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.     

Preparation of highly stable organic steps with a fullerene-based molecule

We report the formation of highly stable Langmuir-Blodgett (LB) organic steps made with a hexa-adduct fullerene-based amphiphile. This amphiphile forms films of excellent quality, with a very low roughness, that are structurally stable: X-ray reflectivity spectra recorded on fresh and 12-month-old samples are undiscernible. Such a behavior contrasts with that of more traditional amphiphiles, which are unfortunately well-known for their instability in time. The stability of the films stems, among others, from the spheroidal shape of the constitutive molecules. These experiments show that it is possible to circumvent the major drawback of LB films and to prepare materials more suited for applications. We show that the LB film prepared with this fullerene derivative can successfully be used as thickness gauges for atomic force microscopy or light microscopy studies.     

Stereocontrolled synthesis of heterocyclic C-nucleosides. Protecting group effect and molecular modeling studies

We report herein a short stereocontrolled synthesis of heterocyclic C-nucleosides (indole, imidazole, benzimidazole, and 6-iodobenzimidazole). First, condensation of 2-lithiated heterocycles 2-5 with 5-(tert-butyldiphenylsilyl)-2,3-O-isopropylidene-D-gamma-ribonolactone (1) afforded the hemiacetals 6-9 in good yields. Then, borohydride reduction (NaBH(4)) of the protected hemiacetals proceeded stereoselectively to give predominantly the S diols 10-13, which upon Mitsunobu cyclization afforded the alpha-C-nucleosides 14-17. In contrast, the same PPh(3)/DEAD treatment of the 1:1 diastereomeric mixture of the free heterocyclic diols 10d and 11d gave exclusively the beta-anomers 14dbeta and 15dbeta, respectively, by a stereocontrolled process. The mechanisms of these stereocontrolled steps are discussed with the support of molecular modeling studies.     

Headspace SPME followed by GC/PFPD for the analysis of malodorous sulfur compounds in liquid industrial effluents

Headspace SPME was used to analyse malodorous sulfur compounds in liquid industrial effluents. A pulsed flame photometric detector (PFPD) was selected for a specific and sensitive analysis. Two fibres, PDMS/Dvb and PDMS/Carboxen, which are particularly convenient for extracting small and volatile molecules were tested. To compare these fibres, both sensitivity and artefact formation were considered. The PDMS/Carboxen fibre showed the lower limits of detection and moreover the least artefact formation yields. It was therefore selected and headspace SPME extraction conditions were optimised. Limits of detection of the target compounds evaluated were 12–31 ng L^–1 and repeatability was around 7%. Due to the adsorption mechanism involved, extraction is strongly influenced by the sample matrix and the low affinity compounds can suffer displacement effects. To investigate the occurrence of this phenomenon, two sampling times corresponding to non-equilibrium (5 min) and equilibrium conditions (60 min) were investigated. An external calibration was carried out by using standard solutions for both sampling times. The developed procedure was then compared to the standard addition method on a real industrial effluent. The results obtained from the two methods and for the two extraction times were in good agreement, demonstrating that even a long sampling time can be used. Therefore, the simple and timesaving external calibration was defined as relevant for an accurate quantification of sulfur compounds by headspace SPME.     

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.     

Cosurfactant effect of a semifluorinated alkane at a fluorocarbon/water interface: impact on the stabilization of fluorocarbon-in-water emulsions

Previous work has demonstrated that semifluorinated alkanes CnF2n+1CmH2m+1 (FnHm diblocks), when used in conjunction with phospholipids, strongly stabilize fluorocarbon (FC)-in-water emulsions destined to be used as oxygen carriers. Although the presence of FnHm diblocks in the emulsion's interfacial phospholipid film was suggested to account for the observed stabilization, no direct proof of the diblock's location has been provided so far. We now report definite experimental evidence of the diblock's presence at the interfacial film, both on a macroscopic level by investigating the FC/water interface using the pendant drop method and directly on emulsions by monitoring their stability for various phospholipid chain lengths. We first establish that F8H16 has a strong cosurfactant effect with phospholipids [dimyristoylphosphatidylcholine (DMPC), dilaurylphosphatidylcholine (DLPC), dioctanoylphosphatidylcholine (PCL8)] at a perfluorooctyl bromide (PFOB)/water interface, as evidenced by a dramatic F8H16-concentration-dependent decrease of the interfacial tension. Where FC emulsions are concerned, we show that the stabilization effect, which consists of a decrease of the rate of molecular diffusion of the FC, depends strongly on the length of the phospholipid's fatty chain as compared to the length of the hydrocarbon segment, Hm, of the diblock. Stabilization is maximized when the Hm length is similar to that of the phospholipid's fatty chains. A strong mismatch between Hm and the phospholipid chain length can actually destabilize the emulsion. A different destabilization mechanism is then at work: coalescence. The presence of F8H16 at the interfacial film is further supported by the fact that perfluorodecyl bromide, a heavy analogue of PFOB that stabilizes PFOB emulsions by lowering the solubility and diffusibility of the emulsion's dispersed FC phase, exercises its stabilizing effect similarly for all the phospholipids investigated.     

Selective recognition of G-qQuadruplex telomeric DNA by a bis(quinacridine) macrocycle

The interaction of G-quadruplex DNA with the macrocyclic compound BOQ1, which possesses two dibenzophenanthroline (quinacridine) subunits, has been investigated by a variety of methods. The oligonucleotide 5'-A(GGGT(2)A)(3)G(3), which mimics the human telomeric repeat sequence and forms an intramolecular quadruplex, was used as one model system. Equilibrium binding constants measured by biosensor surface plasmon resonance (SPR) methods indicate a high affinity of the macrocycle for the quadruplex conformation (K > 1 x 10(7) M(-)(1)) with two equivalent binding sites. The affinity of BOQ1 for DNA duplexes is at least 1 order of magnitude lower. In addition, the macrocycle is more selective than the monomeric control compound (MOQ2), which is not able to discriminate between the two DNA structures (K(duplex) approximately K(quadruplex) approximately 10(6) M(-)(1)). Strong binding of BOQ1 to G4 DNA sequences was confirmed by fluorometric titrations with a tetraplex-forming oligonucleotide. Competition dialysis experiments with a panel of different DNA structures, from single strands to quadruplexes, clearly established the quadruplex binding specificity of BOQ1. Fluorescence resonance energy transfer (FRET) T(m) experiments with a doubly labeled oligonucleotide also revealed a strong stabilization of the G4 conformation in the presence of BOQ1 (DeltaT(m) = +28 degrees C). This DeltaT(m) value is one of the highest values measured for a G-quadruplex ligand and is significantly higher than observed for the monomer control compounds (DeltaT(m) = +10-12 degrees C). Gel mobility shift assays indicated that the macrocycle efficiently induces the formation of G-tetraplexes. Strong inhibition of telomerase was observed in the submicromolar range (IC(50) = 0.13 microM). These results indicate that macrocycles represent an exciting new development opportunity for targeting DNA quadruplexes.     

Photoionisation of atoms and Möller operators

The motion of an hydrogenoïd atom in a laser field is usually given by the time-dependent hamiltonian H(t)=[p?A(t)]²/2+V(r) where V(r) is the atomic potential whileA(t) is to be connected with the laser field. The existence and unicity for the Cauchy problem of the solutions of the corresponding Schrödinger equation are established under mild conditions onA(t) and V(r). The existence of Möller operators is investigated in two cases, namely, when the laser field is a function of time only and when it vanishes asymptotically in time. Special attention is paid for the Coulomb case for which a “distorted” Möller operator is derived. Finally, when the laser field vanishes ast→∞, the photoionisation probability is properly defined by means of the Möller operator $$\Omega (H_{At} ,H) = s - \mathop {\lim }\limits_{t \to \infty } U_{At} (t)^{ - 1} U(t)$$ , whereU(t) is the evolution operator for the system whileU _Att (t) is the evolution operator for the atom.     

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.