Showing papers by "Vadim G. Kessler published in 2012"

Visualization of custom-tailored iron oxide nanoparticles chemistry, uptake, and toxicity.

Abstract: Nanoparticles of iron oxide generated by wearing of vehicles have been modelled with a tailored solution of size-uniform engineered magnetite particles produced by the Bradley reaction, a solvothermal metal–organic approach rendering hydrophilic particles. The latter does not bear any pronounced surface charge in analogy with that originating from anthropogenic sources in the environment. Physicochemical properties of the nanoparticles were thoroughly characterized by a wide range of methods, including XPD, TEM, SEM, DLS and spectroscopic techniques. The magnetite nanoparticles were found to be sensitive for transformation into maghemite under ambient conditions. This process was clearly revealed by Raman spectroscopy for high surface energy magnetite particles containing minor impurities of the hydromaghemite phase and was followed by quantitative measurements with EXAFS spectroscopy. In order to assess the toxicological effects of the produced nanoparticles in humans, with and without surface modification with ATP (a model of bio-corona formed in alveolar liquid), a pathway of potential uptake and clearance was modelled with a sequence of in vitro studies using A549 lung epithelial cells, lymphocyte 221-B cells, and 293T embryonal kidney cells, respectively. Raman microscopy unambiguously showed that magnetite nanoparticles are internalized within the A549 cells after 24 h co-incubation, and that the ATP ligand is retained on the nanoparticles throughout the uptake process. The toxicity of the nanoparticles was estimated using confocal fluorescence microscopy and indicated no principal difference for unmodified and modified particles, but revealed considerably different biochemical responses. The IL-8 cytokine response was found to be significantly lower for the magnetite nanoparticles compared to TiO2, while an enhancement of ROS was observed, which was further increased for the ATP-modified nanoparticles, implicating involvement of the ATP signalling pathway in the epithelium.

High surface area ordered mesoporous nano-titania by a rapid surfactant-free approach

Abstract: Immersion of solid nanorods of the commercial metal–organic precursor [Ti(OCH3)4]4 into boiling water results in their rapid topotactic transformation into rod-shaped colloid crystals built up of uniform crystalline anatase nanoparticles with average particle diameter 5.0 ± 1 nm forming rather regular wormhole-type mesoporosity with average pore diameter 4.1 nm and a record-high surface area and mesopore volume of 288 m2 g−1 and 0.42 cm3 g−1 respectively. This structure emerges through reorganization of the intermediate ordered mesoporous lamellar structure. The distance between lamellae is about 3 nm. They are oriented parallel to the {1 0 0} crystallographic direction in the precursor crystals and originate most probably through contraction and densification of the layers of precursor molecules in the course of the process. Similar mechanisms are observed even for hydrolytic transformation of nanocrystals of other alkoxide precursors, derivatives of volatile alcohols, permitting to achieve surface area up to 350 m2 g−1. The obtained material is completely free from organics, but highly hygroscopic. Powders produced within 3 min show very broad X-ray diffraction peaks, indicating low volume coherence domains, but continued refluxing offers a strongly improved XPD pattern after 10 min and a fully crystalline material with coherence domain equivalent to the individual particle size after only 30 min. The latter material exhibits well defined Ti–Ti distances in the structure typical for a crystalline anatase phase according to EXAFS spectroscopy. It displays strong photochemical activity in destruction of methylene blue dye. When an aqueous dispersion of superparamagnetic Fe3O4 nanoparticles is applied for hydrolysis the product is a magnetic nanocomposite, easily and rapidly removable from solution by a magnet. The produced fully crystalline porous TiO2 possesses attractive characteristics as an adsorbent for water remediation tested through adsorption of dichromate anions.

First principles simulation of reaction steps in the atomic layer deposition of titania: dependence of growth on Lewis acidity of titanocene precursor.

Abstract: It is a common finding that titanocene-derived precursors do not yield TiO2 films in atomic layer deposition (ALD) with water. For instance, ALD with Ti(OMe)4 and water gives 0.5 A/cycle, while TiCp*(OMe)3 does not show any growth (Me = CH3, Cp* = C5(CH3)5). From mass spectrometry we found that Ti(OMe)4 occurs in the gas phase practically exclusively as a monomer. We then used first principles density functional theory (DFT) to model the ALD reaction sequence and find the reason for the difference in growth behaviour. Both precursors adsorb initially via hydrogen-bonding. The simulations reveal that the Cp* ligand of TiCp*(OMe)3 lowers the Lewis acidity of the Ti centre and prevents its coordination to surface O (‘densification’) during both of the ALD pulses. The effect of Cp* on Ti seems to be both steric (full coordination sphere) and electronic (lower electrophilicity). This crucial step in the sequence of ALD reactions is therefore not possible in the case of TiCp*(OMe)3 + H2O, which means that there is no deposition of TiO2 films.

Structural characterization, solution stability, and potential health and environmental effects of the Nano-TiO2 bioencapsulation matrix and the model product of its biodegradation TiBALDH

Abstract: Dispersions of small TiO2 nanoparticles in alcohol, stabilized by surface complexation with protonated triethanolamine ligands, are proposed as bio-encapsulation matrices. They were characterized by TEM and EXAFS spectroscopy, and DLS was used to investigate the nanoparticles stability over time in their pure form and after insertion into aqueous medium. This study reveals unusual structural features that explain the recently demonstrated facile formation of dense encapsulates on the surface of biological objects. In the view of the potentially broad application of this already industrially available material in agriculture as an encapsulation matrix for biocontrol organisms, its potential health and environmental effects were characterized by employing a number of model systems. The potential health effects of the produced stable aqueous dispersions were studied in vitro using A549 and U1810 lung carcinoma cell lines. The nanotitania in the environment is partly bio-digested with the formation of citrate and lactate complexes. The effects on the growth of tobacco pollen grains by the nanotitania and of the ammonium lactato-oxo-titanate (TiBALDH, a product already broadly used in biomineralization studies) were investigated to gain insight into the impact of these materials on the environment and specifically on plant reproduction. TiBALDH was used as a model product of the bio-digestion and its structure has been probed in this work by X-ray powder diffraction and EXAFS spectroscopy. No acute negative bio-effects could be observed for the studied materials at significantly high concentrations, such as 50 μg ml−1 for the viability of human lung cancer cells and up to about 120 μg ml−1 for the growth of pollen grains, corresponding to the conditions of proposed field applications. This observation was contrasted by the apparently high toxicity of the LaAlO3 based nanophosphor which was applied as a positive control.

Rhenium Nanochemistry for Catalyst Preparation

Abstract: The review presents synthetic approaches to modern rhenium-based catalysts. Creation of an active center is considered as a process of obtaining a nanoparticle or a molecule, immobilized within a matrix of the substrate. Selective chemical routes to preparation of particles of rhenium alloys, rhenium oxides and the molecules of alkyltrioxorhenium, and their insertion into porous structure of zeolites, ordered mesoporous MCM matrices, anodic mesoporous alumina, and porous transition metal oxides are considered. Structure-property relationships are traced for these catalysts in relation to such processes as alkylation and isomerization, olefin metathesis, selective oxidation of olefins, methanol to formaldehyde conversion, etc.

Rhenium Nanochemistry for Catalyst Preparation

Abstract: The review presents synthetic approaches to modern rhenium-based catalysts. Creation of an active center is considered as a process of obtaining a nanoparticle or a molecule, immobilized within a matrix of the substrate. Selective chemical routes to preparation of particles of rhenium alloys, rhenium oxides and the molecules of alkyltrioxorhenium, and their insertion into porous structure of zeolites, ordered mesoporous MCM matrices, anodic mesoporous alumina, and porous transition metal oxides are considered. Structure-property relationships are traced for these catalysts in relation to such processes as alkylation and isomerization, olefin metathesis, selective oxidation of olefins, methanol to formaldehyde conversion, etc.

Biocompatible titania hydrogels with chemically triggered release of a photosensitive dye

Abstract: 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin was entrapped into biocompatible hydrogels formed by self-assembling micelles of the titanium dioxide prepared by hydrolysis of titanium ethoxide modified with triethanolamine (TEA). The materials were characterized by their optical and photosensitive properties. The immobilization led to changes of the absorption spectra of the dye and decreased its molar absorption coefficient. The TiO2 matrix did not degrade the entrapped porphyrin upon u.v. irradiation. The formation of TEA–titanium(IV) chelates facilitated a controlled and triggered release of the immobilized dye from the hydrogels in lactate and citrate buffers. The released dye prolonged the sterility of citrate–phosphate buffer and its illumination with visible light inhibited growth of Aspergillus niger.