Étude de réactions à l'état solide entre l'arbre de Saturne et des sels contenant le groupement XO3

Résumé Le plomb utilisé sous forme d'arbre de Saturne possède une grande réactivité et permet de réduire les nitrates en nitrites. Il s'agit d'une réaction à l'état solide, débutant dès la température ordinaire. On a pu caractériser ainsi la présence de nitrites en mélangeant le plomb avec les nitrates de lithium, sodium, potassium, césium, cuivre, argent, magnésium, calcium, strontium, baryum, zinc, thallium, plomb, cobalt et nickel.

---

Summary Lead used in the form of the lead tree has great reactivity and is able to reduce nitrates to nitrites. This involves a solid state reaction and starts at room temperature. In this way it is possible to detect the presence of nitrites after mixing the lead with the following nitrates — Li, Na, K, Cs, Cu, Ag, Mg, Ca, Sr, Ba, Zn, Tl, Pb, Co, Ni.

---

Zusammenfassung In der Form des Bleibaumes ist Pb sehr reaktionsfähig und reduziert Nitrat zu Nitrit. Dabei handelt es sich um eine Festkörperreaktion, die bei gewöhnlicher Temperatur einsetzt. Nach Vermengen von Blei mit den Nitraten von Li, Na, K, Cs, Cu, Ag, Mg, Ca, Sr, Ba, Zn, Th, Pb, Co und Ni konnte die Anwesenheit von Nitrit festgestellt werden.

---

---

En l'honneur du ProfesseurA. A. Benedetti-Pichler, pour son 70^e anniversaire.     

Two‐step Synthesis of New γ‐Lactones via Cyclization of 7‐Chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐(2E,4E,6E)‐trienoic acid

A new rapid synthesis of γ‐lactones, cis fused with a cyclopentenic ring by thermal cyclization of 7‐chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐7‐phenyl (or methyl) (2E,4E,6E)‐trienoic acids was reported. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π_2s + π_2a conrotatory process, published in a recent paper (from the corresponding diacids). We have investigated the thermal behavior of the corresponding half‐esters since; if the cyclization obeys to the proposed mechanism, the diacids, half‐esters must also cyclize in a similar manner. Saponification of these led to γ‐dilactones via intermediary cyclopropanes. Mechanistic pathways were investigated.     

Aqua­bis­(crotonato)­bis­(pyridine)­copper(II)

The title compound, [Cu(O₂CCH=CHCH₃)₂(C₅H₅N)₂(H₂O)], crystallizes as a monomer, with the copper ion in a pentacoordinated square‐pyramidal environment, bisected by a twofold axis passing through the metal atom and the apex. The mol­ecules organise in chains connected by hydrogen bonds running along the unique b axis.     

Enantioselective aptameric molecular recognition material: Design of a novel chiral stationary phase for enantioseparation of a series of chiral herbicides by capillary electrochromatography

A chiral stationary phase derived from an L-RNA aptamer is evaluated for the enantiomer separation of a series of herbicide molecules (aryloxypropionic, aryloxyphenoxypropionic, and aminopropionic acid) by CEC after binding to biotin and grafting upon streptavidin-modified porous glass beads. We demonstrated that the aptamer capillary was stable in term of efficiency and retention during a long period. The influences of the mobile phase constitution and its flow-velocity on the enantioseparation were also investigated. The results suggest that the interactions of the enantiomer during CEC are solely based on chromatographic mechanisms and that the electrophoresis plays only a minor role. The separation efficiency and peak shape could be improved by Mg2+ divalent cation that stabilized the aptamer secondary structure and thus enhanced the mass transfer kinetics during the ligand-aptamer binding process. In addition, it was demonstrated that the determination of the enantiomerization barrier of flamprop was possible using this chiral stationary phase.     

Modification of the wettability of a polymeric substrate by pH effect. Determination of the surface acid dissociation constant by contact angle measurements

The wetting properties of a substrate can be changed by chemical reaction. Here, we studied simple materials with acid-base properties, by preparing poly(vinyl chloride) films containing lauric acid. These substrates constitute simple polymeric surfaces the wettability of which can be easily controlled by the acid-base equilibrium. The roughness of the material was then varied by adding Aerosil (hydrophobic fumed silica). We then studied the wettability of these materials toward aqueous buffer solutions between pH 2 and 12 from contact angle measurements. The variation of the contact angle of a droplet of buffer solution with the pH of the solution was described by a simple thermodynamic model requiring only two parameters. Thus, we could characterize the acid polymer by an effective surface acid dissociation constant the value of which was consistent with those obtained with a similar surface. We showed that the behavior of any substrate could be described even if the surface geometry was not well-known.     

Toward the comparison of rare earth element and actinide behavior in materials: a computational study of Ce- and U-bearing britholites

We present a computational investigation into the nature of bonds formed by f-elements in materials. The paper presents an example of the incorporation of rare earth elements (REE) and actinides in minerals derived from fluorapatite: Ca(10)(PO(4))(6)F(2). These minerals, called britholites, allow many substitutions on all three Ca, P, and F sites and are considered as potential host phases for radioactive elements separated from nuclear waste. REE and actinides have very similar physical and chemical properties, but REE are not radioactive and much more easily handled. REE are, therefore, very often used as a surrogate for actinides in experimental studies. The representative elements of rare earths and actinides chosen for this first investigation are cerium and uranium, respectively. We have studied all the various configurations of Ca(9)X(PO(4))(6)(-)(y)()(SiO(4))(y)()F(2), where X stands for Ce(3+), Ce(4+), U(3+), and U(4+), and y is equal to 1 and 2 for three-time and four-time charged cations, respectively. Calculations have been performed within the density functional theory (DFT) framework according to the computation scheme determined in a previous study. The analysis of the energies of the various configurations shows that the incorporation of all the cations considered stabilizes the apatitic structure. This stabilization, however, is greater for four-time charged cations than for three-time charged ones, which shows that Ce and U are both preferentially substituted in the +IV oxidation state. In addition, the substitution in one of the two cationic sites of the apatitic structure is always more favorable. Then, the geometry analysis shows a larger decrease in size of this cationic site for U than for Ce, as well as different volume variations for Ce and U substitutions in the two cationic sites. This cannot be explained by steric effects alone. Finally, the electronic density analysis yields three essential results: U and Ce form significantly covalent bonds, U forms bonds more covalent than Ce, and finally four-time charged cations form more covalent bonds than three-time charged ones. The comparison of these results with the formation enthalpies of the various phases shows a positive correlation between the covalence degree of the bonds formed by the f-element and the stability of the structure. In addition, our results prove that Ce- and U-bearing britholites exhibit very similar energetic, structural, and electronic properties. Ce, therefore, appears to be a good simulant for U.     

Evidence of a phase transition in water-1-butyl-3-methylimidazolium tetrafluoroborate and water-1-butyl-2,3-dimethylimidazolium tetrafluoroborate mixtures at 298 K: determination of the surface thermal coefficient, bT,P

We studied the aggregation behavior of two short-chain room-temperature ionic liquids. Previous surface tension studies have shown that 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)) aggregates in water. We observed the same behavior for another ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (bdmimBF(4)). We carried out a thermodynamic study of the mixtures between water and the two butylimidazolium salts to investigate this unusual behavior for cations with short chains by determining the surface thermal coefficient, b(T,P). Plotting b(T,P) as a function of the molar fraction (X) of the two salts showed a clear discontinuity at X = 0.016 for bmimBF(4) and X = 0.004 for bdmimBF(4). This discontinuity could be attributed to a transition such as an aggregation.     

Polyethylene glycol adsorption on silica: from bulk phase behavior to surface phase diagram

A characterization of the bulk-phase diagram from literature data and new NMR and DSC measurements provided us with valuable elements that are helpful for gaining, from aqueous solution, better insight into the surface behavior of polyethylene glycol on Aerosil 200. Adsorption isotherms built further to measurements by a depletion method showed a strong and temperature-dependent variation of the isotherm shape in agreement with the variations of interactions already evidenced in the bulk. In temperature-concentration areas, where water is behaving as a helix-promoting solvent, the finding of positive PEG adsorptions and stairlike isotherms agrees with observations reported in the literature. We identified some of the vertical parts as corresponding to the formation of monolayers of helix-shaped PEG molecules. In poor-solvent zones, adsorptions were null or negative, and the isotherms exhibited oscillations suggesting very different surface behavior. Our data analysis evidenced the presence of a much greater amount of water than in the previous surface states; however, the similar analysis of PEG behavior remains relevant. Indeed, the occurrence of first-order transitions in the surface layer implies some water reorganization, permitting the PEG molecules to move closer to the surface and become helix-shaped to rearrange in a monolayer. The surface phase diagram confirmed this analysis in a very satisfying way.