Single crystal manganese oxide multipods by oriented attachment

Nonhydrolytic sol-gel processes in organic solvents have become very popular for the synthesis of metal oxide NCs. We report an affordable, high-yield, shape-control synthesis of MnO multipod nanocrystals with a quick reaction time. The reaction yields exclusively multipods; two to six pod nanocrystals are synthesized. The mechanism leading to this hierarchical nanostructure is studied in relation with an oriented attachment mechanism; all nanocrystals are found to be single crystals. The study is completed by high-resolution TEM, X-ray powder diffraction, and magnetic measurements.     

Pentacoordinate silicon compounds: Stereochemical non-rigidity of chelates formed by intramolecular ring-closure. Crystal structure of 8-dimethylamino-1-trifluorosilylnaphthalene

The application of dynamic NMR spectroscopy to the study of stereochemical non-rigidity in pentacoordinate chelated organosilicon compounds is described. It is shown that in the compounds Me₂ iXYZ, non-dissociative ligand permutation at silicon can be distinguished unambiguously from processes associated with rupture of the chelate ring and nitrogen inversion. The crystal and molecular structure of 8-Me₂NC₁₀H₆SiF₃ has been determined. Pentacoordination of the silicon atom is confirmed, with the donor nitrogen atom and a fluorine atom occupying axial sites in an overall trigonal bipyramidal geometry. The N → Si separation is 2.3 Å (average of two distinct but closely related molecular conformations), which is less than the C¹---C⁸ distance in the naphthalene nucleus, indicating a substantial bonding interaction. NMR studies of the dynamic behaviour of the Me₂N group, and where possible (¹⁹F, ¹H) of the monodentate ligands in 8-dimethylamino-1-silylnaphthalene compounds, together with the results for the chelated benzylaminosilicon compounds, confirm that inversion of the absolute configuration at the silicon atom is not achieved by this process. The free energies of activation for non-dissociative ligand permutation at a silicon range from less than 7 kcal mol⁻¹ [SiH₃, Si(OR)₃], which is below the limit of direct measurement, to 13 kcal mol⁻¹ for Me₂NCH(Me)C₆H₄SiF₃; difunctional silicon chelate compounds (Cl, F, OR) display values from 9–12 kcal mol⁻¹. These are comparable with those determined for fluxional processes in acyclic pentacoordinate silicon compounds.     

Organic nanoparticles suspensions preparation by underwater excimer laser ablation of polycarbonate

Ablation with excimer laser pulses on polycarbonate (PC) film has been performed in ultrapure water. It is demonstrated that it is a new efficient method for organic nanoparticles (ONP) suspensions synthesis. Proof of the formation of ONP is given by analysis of the water phase with AFM and UV-vis spectroscopy. The obtained transmission measurements are approached with the aid of Mie theory to estimate composition of suspensions. Results indicate that the polycarbonate film is partly ablated into nanometric particles with size ranging from 8 up to 180 nm. This is also supported by force atomic microscopy. Confocal Raman microspectroscopy was done directly on water suspensions. Thanks to the optical trapping phenomenon of the nanoparticles, their vibrational Raman spectrum was more easily obtained. Original polycarbonate is lost although some polymeric structures are detected along with graphitic carbon.     

Glutamatergic alterations in the cortex of genetic absence epilepsy rats

Background  

In absence epilepsy, the neuronal hyper-excitation and hyper-synchronization, which induce spike and wave discharges in a cortico-thalamic loop are suspected to be due to an imbalance between GABA and glutamate (GLU) neurotransmission. In order to elucidate the role played by GLU in disease outcome, we measured cortical and thalamic extracellular levels of GLU and GABA. We used an in vivo quantitative microdialysis approach (no-net-flux method) in an animal model of absence epilepsy (GAERS). In addition, by infusing labelled glutamate through the microdialysis probe, we studied in vivo glutamate uptake in the cortex and thalamus in GAERS and non-epileptic control (NEC) rats. Expression of the vesicular glutamate transporters VGLUT1 and VGLUT2 and a synaptic component, synaptophysin, was also measured.     

K x-ray emission spectra from natural silicates

Chemical shifts of Si Kα_1,2 and Al Kα_1,2 lines in seven natural silicates has been measured comparatively to the lines of the pure elements. An attempt is made to correlate these shifts to the surroundings of Si and Al in the minerals.     

Potassium barium bismuth oxide

KBa₄Bi₃O crystallizes in the centrosymmetric tetragonal space group I4/mcm. In this compound, bismuth is present as two anionic species, i.e. Bi₂^4? dumbbells [Bi—Bi 3.113 (3) Å] and isolated Bi^3?. Atom Bi1 (Bi^3?) lies inside a bicapped square antiprism (2 × K and 8 × Ba). Atom Bi2, which forms the Bi₂^4? dumbbell, sits inside a bicapped distorted trigonal prism (2 × K and 6 × Ba). O atoms occupy tetra­hedral voids between Ba atoms.     

Laser spectroscopy investigation of the hyperfine structure of highly excited 2P32 states in alkali atoms

Highly excited ²P_{$\text{3}\text{2}$} levels in alkali atoms were populated using a multi-step excitation, involving a tunable dye laser. The hyperfine structure of the 9 ²P_{$\text{3}\text{2}$} level in ⁸⁷Rb and the 11, 12 ²P_{$\text{3}\text{2}$} levels in ¹³³Cs was determined with optical double resonance.