Iron-substituted cubic silsesquioxane pillared clays: Synthesis, characterization and acid catalytic activity

Novel pillared structures were developed from the intercalation of iron-substituted cubic silsesquioxanes in a sodium and an acid-activated montmorillonite nanoclay and evaluated as acid catalysts. Octameric cubic oligosiloxanes were formed upon controlled hydrolytic polycondensation of the corresponding monomer (a diamino-alkoxysilane) and reacted with iron cations to form complexes that were intercalated within the layered nanoclay matrices. Upon calcination iron oxide nanoparticles are formed which are located on the silica cubes (pillars) and on the surfaces of the clay platelets. Acid activation of the nanoclay was performed in order to increase the number of acid active sites in the pristine clay and thus increase its catalytic activity. A plethora of analytical techniques including X-ray diffraction, thermal analyses, Fourier transform infrared, electron paramagnetic resonance, Raman, Mössbauer and X-ray photoelectron spectroscopies and porosimetry measurements were used in order to follow the synthesis steps and to fully characterize the final catalysts. The resulting pillared clays exhibit a high specific area and show significant acid catalytic activity that was verified using the catalytic dehydration of isopropanol asa probe reaction.

Cytotoxicity of prion protein-derived cell-penetrating peptides is modulated by pH but independent of amyloid formation

Prion diseases are associated with conversion of cellular prion protein (PrP^C) into an abnormally folded and infectious scrapie isoform (PrP^Sc). We previously showed that peptides derived from the unprocessed N-termini of mouse and bovine prion proteins, mPrP_1-28 and bPrP_1-30, function as cell-penetrating peptides (CPPs), and destabilize model membrane systems, which could explain the infectivity and toxicity of prion diseases. However, subsequent studies revealed that treatment with mPrP_1-28 or bPrP_1-30 significantly reduce PrP^Sc levels in prion-infected cells. To explain these seemingly contradictory results, we correlated the aggregation, membrane perturbation and cytotoxicity of the peptides with their cellular uptake and intracellular localization. Although the peptides have a similar primary sequence, mPrP_1-28 is amyloidogenic, whereas bPrP_1-30 forms smaller oligomeric or non-fibrillar aggregates. Surprisingly, bPrP_1-30 induces much higher cytotoxicity than mPrP_1-28, indicating that amyloid formation and toxicity are independent. The toxicity is correlated with prolonged residence at the plasma membrane and membrane perturbation. Both ordered aggregation and toxicity of the peptides are inhibited by low pH. Under non-toxic conditions, the peptides are internalized by lipid-raft dependent macropinocytosis and localize to acidic lysosomal compartments. Our results shed light on the antiprion mechanism of the prion protein-derived CPPs and identify a potential site for PrP^Sc formation.

Identification of selective oxidation of TiC/SiC composite with X-ray diffraction and Raman spectroscopy

Open cell 3D titanium carbide/silicon carbide (TiC/SiC) composite was oxidised to titanium oxide/silicon carbide (TiO

Influence of decomposition time and H2 pressure on properties of unsupported ammonium tetrathiomolybdate-derived MoS2 catalysts

Background

Molybdenum sulfide (MoS2) catalysts to be used for hydrodesulfurization (HDS) processes were prepared via the reductive thermal decomposition of ammonium tetrathiomolybdate at fixed temperature (653 K) by varying decomposition times and H2 pressures. Both parameters were found to strongly influence textural and catalytic properties of the resulting MoS2 catalysts.

Methods

Nitrogen sorption, FT-IR, and XRD analyses revealed the effect of varying decomposition times (3 to 7 h) and H2 pressure (20 to 1,000 psig) on the morphology and structure of the catalysts. Dibenzothiophene (DBT) was used to assess catalytic efficiency for HDS reactions.

Results

The influence of time on specific surface was minimal at low pressures but increased at higher decomposition pressures. Vibrational energies of Mo-S bonds in FT-IR indicate that MoS2 catalysts prepared at higher pressures exhibit weaker Mo-S bonds. Analysis of XRD patterns point towards an increase in stacking and crystallite size with increasing pressure; interlayer rotation about both the a- and c-axes of the stacks was also observed. Catalytic testing results show that conversion increases at higher values of decomposition time and pressure. Partially hydrogenated products were also observed at higher pressures, and the ratio of partially to fully hydrogenated DBT was calculated as an additional measure of catalytic efficiency.

Conclusions

Decomposition time and H2 pressure during ammonium tetrathiomolybdate (ATM) thermal decomposition have a significant impact on the morphological and catalytic properties of the derived MoS2 catalysts. Samples prepared for 5 h at 1,000 psig exhibited the highest conversion of DBT and the lowest ratio of partially to fully hydrogenated products.

Interactions, morphology and thermal stability of graphene-oxide reinforced polymer aerogels derived from star-like telechelic aldehyde-terminal benzoxazine resin

Graphene oxide (GO)-reinforced nanocomposite aerogels of polybenzoxazine preparedviafreeze-drying of GO suspensions in benzoxazine precursor solutions have been studied.

Effect of solvent on the uncatalyzed synthesis of aminosilane-functionalized graphene

Toluene affects the distribution of APTS on the surface of thermally reduced graphene during the catalyst free silylation.