Study of the N = 50 major shell effect toward 78Ni at PARRNe⋆

The γ-ray de-excitations following the β-decay of ⁸³Ga and the β-n decay of ⁸⁴Ga have been studied. The radioactive species were produced using the PARRNe on-line mass-separator installed at the IPN Orsay Tandem accelerator. Two γ-lines were attributed to ⁸³Ge with the aid of β-γ and γ-γ coincidences. The Z identification of the γ-lines was provided by time analysis of a buid-up/decay cycle. The excited levels of ⁸³Ge can be explained by the coupling of the single neutron state ν2d _5/2 to the first 2⁺ excitation of the ⁸²Ge core.     

Films minces de cristal liquide nématique sur support liquide Structure,tensions superficielles et tension de ligne

Résumé L'étude de la structure d'un film mince de cristal liquide nématique (le 4-4'-pentyl-cyanobiphenyl) sur l'eau permet de déterminer l'orientation des molécules dans le volume et aux interfaces et d'en déduire la variationy =y -y _I de la tension superficielle selon que les molécules seraient orientécs parallélement (y ) ou perpendiculairement (y _I) à la surface libre.De l'emistence et de la stabilité de trous dans le film mince, on déduit Fordre de grandeur de la tension de ligne. Cette tension de ligne est comparée aux tensions de ligne de déformation élastique du cristal liquide.

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The structure of a liquid crystal (L.C.) thin film on water has been studied optically and the molecular orientation at its interfaces has been deduced. The surface tension shifty corresponding to the orientation of the molecules either normal or parallel to the free surface has been deduced. From the study of the formation and of the stability of holes in the thin film we deduce the order of magnitude of the line tension .This tension originates in the elastic deformation of LC in the neighbourhood of the hole.

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Avec 13 figures et 1 tableau     

Functionalization of polyoxometalates: towards advanced applications in catalysis and materials science

Functionalization via covalent grafting of organic functions allows to tune the redox and acid-base properties, and the solubility of polyoxometalates, to enhance their stability and biological activity and to reduce their toxicity, to facilitate their implementation in extended structures and functional devices. We discuss herein the electronic and binding connections, and the various synthesis methodologies. We emphasize on organonitrogen, organosilyl and organophosphonyl derivatives with special attention to synthesis, characterization and potential applications in catalysis and materials science. We also consider the giant molybdenum oxide-based clusters especially the porous capsule-type clusters (Keplerates) which have high relevance to this context.     

Synthesis and reactivity of {Ru(p-cymene)}2+ derivatives of [Nb6O19]8-: a rational approach towards fluxional organometallic derivatives of polyoxometalates

Three {Ru(p-cym)}(2+) (p-cym = p-cymene) derivatives of [Nb(6)O(19)](8-)-[Nb(6)O(19){Ru(p-cym)}](6-) (Nb(6)Ru(1)), trans-[Nb(6)O(19){Ru(p-cym)}(2)](4-) (t-Nb6Ru2), and [Nb(6)O(19){Ru(p-cym)}(4)] (Nb(6)Ru(4))--have been synthesized in water by reaction between [Ru(p-cym)Cl(2)](2) and the hexaniobate. In the solid state, Nb(6)Ru(1) and Nb(6)Ru(4) have been characterized by IR and EDX spectroscopies, whereas t-Nb(6)Ru(2) has been characterized by IR spectroscopy and single-crystal X-ray diffraction (crystal data for K(4)-trans-[Nb(6)O(19){Ru(p-cym)}(2)].14H(2)O (K(4)-t-Nb(6)Ru(2).14H(2)O). In solution, all compounds were characterized by (1)H NMR and ESI mass spectrometry analyses, and Nb(6)Ru(1) was also analyzed by (17)O NMR. These studies allowed a comparison of the differences in behaviour of the three complexes in water: Nb(6)Ru(1) is particularly stable, Nb(6)Ru(4) decomposes by loss of {Ru(p-cym)}(2+) fragments, and trans-[Nb(6)O(19){Ru(p-cym)}(2)](4-) isomerizes into cis-[Nb(6)O(19){Ru(p-cym)}(2)](4-). A rational mechanism for the isomerisation of t-Nb(6)Ru(2) is proposed on the basis of a kinetic study.     

Elaboration of covalently linked polyoxometalates with ruthenium and pyrene chromophores and characteriation of their photophysical properties

Keggin and Dawson-type polyoxometalates (POMs) decorated by organometallic [cyclometalated ruthenium(II) polypyridine complex] or organic (pyrene) chromophores were prepared by postfunctionalization of hybrid disilylated POM platforms. The connection is made in a very efficient and modular way via Sonogashira coupling reactions, which provide a rigid linkage between the POM and the photoactive centers. Electronic properties have been inferred from electrochemical and photophysical studies and reflect poor electronic interactions between both partners. The presence of the POM leads to luminescence quenching of the chromophores, which was attributed to an intramolecular electron transfer from the chromophore to the POM. The rate of this process is much faster in the POM-pyrene than in the POM-Ru system. It depends on the driving force dictated by the redox potentials of both partners but also in the case of the POM-Ru system on the presence of the metallacycle, which acts as a molecular insulator and delays the intramolecular electron transfer. In the POM-Ru system, a comparative study of the luminescence quenching showed that the electron transfer is still more important in the covalently bonded hybrids than in systems where the POM and the ruthenium complexes are assembled via electrostatic interactions.     

Insights into the coordination chemistry of phosphonate derivatives of heteropolyoxotungstates

The coordination properties of vacant bisphosphonate derivatives of polyoxometalates, with easily tunable functions, have been explored. The preparation and crystallographic structure of their La(3+) and Zr(4+) complexes are described herein.     

Intense Bessel-like beams arising from pyramid-shaped microtips

We show both numerically and experimentally that intense, narrow, and low-divergence beams of light are produced at the apex of dielectric pyramid-shaped microtips. These beams exhibit a Bessel transverse profile but are narrower than the usual Bessel beam, allowing for a significant enhancement of the light intensity inside the beam. They are generated by axicon-like structures with submicrometric height imprinted in glass by combining optical lithography and chemical etching. The resulting beams are experimentally imaged using fluorescence microscopy, in remarkable agreement with numerical computations.     

Small Fermi surface pockets in underdoped high temperature superconductors: observation of Shubnikov-de Haas oscillations in YBa2Cu4O8

We report the observation of Shubnikov-de Haas oscillations in the underdoped cuprate superconductor YBa2Cu4O8 (Y124). For fields aligned along the c axis, the frequency of the oscillations is 660+/-30 T, which corresponds to approximately 2.4% of the total area of the first Brillouin zone. The effective mass of the quasiparticles on this orbit is measured to be 2.7+/-0.3 times the free electron mass. Both the frequency and mass are comparable to those recently observed for ortho-II YBa2Cu3O6.5 (Y123-II). We show that although small Fermi surface pockets may be expected from band-structure calculations in Y123-II, no such pockets are predicted for Y124. Our results therefore imply that these small pockets are a generic feature of the copper oxide plane in underdoped cuprates.     

Reorganization of lipid nanocapsules at air-water interface: Part 2. Properties of the formed surface film

The state, electrical and dilatational rheological properties of surface films formed at air–water interface from lipid nanocapsules (LNC) with various compositions as well as model monolayers formed by the LNC constituents—Labrafac^®, Solutol^® and Lipoid^® are investigated. These nanocapsules constitute potential drug delivery systems where lypophilic drug will be loaded in their core. The study of the model Labrafac^®/Solutol^® (Lab/Sol) mixed monolayers shows behavior close to the ideal. Small negative deviations in the mean molecular areas a and dipole moments μ are observed. All studied monolayers have elastic behavior during the small continuous compressions. The comparison between the properties of surface films formed from LNC with those of the model monolayers confirms the idea developed in the kinetic study [I. Minkov, Tz. Ivanova, I. Panaiotov, J. Proust, P. Saulnier, Reorganization of lipid nanocapsules at air–water interface: 1. Kinetics of surface film formation, J. Colloids Surf. B: Biointerfaces, submited for publication.] that the surface films formed after a rapid disaggregation of the unstable nanocapsule fraction (LNC I) contains mainly Labrafac and Solutol. The Labrafac molar part (x_Lab) in the formed Lab/Sol mixed layer is established.