O. Yu. Golubeva

Study of antimicrobial and hemolytic activities of silver nanoparticles prepared by chemical reduction

Hydrosols that contain silver nanoparticles with average particle sizes of 10–15 and 20–25 nm have been synthesized using chemical reduction. The antimicrobial activity with respect to the Gram-negative bacteria Escherichia coli ML35p and Pseudomonas aeruginosa ATCC 27853, the antibiotic-resistant clinical isolate of Pseudomonas aeruginosa, and the Gram-positive bacteria Staphylococci aureus SG511 and Listeria monocytogenes EGD, as well as the hemolytic activity of the synthesized samples, has been investigated. The results obtained have shown that the use of the samples under investigation for the development of new bactericides holds promise.

Synthesis and study of antimicrobial activity of bioconjugates of silver nanoparticles and endogenous antibiotics

Bioconjugates of silver nanoparticles and antimicrobial peptides of the bactenecin family, which are endogenous antibiotics, have been synthesized. The biological activity of the prepared bioconjugates has been evaluated. It has been established that the conjugates of silver nanoparticles with the peptide G-Bac3.4 exhibit an antimicrobial activity, including the activity with respect to the strain Pseudomonas aeruginosa resistant to traditional antibiotics and the strain Staphylococcus aureus (MRSA ATCC 33591) resistant to methicillin. It has been demonstrated that the complexes of silver nanoparticles with antimicrobial peptides do not possess a pronounced membranolytic effect inherent in peptides. The results obtained have made it possible to draw the conclusion that the properties of the synthesized conjugates differ from those characteristic of constituting peptides and silver nanoparticles.

Layered silicates with a montmorillonite structure: Preparation and prospects for the use in polymer nanocomposites

Layered silicate nanostructures corresponding to the general formula of the natural mineral montmorillonite are prepared under hydrothermal conditions. It is demonstrated that the phase and chemical compositions of layered silicates and the sizes of their particles can be controlled by varying the hydrothermal synthesis conditions. The possibility of controlling the characteristics of synthetic layered silicates makes them promising as materials for use in the preparation of polymer-inorganic nanocomposites with specified properties.

Synthetic nanoclays with the structure of montmorillonite: Preparation, structure, and physico-chemical properties

Nanosized layered silicates with a montmorillonite structure of varying composition were synthesized under hydrothermal conditions (350°C, 700 atm). The hydrothermal treatment was applied to gels with the compositions calculated with the use of an ideal formula of the final product Na2x(Al2(1 − x), Mg2x) Si4O10(OH)2 · nH2O (0 ≤ x ≤ 1). The obtained samples were investigated by X-ray diffraction, IR and NMR spectroscopy, electron microscopy, and mercury porosimetry. The values of the cation-exchange capacity and specific surface are determined. The mean size of the particles of the synthesized samples is 40 ± 7 nm. A gradual substitution of aluminum for part of the magnesium in the initial gel made it possible to obtain samples with well-defined composition-dependent characteristics.

Structural stabilization of Fe4+ Ions in perovskite-like phases based on the BiFeO3-SrFeOy system

Compounds of the formula Bi1 − xSrxFeO3 − δ with a perovskite structure are prepared by the solid-phase synthesis at the oxygen partial pressure p = 1 atm and studied. An analysis of the experimental data obtained using Mössbauer spectroscopy and X-ray diffractometry allows us to make the inferences regarding the structure of the samples under investigation and the charge state and symmetry of the local environment of iron atoms.

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: I. Viscosity, Thermal Expansion, and Kinetics of Structural Relaxation in Binary Alkali Borate Glasses

Alkali borate glasses with different contents of residual water are prepared by varying the synthesis conditions. The temperature dependences of the viscosity and thermal expansion of glasses are obtained. The structural relaxation parameters are calculated from the hysteresis dilatometric curves measured. The water content is determined using the IR absorption spectra in the range of stretching vibrations of hydroxyl groups at room temperature. It is found that an increase in the water concentration in alkali borate glasses leads to a decrease in the viscosity. The character of variations in the viscosity logarithm with a change in the water content depends on the alkali cation concentration. The glass transition temperatures determined from the dilatometric curves for all the studied glasses decrease with an increase in the water content. As the water concentration increases, the thermal expansion coefficient (above and below the glass transition range) and the degree of fragility decrease for glasses containing 25 mol % Na2O, increase for glasses with an alkali oxide content of 15 mol %, and remain virtually unchanged for glasses involving 5.5 mol % Na2O. A change in the water content in the concentration range under investigation does not affect the structural relaxation parameters.

Structure and chemical composition of the new zeolite ISC -1 from the data of nanocluster modeling

The cluster analysis and modeling of self-assembly of the crystal structures of zeolites, i.e., zeolite RHO, paulingite PAU, and hypothetical zeolite ISC-1 separated as a local structure in the paulingite framework, have been performed. It has been established using the tiling method that the RHO, PAU, and ISC-1 frameworks contain two, seven, and five topological types of cavities, which are occupied by extraframework cations and/or water molecules. The zeolite structures have been described as ensembles of nanoclusters that represent local regions of the tetrahedral T framework and uniquely determine the topological features of the framework. The structure of the synthesized paulingite-Na,K,TEA (where TEA is tetraethylammonium) has been analyzed using X-ray powder diffraction. The chemical formula of the ISC-1 zeolite in the form Na14K24Al38Si202O480 · nH2O has been proposed from the data on the composition and structure of paulingite (minerals and synthetic phases).

Synthesis and study of the biologically active lysozyme–silver nanoparticles–montmorillonite K10 complexes

Bioinorganic complexes based on silver nanoparticles coated with lysozyme shell (bioconjugates) and aluminosilicate matrices have been synthesizeed. Layered aluminosilicates with the structure of montmorillonite of grade K10 were used as matrices. Complexes with the silver mass fraction 0.3% (from the chemical analysis data) were obtained through fivefold treatment of the aluminosilicate matrix by a sol of bioconjugates with an average particle size of 18 nm and a thickness of the biological cell of ∼4 nm. The produced biocomplexes were investigated by the methods of X-ray diffraction, scanning electron microscopy, and UV spectroscopy. The samples’ antibacterial activity against Gram-negative (E. coli ML-35p, P. aeruginosa ATCC 27853) and Gram-positive (MRSA ATCC 33591, L. monocytogenes EGD) bacteria has been studied. The presence of the biocomplex activity toward antibiotic-resistant strains E. coli ML-35p and MRSA has been revealed.

Stabilization of silver nanoparticles and clusters in porous zeolite matrices with Rho, Beta, and paulingite structures

Silver nanoparticles and clusters (Ag2+, Ag4+ and Ag8) in zeolite matrices having the structures of paulingite, Rho, and Beta have been obtained using the method of chemical reduction of silver in the ionic form preliminarily introduced to the pores of the studied zeolites through ion exchange. The effect of the ion exchange conditions, surface properties, and porous-textural characteristics of zeolite matrices on the size, state, and stability of the obtained silver rnanoparticles over time has been investigated. The samples have been studied using the methods fo X-ray diffraction analysis, flame photometry, and UV spectroscopy with integrating spheres.

Optimization of the synthesis and study of stable aqueous dispersions of silver nanoparticles used in medicine

Using chemical reduction, silver nanoparticle hydrosols were obtained and studied in a wide range of ratios of the initial reagents-NaBH4: AgNO3 from 0.1 to 10 and AOT: AgNO3 from 0 to 1—where AOT is dioctyl sulfosuccinate sodium salt. Silver hydrosols are studied using transmission electron microscopy, dynamic light scattering, UV spectroscopy, and ionometry. The optimal ratios of the initial reagents are determined, which make it possible to obtain samples with a narrow particle size distribution of 2 to 20 nm and average size of silver nanoparticles of 10 nm. The samples synthesized are stable over an extended period of time (up to six months) and contain an insignificant amount of ionic silver, which makes them useful for application in medicine.