Radical anions containing the dioxidated 1,2,5‐thiadiazole heterocycle. Part II

Radical anions from several 3,4‐aryl‐disubstituted derivatives of 1,2,5‐thiadiazole 1,1‐dioxide were accumulated through chemical reduction of the substrates in aprotic solvents. The radical anions were characterized by electron spin resonance and cyclic voltammetry. DFT theoretical calculations were also performed for the 3,4‐diphenyl derivative. The course of the reductions was followed using cyclic voltammetry. Uncommon reductants, such as amides, were found to be effective under certain conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

On the reaction of iron oxides and oxyhydroxides with tannic and phosphoric acid and their mixtures

The actions of tannic acid, phosphoric acid and their mixture on lepidocrocite, goethite, superparamagnetic goethite, akaganeite, magnetite, hematite and maghemite for 1 day and 1 month were explored. It was found that these acids form iron tannates and phosphates. Lepidocrocite and magnetite were the iron phases more easily transformed with the mixture of the acids after 1 month of reaction, whereas hematite was the most resistant phase. In the case of goethite, our results suggest that in order to understand properly the action of these acids, we have to take into account its stoichiometry, surface area and degree of crystallinity.     

Interaction of Candida parapsilosis isolates with human hair and nail surfaces revealed by scanning electron microscopy analysis

Candida parapsilosis is found frequently as commensal organism on epithelial tissues, and is also an increasing cause of nosocomial infection. Scanning electron microscope (SEM) observations were used to analyse the capability of C. parapsilosis cells to adhere and grow as biofilm on human natural substrates and to compare the adherence pattern of isolates exhibiting distinct phenotypes. Cells from the crepe phenotype are predominantly elongated and form pseudohyphae whereas cells from the smooth phenotype are yeast-shaped, either in liquid cultures or on human nail and hair surfaces. The electron micrographs revealed that C. parapsilosis cells from the smooth phenotype adhered in higher number to both surfaces compared to the observed for the crepe phenotype. SEM analysis of human hair surface revealed that cells from the smooth phenotype appear as clumped blastoconidia of uniform morphology embedded in a flocculent extracellular material forming biofilm. The extracellular material and biofilm were seeing in a less extension in the crepe phenotype. A distinct adherence pattern was observed when human nail was used as substrate. Here C. parapsilosis cells seem to be linked to surface structures of human nail plate. Fibrillar extracellular material was observed connecting neighbouring cells as well as nail surface.     

XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

Novel organometallic aromatic polyester based on ferrocene

<正>A novel polyester containing ferrocenyl was prepared by low-temperature interface polycondensation of 1,1'-ferrocenedicarboxylic acid chloride with 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one(DHPZ),which is a twisted non-coplanar heterocyclic bisphenol-like monomer.The newly generated polymer was evaluated based on characterization of its solubility,viscosity measurements,elemental analysis,FTIR spectroscopy,differential scanning calorimetric and thermogravimetric studies.     

Potentiometric Studies on the Equilibria of Flufenamic Acid in Aqueous Solutions and in Two-phase Organic Solvent + Water Systems

In this paper, the flufenamic acid equilibria in aqueous solution and in two-phase organic solvent + aqueous solution are described and presented. The dissociation constants K _a1 and K _a2 were determined in MDM + water mixtures. The Yashuda-Shedlovsky extrapolation procedure has been used to obtain the values of K _a1 and K _a2 in aqueous solutions. The distribution ratio D was measured in the toluene + water system over a wide range of pH by the shaking flask method. Based on the results of potentiometric titrations in two-phase organic solvent (benzene, ethylbenzene, toluene, carbon tetrachloride, chloroform, chlorobenzene, and bromobenzene) + aqueous systems, and using models of single and multistep equilibria, the values of distribution constants K _D and dimerization constants K _dim were calculated. The influences of polarity of the applied solvents and pH of the aqueous phase, on the speciation of the particular forms of flufenamic acid in both phases, were demonstrated.     

Stability of ZSM-11 and BETA zeolites during the catalytic cracking of low-density polyethylene

The stability of H-ZSM-11 (H-Z) and H-BETA (H-B) zeolites during the catalytic degradation of low-density polyethylene (LDPE) was studied using the same sample of catalyst in eleven consecutive cycles. The gaseous hydrocarbons, liquid hydrocarbons and waxes generated in each cycle were analyzed as well as the used catalyst. The zeolites were characterized by XRD, FTIR of adsorbed pyridine and N₂ adsorption, while the physical mixtures of LDPE/zeolites were subjected to TG-DTG analysis.The H-Z zeolite exhibited an important stability during the successive cycles of LDPE conversion. On the contrary, the behavior H-B zeolite was completely different; from the sixth cycle the yields of products changed progressively, approaching to that obtained in a purely thermal process.The yields of accumulated coke increased steadily throughout the cycles up to maximum values in the eleventh cycle of &amp;sim;6 and &amp;sim;15&amp;#xA0;wt% for H-Z and H-B, respectively. These results were confirmed by TG under air flow.     

Analytical methods for pesticide residues in rice

Rice consumption has increased worldwide over recent decades, as it has become one of the most common foods. Although the analysis of environmental samples coming from rice areas has been well documented, there is less information regarding the analysis of pesticide residues in rice-grain samples.Rice (paddy, brown and white) can be considered a complex matrix, leading to difficulties in the application of the different multiresidue methods described in the literature. This review addresses and compares the principal extraction and clean-up methodologies [e.g., liquid-liquid extraction, solid-phase extraction, pressurized-liquid extraction, QuEChERS (quick, easy, cheap, effective, rugged and safe), gel-permeation chromatography and supercritical-fluid extraction - with QuEChERS-based methods being the most frequently employed].Traditionally, the determination of pesticide residues in rice has been based on gas chromatography with mass spectrometry (MS). But the application of new classes of pesticides has driven laboratories to increase the use of liquid chromatography with tandem MS. The limits of detection and quantification are in the ranges 0.09-90&amp;#xA0;μg/kg and 1-297&amp;#xA0;μg/kg, respectively, for the methodologies reported. These values agree with the current internationally-accepted maximum residue limits (MRLs).Based on the European Union (EU) database, more than 3000 analyses of pesticide residues in rice have been performed by official EU laboratories over the past decade. Of these, 6% reported pesticide residues above the MRLs.Physico-chemical properties can explain the occurrence of pesticides in rice commodities: lipophilic pesticides are frequently found in brown rice, whereas fungicides are mainly found in milled rice. Carbendazim, malathion, iprodione, tebuconazole, quinclorac and tricyclazole are the pesticides most frequently found in white rice, while buprofezin, hexaconazole, chlorpyrifos and edifenphos are most commonly found in paddy rice.Pesticide-residue concentrations can be affected during rice processing - with concentrations generally lower in the final products. However, few studies focusing on primary processing have addressed the setting of precise values applicable for the processing factors.     

Analytical characterization of alcohol-ethoxylate substances by instrumental separation techniques

The characterization of alcohol-ethoxylate substances is a significant challenge in analytical science. Their importance in industry and society makes it necessary to have methods for their rapid, reliable characterization and quantification. This overview highlights the instrumental separation techniques for their analysis - chromatographic (e.g., gas, liquid and supercritical fluid chromatography) and electrophoretic (e.g., capillary, gel, capillary zone, and non-aqueous capillary electrophoresis and micellar electrokinetic chromatography). We summarize and explain analytical parameters for their characterization. We include selected references and examples to show the appropriateness of instrumental separation techniques for the analytical characterization of alcohol-ethoxylate substances.