O. S. Ivanova

Nanocrystalline ceria based materials—Perspectives for biomedical application

Nanocrystalline ceria possesses a unique complex of physical and chemical properties making it highly bioactive material. In this review, modern data on the action of nanocrystalline ceria on cells, micro- and macroorganisms are analyzed. Special attention is paid to the analysis of the factors affecting protective properties of CeO2 with respect to the living systems.

Panthenol-stabilized cerium dioxide nanoparticles for cosmeceutic formulations against ROS-induced and UV-induced damage.

A method of panthenol-stabilized cerium dioxide nanoparticles synthesis was developed and their effect on the survival rate of human epidermoid cancer cells HEp-2 and diploid epithelial swine testicular cell line (ST-cells) under oxidative stress conditions induced by hydrogen peroxide introduction and UV irradiation was studied. The results obtained indicate that the use of panthenol as a stabilizer supposedly provides a substantial increase in the efficiency of protection. The degree of protection is determined by panthenol-to-ceria molar ratio. The combination of panthenol and nano-ceria protects biological objects under study from reactive oxygen species (ROS) and UV-irradiation more effectively than individual panthenol or ceria. The protective action of panthenol-stabilized cerium dioxide nanoparticles depends strongly on their composition and the means of their application.

High-yield microwave synthesis of layered Y2(OH)5NO3·xH2O materials

A novel, facile, and versatile microwave-assisted method of high-yield synthesis of layered rare earth hydroxo compounds (LRHs) is proposed. Layered yttrium hydroxonitrates synthesized by the microwave-assisted technique crystallize in the form of thin hexagonal plates aggregated into spheroidal particles. Depending on the conditions of microwave-assisted hydrothermal synthesis, the formation of several phases differing in interplanar spacing along the [00l] direction is possible. The materials obtained are shown to possess good anion-exchange properties. This work provides a route to large-scale synthesis of LRH-based advanced materials.

Microwave-hydrothermal synthesis of gadolinium-doped nanocrystalline ceria in the presence of hexamethylenetetramine

A new method is proposed for producing nanodisperse ceria-based solid solutions, involving microwave-hydrothermal (MW-HT) treatment of aqueous solutions containing salts of cerium and dopant elements and hexamethylenetetramine (HMTA). The specifics of HMTA hydrolysis under hydrothermal conditions are studied. X-ray and electron diffraction, Raman spectroscopy, and transmission electron microscopy are used to analyze the physicochemical characteristics of Ce1 − xGdxO2 − x/2 (x = 0.10, 0.15, 0.20) nanocrystalline solid solutions produced using the new method.

Synthesis and antioxidant activity of biocompatible maltodextrin-stabilized aqueous sols of nanocrystalline ceria

A novel method is proposed for preparing biocompatible aqueous CeO2 sols, which allows purposefully adjusting particle sizes and biochemical properties of nanocrystalline ceria (NC). The usefulness of this method for preparing aqueous sols of Ce1 − xGdxO2 − x/2 solid solutions is demonstrated. Nanocrystalline ceria has been demonstrated to have a size-dependent activity in hydroxyl radical inactivation and in protecting mouse fibroblast cells (L929) from oxidative stress induced by hydrogen peroxide administration.

Layer-by-layer assembly of porphyrin-based metal–organic frameworks on solids decorated with graphene oxide

Fabrication of metal–organic frameworks (MOFs) as films on surfaces is a challenging and actively developed field in the context of potential applications of surface-integrated MOFs (SURMOFs) in sensing, catalysis and molecular electronics. Herein, we report a method for the preparation of composites of graphene oxide (GO) and zinc tetracarboxyphenyl porphyrin SURMOFs, which are potentially useful as synergetic catalysts on planar solid supports. The SURMOF films were assembled via layer-by-layer coordination of zinc porphyrins with ZnAc2 clusters on the ultrathin surface coatings of GO. We found that non-covalent adsorption of zinc acetate on the GO films is essential for anchoring porphyrin molecules in the growth-initiating template layer. UV-vis spectroscopy provided evidence for a stepwise assembly of the deposited SURMOF films. By using a combination of X-ray diffraction, scanning electron microscopy and atomic force microscopy methods, we show that the resulting GO-associated SURMOFs exhibit a leaflet-like planar morphology with out-of-plane periodicity. Because of the influence of the well-defined surface geometry, the molecular organization in thin SURMOFs is different from that of synthetic bulk materials with a similar composition. The results of BET method measurements suggest that the fabricated SURMOF films have exceptionally large surface areas and adsorption capacities. Our results provide a basis for new types of composite SURMOF structures using GO surface coatings as growth-guiding scaffolds for metal–organic coordination networks integrated with various solid supports.

Nanocrystalline ceria: a novel material for electrorheological fluids

We report on the preparation of novel electrorheological (ER) fluids based on a nanocrystalline ceria suspension in polydimethylsiloxane (PMS-20 silicone oil). Dielectric relaxation spectra of ER fluids were analyzed in the frequency range from 25 Hz to 106 Hz; the values of dielectric permittivity, dielectric loss tangents and tensile strengths of the prepared ER fluids in applied external electric fields up to 5 kV mm−1 were measured. Relaxation characteristics of the dielectric spectra were interpreted in terms of the Cole–Davidson model. The results obtained indicate that the ceria-based materials exhibit excellent ER performance, which depends strongly on the CeO2 concentration in the fluids. High tensile stress values (more than 20 kPa) were registered for ceria-based ER fluids in 5 kV mm−1 static electric fields.

The dielectric properties and flow of electrorheological fluids based on polymer-coated nanodispersed barium tetraacetate titanyl particles upon a dynamic shear in electric fields

The shear stress in flowing electrorheological fluids consisting of PMS-20 poly(dimethylsiloxane) filled with nanodispersed barium tetraacetate titanyl particles coated with polymers (polyethyleneimine, poly(ethylene glycol), and polyethyloxazoline) has been studied as depending on the strengths of direct- and alternating-current (f = 50 Hz) electric fields. Results of analyzing the dielectric spectra of electrorheological fluids in a frequency range of 25–106 Hz have been presented. The values of the shear stress in the flowing fluids as depending on the nature of a polymer adsorbed on the particle surface decrease in a series corresponding to a reduction in the Maxwell–Wagner relaxation times of the suspensions. The current-voltage characteristics of the electrorheological fluids at high voltages (up to 5 kV) indicate the realization of the mechanism of currents limited by the space charge. The influence of an adsorbed polymer on the magnitude of the electrorheological effect is reduced to blocking polar groups on the particle surface and variations in the conductivity, effective dielectric permittivity, and loss tangents of filler materials. An increase in the contribution from these factors leads to a gradual decrease in the magnitude of the electrorheological effect.

Radioprotective effects of ultra-small citrate-stabilized cerium oxide nanoparticles in vitro and in vivo

A comprehensive study of the radioprotective action mechanisms of ultra-small, citrate-stabilized, nanocrystalline cerium oxide (CeO2 nanoparticles, nanoceria) in vitro and in vivo was carried out. CeO2 nanoparticles were shown to significantly reduce the levels of hydrogen peroxide and hydroxyl radicals in aqueous solutions under X-ray irradiation. Pretreatment of primary mouse fibroblasts by CeO2 nanoparticles in a wide range of concentrations (10−5 to 10−9 M) protects cells from radiation-induced oxidative stress, maintaining a high level of dehydrogenase activity. A protective effect of CeO2 nanoparticles is also manifested in a decrease in the number of apoptotic cells and the level of reactive oxygen species (ROS) in a culture of primary mouse fibroblasts in vitro, as well as in a significant reduction (up to 50% of the control) of cytogenetic damage of mouse bone marrow in vivo. The intraperitoneal administration of CeO2 nanoparticles (200 nM) increased the rate of survival of mice exposed to X-ray radiation at a lethal dose, both in the prophylactic and the therapeutic schemes of administration, testifying the protection at the molecular, cellular and organism levels. The physical, chemical and biological origins of the protective action of CeO2 nanoparticles upon exposure of living systems to ionizing radiation in vitro and in vivo are discussed.

Effect of high intensity ultrasound on the mesostructure of hydrated zirconia

We report structural changes in amorphous hydrated zirconia caused by high intensity ultrasonic treatment studied by means of small-angle neutron scattering (SANS) and X-ray diffraction (XRD). It was established that sonication affects the mesostructure of ZrO2×xH2O gels (i.e. decreases their homogeneity, increases surface fractal dimension and the size of monomer particles). Ultrasound induced structural changes in hydrated zirconia governs its thermal behaviour, namely decreases the rate of tetragonal to monoclinic zirconia phase transition.