l-Arginine-Catalyzed Synthesis of Nanometric Organosilica Particles through a Waterborne Sol-Gel Process and Their Porous Structure Analysis.

We report an efficient and easy-to-implement waterborne sol-gel process for the synthesis of nanometric organosilica particles. In this process, tetraethyl orthosilicate (TEOS) and 3-(methacryloxy)propyl trimethoxy silane (γ-MPS), employed as silica sources, were heterogeneously delivered in an aqueous solution of l-arginine, a basic amino acid used as a catalyst, from a top organic layer. Co-condensation of TEOS with γ-MPS led to the formation of organosilica particles with diameters between 30 and 230 nm when increasing the γ-MPS content from 0 to 10.1 mol % in the silica source. Nitrogen sorption analyses confirmed the microporous nature of the obtained particles after calcination. The Brunauer-Emmett-Teller (BET) surface areas increased from 27 (before calcination) to 684 m2 g-1 (after calcination) for the organosilica particles containing 10.1 mol % of γ-MPS. Fourier transform infrared spectroscopy and 29Si NMR were employed to analyze the chemical structure of the organosilica spheres and provide insight into the mechanism of particle formation. In the second part, hybrid organosilica particles with a core-shell morphology were synthesized through the combination of Pickering emulsion and the sol-gel process. γ-MPS emulsion droplets stabilized by tiny silica particles (formed in a separate step) were first generated and used as seeds to grow a silica shell on their surface through TEOS addition from the top organic layer. Transmission electron microscopy and pore size analyses of the resulting particles after calcination revealed a unique dual-porosity structure with a mesoporous inner core and a micro/mesoporous silica shell with ink-bottle-type pores.

Cubic three-dimensional hybrid silica solids for nuclear hyperpolarization.

Hyperpolarization of metabolites by dissolution dynamic nuclear polarization (D-DNP) for MRI applications often requires fast and efficient removal of the radicals (polarizing agents). Ordered mesoporous SBA-15 silica materials containing homogeneously dispersed radicals, referred to as HYperPolarizing SOlids (HYPSOs), enable high polarization - P(1H) = 50% at 1.2 K - and straightforward separation of the polarizing HYPSO material from the hyperpolarized solution by filtration. However, the one-dimensional tubular pores of SBA-15 type materials are not ideal for nuclear spin diffusion, which may limit efficient polarization. Here, we develop a generation of hyperpolarizing solids based on a SBA-16 structure with a network of pores interconnected in three dimensions, which allows a significant increase of polarization, i.e. P(1H) = 63% at 1.2 K. This result illustrates how one can improve materials by combining a control of the incorporation of radicals with a better design of the porous network structures.

Preparation and characterization - including in situ Small Angle X-Ray Scattering - of gas chromatographic capillary columns with mesoporous silica thin films as stationary phases.

In this study the preparation of various mesoporous silica thin films as new stationary phases for gas chromatography (GC) columns is presented. The synthesis was performed inside capillaries via a sol-gel process using a templating route. The as-obtained columns were found to be highly efficient for the fast separation of light n-alkanes (C1-C5) mixture; these columns exhibiting a normalized retention 30 times higher than that of a commercially available silica column used as standard. A particular effort was directed towards the characterization of the stationary phase physical features: thin film inspection by Scanning Electron Microscopy and, for the first time to our knowledge, in situ SAXS characterization using synchrotron radiation were used to study the impact of the pore-network structuration on the GC properties. Worm-like, cubic and hexagonal phases were observed for specific preparation conditions. Unexpectedly, the normalized retention relative to film thickness appeared higher with disordering of the pores network.

Dinitrogen dissociation on an isolated surface tantalum atom.

Both industrial and biochemical ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong triple bond of dinitrogen. Such multimetallic cooperation for dinitrogen cleavage is also the general rule for dinitrogen reductive cleavage with molecular systems and surfaces. We have observed cleavage of dinitrogen at 250 degrees C and atmospheric pressure by dihydrogen on isolated silica surface-supported tantalum(III) and tantalum(V) hydride centers [(identical with Si-O)2Ta(III)-H] and [(identical with Si-O)2Ta(V)H3], leading to the Ta(V) amido imido product [(identical with SiO)2Ta(=NH)(NH2)]: We assigned the product structure based on extensive characterization by infrared and solid-state nuclear magnetic resonance spectroscopy, isotopic labeling studies, and supporting data from x-ray absorption and theoretical simulations. Reaction intermediates revealed by in situ monitoring of the reaction with infrared spectroscopy support a mechanism highly distinct from those previously observed in enzymatic, organometallic, and heterogeneous N2 activating systems.

Paradoxical metabolic response of the human brain to a single electroconvulsive shock.

Regional brain protein synthesis was evaluated with positron emission tomography (PET) and L-(S-[11C]methyl)methionine ([11C]MET) in depressive patients, before and 3 h after an electroconvulsive shock (ECS), when energy supply is restored, and in healthy volunteers. Depressive patients presented apparent lower protein synthesis than normals, in agreement with known reduction of cerebral activity. In contrast, ECS resulted in a significant increase (56%, P < 0.05) in global cortical protein synthesis. This paradoxical hyperactivation of cellular protein metabolism in response to seizures and the fact that synaptic activity is further reduced after electroconvulsive therapy (ECT), may provide new insights for understanding the mechanism of action of ECT.

Allodynia after lateral-medullary (Wallenberg) infarct. A PET study.

We used PET to study regional cerebral blood flow (rCBF) changes in nine patients with unilateral central pain after a lateral medullary infarct (Wallenberg's syndrome). All patients presented, on the abnormal side, a combination of hypaesthesia to noxious and thermal stimuli and allodynia to rubbing of the skin with a cold object (i.e. abnormal pain to innocuous stimulation). The rCBF responses during allodynia were compared with those obtained during stimulation of the normal side using (i) a cold non-noxious stimulus identical to that applied to the painful side, and (ii) an electrical high-frequency stimulus at painful ranges. Statistical analysis disclosed two abnormal patterns of rCBF change during allodynia. First, there is a quantitative change whereby the blood flow response was out of proportion with the actual intensity of the stimulus, i.e. the pattern of activation by innocuous rubbing of the skin was in our patients identical to that previously reported in response to painful stimuli in normal subjects. This pattern concerned primarily the contralateral thalamus in its lateral half and the primary and somatosensory areas, as well as inferior parietal [Brodmann area (BA) 39/40], anterior insular (BA 6) and medial prefrontal (BA 10) cortices. Thalamic over-activity may reflect abnormal transduction and amplification of sensory inputs after spinothalamic deafferentation. This might be responsible for both increased rCBF in multiple cortical targets and the perceived shift of stimulus intensity from innocuous to painful ranges. The second abnormality associated with allodynic sensation was qualitative. It concerned exclusively the contralateral cingulate gyrus, which did not exhibit the usual pain-related rCBF increase reported in normal subjects. This abnormal cingulate response may account for the peculiar response of lateral medullary infarct patients to allodynic pain, which is not simply perceived as an exaggerated pain sensation, but as a new, strange and extremely unpleasant feeling, not previously experienced by the patients.

Gillespie syndrome phenotype with a t(X;11)(p22.32;p12) de novo translocation.

PURPOSE: To report a patient with a phenotype suggestive of Gillespie syndrome and with a chromosomal abnormality. METHODS: Clinical evaluation showed bilateral superior coloboma, foveal hypoplasia, and inferior cerebellar hypoplasia. Karyotyping as well as investigation of the PAX6 gene were performed. RESULTS: The karyotype of the patient disclosed a de novo translocation t(X;11)(p22.32;p12). Fluorescent in situ hybridization and the search for mutations excluded direct implication of the PAX6 gene. CONCLUSION: This is, to our knowledge, the first report of a chromosomal abnormality detected in a patient with a Gillespie syndrome phenotype.

Brain glucose metabolism with [18F]-fluorodeoxyglucose and positron emission tomography before and after surgical resection of epileptogenic cavernous angiomas.

Surgery of cavernous angiomas is often proposed due to the epileptogenic and hemorrhagic potential of this lesion. Little information is available on the impact of surgical resection on brain metabolism, locally or at a distance from the lesion. Fifteen patients presenting with a cavernoma and epileptic seizures underwent positron emission tomography examinations before and 1 year after surgical resection. We studied the quantitative cerebral metabolic rate of glucose (CMRGlu) with [18F]-fluorodeoxyglucose. The global brain CMRGlu remained unchanged after surgery. There was a significant decrease of metabolism in the lesion hemisphere, which remained unchanged after surgery. The perilesional regions were less metabolic than the contralateral ones and less metabolic than remote regions within the same hemisphere, before and after surgery. The absence of pre- to postsurgical variations suggests that the metabolic consequences of the lesion are maintained despite the surgical procedure during long-term follow-up studies.