Group 3 metal (Sc, La) triflates as catalysts for the carbomethoxylation of aliphatic amines with dimethylcarbonate under mild conditions

The activity of Sc(OTf)₃ and La(OTf)₃ (OTf=SO₃CF₃) as catalysts for the phosgene-free synthesis of carbamate esters via carbomethoxylation of aliphatic amines with dimethylcarbonate (DMC) has been investigated. In the presence of M(OTf)₃ (M=Sc, La), primary and secondary aliphatic amines easily react with dimethylcarbonate, under very mild conditions (20 °C), to afford carbamate esters with good yield and excellent selectivity (≌100%). Sc(OTf)₃ is a more effective catalyst than the homologue La salt. The carbomethoxylation reaction requires as strict anhydrous conditions, as, at 20 °C, the presence of water inhibits markedly the catalytic activity of both triflate salts. Temperature influences carbamate selectivity, which is lower at higher temperature because of deleterious formation of N-methylation side-products.     

Sims characterization of La0.7Sr0.3MnO3 films for solid oxide fuel cell applications

Among solid oxides exploited to prepare efficient fuel cells, La(1-x)SrxMnO3 manganites have been widely studied and used as cathodes, because of their high conductivity at the working temperatures, good thermal stability and compatibility with other cell components. A fundamental goal in solid oxide fuel cells technology consists in lowering the normal operating temperatures, e.g. increasing the surface/volume ratio of electrodic materials, so as to enhance their catalytic performances. In this work, the preparation of high surface area La(1-x)SrxMnO3 (x approximately 0.3) films on silicon wafers by the nitrate-citrate Pechini process is described. The films were characterized by X-ray diffraction, Atomic Force Microscopy and Secondary Ion Mass Spectrometry. Good quality nanostructured perovskite-type films were obtained. SIMS methodology enabled to show the surface and in-depth coatings composition and residual contaminants. Moreover, it allowed defining the best synthesis conditions for complete in-depth decomposition of precursors and obtaining homogeneously thick coatings.     

Fast GC analysis with a 50 microm ID column: theory, practical aspects, and application to a highly complex sample

This research focuses on the minimization of GC analysis times through the use of a 5 m x 0.05 mm ID x 0.05 microm (film thickness) column. Experimental minimum plate height (Hmin) and optimum linear velocity values were derived from standard compound applications, under various analytical conditions, and then related to classical chromatographic theory. Deviations from the latter are measured and discussed. Practical aspects linked to the use of such capillaries, such as column sample capacity and detector acquisition rates, are also considered. Furthermore, a fast, and what can be considered a very fast method, were applied to the separation of a fuel sample. Coefficients of variation of elution times and relative peak areas were calculated in the very fast application. All analytical results are compared with those obtained by conventional 0.25 mm ID column applications.     

Determination of anthocyanins and related components in red wines by micro- and capillary HPLC

Anthocyanins and derived components of red wines were determined by microHPLC using a 1 mm ID HPLC column coupled on-line with an MS detector equipped with an ESI (ElectroSpray Ionisation) source. The use of microcolumn HPLC greatly enhanced detection performance, allowing direct identification of components present in the fraction. Nineteen anthocyanins were detected. Fifteen were identified, two were tentatively identified, and only the aglycon of the remaining two components was certainly identified. Six anthocyanin-derived pigments, supposedly formed during wine maturation, were also investigated and found in a wine sample. The analysis of red wine anthocyanins was also carried out by injecting a large sample volume onto a 0.32 mm ID HPLC column, using the column focusing technique, in order to decrease the limit of detection and quantification of components present in a very small amounts.     

Microwave assisted stereoselective synthesis of cis-substituted TinIV phthalocyanine dicarboxylates. application as corrosion inhibitors

Two PcSn(IV) dicarboxylate molecules were obtained through efficient microwave methodology with the aim to test them as corrosion inhibitors in the oil industry. The compounds were characterized by elemental analysis, IR, UV-vis, (1)H, (13)C NMR, and X-ray diffraction. The relative configuration of the two carboxylates is cis, placing the fatty acid moieties on the same face of the phthalocyanine macrocycle. In the solid-state the tin atoms possess square antiprismatic octacoordinated geometries. Both tin phthalocyanines were tested as corrosion inhibitors for hydrogen sulfide corrosive media showing a chemisorption process of the nanocap motifs on the metallic surface. Apparently, the length of the hydrophobic chain contributes significantly to the inhibition efficiency, in the sense that shorter chains increase the efficiency.     

Retention time reproducibility in comprehensive two-dimensional gas chromatography using cryogenic modulation. II. An interlaboratory study

An interlaboratory survey was conducted to determine the reproducibility of retention times in both the first (1D) and second dimension (2D) axes of the two-dimensional separation space, using the longitudinal cryogenic modulation comprehensive two-dimensional gas chromatographic approach. Intralaboratory reproducibility has been demonstrated in part 1 of this investigation [J. Chromatogr. A 968 (2002) 161]. Confidence in absolute retention times (hence component positions) in the two-dimensional separation space is critical to component identification. Comparing data from four independent laboratories, five independent gas chromatographs, five independent LMCS units, and numerous operators has determined that the LMCS cryogenic modulation approach provides reliable comprehensive two-dimensional GC results.     

The determination of the oxygen consumption in autoxidation studies by means of EPR spectroscopy

Stable paramagnetic species give rise in the presence of oxygen to EPR spectra characterized by broad lines due to Heisenberg spin exchange. This property can be conveniently used to determine the amount of oxygen present in the system under investigation. In the present paper we describe the use for this purpose of two radical probes: one is the stable aliphatic nitroxide 2,2,6,6-tetramethyl-l-piperidinyloxyl (TEMPO) which is employed as a homogeneous probe and the other is fusinite, a derivative of coal used as a finely grinded black powder totally insoluble both in water and in organic solvents. Both have been employed to follow the autoxidation reaction of three representative oxidizable substrates, i.e. cumene, styrene and methyl linoleate, in solution of chlorobenzene or of tert-butyl alcohol. The advantages of this technique with respect to traditional methods are emphasized.     

Micro Assay for Malondialdehyde in Human Serum by Extraction-Spectrophotometry Using an Internal Standard

Malondialdehyde (MDA) is a widely accepted biomarker of lipid peroxidation. Thus, the measurement of MDA in clinical samples is useful in the evaluation of oxidative stress. In this study, a micro-extraction-spectrophotometric assay was developed, based on the formation of MDA–thiobarbituric acid (TBA) adduct. To enhance the analytical performance, Erioglaucine A was used as an internal standard (IS), and the first derivative spectra were obtained. The volume of serum sample was 20µL and the total volume of aqueous phase 420µL (200µL of 0.6% TBA in acetic acid, pH 2.5 and 200µL of 6.25·10^–4% IS). The extraction of adduct and IS was carried out with 300µL of aliquat 336 (0.06%) in ethyl acetate. The analytical signal S was defined as the ratio between the first derivative absorbances measured at 543.1nm (adduct) and 644.4nm (IS). In the calibration range up to 10µmolL^–1 MDA, the linear regression coefficient was 0.9998. The quantification limit was 0.19µmolL^–1 and the CV values for 2µmolL^–1 and 5µmolL^–1 MDA, respectively, were 0.8% and 0.7%. The procedure was applied to the analysis of diabetic sera and the results compared with those obtained by HPLC (derivatization with 2,4-dinitrophenylhydrazine). Lower HPLC results (about 15%) indicated that interferences from other TBA reactive substances had not been completely eliminated by the extraction procedure and derivatization of spectral data. On the other hand, the micro-procedure presents important advantages: it is simple, precise and environmentally friendly (small amounts of reagents), which makes it readily adaptable to the analysis of large sample series. The feasibility of micro-assay in the evaluation of lipid peroxidation status was demonstrated in the analysis of 156 serum samples from diabetic patients divided into three groups according to the stage of development of typical complications.     

Effects of static electric fields on the photoionization spectra of two-electron atoms and ions

The simultaneous photoexcitation of two electrons is a highly correlated process, producing doubly excited states, observed as resonant structure in the ionization cross-section. This review paper explores the ability of a static electric field to affect these correlations, as evidenced by changes in the shape and energy of resonances. A comparison of field effects on the spectra of H⁻, Ps⁻, He, Ba and Cs⁻ summarizes current understanding of the processes and the capability of theory to predict the cross-sectional features.     

Effect of calcium and carbonate concentrations on cationic membrane fouling during electrodialysis

Fouling, which is the accumulation of undesired solid materials at the phase interfaces of permselective membranes, is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect on the fouling of cation-exchange membranes of the composition in calcium and carbonate of a model solution to be treated by electrodialysis. No fouling was observed at 400 and 800 mg/L of CaCl(2) in the absence of carbonate, while at only 400 mg/L CaCl(2) with carbonate, a deposit was observed. This difference could be explained by the buffering capacity of the carbonate, which affects the treatment duration with and without sodium carbonate. Since the duration was longer with carbonate, more calcium ions were able to migrate across the CMX-S membrane, which explained the higher deposit on its surface. Furthermore, whether there was carbonate in the solution treated by electrodialysis or not, the deposit on the surface of the cationic membrane was calcium hydroxide. However, this fouling formed during conventional ED was easily cleaned by an acid procedure.