Interfacial impregnation chemistry in the synthesis of nickel catalysts supported on titania

The interfacial chemistry of the impregnation step involved in the preparation of nickel catalysts supported on titania is presented. Several methodologies based on deposition data, pH measurements, potentiometric mass titrations, and microelectrophoresis have been used in conjunction with diffuse reflectance UV/Vis/NIR spectroscopy, simulations, and semiempirical quantum chemical calculations. Three mononuclear inner-sphere complexes were formed at the compact layer of the "titania/electrolyte solution" interface: A monosubstituted, dihydrolyzed complex above a terminal oxo group, a disubstituted, dihydrolyzed complex above two terminal adjacent oxo groups, and a disubstituted, nonhydrolyzed complex above one terminal and one bridging adjacent oxo groups. The monosubstituted, dihydrolyzed complex predominates. The contribution of the disubstituted configurations is also important at very low Ni(II) surface concentration, but it decreases as the Ni(II) surface concentration increases. In addition, bi- and trinuclear inner-sphere complexes were formed. The receptor site involves one bridging and two terminal oxo groups in the first case and two bridging and three terminal oxo groups in the second case. The relative surface concentrations of these configurations increase initially with Ni(II) surface concentration and then remain practically constant. The understanding of these interfacial processes at a molecular level is very important to shift the catalytic synthesis from an art to a science as well as to obtain strict control of the impregnation step and, to some extent, of the whole preparative sequence. This study is very relevant to the synthesis of submonolayer/monolayer nickel catalysts supported on TiO(2) following equilibrium deposition filtration (otherwise called equilibrium adsorption).     

Palladium catalyzed C-C coupling reactions of 3,5-dichloro-4H-1,2,6-thiadiazin-4-one

Palladium catalyzed Suzuki-Miyaura, Stille, and Sonogashira coupling reactions are reported for the electron-deficient heterocyclic scaffold 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (1). Furthermore, 3,5-di(thien-2-yl)-4H-1,2,6-thiadiazin-4-one (7m) is further elaborated to afford the tetrathienyl 3,5-bis[(2,2'-bithien)-5-yl]-4H-1,2,6-thiadiazin-4-one (9). All compounds are fully characterized.     

Organic–inorganic bonding in chitosan–silica hybrid networks: Physical properties

Novel biomaterials are needed for bone tissue repair with improved mechanical performance compared to classical bioceramics. The objective of this work was to characterize a hybrid filler material, which is capable to coat as a thin film porous scaffolds improving their mechanical properties for bone tissue engineering. The hybrid filler material is a blend of chitosan and silica network formed through in situ sol–gel using tetraethylortosilicate and 3‐glycidoxypropyltrimethoxysilane (GPTMS) as silica precursors. The hypothesis was that the epoxy ring of GPTMS could react with the amino groups of chitosan in acidic media while it is also reacting the siloxane groups of hydrolyzed silica precursors. The formation of the hybrid organic–inorganic network was assessed by different physical techniques revealing changes in molecular mobility and hydrophilicity upon chemical reaction. Finally, the cytotoxicity of the samples was also evaluated by MTT assay. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1391–1400     

Ultra‐Small Plutonium Oxide Nanocrystals: An Innovative Material in Plutonium Science

Apart from its technological importance, plutonium (Pu) is also one of the most intriguing elements because of its non‐conventional physical properties and fascinating chemistry. Those fundamental aspects are particularly interesting when dealing with the challenging study of plutonium‐based nanomaterials. Here we show that ultra‐small (3.2±0.9 nm) and highly crystalline plutonium oxide (PuO₂) nanocrystals (NCs) can be synthesized by the thermal decomposition of plutonyl nitrate ([PuO₂(NO₃)₂] ? 3 H₂O) in a highly coordinating organic medium. This is the first example reporting on the preparation of significant quantities (several tens of milligrams) of PuO₂ NCs, in a controllable and reproducible manner. The structure and magnetic properties of PuO₂ NCs have been characterized by a wide variety of techniques (powder X‐ray diffraction (PXRD), X‐ray absorption fine structure (XAFS), X‐ray absorption near edge structure (XANES), TEM, IR, Raman, UV/Vis spectroscopies, and superconducting quantum interference device (SQUID) magnetometry). The current PuO₂ NCs constitute an innovative material for the study of challenging problems as diverse as the transport behavior of plutonium in the environment or size and shape effects on the physics of transuranium elements.     

Air‐Stable Solid Aryl and Heteroaryl Organozinc Pivalates: Syntheses and Applications in Organic Synthesis

A wide range of air‐stable, solid, polyfunctional aryl and heteroarylzinc pivalates were efficiently prepared by either magnesium insertion or Hal/Mg exchange followed by transmetalation with Zn(OPiv)₂ (OPiv=pivalate). By reducing the amount of LiCl the air stability could be significantly enhanced compared with previously prepared reagents. An alternative route is directed magnesiation using TMPMgCl ? LiCl (TMP=2,2,6,6‐tetramethylpiperidyl) followed by transmetalation with Zn(OPiv)₂ or, for very sensitive substrates, direct zincation by using TMPZnOPiv. These zinc reagents not only show excellent stability towards air, but they also undergo a broad range of C?C bond‐formation reactions, such as allylation and carbocupration reactions, as well as addition to aldehydes and 1,4‐addition reactions. Acylation reactions can be performed by using an excess of TMSCl to overcome side reactions of the omnipresent pivalate anion.     

Capillary waveguide fluoroimmunosensor with improved repeatability and detection sensitivity

An optical capillary waveguide fluoroimmunosensor based on glass capillaries internally coated with an ultrathin poly(dimethylsiloxane) (PDMS) film is presented. The evaluation of the capillaries developed was done in comparison with aminosilanized [3-(aminopropyl)triethoxysilane, APTES] glass and poly(methylpentene) (PMP) capillaries by immobilizing rabbit γ-globulins on the internal capillary wall. Following reaction with (R)-phycoerythrin-labelled antibody, the capillary was scanned with a laser beam and the fluorescence waveguided through the capillary wall was detected by a photomultiplier placed at one of its ends. The capillaries developed provided considerably improved protein coating homogeneity (intracapillary coefficients of variation 2.9–6.6%) and repeatability (intercapillary coefficients of variation 2.1–5.0%) compared with APTES-treated ones (7.9–13.4 and 8.5–15.2%, respectively). With use of these capillaries in a sandwich-type immunosensor for the determination of rabbit γ-globulins, the assay detection limit was improved eightfold (4.4 ng/mL) compared with that obtained using PMP capillaries (35.3 ng/mL), whereas the assay repeatability was improved threefold (intra-assay coefficients of variation 5.9–13.1%) compared with APTES-treated capillaries (15.6–36%). Optoelectronic set-up used to scan the capillaries (left) and representative fluorescence scannings of dual-band poly(methylpentene) (PMP), PDMS-modified glass and APTES treated glass capillaries     

Direct Evidence for Intermolecular Oxidative Addition of σ(SiSi) Bonds to Gold

Oxidative addition plays a major role in transition‐metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl₃, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative ³¹P and ²⁹Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si? Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si? Si) bonds to gold and open promising perspectives for the development of new gold‐catalyzed redox transformations.     

Targeting of sebocytes by aminolevulinic acid-dependent photosensitization

Photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX has been developed as a very useful therapeutic modality. Recently, several authors have reported on the efficacy of this procedure for acne. This approach is based on the fact that 5-aminolevulinic acid-induced protoporphyrin IX has strong selectivity for sebaceous glands. We used the immortalized human sebaceous gland cell line SZ95 to investigate cellular mechanisms of photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX. Quantification of induced protoporphyrin IX production showed dependence on the applied 5-aminolevulinic acid dose. When SZ95 sebocytes were differentiated by arachidonic acid treatment, there was no difference between them and the control cells with respect to both the amount of 5-aminolevulinic acid-induced protoporphyrin IX and the phototoxic effects. We altered protoporphyrin IX formation rates by growing cells scattered as single cells in the culture dishes. Single cells produced significantly lower protoporphyrin IX levels than those grown with intercellular contacts. Intracellular localization of protoporphyrin IX was imaged using confocal laser scanning microscopy. The differentiation-specific lipid droplets were virtually excluded from protoporphyrin IX fluorescence. In addition to weak mitochondrial and strong membrane fluorescence, distinctive spots with strong fluorescence were observed. These did not colocalize with fluorescent probes for mitochondria, lysosomes or the Golgi apparati.     

A Direct and Versatile Synthesis of 5-(2-Di-n-Propylaminoethyl)-7-methoxyindole

The Pummerer intermediate generated from 10 with TFAA was trapped intermolecularly in the presence of Lewis acid by the indoline 2 at position 5. Sequential treatment of the resulted compound 3 with Ra-Ni, LiAlH₄ and active MnO₂ gave compound 6 in high overall yield.