Spectrométrie de Masse d'Hétérocycles Azotés. VIII–Comportement sous l'Impact Electronique de Nitroarylazoles

The mass spectra of nitrophenylimidazoles and nitrophenylpyrazoles have been examined in order to establish whether neighbouring ortho-ortho′ substituents have an appreciable influence on the fragmentation patterns. For compounds having an ortho nitro group on the heterocycle, specific effects are observed. Isotope effects observed with deuterated derivatives confirm this and establish that in the case of o-nitroimidazoles the 2-H proton adjacent to both nitrogen atoms is involved in the loss of OH. Fragmentation of each compound is specific and study could eventually provide a satisfactory means for structure determination.     

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.     

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.     

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.     

Tripling of the unit cell volume of the non-centrosymmetric AlPO4-SOD after dehydration: a structural study of a reversible process

The structure of AlPO4-SOD, a microporous aluminophosphate synthesized in a quasi-nonaqueous system using dimethylformamide as template and solvent, was previously reported. Then, various solid state nuclear magnetic resonance techniques applied on the dehydrated compound at 200 degrees C were performed and suggested a rearrangement of one-third of the template molecules inside the sodalite cages and a tripling of the unit cell parameter c. We present here the structure determined from molecular modeling and Rietveld analysis on synchrotron data of AlPO4-SOD dehydrated under vacuum at 100 degrees C together with some solid state NMR experiments of the rehydrated product.     

Theoretical investigation of the origins of catalysis of a retro-Diels-Alder reaction by antibody 10F11

The antibody 10F11 catalyzes a retro-Diels-Alder reaction that forms HNO. Deductions about the mechanism of catalysis were made by Reymond, Baumann et al. from X-ray crystal structures and from kinetic measurements for mutated antibodies. We report a study of these reactions with quantum mechanical methods and a study of the substrate and transition state binding to the active site of the antibody 10F11 using density functional theory and empirical docking methods. We have quantitated the likely contributions to catalysis of three residues identified as possible causes of catalysis: Trp H104, Phe H101, and Ser H100. Trp H104 can make a significant contribution to catalysis through dispersive interactions (pi-stacking aromatic-aromatic stabilization). On its own, Phe H101 makes only a small contribution to catalysis. When both aromatic residues are present, they act cooperatively and can make greater contributions to catalysis than expected for each residue alone. Ser H100 and the backbone NH of Phe H101 are expected to act through hydrogen bonding to speed up the reaction, but our calculations suggest that they make only a small contribution to catalysis. Reymond's studies suggest that the hydrogen-bonding network may be mediated through a water molecule in the binding site.     

Imaging combinatorial libraries by mass spectrometry: from peptide to organic-supported syntheses

Supported peptide and drug-like organic molecule libraries were profiled in single nondestructive imaging static secondary ion mass spectrometric experiments. The selective rupture of the bond linking the compound and the insoluble polymeric support (resin) produced ions that were characteristic of the anchored molecules, thus allowing unambiguous resin bead assignment. Very high sensitivity and specificity were obtained with such a direct analytical method, which avoids the chemical release of the molecules from the support. Libraries issued from either mix-and-split or parallel solid-phase organic syntheses were profiled, demonstrating the usefulness of such a technique for characterization and optimization during combinatorial library development. Moreover, the fact that the control was effected at the bead level whatever the structure and quantity of the anchored molecules allows the sole identification of active beads selected from on-bead screening. Under such circumstances, the time-consuming whole-library characterization could thus be suppressed, enhancing the throughput of the analytical process.     

Efficient Syntheses of Pure Mixed Triglycerides

Pure mixed triglycerides can be prepared from diglycerides and by acylolysis of glycerolformal tosylate without isomerization. The last fatty chain, with or without a functional group, can be introduced on any position of glycerol.     

SURFACTANT-OIL-WATER SYSTEMS NEAR THE AFFINITY INVERSION. PART XI. pH SENSITIVE EMULSIONS CONTAINING CARBOXYLIC ACIDS

Surfactant-oil-water systems in which the surface active substance is a mixture of carboxylic acid and its sodium salt (soap), exhibit emulsion property maps that are consistent with the phase behavior and the general emulsion phenomenology. However they present specific features such as an extended C⁺ multiple emulsion region and a skinked A⁺ W/O emulsion zone. In this case the aqueous phase pH drives the relative hydrophilicity of the acid/salt mixture at interface and plays the role of the most sensitive formulation variable. Studied systems contain C10 to C14 carboxylic acid, NaCl brine and a light distillation cut, as well as alcohols.