Interlaboratory Study to Improve the Quality Control of Methylmercury Determination in Sediment

The results are presented of an interlaboratory study on methylmercury (MeHg) in sediment carried out by a group of European laboratories within the framework of a project managed by the EC Standards, Measurements and Testing Programme (formerly BCR). The aim of this exercise was to evaluate the performance of current methods used for MeHg determination in sediment in order to improve the state-of-the-art prior to the certification of a candidate reference material. The paper describes the organization of the interlaboratory study, the preparation of the sediment material used, the techniques evaluated and the results obtained by the participating laboratories. The outcome of the collaborative project showed that certification could be contemplated, providing that certain analytical techniques were optimized, especially with regard to extraction methods.     

Electroclinic properties of chiral smectic a liquid crystalline polymers and block copolymers

The scope for the synthesis and investigation of chiral smectic A liquid crystalline (LC) polymers and block copolymers is discussed. LC block copolymers can combine the molecular order of liquid crystals and the supramolecular order typical of block copolymers, thus allowing to attain information on mesomorphic responses in restricted geometries. We present a general overview on several aspects of the syntheses and properties of LC block copolymers, specifically those obtained by starting from azomacroinitiators. These materials can exhibit an electroclinic effect, that is an electrically induced molecular tilt, which is characterized by a linear dependence on the applied field and a very fast response time in the paraelectric smectic A phase. The current progress in their potential application in electrooptics is outlined.     

Information Network Modeling for U.S. Banking Systemic Risk

In this work we investigate whether information theory measures like mutual information and transfer entropy, extracted from a bank network, Granger cause financial stress indexes like LIBOR-OIS (London Interbank Offered Rate-Overnight Index Swap) spread, STLFSI (St. Louis Fed Financial Stress Index) and USD/CHF (USA Dollar/Swiss Franc) exchange rate. The information theory measures are extracted from a Gaussian Graphical Model constructed from daily stock time series of the top 74 listed US banks. The graphical model is calculated with a recently developed algorithm (LoGo) which provides very fast inference model that allows us to update the graphical model each market day. We therefore can generate daily time series of mutual information and transfer entropy for each bank of the network. The Granger causality between the bank related measures and the financial stress indexes is investigated with both standard Granger-causality and Partial Granger-causality conditioned on control measures representative of the general economy conditions.     

Effect of salinity on petroleum biodegradation

Summary The biodegradation of Ashtart crude oil by a mixed bacterial community (EH1) isolated from a marine sediment was investigated in varying concentration of sodium chloride (0 to 2 mol/l). Each fraction of Ashtart crude oil was biodegraded after a 30 day incubation period for a NaCl concentration equivalent to the one of seawater (0.4 mol/l). Saturates were more readily degraded than aromatics. The amount of oil degraded increased initially with increasing salt concentrations to a maximum level for 0.4 mol/l NaCl concentration. Thereafter the amount of oil degraded decreased with increasing salt concentrations. The polar fraction increased for the 0.4 to 1.4 mol/l NaCl concentration range. Asphaltenes were only slightly degraded (10%) for a NaCl concentration equivalent to the one of seawater (0.4 mol/l). NaCl concentrations seemed to affect the relative biodegradation of pristane and phytane. GC, UV fluorescence and FTIR techniques were used to study the evolution of each fraction of Ashtart crude oil.     

Determination of the β-Glucosidase Activity in Different Soils by Pre Capillary Enzyme Assay Using Capillary Electrophoresis with Laser-Induced Fluorescence Detection

Enzyme activities can provide indication for quantitative changes in soil organic matter (SOM). It is known that the activities of most enzymes increase as native SOM content reflecting larger microbial communities and stabilization of enzymes on humic materials. β-Gucosidase (β-Glu) activities have been frequently used as indicators of changes in quantity and quality of SOM. In this study we propose a simple and very sensitive method, which has lower limit of detection compared with classic spectrophotometric method with the aim of determinate the β-Glu activity in soil samples using Fluorescein mono-β-D-glucopyranoside (FMGlc) as a substrate. The fluorescein released by the enzymatic reaction was quantified by capillary electrophoresis-laser induced fluorescence (CE-LIF) method. The background electrolyte (BGE) consisted in 40 mM phosphate buffer, pH 6. The LOD and LOQ for fluorescein were 1.3 10⁻⁷ mg mL⁻¹ and 6.4 10⁻⁶ mg mL⁻¹, respectively. This work deals with the minimization of the mixture for the enzymatic reaction and with the optimization conditions of CE separation. To the best of our knowledge, this is the first time that an enzymatic activity was detected in soil using CE-LIF system.     

Synthesis,spectroscopic characterization (IR, 1H, 13C and 119Sn NMR,electrospray mass spectrometry) and toxicity of new organotin(IV) complexes with N,N′,O‐ and N,N′,S‐scorpionate ligands

New organotin(IV) derivatives containing the anionic ligands bis(3,5‐dimethylpyrazol‐1‐yl)dithioacetate [LCS₂]⁻ and bis(3,5‐dimethylpyrazol‐1‐yl)acetate [LCO₂]⁻ have been synthesized from reaction between (CH₃)₂SnCl₂ and lithium salts of the ligands. Mononuclear complexes of the type {[LCX₂](CH₃)₂SnCl} (X = S or O) have been obtained and fully characterized by elemental analyses and FT‐IR in the solid state and by NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy, conductivity measurements and electrospray ionization mass spectrometry in solution. The acute toxicity of new organotin(IV) derivatives on rat was studied, comparing their effect with those of dimethyltin chloride (CH₃)₂SnCl₂. The comparison of LD₅₀ of organotin(IV) complexes and (CH₃)₂SnCl₂ administered intraperitoneally, as a single dose, evaluated in vivo on rats, showed that toxicity decreases as follows: (CH₃)₂SnCl₂ > LCO₂ > LCS₂. The effect of these organotin(IV) complexes on DNA was evaluated in vitro and in vivo on rats treated with different doses of these compounds (1/20 LD₅₀ and 1/100 LD₅₀). The lymphocyte DNA status was assessed by the comet assay, a rapid and sensitive single‐cell electrophoresis technique, used to detect primary DNA damage in individual cells. After 36 h from the start of treatment the two new organotin(IV) derivatives induced a significant rise in comet assay parameters, indicating an increasing presence of damaged DNA. Copyright © 2005 John Wiley & Sons, Ltd.     

Hierarchical Analysis of Self‐Assembled PEGylated Hexaphenylalanine Photoluminescent Nanostructures

Despite the growing literature about diphenylalanine‐based peptide materials, it still remains a challenge to delineate the theoretical insight into peptide nanostructure formation and the structural features that could permit materials with enhanced properties to be engineered. Herein, we report the synthesis of a novel peptide building block composed of six phenylalanine residues and eight PEG units, PEG₈‐F6. This aromatic peptide self‐assembles in water in stable and well‐ordered nanostructures with optoelectronic properties. A variety of techniques, such as fluorescence, FTIR, CD, DLS, SEM, SAXS, and WAXS allowed us to correlate the photoluminescence properties of the self‐assembled nanostructures with the structural organization of the peptide building block at the micro‐ and nanoscale. Finally, a model of hexaphenylalanine in aqueous solution by molecular dynamics simulations is presented to suggest structural and energetic factors controlling the formation of nanostructures.     

Radical copolymerization of vinylidene cyanide with 2,2,2‐trifluoroethyl methacrylate: Structure and characterization

A novel copolymer of vinylidene cyanide (VCN) and 2,2,2‐trifluoroethyl methacrylate (MATRIF) was synthesized by bulk free radical process in a 52% yield from an equimolar comonomer feed. The copolymer's composition and microstructure were analyzed by FTIR, ¹H‐ and ¹³C‐NMR spectroscopy, SEC, and elemental analysis. The reactivity ratios calculated from both the Q‐e Alfrey‐Price parameters and the Jenkins' Patterns Scheme indicate a tendency to alternation in the copolymerization, the latter method suggesting that MATRIF homopropagation be slightly favoured (r_V = r₁₂ = 0.1, r_M = r₂₁ = 0.3). The molar incorporation of VCN in the copolymer was only 42 mol % according to the 9.0 wt % nitrogen content determined by elemental analysis, in good agreement with the value obtained by ¹H‐NMR. High‐resolution ¹H and ¹³C‐NMR spectra were used to study the microstructure of the copolymer. As an example, the three well‐resolved carbonyl resonances in the ¹³C‐NMR spectrum were assigned to the MATRIF‐centered triads VMV, VMM, and MMM, respectively, (V and M stand for VCN and MATRIF, respectively). The presence of VCN dyads (e.g., in VVM and VVV sequences) was shown to be marginal or absent altogether. Thermogravimetric analysis of poly(VCN‐co‐MATRIF) copolymer showed good thermal stability, and its main pyrolytic degradation taking place only above 368 °C. A 4% weight loss at about 222 °C suggested the presence of a few VCN homodyads, possibly inducing thermal depolymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A New Easy Access to Enantiomerically Pure 2,2'-Dihydroxy-1,1'-Binaphthyl

Optically pure binaphthyl structures make up the most important family of auxiliaries, ligands and catalysts used in enantioselective reactions. Syntheses of 2,2'-disubstituted-1,1'-binaphtyl derivatives were carried out one pot in water by oxidative coupling with FeCl₃ in the presence of - and -cyclodextrin (CD) derivatives. A new efficient and inexpensive preparation of trihydroxyethyl- and tri-2-hydroxypropyl- - and -CD afforded these powerful solubilizing agents. The resolution of racemic 2,2'-dihydroxy-1,1'-binaphthyl was easily achieved by semipreparative HPLC separating diastereomers obtained from the reaction with (-)menthyl chloroformate. Final basic hydrolysis afforded the enantiomerically pure product.