Andrea Siska

Production of nanotubes by the catalytic decomposition of different carbon-containing compounds

Carbon nanotubes were prepared in the catalytic decomposition of different carbon containing compounds over supported transition metal catalysts. Besides acetylene, ethylene, propylene, acetone, n-pentane, methanol, toluene, and methane were tested and each resulted in carbon nanotube formation. The quality of as-made nanotubes was investigated by TEM and was found to be at least as good as obtained in acetylene decomposition. Ethylene and propylene showed somewhat lower reactivity in the buckytube formation with respect to acetylene, simultaneously suppressed formation of amorphous carbon on the outer surface was found.

Reactivity of different kinds of carbon during oxidative purification of catalytically prepared carbon nanotubes

In the purification procedure of catalytically prepared carbon nanotube samples, the oxidative removal of amorphous carbon was investigated. Oxidation was carried out by KMnO4, H2O2, O3 or HClO4. The selectivity of the amorphous carbon burning reaction was studied as a function of the reaction temperature by transmission electron microscopy. The advantages of the different methods are as follows: although oxidation by KMnO4 in an acidic suspension provides nanotubes free of amorphous carbon, and can easily be controlled, it must be followed by filtration and cc HCl treatment in order to dissolve the MnO2 formed during the reaction. Oxidation with hydrogen peroxide does not give undissolved residue on the surface of the tubes. Ozone treatment produces gaseous by-products, but requires higher reaction temperature. This method is more difficult to control. During oxidation, competitive oxidation always takes place: carbon nanotubes and amorphous carbon react simultaneously. While amorphous carbon can be attacked from any direction, carbon nanotubes can be oxidized only from the ends.

ON THE ROLE OF CATALYST, CATALYST SUPPORT AND THEIR INTERACTION IN SYNTHESIS OF CARBON NANOTUBES BY CCVD

The catalytic growth of carbon nanotubes was investigated from the point of view of reaction mechanism. A great variety of catalyst supports (silica gel, zeotype materials, alumina, etc.) with different pore diameter was tested in acetylene decomposition at 1000 K. Quality and existence of carbon deposit was followed by transmission electron microscopy and the state of catalyst was investigated by in situ X-ray photoelectron spectroscopy measurements. It was proved that only catalyst particles deposited on the external surfaces of porous support could take part in the catalytic carbon nanotube formation.

Mechanical and chemical breaking of multiwalled carbon nanotubes

Catalytically prepared multiwall carbon nanotubes (MWNTs) were cut and functionalised by mechanical and/or chemical methods. Products were characterised by transmission electron microscopy, infrared spectroscopy and BET method. It can be concluded that physical and chemical breaking procedures complete each other very well. With certain MWNT samples containing surface oxides preliminary investigations were done for testing them as catalyst support.

XPS characterisation of catalysts during production of multiwalled carbon nanotubes

Characterisation of alumina supported catalysts was performed by TEM and XPS spectroscopy during formation of multiwalled carbon nanotubes from acetylene at 1000 K. TEM images showed that thick carbon fibres (outer diameter is around 20–40 nm) were generated on Fe/Al2O3 and Co/Al2O3 samples. The only sample producing carbon nanotubes with an average diameter of 8–12 nm was the bimetallic CoFe/Al2O3. XPS spectra revealed that Fe–Co alloy formed during the interaction of CoFe/Al2O3 and acetylene at 1000 K.

The Crucial Role of Early Mitochondrial Injury in L-Lysine-Induced Acute Pancreatitis

AIMS Large doses of intraperitoneally injected basic amino acids, L-arginine, or L-ornithine, induce acute pancreatitis in rodents, although the mechanisms mediating pancreatic toxicity remain unknown. Another basic amino acid, L-lysine, was also shown to cause pancreatic acinar cell injury. The aim of the study was to get insight into the mechanisms through which L-lysine damages the rat exocrine pancreas, in particular to characterize the kinetics of L-lysine-induced mitochondrial injury, as well as the pathologic responses (including alteration of antioxidant systems) characteristic of acute pancreatitis. RESULTS We showed that intraperitoneal administration of 2 g/kg L-lysine induced severe acute necrotizing pancreatitis. L-lysine administration caused early pancreatic mitochondrial damage that preceded the activation of trypsinogen and the proinflammatory transcription factor nuclear factor-κB (NF-κB), which are commonly thought to play an important role in the development of acute pancreatitis. Our data demonstrate that L-lysine impairs adenosine triphosphate synthase activity of isolated pancreatic, but not liver, mitochondria. INNOVATION AND CONCLUSION Taken together, early mitochondrial injury caused by large doses of L-lysine may lead to the development of acute pancreatitis independently of pancreatic trypsinogen and NF-κB activation.

VELOCITY OF PROPAGATION IN REACTION-DIFFUSION FRONTS OF THE CHLORITE-TETRATHIONATE REACTION

The effect of the initial concentration of reactants on the velocity of chemical fronts in the acid-catalysed chlorite oxidation of tetrathionate was investigated both numerically and experimentally. Based on a simple two-variable model an expression for front velocity as a function of concentration and diffusion coefficient of reactants was developed which can quantitatively describe the observed velocity dependence in slight chlorite excess.

Production of Carbon Nanotubes on Different Metal Supported Catalysts

Multiwall carbon nanotubes have been prepared by catalytic chemical vapor deposition (CCVD) method in high yield using various metals supported on different supports. Measurements by transmission electron microscopy (TEM) revealed the presence of high quality nanotubes on each catalyst, however, comparing the different catalysts in nanotube production it can be stated that beyond metals, the support also affects both the quality and the quantity of nanotubes.

Characterization of polyamine homeostasis in l-ornithine-induced acute pancreatitis in rats

Objectives: l-Ornithine is a precursor of polyamine synthesis that is essential for cell survival. In contrast, intraperitoneal (IP) administration of a large dose of l-ornithine results in death of pancreatic acinar cells in rats. We investigated changes in pancreatic and extrapancreatic polyamine homeostasis after injection of l-ornithine and tested the effects of the stable polyamine analogue methylspermidine (MeSpd) on l-ornithine-induced pancreatitis. Methods: Male Wistar rats were injected IP with 3 g/kg l-ornithine and were untreated, pretreated, or treated with 50 mg/kg MeSpd IP. Rats were killed after 0 to 168 hours for determinations of polyamines and activities of ornithine decarboxylase and spermidine/spermine N1-acetyltransferase (SSAT). Pancreatitis severity was assessed by measuring standard laboratory and histological parameters. Results: Injection of l-ornithine paradoxically induced pancreatic spermidine catabolism, possibly via activation of SSAT, after (>6 hours) appearance of the first histological signs of acute pancreatitis. Polyamine levels generally increased in the lung and liver with the exception of lung spermidine levels, which decreased. Methylspermidine did not influence polyamine levels and SSAT activity and did not ameliorate the severity of l-ornithine-induced pancreatitis. Conclusions: l-Ornithine-induced pancreatitis was associated with activation of pancreatic polyamine catabolism. However, administration of a metabolically stable polyamine analogue did not affect disease severity.Abbreviations: ASAT - aspartate aminotransferase, HSP72 - heat shock protein 72, IL-1&bgr; - interleukin 1&bgr;, IP - intraperitoneal(ly), MeSpd - 1-methylspermidine, MPO - myeloperoxidase, N1-acetyltransferase, ODC - ornithine decarboxylase, PS - physiological saline, PW/BW - pancreatic weight/body weight ratio, SSAT - spermidine/spermine

The establishment of tocopherol reference intervals for Hungarian adult population using a validated HPLC method

Evidence suggests that decreased α-tocopherol (the most biologically active substance in the vitamin E group) level can cause neurological symptoms, most likely ataxia. The aim of the current study was to first provide reference intervals for serum tocopherols in the adult Hungarian population with appropriate sample size, recruiting healthy control subjects and neurological patients suffering from conditions without symptoms of ataxia, myopathy or cognitive deficiency. A validated HPLC method applying a diode array detector and rac-tocol as internal standard was utilized for that purpose. Furthermore, serum cholesterol levels were determined as well for data normalization. The calculated 2.5-97.5% reference intervals for α-, β/γ- and δ-tocopherols were 24.62-54.67, 0.81-3.69 and 0.29-1.07 μm, respectively, whereas the tocopherol/cholesterol ratios were 5.11-11.27, 0.14-0.72 and 0.06-0.22 μmol/mmol, respectively. The establishment of these reference intervals may improve the diagnostic accuracy of tocopherol measurements in certain neurological conditions with decreased tocopherol levels. Moreover, the current study draws special attention to the possible pitfalls in the complex process of the determination of reference intervals as well, including the selection of study population, the application of internal standard and method validation and the calculation of tocopherol/cholesterol ratios.