Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials
Founded at 2009

Editor’s column

Synthesis and study of the structure of lanthanum (III) compounds and cerium (III) with aspartic acid

Abstract: A significant part of modern research is devoted to synthesis and study of the structure of compounds of rare earth elements with bioligands – these are those ligands that participate in biochemical processes. Compounds of rare earth elements with amino acids are of particular interest to study, since they are the most important bioligands, natural nanoscale molecules. In the course of the work, compounds of lanthanum (III) and cerium (III) with aspartic acid were synthesized. White crystalline precipitates were obtained for the «La-Asp» (1:2) and «Ce-Asp» (1:3) systems. With the help of optical microscopy, the fundamental difference between the crystals of synthesized compounds (in shape and size) from the crystals of the starting substances used for synthesis is proved. The results of IR-Fourier spectroscopy showed that metal ions interact with the carboxyl group of aspartic acid. The results obtained during the spectrophotometric analysis of the filler fluid for the «La-Asp» system (1:2) made it possible to simulate the spatial structure of this compound taking into account the amount of aspartic acid bound to lanthanum (III) ions. The synthesized compounds are promising for their further use in medicine.

Gate dielectric nitrization and effect on changes in the density of interlayer states of MOS structures

Abstract: The processes occurring in the silicon-oxygen-nitrogen system are of great practical importance, since dielectric layers made from materials of this system are widely used as barriers to the penetration of impurities, elements of storage capacitors, field insulating layers, etc. Interest in the creation of such dielectrics has increased in connection with the use of the rapid thermal annealing stage in technological processes, which are accompanied by the appearance of fast surface states and mechanical stresses on the interface. As a result of the study, it was determined that the change in the threshold voltage in MDS structures is associated with the capture of electrons by the traps formed in the bulk of the semiconductor. MDS structures with nitrided oxide have better stability than conventional oxide. Studies have shown that the suppression of the formation of states at the interface depends on the degree of nitriding. The characteristics of MDS structures under the influence of irradiation substantially depend on the temperature and duration of fast thermal nitrization.

Effect of free valence on the electronic structure of n-alcohol radicals

Abstract: The paper presents the results of a study of the effect of free valence (when a hydrogen atom is separated) on the electronic structure of n-alcohol radicals by the example of radicals of nheptanol derivatives (C●H2(CH2)6OH, CH3C●H-(CH2)5OH, C2H5C●H-(CH2)4OH, C3H7C●H-(CH2)3OH, C4H9C●H-(CH2)2OH, C5H11C●H-CH2OH, C6H13C●H-OH, C7H15-O●). Geometry optimization and the electron density distribution in these compounds was obtained by the density functional method B3LYP/6-311++G(3df,3pd) 6d 10f. The electronic structure of the selected molecules and radicals was investigated within the framework of the «quantum theory of atoms in a molecule» (QTAIM): the electronic parameters of atoms and atomic groups were calculated, the spin density distribution was studied, the concepts of «radical center» and «free valence» were quantitatively characterized. The inductive effect and the tolerability of atomic groups are considered, and a qualitative scale of group electronegatives is compiled. The disturbing effect of various atomic groups, including those containing free valence, on the hydrocarbon chain is compared by comparing the integral parameters of the groups included in the compounds under study with the parameters of the «standard» groups.

Green synthesis of silver nanoparticles. Complementary techniques for characterization

Abstract: The work presents the results of green synthesis (biosynthesis) of silver nanoparticles using aqueous extracts of maple and oak leaves. The efficiency of the synthesis, size and shape of the formed nanoparticles were studied using UV-visible spectroscopy, dynamic light scattering, atomic force microscopy and scanning electron microscopy techniques. It was found that the formation of silver nanoparticles is accompanied by the appearance of a plasmon resonance band in the electronic spectra of aqueous extracts, the maximum of which depends on the concentration of silver nitrate and is in the range of ~420-429 nm in the spectra of maple leaves, and in the spectra of oak extracts there is a shift towards longer wavelengths ~425-435 nm, which correspond to the formation of nanoparticles of larger size. According to the dynamic light scattering data, the size of nanoparticles in the maple extracts is of about 60-68 nm and in the oak samples of ~107 nm. The differences in the size and shape of nanoparticles obtained in the maple and oak phytoextracts detected by atomic force microscopy and scanning electron microscopy are explained by the different composition of bioactive substances in the plants involved in the reduction of silver ions and stabilization or modification of the surface of silver nanoparticles.

Evaluation of the properties of the fucoidan/Fe3O4 nanocomposite as a transport agent of covalently bound molecular cargo

Abstract: Magnetically controlled transport of drugs with targeted release of molecular cargo expands the possibilities of clinical therapy. This article explores the possibility of creating nanoparticles based on fucoidan modified with magnetite for biomedical purposes. The possibility of immobilizing a modelling fibrinolytic enzyme with a cross-linking agent was studied. The maximum loading of the enzyme is 2.06±0.09% of the mass. The particle size with immobilized alteplase according to scanningelectron microscopy was 94.4±24.3 nm, hydrodynamic diameter – 370 nm, zeta potential – -1.66±0.06 mV. The saturation magnetization of the sample is 6 emu/g. To understand the mechanisms of molecular load release, five kinetic models were applied to the results obtained: zero order, Weibull, Hill equation, Higuchi, Korsmeyer-Peppas. The use of mathematical modeling showed that the best model for describing this process is the Korsmeyer-Peppas kinetic equation (r2 = 0.97), and the release process is controlled by the Fick diffusion. The resulting biocomposite material is a promising candidate as a nanocarrier for an enzymatic agent.

Mechanism behind structural changes accompaning the solid-state polymerization in the molybdenumvanadium mixed oxide films

Abstract: In this paper we investigate the changes in the surface topology of inorganic polymerderived films resulted from photostimulated polymerization. With the use of the atomic-force microscopy, the surface structure changes of mixed molybdenum-vanadium oxide thin films (V2O5:MoO3 = 3:2) resulted from the UV light-induced polymerization was investigated. The analysis of atomic-force images evidenced that the solid-state polymerization in the mixed oxide films obtained by condensation of corresponding oxoacids occurs through 3D mechanism. As the result of exposure, MoO3/V2O5 films lose the intrinsic anisotropy which is due to the directional agglomeration of belt-like mixed oxide oligomers. The photopolymerization processes in the mixed oxide film yield agglomerates of nuclei built from the faceted nanometer-sized pseudocrystallites. The exposure is also accompanied with solid-state recrystallization of initially amorphous oxide resulting in the rougher relief of the exposed film. The selective acidic etching uncovers the latent structure of the film, this etching being accompanied with pseudocrystallite dispergation that results in the smoothing of the microrelief of the oxide film surface. These structural features of photosensitive mixed oxide MoO3/V2O5 films facilitate their application as the inorganic photoresists.

Peculiarities of texture formation in strontium hexaferrite-based materials when produced from organic nitrate precursors

Abstract: The processes of strontium hexaferrite (permanent magnet material) fabrication in combustion reactions followed by heat treatment of organic nitrate precursors containing glycine or polyvinyl alcohol have been studied. The formation of iron-glycine complexes of organic precursor components affects the formation of the morphology of the obtained samples. When using glycinecontaining systems during combustion, a branched fibrous texture of the material with extended internal cavities with elongated oxide particles emerges. Such samples have a higher coercivity; the external magnetic field has no significant influence on the texture formation during combustion. It was established that charges are generated in precursors during their combustion, which manifests itself in the appearance of a potential difference between the ground and the precursor. In this case, the appearance of lower intensity charges allows us to obtain samples with higher magnetization, as well as with a greater ability to increase the magnetic characteristics during further thermomagnetic processing.

Synthesis and diagnostics of gas-sensitive nanostructures based on molybdenum compounds

Abstract: In recent years, various transition metal dichalcogenides have been widely investigated, which are of interest for many applications, including gas sensors. In this work, some gas-sensitive nanostructures based on molybdenum disulfide and molybdenum oxide were synthesized by hydrothermal method. The surface chemical composition of the samples was studied by X-ray photoelectron spectroscopy. The gas-sensitive properties of the synthesized structures to isopropyl alcohol and acetone vapors at different working temperatures were analyzed. It was shown that as a result of heat treatment at 150°C, partial oxidation of molybdenum disulfide occured. Annealing of MoS2 samples at 400°C led to complete oxidation to MoO3. Analysis of the gas-sensitive properties of the structures showed that molybdenum oxide has the maximum response to isopropyl alcohol and acetone vapors in the entire temperature range under study. Both molybdenum disulfide and molybdenum oxide show a better response to isopropyl alcohol vapors compared to acetone vapors.

Liquid-phase synthesis of calcium phosphates in the presence of gallic acid

Abstract: Acid, medium, and basic calcium phosphates were obtained by liquid-phase synthesis from aqueous solutions of calcium chloride and ammonium hydrogen phosphate at Ca/P molar ratios of 1,0-1,67 and pH 5-11 in the presence of a polyphenol compound (gallic acid). Using X-ray phase analysis and IR spectroscopy, it has been shown that brushite is formed in a slightly acidic medium (pH 5-6) at a Ca/P molar ratio of 1,0, the unit cell size of which can decrease in the presence of gallic acid. In an alkaline environment (pH 8-11), the polyphenolic compound chelates calcium ions, which leads to the formation of amorphized calcium phosphate, which after heating at 800°C turns into β-tricalcium phosphate and hydroxyapatite. It was found that the presence of gallic acid promotes the formation of basic calcium phosphate at a lower molar ratio (Ca/P 1,5) than for stoichiometric hydroxyapatite (Ca/P 1,67). It has been shown by thermal analysis that the liquid-phase synthesis of calcium phosphates in the presence of gallic acid promotes the transformation of brushite into calcium pyrophosphate, and amorphized calcium phosphates into tricalcium phosphate and hydroxyapatite, upon high-temperature treatment.

The effect of FeSO4 and nanocluster polyoxometalates on the oxidation of phenol persulfate in an alcohol medium

Abstract: The catalytic properties of FeSO4, nanocluster ferro-molybdenum polyoxometalate {Mo72Fe30} and nanocluster molybdenum polyoxometalate {Mo132} have been studied during the oxidation of phenol in ethanolisobutanol solution with persulfate. To determine the oxidation products, phenol, ethanol and isobutanol of an acidic nature, sulfonic cation exchanger KU-2 (the grade of ion exchange resin established by the state standard of the Russian Federation GOST 20298-74) was added to the reaction mixture in each experiment to catalyze the esterification reaction of acid oxidation products with the initial alcohols. Acid esterification products were identified by the vapor-phase chromatography method with a mass spectroscopic detector. According to the conversion of phenol, ethanol and isobutanol, the catalytic properties of a homogeneous FeSO4 catalyst (similar to Fenton’s reagent) with heterogeneous catalysts (polyoxometalates) were compared. These data suggest the possibility of further searching for heterogeneous catalysts containing Fe and Mo in their composition during the destruction of phenol by peroxide compounds.