Complexation of europium(III) by hydroxybenzoic acids: a time-resolved luminescence spectroscopy study

International audienceComplexation of Eu(III) by two hydroxybenzoic acids, namely p-hydroxybenzoic acid (4 dihydroxybenzoic, HPhbH), and protocatechuic acid (3,4-dihydroxybenzoic, HProtoH2), is studied by time-resolved luminescence spectroscopy (TRLS) in mildly acidic solution. Comparable formation constants are determined at 0.1 mol/L NaCl for EuPhbH[2+] – log10β°(EuPhbH[2+]) = 2.18 ± 0.09 (1sigma) – and 0.01 mol/L NaCl for EuProtoH2[2+] – log10β°(EuProtoH2[2+]) = 2.72 ± 0.07 (1sigma). The stoichiometry and carboxylate complexation of the EuProtoH2[2+] complex is ascertained by varying both pH and ligand concentration. The luminescence decay time of EuPhbH[2+] (τ = 107 ± 5 µs) is comparable with that of Eu(H2O)n[3+] (τ = 110 ± 3 µs), suggesting that luminescence quenching processes compensate the expected increase in decay time due to the dehydration associated with complexation. For EuProtoH2[2+], the luminescence decay time is even shorter (τ = 20 ± 5 µs), evidencing intricate quenching processes

Speeding up nuclear magnetic resonance spectroscopy by the use of SMAll Recovery Times - SMART NMR

A drastic reduction of the time required for two-dimensional NMR experiments can be achieved by reducing or skipping the recovery delay between successive experiments. Novel SMAll Recovery Times (SMART) methods use orthogonal pulsed field gradients in three spatial directions to select the desired pathways and suppress interference effects. Two-dimensional spectra of dilute amino acids with concentrations as low as 2 mM can be recorded in about 0.1 s per increment in the indirect domain. (C) 2010 Elsevier Inc. All rights reserved

How can f-block mono-cations behave as Mono-Cations of d-block transition metals ?

International audienceThe electronic structures of LnNH + is studied by DFT (B3LYP) quantum calculation for the Ln = La, Eu and Gd 4f-block elements (lanthanides). Ln ≡N triple bonds of essentially d-character are formed for La and Gd explaining why La + and Gd + behave like d-block elements as experimentally evidenced by mass spectrometry, and why the Ln + reactivity is correlated with its electron-promotion energy: the present theoretical study is a support to such correlation and qualitative knowledge. The Ln + + NH 3 → LnNH 3 + → transition state → HLn=NH 2 + → transition state → Ln≡NH + + H 2 reaction pathway is calculated. The formation of HLn=NH 2 + corresponds to the formation of new covalent bonds associated with more electron pairing, and corresponding lowering of the spin multiplicity-spin crossing reaction. It is in this step that low electron-promotion energy is required to promote an Ln 4f electron onto an Ln 5d orbital as typically for La + and Gd +. Similar geometry, bonding and electronic cofiguration are calculated for NpNH +-an actinide complex observed by mass spectrometry-with higher participation of 5f-valence orbitals (20% and 25% for the σ and π bonds) as compared to the 4f-valence orbitals (3% and 8%) of GdNH + : Gd + and Np + are the only lanthanide and actinide cations with two non-f-valence electrons-one s and one din their ground states. ____________ [a

Temperature influence on lanthanoids (III) hydration from molecular dynamics simulations

a b s t r a c t We studied temperature dependence of lanthanoid (III) cations hydration by molecular dynamics simulations using explicit polarization. The main effect of the temperature (T) is to increase exchange frequencies between the two main stoichiometries and the proportions of the minor species. Activation energies for self-exchange reaction have a minimum in the middle of the series and the CN values of all Ln 3þ ions tends to a limit 8.5 value at high temperature. Linear variations are found through the series for the Gibbs energies of water exchange reactions being at the origin of the coordination number sigmoidal variation across the series

Reactivity of Lanthanoid Mono-Cations with Ammonia : a Combined Inductively Coupled Plasma Mass Spectrometry and Computational Investigation

International audienceThe behavior of La+, Sm+, Eu+ and Gd+ with NH3(g) and ND3(g) was studied to understand gas phase chemical reactions used for separations in the reaction cell of a quadrupole inductively coupled plasma-mass spectrometer (ICP-MS). For Ln+ = La+ and Gd+, the primary reaction channel is the formation of the LnNH+ protonated nitride leading to H2 elimination. The LnNH(NH3)1-5+ ammonia complexes of the Ln protonated nitride are further generated. Sm+ and Eu+ are less reactive: the protonated nitride is not detected, and only small amounts of Ln(NH3)0-6+ are observed. Quantum chemical calculations at the DFT, MP2, CCSD(T) and CASPT2 levels of theory were employed to explore the potential energy surfaces. For the La+ and Gd+ ions of f-block elements, the reaction pathways are composed of three steps: first the formation of LnNH3+, then the isomerization to HLnNH2+, and finally the loss of H2 associated with the formation of an Lnsingle bondN triple bond in the final product LnNH+. On the other hand, the isomerization leading to triple bond formation with H2 loss did not proceed for Sm+ and Eu+ ions

Applications du repliement spectral en RMN à deux dimensions

La résonance magnétique nucléaire est devenue un outil indispensable aux chimistes de synthèse. Basé sur les propriétés nucléaires des atomes, elle apporte des informations cruciales sur la structure, la composition, la dynamique des systèmes qui peuvent aller de la simple molécule organique, à la protéine, en passant par des mélanges complexes hors-équilibres. Ces informations extraites d'expériences de plus en plus complexes nécessitent une résolution suffisante afin de discriminer les signaux correspondants à chacun des atomes. Dans le cas d'expériences multidimensionnelles, l'obtention de la résolution nécessaire augmente considérablement la durée d'expérience

Développement et utilisation de nanotraceurs pour l'étude du transport de colloïdes en milieu poreux. Expérimentations et Modélisations

Natural or engineered mobile colloids are suspected to be a threat for the environment. This thesis aimed at better understanding the mechanisms of transport, deposition and remobilization of colloids in natural porous media. These mechanisms depend on colloid, flow and medium properties, which have to be controlled in the experiment. Consequently, we carried out transport experiment with synthetic colloids with controlled properties in natural sand. The tailor synthesized colloids were labelled silica nanoparticles. They were easy to detect, and their size and zeta potential are controlled during the synthesis. They were used in column experiments to determine the influence of colloid size and concentration and solution ionic strength on the retention in natural sand (Hostun). Both breakthrough curves and spatial distributions were measured and analysed. Experiments carried out with nanotracers of various sizes in conditions unfavourable to attachment highlighted a size- and concentration-dependent deposition mechanism. Colloids are assumed to be retained in constrictions or in the surface roughness of sand grains. Colloids are retained until the retention sites are filled and then are further transported. When ionic strength increases, another retention mechanism was identified and is assumed to be caused by electrostatic interactions. The saturation of retention sites was also underlined. A convection-dispersion-equation based modelling with a sink term attending for deposition was used. With a depth- and concentration-dependent deposition rate, the model was able to reproduce the experimental results for the whole input concentration range.Les colloïdes naturels ou synthétiques peuvent être transportés dans les eaux souterraines et représenter ainsi une menace pour l'environnement. Pour mieux comprendre l'influence des propriétés des colloïdes, de l'écoulement et du milieu poreux sur les mécanismes de transport et de dépôt dans des aquifères, il est nécessaire de découpler les processus en contrôlant expérimentalement un maximum de facteurs. Ainsi, nous avons synthétisés des traceurs de colloïdes qui sont des nanoparticules de silice marquées, facilement détectables, dont les propriétés de surface et de taille sont contrôlées. Ils sont utilisés dans des expériences de transport en colonne pour déterminer l'influence de la taille, de la concentration en particules et de la force ionique de la solution sur le dépôt de colloïdes dans du sable d'Hostun. Les courbes de percée et les profils de dépôt sont mesurés et analysés. Les expériences menées avec des traceurs de différentes tailles en conditions défavorables au dépôt électrostatique ont mis en évidence un mécanisme de dépôt dépendant de la concentration et de la taille des particules. Les sites de dépôt sont supposés être la rugosité de surface des grains de sable et les pores de taille suffisamment petite. Les colloïdes sont retenus dans un volume fini de sites jusqu'à leur saturation. Lorsque la force ionique augmente, le mécanisme de dépôt identifié est lié aux interactions électrostatiques et est également sensible à la concentration en colloïdes. Un modèle avec un terme puits dépendant de la concentration en colloïdes et de la distance parcourue a permis de représenter les résultats expérimentaux sur toute la gamme de concentrations testée