Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

We present new results on the liquid–liquid extraction of uranium (VI) from a nitric acid aqueous phase into a tri‐n‐butyl phosphate/1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (TBP/[C₄mim][Tf₂N]) phase. The individual solubilities of the ionic‐liquid ions in the upper part of the biphasic system are measured over the whole acidic range and as a function of the TBP concentration. New insights into the extraction mechanism are obtained through the in situ characterization of the extracted uranyl complexes by coupling UV/Vis and extended X‐ray absorption fine structure (EXAFS) spectroscopy. We propose a chemical model to explain uranium (VI) extraction that describes the data through a fit of the uranyl distribution ratio D_U. In this model, at low acid concentrations uranium (VI) is extracted as the cationic complex [UO₂(TBP)₂]²⁺, by an exchange with one proton and one C₄mim⁺. At high acid concentrations, the extraction proceeds through a cationic exchange between [UO₂(NO₃)(HNO₃)(TBP)₂]⁺ and one C₄mim⁺. As a consequence of this mechanism, the variation of D_U as a function of TBP concentration depends on the C₄mim⁺ concentration in the aqueous phase. This explains why noninteger values are often derived by analysis of D_U versus [TBP] plots to determine the number of TBP molecules involved in the extraction of uranyl in an ionic‐liquid phase.     

Microwaves-assisted solvent-free synthesis of N-acetamides by amidation or aminolysis

The preparation of acetamides directly from amines and an acetyl donor under microwaves without any catalyst is described. The inexpensive, solvent free, and fast reaction conditions are the important features of this procedure.     

Efficient 1,3-Oxazolidin-2-one Synthesis through Heterogeneous PdII-Catalyzed Intramolecular Hydroamination of Propargylic Carbamates

Herein, we present an operationally simple protocol for the cycloisomerization of propargylic carbamates in which a heterogeneous catalyst consisting of Pd species immobilized on amino-functionalized siliceous mesocellular foam (Pd^II-AmP-MCF) is used. This Pd nanocatalyst displayed high efficiency at low catalyst loading and reaction temperatures, which allowed for the efficient and mild synthesis of a wide range of 1,3-oxazolidin-2-one derivatives and related compounds. Moreover, it proved possible to re-use the Pd nanocatalyst for several reactions, although a gradual decrease in activity was observed in the subsequent cycles.     

Single switch surface hopping for molecular quantum dynamics

The aim of this text is to present a surface hopping approximation for molecular quantum dynamics obeying a Schr?dinger equation with crossing eigenvalue surfaces. After motivating Schr?dinger equations with matrix valued potentials, we describe the single switch algorithm and present some numerical results. Then we discuss the algorithm’s mathematical justification and describe extensions to more general situations, where three eigenvalue surfaces intersect or the eigenvalues are of multiplicity two. We emphasize the generality of this surface hopping approximation for non-adiabatic transitions.     

Evaluation of the anti-oxidant properties of a SOD-mimic Mn-complex in activated macrophages

SOD-mimics are small complexes that reproduce the activity of superoxide dismutases, natural proteins that catalytically dismutate the superoxide anion. Activated macrophages, which produce ROS and RNS fluxes, constitute a relevant model to challenge antioxidant activity in a cellular context and were used to test a Mn-complex which was shown to efficiently alter the flow of O(2)(-), ONOO(-) and H(2)O(2).     

Stability of divalent europium in an ionic liquid: spectroscopic investigations in 1-methyl-3-butylimidazolium hexafluorophosphate

In this work, devoted to 1-methyl-3-butylimidazolium hexafluorophosphate ionic liquid (BumimPF(6)), the importance of the purity of the solvent for spectroscopic investigations is highlighted. Results from small angle X-ray scattering indicate that the pure solvent exhibits a local organization. Europium(II), which appears to be unusually stable in BumimPF(6), is characterized by spectroscopic techniques (absorption, luminescence). Solvation of Eu(II) in BumimPF(6) and complexation effects in the presence of the crown ether 15C5 solubilized in the ionic liquid are discussed.     

A Landau-Zener Formula for Non-Degenerated Involutive Codimension 3 Crossings

In this paper, we study 2 x 2 systems of semi-classical pseudo-differential evolution equations which display eigenvalue crossing. We assume that the classical trajectories which hit the crossing set form the union of two involutive manifolds, with some non-degeneracy hypothesis, which covers the case of the Schrödinger equation with a matrix potential displaying a generic codimension 3 crossing. We derive an explicit formula for the energy transfer induced by the crossing, using two-scale Wigner measures. The proof is based on a normal form theorem which reduces the problem to an operator-valued Landau-Zener formula. Résumé. Cet article est consacré à létude dun système de deux équations dévolution pseudo-différentielles semi-classiques présentant un croisement de modes. Nous supposons que lensemble des trajectoires classiques qui rencontrent le croisement est lunion de deux sous-variétés involutives vérifiant une hypothèse de non-dégénérescence; cette situation contient le cas de léquation de Schrödinger avec un potentiel matriciel présentant un croisement générique de codimension 3. Nous obtenons une formule explicite décrivant le transfert dénergie au-dessus du croisement, à laide des mesures de Wigner à deux échelles. La démonstration repose sur un théorème de forme normale qui permet de se ramener à une formule de Landau-Zener à valeurs opérateurs. Communicated by Bernard Helffer submitted 16/09/02, accepted: 11/03/03     

Structural Studies of Crystalline Pentacalent Organobismuth Compounds

The syntheses and X-Ray analyses of three pentavalent organobismuth compounds are described; one of these compounds has a novel diphenylbis(trifluoroacetato)-bismuthate anion with trigonal bipyramidal geometry and a stereochemically active lone pair. Analysis of these structures together with other data from the literature allows a mapping of the reaction coordinate for bismuth polyhedra.     

Crotonates as dienophiles in high pressure-induced diels-alder cycloadditions: compared intra and intermolecular situations

The cyclization reactions of trienes 1 and 2 related intermolecular systems (5+6) and (9+10) have been investigated.