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 (PrPC) into an abnormally folded and infectious scrapie isoform (PrPSc). We previously showed that peptides derived from the unprocessed N-termini of mouse and bovine prion proteins, mPrP1-28 and bPrP1-30, 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 mPrP1-28 or bPrP1-30 significantly reduce PrPSc 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, mPrP1-28 is amyloidogenic, whereas bPrP1-30 forms smaller oligomeric or non-fibrillar aggregates. Surprisingly, bPrP1-30 induces much higher cytotoxicity than mPrP1-28, 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 PrPSc formation.