminants (toluene, chlorobenzene, phenol, limonene and benzophenone) in samples of contaminated and recycled flakes and virgin pellets of polyethylene terephthalate (PET) coming from the industrial challenge test. A screening analysis of the PET samples was carried out by direct solid-phase microextraction (SPME) in headspace mode (HS). The methods developed and used for quantitative analysis were a) total dissolution of PET samples in dichloroacetic acid and analysis by HS-SPME coupled to gas chromatography–mass spectrometry (GC–MS) and, b) dichloromethane extraction and analysis by GC–MS. The concentration of all surrogates in the contaminated PET flakes analyzed by HS-SPME method was lower than expected according to information provided by the supplier. Dichloroacetic acid interacted with the surrogates, resulting in a tremendous decrease of limonene concentration. The degradation compounds from limonene were identified. Dichloromethane extraction and GC–MS analysis evidenced the highest values of analytes in these PET samples. Based on the foregoing data, the efficiency of the recycling process was evaluated, whereby the removal of 99.9% of the surrogates proceeding from the contaminated flakes was confirmed.     

Determination of steroid hormones in biological and environmental samples using green microextraction techniques: an overview

Residues of steroid hormones have become a cause for concern because they can affect the biological activity of non-target organisms. Steroid hormones are a potential risk for wildlife and humans through the consumption of contaminated food or water. Their determination requires extraction and clean-up steps, prior to detection, to reach low concentration levels. In recent years, a great effort has been made to develop new analytical methodologies, such as microextraction techniques, that reduce environmental pollution. Researchers have modified old methods to incorporate procedures that use less-hazardous chemicals or that use smaller amounts of them. They are able to do direct analysis using miniaturised equipment and reduced amounts of solvents and wastes. These accomplishments are the main objectives of green analytical chemistry. In this overview, we focus on microextraction techniques for the determination of steroid hormones in biological (e.g., human urine, human serum, fish, shrimp and prawn tissue and milk) and environmental (e.g., wastewaters, surface waters, tap waters, river waters, sewage sludges, marine sediments and river sediments) samples. We comment on the most recent applications in sorptive-microextraction modes, such as solid phase microextraction (SPME) with molecularly imprinted polymers (MIPs), in-tube solid-phase microextraction (IT-SPME), stir-bar sorptive extraction (SBSE) and microextraction in packed sorbent (MEPS). We also describe liquid-phase microextraction (LPME) approaches reported in the literature that are applied to the determination of steroid hormones.     

Adsorption of ammonia on multilayer iron phthalocyanine

The adsorption of ammonia on multilayers of well-ordered, flat-lying iron phthalocyanine (FePc) molecules on a Au(111) support was investigated by x-ray photoelectron spectroscopy. We find that the electron-donating ammonia molecules coordinate to the metal centers of iron phthlalocyanine. The coordination of ammonia induces changes of the electronic structure of the iron phthalocyanine layer, which, in particular, lead to a modification of the FePc valence electron spin.     

Biomimetic synthesis of diversifolin

The conversion of a germacranolide structure (tagitinin C) into a furanoheliangolide one (diversifolin) was achieved by hydride conjugate addition using Stryker’s reagent.     

Physicochemical and Biochemical Profiling of Diphenyl Diselenide

The objective of the present study was to evaluate the physicochemical and biochemical profiling of diphenyl diselenide (PhSe)₂, a selenoorganic compound with biological activity. Experimental protocols were established for chemical stability in isotonic phosphate buffer (PBS) pH 7.4 and in simulated gastric and intestinal fluids, biological stability (bovine serum albumin (BSA) and plasma), solubility in PBS pH 7.4, distribution coefficient (Log D) in octanol/PBS, and determination of free (PhSe)₂ concentrations in BSA and plasma by using liquid chromatography with ultraviolet detection and tandem mass spectrometry. (PhSe)₂ was found to be chemically stable and not susceptible to degradation in plasma. The aqueous solubility was 0.98?±?0.072 μM and the Log D in octanol/PBS system was found to be 3.13. The percentage of unbound fractions of (PhSe)₂ obtained by equilibrium dialysis from BSA and plasma incubated with 100 μM (PhSe)₂ were 0.69?±?0.12 and 0.44?±?0.09 %, respectively. The findings indicated that (PhSe)₂ presents chemical and biological stability. Though, the compound showed low aqueous solubility, high Log D value and high binding to plasmatic protein. These data contribute to the knowledge of the toxicokinetic properties of (PhSe)₂ and further explain its low bioavailability in experimental models.