Marios S. Katsiotis

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

Uncatalyzed functionalization of thermally reduced graphene (TRG) with 3-aminopropyltriethoxy silane (APTS) is reported and the effect of the solvent on selective functionalization is discussed. The chemical, morphological and thermal properties of the functionalized TRG (f-TRG) have been studied using FTIR, XPS, EELS, Raman spectroscopy, TEM, and TGA. Our results indicate that the use of organic solvent during the silylation reaction not only increases grafting yield from 7 to 8 atomic% of Si attachment but also directs APTS groups to the edges of TRG as revealed using energy filtered TEM elemental mapping. A reaction mechanism based on attachment of the silane groups on the TRG surface through residual, surface bound phenolic and carbonyl groups is proposed and discussed. The present approach provides an economical route for mass production of APTS-f-TRG and sheds light on the role of organic solvents in silane functionalization of graphene.

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 prepared via freeze-drying of GO suspensions in benzoxazine precursor solutions have been studied. The synthesis of GO is confirmed using Raman and Fourier transform infrared (FT-IR) spectroscopy. The benzoxazine monomer (SLTB(4HBA-t403)) has been synthesized using 4-hydroxybenzaldehyde as a phenolic component, paraformaldehyde, and tri-functional polyetheramine (Jeffamine T-403) as an amine source. The chemical structure of the benzoxazine monomer is confirmed by nuclear magnetic resonance (1H-NMR) spectroscopy and FT-IR. The interactions of GO and SLTB(4HBA-t403) have been investigated using FT-IR. The morphological and thermal stability of nanocomposite aerogels are examined and compared with the neat polybenzoxazine aerogel. The structures of the aerogels and the effect of GO on the morphology of the aerogels are studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of GO on the ring-opening polymerization of benzoxazine is also evaluated using differential scanning calorimetry (DSC) whereas the thermal stability of the nanocomposite aerogels is characterized by thermogravimetric analysis (TGA).

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.

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 (TiO2/SiC) following different temperature profiles in a thermal gravimetric analysis (TGA) instrument in continuous air-flow and static air (oven) environments. The TiC oxidation to anatase, starting at temperatures over 450°C, was confirmed by Raman spectroscopy and X-Ray diffraction (XRD). By increasing the temperature, the mass fraction of anatase diminished, while the mass fraction of rutile increased. SiC oxidation started at 650°C when a mixture of TiO2/SiO2/SiC could be observed by Raman, XRD and HRTEM.