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Nucleophilic opening of bis-epoxide 1 derived from d-mannitol by organolithium species in the presence of boron trifluoride etherate allows the synthesis of enantiopure polyhydroxy tetrahydrofurane skeletons with aromatic moieties in the pseudo-anomeric position. ortho-Lithiation and transmetalation are the most appropriate conditions for the preparation of the organometallic derivatives where halogen–metal exchange is unfavorable. [Copyright &y& Elsevier]

The impact of crystal size on the transition orthorhombic ↔ monoclinic phase in MFI -type purely silica zeolites is investigated between 293 and 473 K using 29 Si MAS NMR and powder X-ray diffraction. Three silicalite-1 zeolites are synthesized: a material constituted of micron-sized crystals, pseudospherical nanometer-sized crystals and hierarchical porous zeolites with a mesoporous network created by the use of a gemini-type diquaternary ammonium surfactant giving nanosheet zeolites. Our results show for the first time that the orthorhombic ↔ monoclinic phase transition already known for micron-sized particles also occurs in nanometer-sized zeolite crystals whereas our data suggest that the extreme downsizing of the zeolite crystal to one unit cell in thickness leads to an extinction of the phase transition. [ABSTRACT FROM AUTHOR]

Abstract: Mass transfers of various molecules in multiphasic food products lead to quality modification and thus require the use of edible films or coatings in-between the foodstuff. Consequently, it is important to assess the barrier properties and efficiencies of edible films as well as to determine the diffusivities of the migrants. Translational diffusion of a reference molecule such as fluorescein, determined by the fluorescence recovery after photobleaching (FRAP) method, displays a threshold of a critical water content inducing an increase of the molecular mobility, and demonstrates that multiple populations of a single molecular specie can be involved in different diffusion kinetics. Further investigations at a molecular scale through high resolution solid state nuclear magnetic resonance (NMR) enables to go deeper into the understanding of the interactions involved in such a system, in particular on the identification of the possible binding sites of the diffusant on the polymer and on the overall effect of interactions on the polymer organization. Therefore, the appraisal of transport properties in foods by means of reference molecules constitutes a relevant approach to use in combination with molecular investigation of physicochemical interactions with the diffusing substances. [Copyright &y& Elsevier]

Here, using liquid crystals as template, an EISA (evaporation-induced self-assembly) method has been used to synthesize amorphous mesostructured alumina. The effect of the synthesis parameters such as the presence of a chelating agent, the amounts of both porogen agent and alumina precursor on the materials properties have been investigated in details. Under the optimum conditions, after Soxhlet extraction, the obtained Al 2 O 3 presents an HMS (Hexagonal Molecular Sieves) structure and a high specific surface area (≈400 m2/g) with a mesopore size distribution centered around 8.3 nm. Investigation of the thermal stability shows that the crystallization into γ-Al 2 O 3 of the amorphous alumina walls delimiting mesopores begins after heating at 800 °C. We have also demonstrated that half of the carbon present in the as-synthesized material can be removed by washing with water or ethanol at room temperature instead of Soxhlet extraction. On the basis of SAXS, XRD and N 2 adsorption-desorption analyses, we have shown that when treated into boiling water or exposed to water vapor the alteration of the mesostructure occurs quickly. Its collapse has been attributed to the crystallization of the amorphous alumina walls into aluminum hydroxides, mainly boehmite, upon the hydration of the alumina. Dual mesoporous alumina have been also obtained from micelles through a cooperative templating mechanism at low P123 amount and in the presence of citric acid. In that case both mesopores networks adopt a wormhole-like mesostructure. [Display omitted] • Mesostructure preserved until 900 °C. • Amorphous mesostructured Al 2 O 3 thermally stable up to 800 °C. • Porogen agent partially removed by water or ethanol at room temperature. • Framework collapses due to aluminum hydroxides crystallization in presence of water. • Dual mesoporous alumina prepared at low amount of porogen agent in presence of citrate. [ABSTRACT FROM AUTHOR]

Pure silica ITQ-7 zeolite of topology ISV synthesized in fluoride media possesses a 3D 12-membered-rings pore system. Originally the structure of ITQ-7 zeolite was solved and refined from a calcined sample in the highest possible space group symmetry P4 2 / mmc . This space group leads to only 5 independent silicon T sites for this structure. However, this high symmetry was not supported by solid state 29 Si MAS NMR spectroscopy. In this short communication, we show from a revised 29 Si solid state MAS NMR and Rietveld analyses, that lowering of the space group symmetry from P4 2 / mmc to P4 2 consolidates structure model and experimental data, in particular, the number of non equivalent crystallographic T sites passing from 5 to 16, is in agreement with 29 Si solid state NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: An alternative to the Evaporation Induced Self Assembly (EISA) method is described as a fast and simplified approach towards mesoporous silica films. The sol–gel process is photochemically triggered with the aid of photoacid generator (PAG), thereby making mesostructuration independent of film deposition conditions, solvent evaporation and complex chemistry associated with a silica sol. The developed solvent-free synthesis uses non-ionic poly(ethylene oxide)-based surfactants and polydimethoxysiloxane, affording after UV irradiation a film with a wormhole porous framework, and a uniform pore size distribution. The disordered mesostructure was characterized by X-ray diffraction, N2 adsorption, 29Si solid-state NMR and transmission electron microscopy. [Copyright &y& Elsevier]

Abstract: The control of the inter-particle porosity in polycrystalline zeolite bodies remains a challenge. The present study reports on the preparation of centimeter-sized zeolite bodies (32×2mm pellets) with reduced inter-particle porosity. The bodies were prepared by assembling zeolite colloidal nanocrystals with monomodal particle size distribution and sub-colloidal aluminum hydroxide binder. A secondary growth treatment under hydrothermal conditions was performed in order to fill up the inter-particle voids and obtain polycrystalline zeolite materials with textural characteristics close to those of single zeolite crystals. Initial material, intermediates and ultimate product were studied with a combination of complementary methods revealing a substantial reduction even an elimination of the inter-particle porosity. Particular attention was paid to the chemical evolution of the binder and the migration of aluminum species, employing X-ray powder diffraction, 27Al-MAS, 27Al-3QMAS NMR and X-ray fluorescence spectroscopy analyses. Evidences for insertion of aluminum from the binder into the zeolite framework during secondary growth step were found. Consequently the ultimate pellets comprised aluminum-rich zeolite beta crystals and very low binder content. [ABSTRACT FROM AUTHOR]

The effect of the introduction of heteroelement (Si, P, Al, Ge, Ga and Zr) by direct synthesis on the thermal stability of mesostructured titania prepared by the soft templating pathway has been investigated. All materials have been surfactant-extracted with EtOH and calcined at different temperatures up to 900 °C. Ti4+ can be partially substituted by most of the investigated heteroelements but they mainly form an oxide amorphous phase surrounding the titania anatase particles. Results obtained by SAXS, X-Ray diffraction, Raman spectroscopy and manometry nitrogen adsorption-desorption show that the crystallization of the amorphous titania into nanosized anatase particles and the transition from anatase to rutile occur at higher temperature with the addition of the heteroelement. Even if the lattice distortion introduced by the partial Ti4+ substitution can participate to this phenomenon, it is mainly due the «glass » effect induced by the presence of the heteroelement in the TiO 2 amorphous phase, which limits the growth of the nanosized anatase crystallites. However, when the crystallites reach a limit size, the collapse of the mesostructure occurs. With increasing the calcination temperature, the anatase titania particles become bigger and bigger, the transition from anatase to rutile takes place and the heteroelement can crystallize or be integrated in a crystalline phase. Among the considered heteroelements and by comparison with the bare mesostructured TiO 2 , the most beneficial effect is obtained in the presence of Si4+ and PO 4 3− for which the mesostructure collapse at higher temperature by about two hundred Celsius degrees. Al3+ and Ge4+ enhance the thermal stability by about a hundred Celsius degrees and Ga3+ or Zr4+ have no significant effect on the temperature at which the mesostructure collapses. Image 1 • Thermal stability of mesostructured TiO 2 enhanced by the addition of heteroelements. • Heteroelements form amorphous phase which embedded the anatase particles and inhibit their growth. • Limit size reached by anatase particles involves the collapse of the mesostructure. • Delay of the anatase to rutile transformation in the presence of heteroelements. • Partial substitution of titanium by the heteroelement. [ABSTRACT FROM AUTHOR]