Immobilization of a Pd(II) complex on hydrophilic graphite oxide and its catalytic investigation in the Heck coupling reaction

Tetraamminepalladium(II) chloride monohydrate was heterogenized on hydrophilic graphite oxide (GO), synthesized by Brodie's method. Two samples, with Pd contents of 2% and 5%, referred to as Pd2 and Pd5, respectively, were prepared by a simple and scalable impregnation method and tested as catalysts in the Heck coupling reaction of styrene and bromobenzene. The reactions were carried out at 423 K for 3 hr by applying Na₂CO₃ as a base and N-methylpirrolidone or dimethylformamide (DMF) as a solvent. The Pd complexes heterogenized on graphene oxide platelets proved to be highly active and selective catalysts, and Pd2 was more efficient than Pd5. The effect of quaternary ammonium salts (tetrabutylammonium bromide and tetrabutylammonium chloride, TBAC) as modifiers and that of an ionic liquid (1-butyl-3-methylimidazolium bromide, bmim) was studied and the highest conversions were obtained when TBAC was employed. The selectivity for the formation of the main product, E-stilbene, was in the range 91–96%. Catalyst recycling was investigated and the extent of leaching was found to depend on the solvent. DMF proved to be a highly feasible reaction medium because both catalysts could be recycled five times in this solvent without any significant loss of activity. A hot filtration test was performed and gave evidence that leaching of the active Pd species did not take place under the above reaction conditions. These results substantiate the fact that simple cationic Pd species can be efficiently immobilized on pristine GO surfaces without the requirement of the functionalization of GO with nitrogen-containing mono or multidentate ligands as binding sites.     

Raman spectroscopy study of the interaction of 3,5,3′‐triiodo‐L‐thyronine with phosphatidylglycerol lipid bilayers

A Raman spectroscopic study of anionic model membranes and their structural alterations exerted by a relatively small biomolecule, such as the hormone 3,5,3′‐triiodo‐L‐thyronine (T3), is presented. Spectral differences between pure dipalmitoylphosphatidylglycerol (DPPG) multilamellar vesicles and DPPG–T3 mixture and between pure dilauroylphosphatidylglycerol (DLPG) and DLPG–T3 mixture were evaluated in order to determine the response of lipid membranes in gel and liquid‐crystalline phases to the hormone incorporation. Density functional theory (DFT) calculations support the band analysis of the complex 1150–1050 cm⁻¹ Raman region. Geometry optimizations and vibrational behaviors of a model charged molecule that mimics the phosphatidylglycerol lipid moiety in solvated state were taken into account for the spectral interpretation of this specific region. The anionic nature of the lipid polar head plays an important role in the interaction with the hormone, as is evidenced by the CO and PO₂⁻ stretching bands. In addition, the differential penetration of T3 into the hydrophobic region of the membranes shows to be dependent on the lipid phase. The spectral data were compared with those previously obtained for zwitterionic membranes. Copyright © 2015 John Wiley & Sons, Ltd.     

Hollow fibre liquid-phase microextraction of parabens from environmental waters

Parabens (alkyl-p-hydroxybenzoates) are antimicrobial preservatives widely used in cosmetics, toiletries, pharmaceuticals, and food. Nowadays, they are considered emerging pollutants and their determination is becoming increasingly important since they are continuously released into the environment. In this work, a hollow fibre liquid-phase microextraction method has been developed for the extraction of parabens from environmental waters. The parameters affecting the extraction of parabens (organic solvent used as liquid membrane; pH of both sample and acceptor solution; salting-out effect; extraction time and stirring speed) were carefully optimized in order to reach high recoveries for all tested analytes. Under optimum conditions, parabens were extracted from river, reservoir and sea water samples with recoveries ranging from 16.7 to 68.6% depending upon the analyte and the sample analyzed, leading to detection limits lower than 0.2?ng?mL^?1 using a simple HPLC-UV instrument.     

Optimisation and assessment of an innovative high sensitivity 90-degree reflecting ICP-MS ion optics system for the validation of simultaneous determination of arsenic and selenium in water matrices

A routine ICP-MS method for the determination of As and Se in fresh and sewage water has been developed. After a first phase of optimisation, where the torch alignment, flow of gases and ion optic adjustments were calibrated, the method was validated successfully. The parameters limits of detection, linearity, working range, sensitivity and the interferences, precision and accuracy were studied with three procedures for the method: measuring two SRMs (BCR-714 of influent wastewater and NIST 1643e of groundwater); spiking four different matrices at three levels of concentration; and doing a proficiency test. The limits of detection obtained were 0.2 and 0.8?µg?L^?1 for As and Se, respectively. The percentages of linearity obtained were 99.2% for As and 99.8% for Se. All recovery values were according to the AOAC intervals, from 95.3% for As in the wastewater matrix to 106.4% for Se in the seawater matrix. The accuracy was also studied determined via a proficiency testing resulting in acceptable Z-scores of 0.65 and 0.4 respectively for As and Se. The complete method allowed analysis of water samples according to European Directive 2000/60 EC and the different guides for method validation.     

Synthesis and MALDI-TOF MS Analysis of Protected Oligosaccharide Components of N-Glycoproteins

Essential components of N-glycoproteins were synthesized in octyl glycoside form starting from 3-O-allyl-D-glucose derivative. The β-mannosidic linkage was formed by the oxidation reduction method. MALDI-TOF mass spectrometry and its post-source decay (PSD) mode were used for identification and structural elucidation of protected synthetic oligosaccharides related to N-glycoproteins. Most fragments, identified in the PSD spectra, were products of the cleavage of glycosidic bonds.     

Cationic Order in Double Perovskite Oxide, Sr2Fe1−x Sc x ReO6 (x = 0.05, 0.1)

We have synthesized by sol–gel method the following polycrystalline double perovskite samples: Sr₂Fe_1?x Sc _x ReO₆ (x = 0, 0.05, 0.1). The results of the Rietveld refinements presented single double perovskite phases with orthorhombic symmetry for the system Sr₂Fe_1?x Sc _x ReO₆, the differences in atomic radii between Fe³⁺ and Sc³⁺ cause a lowering in symmetry with respect to the parent Sr₂FeReO₆ tetragonal compound. The Curie temperatures are found at about 426 and 436 (±5) K for Sr₂Fe_0.9Sc_0.1ReO₆ and Sr₂Fe_0.9Sc_0.05ReO₆, respectively. The Mössbauer spectra measured at 77 K show complex hyperfine structures resulting from different magnetic contributions at Fe³⁺ sites; the average hyperfine field is estimated 50 T and the isomer shift at 0.5 mm/s. At room temperature an intermediate valence state for Fe is also observed.     

On the Maximum Number of Equilateral Triangles, I

The following problem was posed by Erdős and Purdy: ``What is the maximum number of equilateral triangles determined by a set of n points in R ^d ?' New bounds for this problem are obtained for dimensions 2, 4, and 5. In addition it is shown that for d=2 the maximum is attained by subsets of the regular triangle lattice. Received April 9, 1998, and in revised form October 30, 1998.     

A recursion for alternating harmonic series

We present a convenient recursive formula for the sums of alternating harmonic series of odd order. The recursion is obtained by expanding in Fourier series certain elementary functions.     

Mössbauer and magnetic studies of La0.8Sr0.2CoO3-δ CMR perovskite

In this paper we present ⁵⁷Co emission Mössbauer and AC magnetic susceptibility studies of La_0.8Sr_0.2CoO_3-δ perovskite. The observed coexistence of paramagnetic and magnetic subspectra in the ⁵⁷Co emission Mössbauer spectra, as well as the difference of their isomer shifts support the existence of electronic phase separation in this perovskite, in good agreement with the double exchange based cluster model.