Impact of Mineralizing Agents on Aluminum Distribution and Acidity of ZSM-5 Zeolites.

Intensive research on improving the catalytic properties of zeolites is focused on modulating their acidity and the distribution of associated Al sites. Herein, by studying a series of ZSM-5 zeolites over a broad range of Al content, we demonstrate how the nature of the mineralizing agent (F- or OH- ) used in hydrothermal syntheses directly impacts Al sites distribution. The proportions of Al sites, probed by 27 Al NMR, depend on the Si/Al ratio for F- , but remain identical for OH- (from Si/Al=30 to 760). This leads to contrasting variations in weak and strong acidities. Such opposite effect of mineralizers is explained by the spatial location of negative charges and the resulting balance between short- and long-range electrostatic interactions. This understanding paves the way for additional and simple opportunities to control zeolites' acidity.

High-Pressure Synthesis and Gas-Sensing Tests of 1-D Polymer/Aluminophosphate Nanocomposites.

Recently, filling zeolites with gaseous hydrocarbons at high pressures in diamond anvil cells has been carried out to synthesize novel polymer-guest/zeolite-host nanocomposites with potential, intriguing applications, although the small amount of materials, 10-7 cm3, severely limited true technological exploitation. Here, liquid phenylacetylene, a much more practical reactant, was polymerized in the 12 Å channels of the aluminophosphate Virginia Polytechnic Institute-Five (VFI) at about 0.8 GPa and 140 °C, with large volumes in the order of 0.6 cm3. The resulting polymer/VFI composite was investigated by synchrotron X-ray diffraction and optical and 1H, 13C, and 27Al nuclear magnetic resonance spectroscopy. The materials, consisting of disordered π-conjugated polyphenylacetylene chains in the pores of VFI, were deposited on quartz crystal microbalances and tested as gas sensors. We obtained promising sensing performances to water and butanol vapors, attributed to the finely tuned nanostructure of the composites. High-pressure synthesis is used here to obtain an otherwise unattainable true technological material.

Labeling and Probing the Silica Surface Using Mechanochemistry and 17 O†NMR Spectroscopy*.

In recent years, there has been increasing interest in developing cost-efficient, fast, and user-friendly 17 O enrichment protocols to help to understand the structure and reactivity of materials by using 17 O NMR spectroscopy. Here, we show for the first time how ball milling (BM) can be used to selectively and efficiently enrich the surface of fumed silica, which is widely used at industrial scale. Short milling times (up to 15 min) allowed modulation of the enrichment level (up to ca. 5 %) without significantly changing the nature of the material. High-precision 17 O compositions were measured at different milling times by using large-geometry secondary-ion mass spectrometry (LG-SIMS). High-resolution 17 O NMR analyses (including at 35.2 T) allowed clear identification of the signals from siloxane (Si-O-Si) and silanols (Si-OH), while DNP analyses, performed by using direct 17 O polarization and indirect 17 O{1 H} CP excitation, agreed with selective labeling of the surface. Information on the distribution of Si-OH environments at the surface was obtained from 2D 1 H-17 O D-HMQC correlations. Finally, the surface-labeled silica was reacted with titania and using 17 O DNP, their common interface was probed and Si-O-Ti bonds identified.

Looking into the dynamics of molecular crystals of ibuprofen and terephthalic acid using 17 O and 2 H nuclear magnetic resonance analyses.

Oxygen-17 and deuterium are two quadrupolar nuclei that are of interest for studying the structure and dynamics of materials by solid-state nuclear magnetic resonance (NMR). Here, 17 O and 2 H NMR analyses of crystalline ibuprofen and terephthalic acid are reported. First, improved 17 O-labelling protocols of these molecules are described using mechanochemistry. Then, dynamics occurring around the carboxylic groups of ibuprofen are studied considering variable temperature 17 O and 2 H NMR data, as well as computational modelling (including molecular dynamics simulations). More specifically, motions related to the concerted double proton jump and the 180° flip of the H-bonded (-COOH)2 unit in the crystal structure were looked into, and it was found that the merging of the C=O and C-OH 17 O resonances at high temperatures cannot be explained by the sole presence of one of these motions. Lastly, preliminary experiments were performed with a 2 H-17 O diplexer connected to the probe. Such configurations can allow, among others, 2 H and 17 O NMR spectra to be recorded at different temperatures without needing to tune or to change probe configurations. Overall, this work offers a few leads which could be of use in future studies of other materials using 17 O and 2 H NMR.

Development of alginate esters as novel multifunctional excipients for direct compression.

Methyl ester derivatives of alginic acid have been evaluated as potential multifunctional excipients for pharmaceutical direct compression. The use of alginic acid as an excipient in tablet formulation is limited because of certain drawbacks such as low tablet hardness and poor compressibility. The objective of this work is to improve these properties through esterification of alginic acid, chemical modification commonly used for enhancing the functionality of tableting excipients. It has been observed that the degree of methylation (DM) has a profitable impact in the physico-chemical and mechanical properties of the obtained materials. In general, an increase in the degree of methylation yielded tablets with higher tensile strength and better compressibility. Furthermore, modified alginates exhibited extended disintegration times compared to native alginic acid due to the introduced hydrophobicity. Finally, the functional versatility of the modified alginates as disintegrating and filling/binding agents was tested by formulating them with microcrystalline cellulose and lactose.

Direct 17O Isotopic Labeling of Oxides Using Mechanochemistry.

While 17O NMR is increasingly being used for elucidating the structure and reactivity of complex molecular and materials systems, much effort is still required for it to become a routine analytical technique. One of the main difficulties for its development comes from the very low natural abundance of 17O (0.04%), which implies that isotopic labeling is generally needed prior to NMR analyses. However, 17O-enrichment protocols are often unattractive in terms of cost, safety, and/or practicality, even for compounds as simple as metal oxides. Here, we demonstrate how mechanochemistry can be used in a highly efficient way for the direct 17O isotopic labeling of a variety of s-, p-, and d-block oxides, which are of major interest for the preparation of functional ceramics and glasses: Li2O, CaO, Al2O3, SiO2, TiO2, and ZrO2. For each oxide, the enrichment step was performed under ambient conditions in less than 1 h and at low cost, which makes these synthetic approaches highly appealing in comparison to the existing literature. Using high-resolution solid-state 17O NMR and dynamic nuclear polarization, atomic-level insight into the enrichment process is achieved, especially for titania and alumina. Indeed, it was possible to demonstrate that enriched oxygen sites are present not only at the surface but also within the oxide particles. Moreover, information on the actual reactions occurring during the milling step could be obtained by 17O NMR, in terms of both their kinetics and the nature of the reactive species. Finally, it was demonstrated how high-resolution 17O NMR can be used for studying the reactivity at the interfaces between different oxide particles during ball-milling, especially in cases when X-ray diffraction techniques are uninformative. More generally, such investigations will be useful not only for producing 17O-enriched precursors efficiently but also for understanding better mechanisms of mechanochemical processes themselves.

Zeolite Structure Direction: Identification, Strength and Involvement of Weak CH⋠⋠⋠O Hydrogen Bonds.

We demonstrate that weak CH⋅⋅⋅O hydrogen bonds (HBs) are important host-guest interactions in zeolite assemblies involving structure directing organocations. This type of HB is identified between alkyl groups of the organic structure directing agent (OSDA) and the silica framework in as-synthesized silicalite-1 of complex topology (MFI) using a combination of experimental and theoretical data obtained at low and room temperatures. The 28 weak CH⋅⋅⋅O HBs, evidenced along dynamics simulation at room temperature, represent 30 % of the energy of the Coulomb electrostatic interaction between OSDA and the zeolite framework. The strongest and most stable HB found here connects the OSDA to the [41 52 62 ] cage containing F atoms and should contribute to preserve zeolite topology during crystal growth. An inspection of other as-synthesized zeolites of very different framework topology indicates that the directional CH⋅⋅⋅O HBs have to be considered when discussing zeolite structure directing phenomena.

Misplaced Golgi Elements Produce Randomly Oriented Microtubules and Aberrant Cortical Arrays of Microtubules in Dystrophic Skeletal Muscle Fibers.

Differentiated mammalian cells and tissues, such as skeletal muscle fibers, acquire an organization of Golgi complex and microtubules profoundly different from that in proliferating cells and still poorly understood. In adult rodent skeletal muscle, the multinucleated muscle fibers have hundreds of Golgi elements (GE), small stacks of cisternae that serve as microtubule-organizing centers. We are interested in the role of the GE in organizing a peculiar grid of microtubules located in the fiber cortex, against the sarcolemma. Modifications of this grid in the mdx mouse model of Duchenne muscular dystrophy have led to identifying dystrophin, the protein missing in both human disease and mouse model, as a microtubule guide. Compared to wild-type (WT), mdx microtubules are disordered and more dense and they have been linked to the dystrophic pathology. GE themselves are disordered in mdx. Here, to identify the causes of GE and microtubule alterations in the mdx muscle, we follow GFP-tagged microtubule markers in live mdx fibers and investigate the recovery of GE and microtubules after treatment with nocodazole. We find that mdx microtubules grow 10% faster but in 30% shorter bouts and that they begin to form a tangled network, rather than an orthogonal grid, right after nucleation from GE. Strikingly, a large fraction of microtubules in mdx muscle fibers seem to dissociate from GE after nucleation. Moreover, we report that mdx GE are mispositioned and increased in number and size. These results were replicated in WT fibers overexpressing the beta-tubulin tubb6, which is elevated in Duchenne muscular dystrophy, in mdx and in regenerating muscle. Finally, we examine the association of GE with ER exit sites and ER-to-Golgi intermediate compartment, which starts during muscle differentiation, and find it persisting in mdx and tubb6 overexpressing fibers. We conclude that GE are full, small, Golgi complexes anchored, and positioned through ER Exit Sites. We propose a model in which GE mispositioning, together with the absence of microtubule guidance due to the lack of dystrophin, determines the differences in GE and microtubule organization between WT and mdx muscle fibers.

ZSM-5 Zeolite: Complete Al Bond Connectivity and Implications on Structure Formation from Solid-State NMR and Quantum Chemistry Calculations.

Al site distribution in the structurally complex and industrially important ZSM-5 zeolite is determined by studying the spectroscopic response of Al(OSi)4 units and using a self-consistent combination of up-to-date solid-state NMR correlations (29Si-27Al and 1H-27Al D-HMQC) and quantum chemistry methods (DFT-D). To unravel the driving forces behind specific Al sitting positions, our approach focuses on ZSM-5 containing its more efficient OSDA, tetrapropylammonium.

PeakForce QNM AFM study of chitin-silica hybrid films.

Chitin-silica hybrid thin films, prepared through the colloidal self-assembly of chitin nanorods and siloxane oligomers, have been studied for the first time by PeakForce QNM AFM mode to explore their structure and mechanical behaviour. The change in structure and mechanical properties of chitin-silica hybrids is mainly driven by the relative quantities in chitin nanorods and silica, expressed as the chitin volume fraction ϕchi. The coating of the chitin polysaccharide by silica leads to an increase of the nanorods diameter and films surface roughness at small ϕchi values. The DMT (Derjaguin-Muller-Toporov) modulus increased both at small ϕchi due to a large amount of silica and at very high ϕchi→1 due to an incomplete tip penetration between nanorods. The local parallel orientation of nanorods observed at different ϕchi values resulted in a modulus increase due to an enhancement of the cohesion between nanorods.

Intermolecular interactions in AST zeolites through 14N NMR and DFT calculations.

The structure of the silica AST zeolites (octadecasil) synthesized in fluoride medium using tetramethylammonium (TMA) as the organic structure-directing agent has been reinvestigated using 14N NMR quadrupolar parameters and DFT calculations. The value of the experimental 14N quadrupolar coupling constant (CQ = 27 kHz) is larger than expected for a TMA cation possessing a high degree of motion. The analysis of a DFT-optimized octadecasil cluster along with the comparison between measured and calculated 14N NMR parameters demonstrate the presence of weak C-H...O hydrogen bonds between the TMA in the [46612] cages and the silica skeleton. These intermolecular interactions can be related to the presence of Si...F tetrel bonds within the [46] cages. These new results provide additional information with regard to the formation mechanisms and structure of the octadecasil zeolites.

Multinuclear NMR as a tool for studying local order and dynamics in CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites.

We report on 207Pb, 79Br, 14N, 1H, 13C and 2H NMR experiments for studying the local order and dynamics in hybrid perovskite lattices. 207Pb NMR experiments conducted at room temperature on a series of MAPbX3 compounds (MA = CH3NH3+; X = Cl, Br and I) showed that the isotropic 207Pb NMR shift is strongly dependent on the nature of the halogen ions. Therefore 207Pb NMR appears to be a very promising tool for the characterisation of local order in mixed halogen hybrid perovskites. 207Pb NMR on MAPbBr2I served as a proof of concept. Proton, 13C and 14N NMR experiments confirmed the results previously reported in the literature. Low temperature deuterium NMR measurements, down to 25 K, were carried out to investigate the structural phase transitions of MAPbBr3. Spectral lineshapes allow following the successive phase transitions of MAPbBr3. Finally, quadrupolar NMR lineshapes recorded in the orthorhombic phase were compared with simulated spectra, using DFT calculated electric field gradients (EFG). Computed data do not take into account any temperature effect. Thus, the discrepancy between the calculated and experimental EFG evidences the fact that MA cations are still subject to significant dynamics, even at 25 K.

Preferential orientations of structure directing agents in zeolites.

The local structure of as-synthesised silicalite-1 zeolites is modified using asymmetric R(Pr)3N(+) structure directing agents. Using multi-nuclear NMR ((1)H, (13)C, (14)N, (19)F, (29)Si), we show for the first time the ability of these cations to adopt preferential orientations at the zeolite channels' crossing.

Mesoporous alumina from colloidal biotemplating of Al clusters.

A simple and green synthesis route was disclosed for the achievement of mesoporous alumina microparticles employing polysaccharide nanoparticles (α-chitin nanorods) as templates. Pore textures can be tuned by the cationic alumina precursor. Compared to small cations, the use of Al13 and Al30 oxo-hydroxo clusters leads to better defined and elongated mesopores. Electron microscopy and spectroscopic ((13) C, (27) Al NMR, XPS) measurements demonstrated that this is related to the effective coating of α-chitin nanorods by these pre-condensed colloids.

DFT-D study of 14N nuclear quadrupolar interactions in tetra-n-alkyl ammonium halide crystals.

The density functional theory-based method with periodic boundary conditions and addition of a pair-wised empirical correction for the London dispersion energy (DFT-D) was used to study the NMR quadrupolar interaction (coupling constant CQ and asymmetry parameter ηQ) of (14)N nuclei in a homologous series of tetra-n-alkylammonium halides (C(x)H(2x+1))4N(+)X(-) (x = 1-4), (X = Br, I). These (14)N quadrupolar properties are particularly challenging for the DFT-D computations because of their very high sensitivity to tiny geometrical changes, being negligible for other spectral property calculations as, for example, NMR (14)N chemical shift. In addition, the polarization effect of the halide anions in the considered crystal mesophases combines with interactions of van der Waals type between cations and anions. Comparing experimental and theoretical results, the performance of PBE-D functional is preferred over that of B3LYP-D. The results demonstrated a good transferability of the empirical parameters in the London dispersion formula for crystals with two or more carbons per alkyl group in the cations, whereas the empirical corrections in the tetramethylammonium halides appeared to be inappropriate for the quadrupolar interaction calculation. This is attributed to the enhanced cation-anion attraction, which causes a strong polarization at the nitrogen site. Our results demonstrated that the (14)N CQ and ηQ are predominantly affected by the molecular structures of the cations, adapted to the symmetry of the anion arrangements. The long-range polarization effect of the surrounding anions at the target nitrogen site becomes more important for cells with lower spatial symmetry.

14N solid-state NMR: a sensitive probe of the local order in zeolites.

Local order in as-synthesised zeolites templated by tetraalkylammonium cations is proven from solid-state (14)N NMR and related quadrupolar parameters, opening new perspectives in the study of porous materials.

Electric-field alignment of chitin nanorod-siloxane oligomer reactive suspensions.

Uniaxially anisotropic chitin-silica nanocomposite solids have been obtained thanks to the electric field-induced macroscopic alignment of liquid-crystalline reactive cosuspensions. We demonstrate how chitin nanorods (260 nm long, 23 nm thick) can be aligned upon the application of an alternating current (ac) electric field, and within water-ethanol suspensions containing reactive siloxane oligomers (D(h) ∼ 3 nm). The alignment at the millimeter length scale is monitored by in situ small-angle X-ray scattering (SAXS) and polarized light optical microscopy. The composition and state (isotropic, chiral nematic) of the cosuspensions are proven to be determining factors. For nematic phases, the alignment is preserved when the electric field is switched off. Further solvent evaporation induces sol-gel transition, and uniaxially anisotropic chitin-silica nanocomposites are formed after complete drying of the aligned nematic suspensions. Here, the collective response of colloidal mesophases to external electric fields and the subsequent formation of ordered nanocomposite solids would represent a new opportunity for materials design.

Solid-state NMR studies of micelle-templated mesoporous solids.

In this tutorial review we intend to give an overview of the potential of NMR spectroscopy, and in particular solid-state NMR, in characterising micelle-templated mesoporous materials. Different topics are covered including the study of formation mechanisms, the characterisation of structures, textures, surfaces and interfaces, functionalisation, dynamic properties and structure-reactivity correlations. Some selected examples illustrate the variety of information provided by this spectroscopy. Particular attention is paid to recent technological and/or methodological developments.

Efficient mesoporous silica-titania catalysts from colloidal self-assembly.

Mesoporous silica-titania materials of tunable composition and texture, which present a high catalytic activity in the mild oxidation of sulfur compounds, have been obtained by combining the spray-drying process with the colloidal self-assembly of α-chitin nanorods (biopolymer acting as a template) and organometallic oligomers.

Drug nano-domains in spray-dried ibuprofen-silica microspheres.

Silica microspheres encapsulating ibuprofen in separated domains at the nanometre scale are formed by spray-drying and sol-gel processes. A detailed (1)H and (13)C NMR study of these microspheres shows that ibuprofen molecules are mobile and are interacting through hydrogen bonds with other ibuprofen molecules. (1)H magnetisation exchange NMR experiments were employed to characterize the size of the ibuprofen domains at the nanometre scale. These domains are solely formed by ibuprofen, and their diameters are estimated to be ∼40 nm in agreement with TEM observations. The nature and formation of these particular texture and drug dispersion are discussed.