Electrochemical Properties of a Conducting Film Derived from Iron(II) Tris(diaminopolypyridyl) Complex in the S(IV) Oxoanions Reduction

A new conducting film derived from the complex [Fe (diaphen)₃]²⁺, (diaphen=5,6‐diamino‐1,10‐phenanthroline) was electropolymerized by cyclic voltammetry onto a glassy carbon electrode. Poly‐[Fe^II (diaphen)₃] was studied by cyclic voltammetry, SEM, UV‐vis and micro‐Raman spectroscopy. Poly‐[Fe^II (diaphen)₃] shows electrocatalytic activity in HSO₃^? reduction in an ethanol/water solution. Electrocatalysis is centered at the π ring of phenanthroline. Rotating disk electrode studies showed a 0.117 V/dec Tafel slope, suggesting an EC process where the electrochemical process is the determining step. The chemical step was studied by UV‐vis spectroelectrochemistry. Amperometric behavior showed a linear range between 47.5 µM to 417 µM and the LOD was 19.5 µM.     

(Liquid + liquid) equilibria for ternary mixtures of (alkane + benzene + [EMpy] [ESO4]) at several temperatures and atmospheric pressure

In this work, the separation of benzene from aliphatic hydrocarbons (hexane, or heptane) is investigated by extraction with 1-ethyl-3-methylpyridinium ethylsulphate ionic liquid, [EMpy][ESO₄]. (Liquid + liquid) equilibria (LLE) data are determined for the ternary systems: {hexane (1) + benzene (2) + [EMpy][ESO₄] (3)} at T = (283.15, 293.15, 298.15, and 303.15) K and {heptane (1) + benzene (2) + [EMpy][ESO₄] (3)} at T = (283.15 and 298.15) K and atmospheric pressure. The selectivity and distribution coefficient, derived from the tie line data, were used to determine whether the ionic liquid is a good solvent for the extraction of aromatic from aliphatic compounds. The consistency of the tie line data was ascertained by applying the Othmer–Tobias and Hand equations. The experimental results for the ternary systems were well correlated with the NRTL equation. A study of the temperature effect and the influence of the chain length of the alkanes were realized. The results obtained were compared with other ionic liquids. There are no literature data for the mixtures discussed in this paper.     

The cationic halochromism of phenolate betaines: Molecular dynamics and quantum mechanics studies

The cationic halochromism of phenolate betaines was reproduced with the aid of a simple theoretical model, by calculation of the longest wavelength transition energies of supermolecules obtained by positioning a cation Mⁿ⁺ at a variable distance from the oxygen atom of the dye. The theoretical results were compared with experimental data for three systems, Reichardt’s betaine 1, Brooker’s merocyanine 2 and the N-methyl-8-oxyquinolinium dye 3. The model was validated by molecular dynamics simulations of solutions of dye 3, in methanol and DMSO, in the presence of variable concentrations of Na⁺.     

Electrochemically assisted anion insertion in Au(I)–Cu(I) heterotrimetallic clusters bearing ferrocenyl groups: Application to the fluoride/chloride discrimination in aqueous media

The heterotrimetallic Au(I)–Cu(I) aggregate [{Au₃Cu₂(C₂C₆H₄Fc)₆}Au₃(PPh₂C₆H₄PPh₂)₃](PF₆)₂ exhibits a well-defined solid state electrochemistry in contact with aqueous media, based on ferrocenyl-centred oxidation processes involving anion insertion. Upon attachment of microparticulate deposits of the cluster to graphite electrodes, distinctive electrochemical responses can be obtained for fluoride and chloride ions in aqueous media.     

Biocatalysis,sustainability, and industrial applications: Show me the metrics

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Identification of lipid binders in paintings by gas chromatography. Influence of the pigments

The influence of the presence and the type of pigments in the lipid binding media of paintings were studied by gas chromatography with flame ionization detector. The drying oils were linseed stand oil, poppy oil and sunflower oil, and the pigments studied were cadmium red, cobalt blue, tin white, lead white, chalk and plaster of Paris, commonly used in paintings. The results indicate that the stearic/palmitic ratio and the presence of pigments are quite stable during ageing. However, some differences in the oleic acid/palmitic acid ratio were found, depending on the type of pigment present in the lipid binding media. These variations are related to the drying effect of the pigments. The proposed method has been applied to the identification of drying oils in two samples from baroque paintings in the "Basilica de la Virgen de los Desamparados" of Valencia, Spain.     

Electrochemical Generation of Lead Volatile Species as a Method of Sample Introduction for Lead Determination by Atomic Absorption Spectrometry

An electrochemical lead volatile species generation system, as a means for sample introduction into a flame atomic absorption spectrometer, has been developed and evaluated for the determination of lead in urine samples. The reaction cell, designed and manufactured in our laboratory, consists of a reaction compartment housing a reticulated glassy carbon cathode and a platinum wire anode. The cell can easily be coupled to the spectrometer via a gas‐liquid separator. The characteristic of the cathode material, the volatile species generation efficiency and the possible interferences of some concomitants have been studied. Calculated detection limit based on the variability of a blank solution (3 s_b criterion) for ten measurements was 11 µg L^?1 and the sensitivity determined from the slope of the calibration graph, was 0.152 L mg^?1. The reproducibility (RSD) for ten replicate measurements at 1.0 mg L^?1 lead level, was 1.4 %. The accuracy of the method was determined through the analysis of spike urine samples. Recovery of 103.71 %±0.05 was achieved.     

Layer-by-layer identification of copper alteration products in metallic works of art using the voltammetry of microparticles

An in situ technique for layer-by-layer electrochemical analysis of solid surfaces using the voltammetry of microparticles is presented. The method is based on the determination of several shape-dependent parameters for voltammetric curves recorded at a graphite pencil working electrode in contact with the sample, all immersed into aqueous electrolytes. Repetitive square wave voltammetry and sequential application of constant potential reductive steps and voltammetric scans yield discernible responses for the corrosion products distributed in stratified layers on metal-based surfaces. This methodology is applied to identify alteration products of copper and copper alloys distributed in different layers in copper coupons submitted to different corrosive treatments and a contemporary brass sculpture.     

Protective effect against oxygen reactive species and skin fibroblast stimulation of Couroupita guianensis leaf extracts

In this study, hydroalcoholic leaf extracts of Couroupita guianensis were examined for antioxidant activity, phytochemical and total phenolic composition, stimulation of human skin fibroblast (HSF) proliferation and UV-absorption. The radical scavenging capacity, reducing power and protection against joint oxidation of linoleic acid and β-carotene bleaching oxidation in emulsion were used to evaluate the antioxidant activity. The results of this study strongly indicate in?vitro antioxidant activity, which may be due to the presence of a high total phenolic content. In order to identify active principles, the extracts were submitted to fractionation and the compounds isolated were the flavonoids 2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone (1), 7-hydroxy-5-methoxy-6,8-dimethylflavanone (2) and the phenolic acid 4-hydroxybenzoic acid (3). In addition, a high level of stimulation of HSF proliferation and significant absorption of UV radiation were also observed. The results suggest that the hydroalcoholic leaf extracts of C. guianensis have promising skin care properties.     

Determination of nitrotyrosine in Arabidopsis thaliana cell cultures with a mixed-mode solid-phase extraction cleanup followed by liquid chromatography time-of-flight mass spectrometry

In this work, a method for the determination of trace nitrotyrosine (NO₂Tyr) and tyrosine (Tyr) in Arabidopsis thaliana cell cultures is proposed. Due to the complexity of the resulting extracts after protein precipitation and enzymatic digestion and the strong electrospray signal suppression displayed in the detection of both Tyr and NO₂Tyr from raw A. thaliana cell culture extracts, a straightforward sample cleanup step was proposed. It was based on the use of mixed-mode solid-phase extraction (SPE) using MCX-type cartridges (Strata?-X-C), prior to identification and quantitation using fast liquid chromatography–electrospray time-of-flight mass spectrometry. Unambiguous confirmation of both amino acids was accomplished with accurate mass measurements (with errors lower than 2 ppm) of each protonated molecule along with a characteristic fragment ion for each species. Recovery studies were accomplished to evaluate the performance of the SPE sample preparation step obtaining average recoveries in the range 92–101 %. Limit of quantitation obtained for NO₂Tyr in A. thaliana extracts was 3 nmol L^?1. Finally, the proposed method was applied to evaluate stress conditions of the plant upon different concentrations of peroxynitrite, a protein-nitrating compound, which induces the nitration of Tyr at the nanomolar range. Detection and confirmation of the compounds demonstrated the usefulness of the proposed approach.