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The mesoporous silica particles were prepared by the sol–gel method in one-step synthesis, in acidic conditions, from tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), varying the mole ratio of the silica precursors. Nitric acid was used as catalyst at room temperature and hexadecyltrimethyl ammonium bromide (CTAB) as structure directing agent. Optical properties, porosity and microstructure of the materials in function of the MTES/TEOS ratio were evaluated using infrared spectroscopy, nitrogen adsorption and small angle X-ray scattering. All materials showed the ordered pore structure and the high specific surfaces, making them suitable as the drug delivery systems. Drug loading and release tests using ketoprofen were performed to assess their performance for drug delivery applications. The amount of the methylated precursor used in the synthesis had little effect on the drug loading capacity, but had a strong influence on the initial rate of the drug release.

Amyloglucosidase (AMG) from Aspergillus niger was encapsulated in various matrices derived from tetraethoxysilane, methyltriethoxysilane, phenyltriethoxysilane and vinyltriacetoxysilane by different methods of immobilization. The immobilized enzyme was prepared by entrapment in two steps, in one-step and entrapment/deposition, respectively. The activities of the immobilized AMG were assayed and compared with that of the native enzyme. The effects of the organosilaneprecursors and their molar ratios, the immobilization method, the inorganic support (white ceramic, red ceramic, purolite, alumina, TiO2, celite, zeolite) and enzyme loading upon the immobilized enzyme activity were tested. The efficiency of the sol-gel biocomposites can be improved through combination of the fundamental immobilization techniques and selection of the precursors.

Sol-gel method and successive thermal treatments in vacuum and nitrogen atmosphere were employed to synthesize magnetite nanoparticles isolate them with the aid of amorphous silica. Thermogravimetric and differential thermal analyses coupled with mass spectrometry, X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy and vibrating sample magnetometry measurements were performed on the obtained nanocomposites. The effect of atmosphere on the formation of magnetite phase was remarkable.

The purpose of the study was to investigate the appearance of certain microstructures developing in the SiO2/PVA nanocomposite xerogels at different temperatures by small-angle neutron scattering (SANS). The samples were prepared by the alcoxide route of the sol-gel method. The SANS measurements were performed over a q (scattering vector) range from 0.05 to 3.7 nm-1, providing structural information at length scales (2π/q) between approximately 1 and 100 nm. The measured small-angle scattering intensities of silica and silica/PVA samples aged at 60°C and heat-treated at different temperatures, are presented in log-log plots. It is shown that both the molecular mass of organic and the temperature of thermal treatment have strong influence on transition tendency from mass fractal toward surface fractal structures.

Two series of magnetic nanopowders were synthesized at room temperature starting from a mixture of iron II and III precursors, FeSO4 and FeCl3, respectively. Precipitation agents, as KOH and NaOH were used. While the concentration of the added ferrous and ferric solutions ranged between 0.1 M and 0.0125 M, the hydroxide solution concentration was maintained constant (1 M). TEM images of the samples showed that the particles shape changes from quasi spherical to spherical. For both series the crystallite size decreases with iron concentration, from 9 to 2 nm for KOH series and from 10 to 3 nm for NaOH series. Moessbauer Spectroscopy was signaling only Fe3+ in the final spinel product. BET measurements revealed the material mesoporosity and fractal structure of maghemite nanoparticles that explain the unusual high surface area, ~240 m2/g. All the samples actually exhibit superparamagnetic behavior at room temperature with saturation magnetization up to 73 emu/g value closed to those of bulk maghemite. [ABSTRACT FROM AUTHOR]

Here, we focus on the obtaining of mesocrystalline submillimeter-sized (150/50 µm) rhombohedral hematite (α-Fe2O3) by thermal treatment in air of single crystalline submillimeter-sized (150/50 µm) rhombohedrons of ferrous carbonate (FeCO3). Mass spectrometer-coupled thermogravimetric analysis and TGA-MS revealed the chemical reactions occurring during the thermal treatment of ferrous carbonate sample. The X-ray Diffraction (XRD) data sustain that the final product is hematite. The XRD line-profile analysis indicates that the resulted hematite is built of individual ordered crystallites with 66 ± 5 nm average sizes, confirmed by scanning electron microscopy and transmission electron microscopy images. Small-angle x-ray scattering investigation of hematite sample was presented. The log-log plot of scattering intensity decay showed the same slope, α = −3.76, corresponding to both high and low scattering vector regions; the fractal surface isDs = 2.24. This fractality is extended over a range of sizes and can touch high molecular dimensionality. The internal morphology and the synthesis mechanism of the obtained hierarchical superstructure were described. [ABSTRACT FROM AUTHOR]

The present work deals with the synthesis of Fe2O3–SiO2 composites, obtained by embedding iron oxide particles in a silica matrix, through sol–gel method based on hydrolysis and condensation of a silicon alkoxide and thermal treatment. Methods employed in characterisation of the materials obtained at different iron concentration and at suitable thermal treatments are infrared spectroscopy, X-ray diffraction analysis and SEM analysis. In purpose to evaluate magnetic properties of these composites, static magnetic and Mo¨ssbauer spectra measurements were carried out. [Copyright &y& Elsevier]

It is widely accepted that mitochondria contribute to their own damage in the settings of experimental ischemia/reperfusion injury. The aim of the present work was to investigate the degree of mitochondrial dysfunction elicited by an in vivo rat heart model of regional ischemia/reperfusion injury. Mitochondria were isolated from ischemic and non-ischemic zones rat hearts subjected to 30 min of regional ischemia by coronary ligation and 15 min of reperfusion. Oxygen consumption was assessed by polarographic oxymetry in a Clark-type electrode in the presence of complex I substrates (glutamate/malate) and complex II (succinate). State 3 respiration rate and the respiratory control ratio for glutamate/malate were significantly decreased in mitochondria isolated from the ischemic area, suggesting an early alteration of complex I supported respiration (p < 0.01 vs. non-ischemic area). In another set of experiments mitochondrial calcium retention capacity was evaluated by luminescence spectroscopy using the calcium-sensitive probe Calcium Green 5N and mitochondrial swelling was monitored as the decrease in light scattering at 520 nm. In the presence of complex IIdependent substrate, less calcium was required to zone induce permeability transition, suggesting the pre-existence of calcium overload in mitochondria isolated from ischemic zone vs. non-ischemic zone. Mitochondria isolated from the ischemic (vs. non-ischemic) zone presented an increased rate of swelling in the case of complex I supported respiration. These results are suggestive for an early damage to the phosphorylation apparatus at complex I in mitochondria isolated at reperfusion after regional ischemia in the in vivo rat hearts. [ABSTRACT FROM AUTHOR]

Template free, base catalysed sol-gel route (Stöber method) and low power sonic-activated sol-gel process (20 kHz ultrasonic bath) were used to obtain two series of samples. The influence of the concentration of the supplying ammonia solution upon the silica sols stability and solid products properties was followed. The reactants molar ratio TEOS: H2O: ETOH: NH3 of 1: 25: 20: 0.2 was rigorously kept constant. We have examined the influence of adding the ammonia solutions of different concentrations, specifically: 25% NH3, 12% NH3, 6% NH3, and 3% NH3. Either relatively stable colloidal suspensions or precipitates were obtained. The silica sols stability was related to the evolution of the turbidity over time. The resulted solid materials, xerogel's and sonogel's texture and morphology have been studied by using BET, SEM techniques. FT-IR was used to exhibit the main silica bonds. It was observed that by supplying base catalyst of variable concentrations, by changing initial pH of the process, it makes a difference concerning silica suspension behaviour and also in silica particle morphology. The used variable produced distinct effects upon both classic process and resulted xerogels, and sonoactivated sol-gel process and resulted sonogels. For all concentrations of ammonia solution, by classic sol-gel process, silica precipitates were obtained, and under ultrasonic field action, relatively stable translucent silica colloids resulted. [ABSTRACT FROM AUTHOR]

Mitochondria have emerged as key players in cardioprotection against ischemia/reperfusion (I/R) injury. Diazoxide (Dx) has been shown to reduce infarct size in several experimental models through the opening of mitochondrial ATP-dependent potassium channels (mKATP) and also to exert a substrate-dependent effect on mitochondrial respiration. The aim of the present study performed in mitochondria isolated from rat hearts subjected to 30 min global ischemia and 60 min of reperfusion was to investigate the effects of Dx (100 ?M) given at reperfusion on respiratory function. Oxygen consumption was assessed by polarographic oxymetry in a Clark-type electrode. State 3 respiration rate (oxygen uptake during ADP phosphorylation, expressed in natoms oxygen/min/mg mitochondrial protein) and the respiratory control ratio (RCR, the ratio of state 3 and state 2 oxygen uptake rates) were assessed in the presence of complex I substrates (glutamate/malate). Our data showed that RCR was significantly reduced in the non-treated group vs. the group treated with Dx (RCR = 3.45 vs. 4.5; p < 0.05). In a second set of experiments performed in mitochondria isolated from hearts treated with Dx at reperfusion, mitochondrial calcium retention capacity (CRC) was further evaluated by luminescence spectroscopy using the calcium-sensitive probe Calcium Green 5N in the presence of different substrates. The amount of calcium required by ischemic mitochondria to undergo permeability transition was higher, albeit not statistically significant in the presence of CI substrates (glutamate/malate) as compared to CII substrate (succinate). [ABSTRACT FROM AUTHOR]

Spherical silica nanoparticles were synthesized by sol-gel process from tetra-ethylorthosilicate without using template. The TEOS: H2O: ETOH: NH3 mole ratio was n: 0.43: 0.789: 0.06, where n varied in the 0.022÷ 0.31 range. SEM images showed that almost spherical in shape silica nanoparticles were obtained. The synthesized particles have the diameter between 3 and 9 nm and variable surface area, specifically between 13 and 112 m²/g. Pore size distribution was significantly narrower for samples with the higher precursor concentration. The particles size decreases gradually as the concentration of the TEOS increases. The obtained results showed the precursor concentration effects. [ABSTRACT FROM AUTHOR]

Synthetic research related to iron oxide/mesoporous silica nanocomposites has focused on the tuning of the material's properties, such as, the silica shell thickness, pore size and total pore volumes. In this concern, in the paper, we studied the influence of CTAB/SiO2 molar ratio. At first, the iron oxide particles were synthesized by co-precipitation method. Than the resulted iron oxide nanoparticles where coated with silica using cethyl-trimethyl ammonium bromide (CTAB) as template. The coated and uncoated iron oxide samples were submitted to a comparative study. The influence of CTAB/SiO2 molar ratio upon the mentioned properties of the silica shell was obvious. [ABSTRACT FROM AUTHOR]

The studies were focused on the relationship between morphology features and synthesis variables, looking for their implications in the drug loading and release capacities. Increasing the amount of methylated tri-alcoxide toward the tetra-alcoxide precursor caused shrinkage of the hexagonally ordered mesoporous structure and also the reduction of the pore diameters, while the total pore volumes and surface areas remain high and suitable for drug loading. In drug release profiles: silica prepared with the largest amount of hydrophobic precursor retained about twice as much of drug, compared with the sample obtained of pure TEOS.The studies were focused on the relationship between morphology features and synthesis variables, looking for their implications in the drug loading and release capacities. Increasing the amount of methylated tri-alcoxide toward the tetra-alcoxide precursor caused shrinkage of the hexagonally ordered mesoporous structure and also the reduction of the pore diameters, while the total pore volumes and surface areas remain high and suitable for drug loading. In drug release profiles: silica prepared with the largest amount of hydrophobic precursor retained about twice as much of drug, compared with the sample obtained of pure TEOS. [ABSTRACT FROM AUTHOR]

Monoliths of iron oxide-silica aerogel nanocomposites have been synthesized using a novel synthesis route which consists of impregnating silica wet gels with anhydrous iron(II) precursors followed by ethanol supercritical drying of the gels. The process yields aerogels exhibiting high porosity, large surface areas (approximately 900 m2/g), rather low densities (approximately 0.6 g/cm3), and a homogeneous distribution of single-phase maghemite, gamma-Fe2O3, nanoparticles with average sizes in the 7-8 nm range. Remarkably, the gamma-Fe2O3 nanoparticles are obtained in the as-dried state without the need of postannealing. The nanoparticles are mostly superparamagnetic at room temperature but become blocked in a ferrimagnetic state at lower temperatures.