A Mössbauer-effect investigation of some electrochemically inserted lithium thiospinels

Summary We present here a study carried out on In₁₆Sn₄S₃₂ and In₁₆Fe₈S₃₂ spinels. Electronic and local environment changes of Sn and Fe are discussed from recorded M?ssbauer parameters. In the case of the tin thiospinel, a reduction process from Sn^IV to Sn^II is obvious till an amount of 8 inserted Li. For the iron thiospinel a migration of iron atoms from the octahedral to the tetrahedral sites is observed. In the region of higher lithium amounts (10– Li), in both spinels a further environment appears indicating an increase of covalency. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Topological singularities in W S,P ( S N , S 1)

We are interested in the location of the singularities of maps u ∈ W ^s,p (S ^N , S ¹) when 1 ≤ sp and 1 < sp < 2. To this end, we consider the distributional Jacobian. We show that the range of this operator on W ^s,p (S ^N , S ¹) is the closure in W ^s−2,p ⋂ W ^−1,sp of the set of N − 2-currents defined as the integration on smooth oriented N − 2-dimensional boundaryless submanifolds.     

Synthesis of Isobrassilexin,a Biologically Active Isomer of Brassilexin,a Cruciferac Phytoalexin

The synthesis of isobrassilexin 2, a hitherto non natural indoloisothiazole is reported (two steps, 43% yield). This substance, an isomer of brassilexin 1 has shown important biological properties in vitro.     

InGaN multiple quantum well laser diodes grown by molecular beam epitaxy

The first InGaN multiple quantum well laser diodes produced by molecular beam epitaxy are reported. Ridge waveguide lasers have been demonstrated at room temperature under pulsed current injection conditions. The lasers emit at a wavelength of approximately 400 nm with a spectral line-width of less than 0.2 nm, and a threshold current density of /spl sim/30 kA cm/sup -2/.     

Comportement des hydroperoxydes pendant la photo-oxydation d'un copolymère de styrène-butadiène

During the photo-oxidation at 254 nm of a styrene-butadiene copolymer, the quenching by hydroperoxides of singlet excited states of phenyl groups (and to a small extent of excimers) yield their photosensitized decomposition. The created radicals initiate hydroperoxide propagation reaction into the polymeric bulk. The natures of the various phases, through which this chain reaction develops, depend on the amount of available polymeric sites which can be easily oxidized (particularly allylic positions). Moreover, according to their behaviour, hydroperoxides have been placed in two classes: the “active” groups which are located at a stationary concentration in the vicinity of phenyl groups and the “inactive” groups which are outside this active sphere and remain stable after formation because they are not involved in the primary photophysical process.     

Oxidized isoquinolinoisoindolinone and benzazepinoisoindolinone alkaloids cores by convergent cyclisation processes: π-aromatic attack of thionium and oxonium species

An efficient methodology for synthesis of isoindoloisoquinoline 5a and isoindolobenzazepine 5b in oxidized forms as tetracyclic alkaloids cores are reported from N-bromoethylphthalimide (6) or phthalic anhydride and 2-phenylthioethylamine (8) in a five- or six-step sequence, respectively, in overall very good yields. The key step of this methodology is based on an intramolecular π-cationic cyclization of the thionium ion species. Alternatively, another four-step route was explored and based in an ultimate step on the cyclodehydration of an aldehyde functionality, which used as intermediate in the latest strategy, via the oxonium ion cation.     

N-trialkylsilyl bistrifluoromethanesulfonimides (R3SiNTf2) are powerful catalysts for the highly efficient alpha-amido alkylation reactions of silicon-based nucleophiles

[reaction: see text] In situ formed N-trialkylsilyl bistrifluoromethanesulfonimides (R3SiNTf2) species have been shown to efficiently catalyze the nucleophilic substitution reactions of chiral 5-oxypyrrolidin-2-ones by silicon-based nucleophiles. The reaction rates were significantly accelerated in comparison to the cases where the usual triflate catalysts are used. Adducts were obtained in high yields and usual stereoselectivities within short reaction times, and the process was compatible with a semipreparative scale.     

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.     

Optical properties of zinc oxide nanoparticles and nanorods synthesized using an organometallic method.

The emission properties of nanocrystalline ZnO particles prepared following an organometallic synthetic method are investigated. Spherical particles and nanorods are studied. The shape of the particles and the ligands used are shown to influence the luminescence properties in the visible domain. Two different emissions are observed at 440 nm (approximately 2.82 eV) and at 580 nm (approximately 2.14 eV) that are associated with the presence of surface defects on the particles. The first emission corresponds to the well-known yellow emission located at 580 nm (approximately 2.14 eV) with a lifetime of 1850 ns for 4.0 nm size ZnO nanoparticles. The second emission at 440 nm (approximately 2.82 eV) is observed when amine functions are present. This strong blue emission is associated with an excitation energy less than that associated with the yellow emission displaying a lifetime of nine nanoseconds. A possible hole trapping effect by the amine groups on the surface of the ZnO particles is discussed as the origin of this emission. The modification of the intensities between the two visible emissions for different particle shapes is proposed to be related to a specific location of the amine ligands on the surface of the particles.