Enhancement of the stability of microporous silica films in non-aqueous solvents at elevated temperature

The effect of Al incorporation and pH adjustment during hydrolysis of the silica precursor on the thermal and structural stability of ordered microporous silica films with a 2D structure is presented. The structural stability of the films was determined from a combination of LA XRD/TEM data with porosity data obtained from ethanol adsorption isotherms. Thermogravimetric analysis and MR data were used to determine the template removal and the thermal stability. Stability of aluminium incorporated silica films has further been examined in several organic solvents with different polarity. A solvent with a higher polarity interacts more strongly with the films; the long-order structure disappeared after exposure to polar solvents. After exposure to non-polar solvents, the pore size uniformity was retained after 48 h. The samples with an Al/Si ratio of 0.007 showed the smallest d-spacing shift after exposure to hexane. The stability was further tested in the hydrogenation of phenylacetylene performed in a batch reactor over 1 wt.% Pd/Si(Al)O-2/Si (Al/Si = 0.007) films at 30 degrees C and 10 bar H-2 with hexane as solvent. No deactivation was observed in two subsequent hydrogenation runs. (C) 2009 Elsevier Inc. All rights reserved.

A PHARMACOKINETIC AND PHARMACODYNAMIC COMPARISON OF PLAIN AND ENTERIC-COATED PREDNISOLONE TABLETS

1 Eight healthy volunteers and eight patients suffering from chronic obstructive pulmonary disease (COPD) received 30 mg prednisolone as plain (P) and enteric-coated tablets (EP) in a randomised, cross-over manner. Plasma prednisolone and cortisol and blood glucose were measured over 24 h.

Observations of collimated ionization channels in aluminum-coated glass targets irradiated by ultraintense laser pulses

Filamentary ionization tracks have been observed via optical probing inside Al-coated glass targets after the interaction of a picosecond 20-TW laser pulse at intensities above 10(19) W/cm(2). The tracks, up to 700 mu m in length and between 10 and 20 mu m in width, originate from the focal spot region of the laser beam. Simulations performed with 3D particle-in-cell and 2D Fokker-Planck hybrid codes indicate that the observations are consistent with ionization induced in the glass target by magnetized, collimated beams of high-energy electrons produced during the laser interaction.

Pharmacological Activity of Ibuprofen Release from Measoporous Silica

Novel drug delivery systems (DDS) to improve the pharmacokinetic profile of hydrophobic drugs following oral administration are an area of keen interest in drug research. An ideal DDS should not adversely affect drug activity, be capable of delivering a therapeutic dose of drug, and allow homogenous drug loading and drug release. Mesoporous silica has been proposed for this application, with ibuprofen employed as the model drug. It was hypothesised that mesoporous silica MCM-41 is capable of delivering a pharmacologically therapeutic dose of ibuprofen. Ibuprofen-loaded MCM-41 can be prepared reproducibly at a drug to carrier ratio of 30% (wt/wt). The release profile was seen to be 90% within 2 h. Initial assessment of COX-1 inhibitory activity suggests the absence of adverse effects attributable to drug-carrier interaction. The results of this study provide further evidence in support of the proposed use of mesoporous silica in drug delivery.

Modeling colloid deposition on a protein layer adsorbed to iron-oxide-coated sand

Our recent study reported that conformation change of granule-associated Bovine Serum Albumin (BSA) may influence the role of the protein controlling colloid deposition in porous media (Flynn et al., 2012). The present study conceptualized the observed phenomena with an ellipsoid morphology model, describing BSA as an ellipsoid taking a side-on or end-on conformation on granular surface, and identified the following processes: (1) at low adsorbed concentrations, BSA exhibited a side-on conformation blocking colloid deposition; (2) at high adsorbed concentrations, BSA adapted to an end-on conformation promoted colloid deposition; and (3) colloid deposition on the BSA layer may progressively generate end-on molecules (sites) by conformation change of side-on BSA, resulting in sustained increasing deposition rates. Generally, the protein layer lowered colloid attenuation by the porous medium, suggesting the overall effect of BSA was inhibitory at the experimental time scale. A mathematical model was developed to interpret the ripening curves. Modeling analysis identified the site generation efficiency of colloid as a control on the ripening rate (declining rate in colloid concentrations), and this efficiency was higher for BSA adsorbed from a more dilute BSA solution. © 2012 Elsevier B.V.

Acidity Characterization of Amorphous Silica-Alumina

Surface characterization of amorphous silica-alumina (ASA) by COads IR, pyridine(ads) IR, alkylamine temperature-programmed desorption (TPD), Cs+ and Cu(EDA)(2)(2+) exchange, H-1 NMR, and m-xylene isomerization points to the presence of a broad range of Bronsted and Lewis acid sites. Careful interpretation of IR spectra of adsorbed CO or pyridine confirms the presence of a few very strong Bronsted acid sites (BAS), typically at concentrations lower than 10 mu mol/g. The general procedure for alkylamine TPD, which probes both Bronsted and Lewis acidity, is modified to increase the selectivity to strong Bronsted acid sites. Poisoning of the m-xylene isomerization reaction by a base is presented as a novel method to quantify strong BAS. The surface also contains a weaker form of BAS, in concentrations between 50 and 150 mu mol/g, which can be quantified by COads IR Cu(EDA)(2)(2+) exchange also probes these sites. The structure of these sites remains unclear, but they might arise from the interaction of silanol groups with strong Lewis acid Al3+ sites. The surface also contains nonacidic aluminol and silanol sites (200-400 mu mol/g) and two forms of Lewis acid sites: (i) a weaker form associated with segregated alumina domains containing five-coordinated Al, which make up the interface between these domains and the ASA phase and (ii) a stronger form, which are undercoordinated Al sites grafted onto the silica surface. The acid catalytic activity in bifunctional n-heptane hydroconversion correlates with the concentration of strong BAS. The influence of the support electronegativity on the neopentane hydrogenolysis activity of supported Pt catalysts is considerably larger than that of the support Bronsted acidity. It is argued that strong Lewis acid sites, which are present in ASA but not in gamma-alumina, are essential to transmit the Sanderson electronegativity of the oxide support to the active Pt phase.

Dry gel conversion of organosilane templated mesoporous silica: from amorphous to crystalline catalysts for benzene oxidation

Mesoporous silica grown using [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride as the mesoporogen in the presence of Fe and Al is X-ray amorphous, but contains very small domains with features of MFI zeolite as evidenced by IR and Raman spectroscopy. When applied as a catalyst, this amorphous sample shows good performance in the selective oxidation of benzene using nitrous oxide. Addition of tetrapropylammonium as structure directing agent to the as-synthesized mesoporous silica and subsequent dry gel conversion results in the formation of hierarchical Fe/ZSM-5 zeolite. During dry gel conversion the wormhole mesostructure of the initial material is completely lost. A dominant feature of the texture after crystallization is the high interconnectivity of micropores and mesopores. Substantial redistribution of low-dispersed Fe takes place during dry gel conversion towards highly dispersed isolated Fe species outside the zeolite framework. The catalytic performance in the oxidation of benzene to phenol of these highly mesoporous zeolites is appreciably higher than that of the parent material.

Isomorphism between ice and silica

Both ice and silica crystallize into solid-state structures composed of tetrahedral building units that are joined together to form an infinite four-connected net. Mathematical considerations suggest that there is a vast number of such nets and thus potential crystal structures. It is therefore perhaps surprising to discover that, despite the differences in the nature of interatomic interactions in these materials, a fair number of commonly observed ice and silica phases are based on common nets. Here we use computer simulation to investigate the origin of this symmetry between the structures formed for ice and silica and to attempt to understand why it is not complete. We start from a comparison of the dense phases and then move to the relationship between the different open (zeolitic and clathratic) structures formed for both materials. We show that there is a remarkably strong correlation between the energetics of isomorphic silica and water ice structures and that this correlation arises because of the strong link between the total energy of a material and its local geometric features. Finally, we discuss a number of as yet unsynthesized low-energy structures which include a phase of ice based on quartz, a silica based on the structure of ice VI, and an ice clathrate that is isomorphic to the silicate structure nonasil.