Evaluation of the use of microwave oven systems for the digestion of environmental samples

In most chemical analyses for inorganic determinations in environmental matrices the sample is physically destroyed by dissolution, calcination etc. These digestion procedures have to be validated in order to ensure that no contamination and/or losses have occurred which could affect the accuracy of the final results obtained; this validation can be made by using certified reference materials (CRMs).In the recent past, microwave digestion procedures have been developed and have been shown to offer the benefits of rapid sample preparation and reduced contamination risks; however, an incomplete dissolution was suspected in some cases, e.g. in interlaboratory exercises, for the analysis of organic matrices.The aim of this study was to test microwave digestion procedures for different environmental CRMs and to evaluate the suitability of these methods for the determination of some trace elements. The effects of chemical species (As, Hg and Se-species) on the total element recovery after digestion are discussed.     

Synthesis and antiviral evaluation of β-L-Xylo-fuanosyl nucleosides of the five naturally occurring nucleic acid bases

The β-L-xylo-furanosyl analogues of the naturally occurring nucleosides have been synthesized and their antiviral properties examined. All these compounds were hitherto unknown and they were stereospecifically prepared by glycosylation of pyrimidine and purine aglycons with a suitably peracyl-L-xylo-furanose (specially synthesized from L-xylose for our present purpose), followed by removal of the protecting groups. All the prepared compounds were tested for their activity against a variety of DNA and RNA viruses (including HIV), but they did not show significant antiviral activity.     

Ion exchange properties of β-eucryptite (LiAlSiO4): EPR investigation on copper-doped single crystals

Investigation of the ion exchange properties of β-eucryptite (LiAlSiO₄) single crystals indicates that it is impossible to substitute Li⁺ by other bigger univalent cations such as Na⁺, K⁺, or Ag⁺. On the contrary, Li⁺ exchange by bivalent cations, Cu²⁺ or Mn²⁺, is very easy. For a general orientation of the crystal with respect to the magnetic field, the EPR spectrum of Cu²⁺ ions in β-eucryptite consists of 12 sharp lines partially superimposed on a broad line. The sharp lines are attributed to isolated copper ions in the conducting channels. Cu²⁺ lies in sixfold coordinated Li″ sites, but not in the fourfold coordinated Li″ sites. The corresponding spin Hamiltonian parameters at T = 140 K are found to be: g_x = 2.362, g_y = 2.340, g_z = 1.990; ∥A_x∥ = 85 × 10^?4cm^?1, ∥A_y∥ = 71 × 10^?4cm^?1, ∥A_z∥ = 203 × 10^?4 cm^?1. The broad line is attributed to clusters of Cu²⁺ located in neighboring Li″ sites.     

X-Ray Microanalysis of Thin Surface Films and Coatings

 The paper gives an overview of the present knowledge in the field of X-ray analysis of surface films and more generally stratified specimens. The aim of the paper is not to report the details and formulas of the available quantitative procedures, but to concentrate on the general ideas and orders of magnitude illustrating the capability and limits of the method, and on the optimal adaptation of the operating conditions to every particular problem. The various specific pitfalls which can be encountered are pointed out, in particular the fluorescence effects when using high-energy X-ray lines, or the anomalies due to chemical bonding, absorption uncertainties, and contamination effects when soft radiations are employed.     

Kinetics and Bacterial Inactivation Induced by Peroxynitrite in Electric Discharges in Air

The mechanism of bacterial inactivation by electric discharges (non-thermal plasma) is examined on the basis of the action of the formed peroxynitrite and hydrogen peroxide on the external membrane of bacteria. A model accounts for the gas to liquid transfer of the active species which react with the bacterial wall at the liquid surface or /and in the bulk solution. Direct exposure to the glidarc discharge induces a pseudo zero order decay of the bacterial concentration, followed by a pseudo 1st order step for low concentrations. Post-discharge reactions develop after switching off the discharge according to a 1st order mechanism and show that active species drift in the solution. Additionally the bactericidal properties of pure water exposed to the discharge (i.e., ??Plasma Activated Water??) was evidenced even 24?h after performing the plasma treatment.     

Phosphotriesterase: A complementary tool for the selective detection of two organophosphate insecticides: Chlorpyrifos and chlorfenvinfos

This work shows the possibility of combining the high sensitivity of genetically-modified Drosophila melanogaster acetylcholinesterase (B394) with the ability of phosphotriesterase (PTE) to hydrolyse organophosphate compounds, in the aim of developing a biosensor selective to two insecticides of interest: chlorpyrifos and chlorfenvinfos. The studies clearly demonstrate that chlorfenvinfos is a substrate that acts as competitive inhibitor of PTE, therefore preventing the efficient hydrolysis of other pesticides, including chlorpyrifos. A bi-enzymatic sensor was designed by immobilizing both B394 and PTE in a polyvinylalcohol matrix. The sensor was shown to be able to discriminate between chlorpyrifos and chlorfenvinfos inhibitions.     

Biosensors to detect marine toxins: Assessing seafood safety

This article describes the different types of marine toxins and their toxic effects, and reviews the bio/analytical techniques for their detection, putting special emphasis to biosensors. Important health concerns have recently appeared around shellfish (diarrheic, paralytic, amnesic, neurologic and azaspiracid) and fish (ciguatera and puffer) poisonings produced by different types of phycotoxins, making evident the urgent necessity of counting on appropriate detection technologies. With this purpose, several analysis methods (bioassays, chromatographic techniques, immunoassays and enzyme inhibition-based assays) have been developed. However, easy-to-use, fast and low-cost devices, able to deal with complicated matrices, are still required. Biosensors offer themselves as promising biotools, alternative and/or complementary to conventional analysis techniques, for fast, simple, cheap and reliable toxicity screening. Nevertheless, despite the wide range of seafood toxins and the already rooted biosensing systems, the literature on biosensors for phycotoxins is scarce. This article discusses the existing biosensor-based strategies and their advantages and limitations. Finally, the article gives a general overlook about the regulation toxin levels and monitoring programmes currently established around the world concerning seafood safety.     

Nucléosides de synthèse XXI. Obtention spécifique de ribonucléosides de configuration anomérique α

A new and stereospecific synthesis of a chemical precursor of α-D-ribonucleosides, namely, 1-α-D-ribofuranosyl-4-carboxamido-5-aminoimidazole ( 1 ) is described using 2-thio-α-D-ribofurano[1,2-d]-oxazolidine as the starting material.     

Prospect of Thiazole-based γ-Peptide Foldamers in Enamine Catalysis: Exploration of the Nitro-Michael Addition

As three-dimensional folding is prerequisite to biopolymer activity, complex functions may also be achieved through foldamer science. Because of the diversity of sizes, shapes and folding available with synthetic monomers, foldamer frameworks enable a numerous opportunities for designing new generations of catalysts. We herein demonstrate that heterocyclic γ-peptide scaffolds represent a versatile platform for enamine catalysis. One central feature was to determine how the catalytic activity and the transfer of chiral information might be under the control of the conformational behaviours of the oligomer.