Vukoman Jokanovic

The protection of cells from nitric oxide-mediated apoptotic death by mechanochemically synthesized fullerene (C60) nanoparticles

The influence of fullerene (C(60)) nanoparticles on the cytotoxicity of a highly reactive free radical nitric oxide (NO) was investigated. Fullerene nanoparticles were prepared by mechanochemically assisted complexation with anionic surfactant sodium dodecyl sulfate, macrocyclic oligosaccharide gamma-cyclodextrin or the copolymer ethylene vinyl acetate-ethylene vinyl versatate. C(60) nanoparticles were characterized by UV-vis and atomic force microscopy. While readily internalized by mouse L929 fibroblasts, C(60) nanoparticles were not cytotoxic. Moreover, they partially protected L929 cells from the cytotoxic effect of NO-releasing compounds sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione (GSNO) and 3-morpholino-sydnonimine (SIN-1). C(60) nanoparticles reduced SNP-induced apoptotic cell death by preventing mitochondrial depolarization, caspase activation, cell membrane phosphatidylserine exposure and DNA fragmentation. The protective action of C(60) nanoparticles was not exerted via direct interaction with NO, but through neutralization of mitochondria-produced superoxide radical in NO-treated cells, as demonstrated by using different redox-sensitive reporter fluorochromes. These data suggest that C(60) complexes with appropriate host molecules might be plausible candidates for preventing NO-mediated cell injury in inflammatory/autoimmune disorders.

Ultrasonic spray pyrolysis of TiO2 nanoparticles

Abstract Synthesis of ultrafine spherical TiO 2 particles was achieved by using ultrasonic spray pyrolysis and nanoparticles of TiO 2 (≈2.5nm) as a precursor. The size distribution and morphology of TiO 2 particles obtained after ultrasonic spray pyrolysis were characterized by SEM and STM. Agreement between experimentally obtained results and theoretical calculation of particle size was found.

Synthesis of mullite nanostructured spherical powder by ultrasonic spray pyrolysis

In this paper the synthesis of nanostructured spherical particles of mullite powders by ultrasonic spray pyrolysis is presented. The mullite crystallization and the nanostructure development during heating were examined by infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscope analysis. Comparative analysis of experimentally determined and theoretically calculated particle size distribution, obtained on the basis of three-dimensional (3D) model of spherical/ellipsoidal waves generated by incident ultrasonic field, confirmed that the process of aerosol/powder particle synthesis can be regarded as deterministic process.

Synthesis, morphology, and formation mechanism of mullite particles produced by ultrasonic spray pyrolysis

Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO 3 ) 3 · 9H 2 O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al 2 O 3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO 2 , as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al 2 O 3 between 900 and 1000 °C and its further reaction with amorphous SiO 2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.

Synthesis and formation mechanism of submicrometre spherical cordierite powders by ultrasonic spray pyrolysis

Cordierite powders containing very pure submicrometre spherical particles have been synthesized by the ultrasonic spray pyrolysis. Aqueous solutions of silicic acid, Al(NO3)3·9H2O and MgCl2·6H2O were used as precursors. Scanning electron micrographs have shown that particle surfaces were smooth and the mean particle diameter was 0.834 μm. For the estimation of chemical and phase composition and phase transformation temperatures, differential thermal analysis, thermogravimetric analysis, X-ray diffraction, energy dispersive spectroscopy and infrared analysis have been applied. It was found that during spray pyrolysis, the condensation of silicic acid mostly occurred while aluminium and magnesium ion remained incorported between Si–O–Si chains. By subsequent heating to over 800°C, Si–O–M bonds (M=Al, Mg) were formed. The synthesis of cordierite occurred by the crystallization of μ-cordierite from the amorphous phase at 900°C followed by the phase transformation of μ- into α-cordierite in the temperature range 1100–1200°C.

Influence of synthesis parameters on the structure of boehmite sol particles

Abstract Influence of the type and amount of acid, used for aluminium hydroxide peptization, on the crystallinity and specific surface area of the dispersed phase of boehmite sols as well as the pH of sols, was investigated. The ratio n (HCl)/ n (Al(OH) 3 )=0.1 was found to be optimum for aluminium hydroxide peptization. Higher acid to aluminium hydroxide ratio leads to a decrease in specific surface area and crystallinity of the solid phase as well as in pH of sols. Increase in counter ion (Cl − ) concentration causes a shift in d values of (020) crystallographic plane, from the value corresponding to boehmite to that for pseudoboehmite, and a decrease in specific surface area of the sol solid phase. Using HNO 3 as a peptizing agent, greater crystallinity and higher specific surface area values of the solids were registered.

Influence of aerosol formation mechanism by an ultrasonic field on particle size distribution of ceramic powders

Abstract Aerosol droplet genesis by ultrasonic atomization has been theoretically studied using a model for three-dimensional spherical/ellipsoidal waves generated by excitation of a system of given geometry by forced frequency of an ultrasonic oscillator. Analyzing the harmonic function of the rate potential, an equation has been derived that defines the mean diameter and the distribution spectrum of aerosol droplets formed at the surface of a liquid. Comparison has been made between the calculated values for the mean particle sizes and their distribution with those obtained experimentally for Al 2 O 3 , mullite and cordierite powders synthesized from different precursors.

Tailor made synthesis of Q-TiO2 powder by using quantum dots as building blocks

Abstract A simple synthetic procedure based on ultrasonic spray pyrolysis and usage of TiO 2 quantum dots as building blocks leads to the formation of submicronic TiO 2 spheres which preserved optical and catalytic properties of the constituting elements. The methodology is not limited to semiconductor quantum dots, but provides general procedures for the rational design of novel and potentially useful composite materials.

Modeling of nanostructural design of ultrafine mullite powder particles obtained by ultrasonic spray pyrolysis

Abstract In this paper, a model of substructure design of mullite powder particles obtained by spray pyrolysis in the field of ultrasound excitation is described. Based on this model, the size of subparticles (nanoparticles) constituting the substructure of so obtained powder is described and compared to experimentally determined values. High agreement between theoretical and experimental values confirmed the value of the theoretical model and its wide applicability in estimation of particle substructure for mullite powder obtained under the conditions of the periodical physical field activity.

Synthesis of nanostructured mullite from xerogel and aerogel obtained by the non-hydrolytic sol-gel method

Abstract Synthesis and nanostructure evolution of mullite (3Al2O3.2SiO2) from xero- and aerogels, obtained by the non-hydrolytic sol-gel process are described. Mullite crystallization and gel nanostructure evolution after heat treatment were studied by differential-thermal, x-ray diffraction, infrared and thermomicroscopic analysis as well as by scanning electron microscopy. Crystallization of mullite from both gels starts at 900 °C and further increase in temperature increases the size of crystallites formed from 32 to 100 nm and 12 to 20 nm in the case of xero- and aerogels, respectively. Accelerated sintering of aerogels in the temperature range 900 to 1000° C is a consequence of the viscous flow of the amorphous SiO2 phase.