L. A. Belyakova

Study of interaction of poly(1-vinyl-2-pyrrolidone) with a surface of highly dispersed amorphous silica

Interaction of poly(1-vinyl-2-pyrrolidone) with the surface of highly dispersed silica and character of its thermal destruction were investigated by means of ad-desorption measurement, vibration and electron spectroscopy, and thermal gravimetric analysis with programmed heating. The correlation between the character of polymer keeping on the surface of silicon dioxide and its thermal decomposition was established.

Role of surface nature of functional silicas in adsorption of monocarboxylic and bile acids

The chemical modification of silica surfaces by nitrogen-containing organic reagents (γ-aminopropyltriethoxysilane, imidazole, or N-vinyl-2-pyrrolidone) and also with hexamethyl disilazane and hydrocarbon oligomers was proposed to enhance the adsorptive capacity of silica with respect to monocarboxylic and bile acids. The calculation of the content of protonated and deprotonated groups on the surfaces of synthesized organosilicas with distinguished basicity of functional groups was performed using the program GRFIT for the model of a diffuse layer. The contribution of hydrophobic and electrostatic interactions to the adsorption of organic acids was revealed. It has been established that the maximum of organic acid adsorption coincides with the pH at which the curve of increasing concentration of the anion of an organic acid and the curve of decreasing concentration of the protonated functional groups of aminopropyl silica are intercrossed.

Designing Adsorption Centres for Biological Active Molecules on a Silica Surface

The chemical interaction between the surface of hydroxylated or aminated silicas and β-cyclodextrin, mono-tosyl-β-cyclodextrin and the bromine derivative of heptakis-[6-O-(p-tosyl-β-cyclodextrin)] has been investigated using IR spectroscopy, thermogravimetric analysis with programmed heating, pH titration, weight adsorption method, elemental analysis and quantitative chemical analysis of the surface compounds. The optimum conditions for chemical grafting of β-cyclodextrins onto the silica surface were established. The formation of supramolecular structures, viz. inclusion complexes between immobilized β-cyclodextrin and the hormone of pineal gland (melatonin), on the surface of highly dispersed silicas of 1:1 composition was demonstrated.

Adsorption of antitumor antibiotic doxorubicin on MCM-41-type silica surface

The aim of this study was to evaluate the adsorption behavior of doxorubicin on MCM-41 silica, which was synthesized by templated sol–gel method, as a function of contact time, pH of solution, and drug equilibrium concentration. Experimental kinetic curves of adsorption were compared with theoretical models of Lagergren and Ho-McKay for pseudo-first- and pseudo-second-order processes. Equilibrium adsorption of doxorubicin was analyzed by Langmuir, Freundlich, Redlich–Peterson, and Brunauer–Emmet–Teller isotherm models. These results can be the basis for direct modification of MCM-41-type silicas sorption activity to drugs.

Sorption of Cd(II) from multicomponent nitrate solutions by functional organosilicas

The paper has investigated the impact of hardness salts modeling soft and hard waters on sorption of trace amounts of Cd(II) by β-cyclodextrin-containing silicas, which differ by chemical nature of sorption centers. The paper has demonstrated high affinity of organosilicas to Cd(II) in its sorption from multicomponent solutions. Equilibrium sorption of cations from aqueous nitrate solutions within a broad interval of concentrations has been described by means of the Langmuir and Freundlich models and was interpreted in terms of the theory of hard and soft acids and Pearson bases.

The Interaction of β-Cyclodextrin with Benzoic Acid

The interaction of β-cyclodextrin with benzoic acid was studied by UV and IR spectroscopy, X-ray diffraction, and thermogravimetry. The introduction of the benzoic acid molecule into the internal hydrophobic β-cyclodextrin cavity and additional stabilization by weak H-bonds caused the formation of 1: 1 axial inclusion complexes of the host—guest type. The degree of crystallinity of the inclusion complex decreased compared with the initial compounds, whereas its thermal stability increased.

Nanoporous functional organosilicas for sorption of toxic ions

The chemical immobilization of β-cyclodextrin and its bromoacetyl and thiosemicarbazidoacetyl functional derivatives on the surface of highly disperse amorphous nanoporous silica was performed. β-Cyclodextrin-containing silicas were found to have high affinity to mercury(II), cadmium(II), and zinc(II) cations. Supramolecular surface structures formed whose chemical composition depends on the nature of the sorbed cations and the functional substituents in the attached β-cyclodextrin molecules.

Catalysis of the oxidation of hydrogen by a platinum-acetylacetone complex anchored on silica

By binding platinum ions with acetylacetone immobilized on a silica surface, we have obtained a metal complex catalyst containing Pt(II). We have also studied its catalytic activity in the model reaction of oxidation of hydrogen. We have shown that over the course of the catalytic process, this catalyst exhibits high catalytic activity at room temperatures and displays the “surface memory” effect with respect to a previous reaction. The activity of the grafted Pt complex is significantly higher than the activity of a supported platinum catalyst.

The Structure and Catalytic Activity of Pt Complexes Heterogenized on a Silica Surface

The catalytic activity of complex compounds containing different metal contents immobilized on a silica surface towards the oxidation of carbon monoxide and hydrogen has been investigated. In addition, the influence of the concentration of hydrogen and oxygen and the treatment of such catalysts by the individual components in the reaction mixture on their catalytic activity in the hydrogen oxidation reaction has also been studied. The structural peculiarities of platinum complexes heterogenized on a silica surface have been established by diffuse reflectance electronic spectroscopy.

Mesoporous silicas with covalently immobilized β-cyclodextrin moieties: synthesis, structure, and sorption properties

AbstractMesoporous silicas with chemically attached macrocyclic moieties were successfully prepared by sol-gel condensation of tetraethyl orthosilicate and β-cyclodextrin-silane in the presence of a structure-directing agent. Introduction of β-cyclodextrin groups into the silica framework was confirmed by the results of IR spectral, thermogravimetric, and quantitative chemical analysis of surface compounds. The porous structure of the obtained materials was characterized by nitrogen adsorption-desorption measurements, powder X-ray diffraction, transmission electron microscopy, and dynamic light scattering. It was found that the composition of the reaction mixture used in β-cyclodextrin-silane synthesis significantly affects the structural parameters of the resulting silicas. The increase in (3-aminopropyl)triethoxysilane as well as the coupling agent content in relation to β-cyclodextrin leads ultimately to the lowering or complete loss of hexagonal arrangement of pore channels in the synthesized materials. Formation of hexagonally ordered mesoporous structure was observed at molar composition of the mixture 0.049 TEOS:0.001 β-CD-silane:0.007 CTMAB:0.27 NH4OH:7.2 H2O and equimolar ratio of components in β-CD-silane synthesis. The sorption of alizarin yellow on starting silica and synthesized materials with chemically attached β-cyclodextrin moieties was studied in phosphate buffer solutions with pH 7.0. Experimental results of the dye equilibrium sorption were analyzed using Langmuir, Freundlich, and Redlich-Peterson isotherm models. It was proved that the Redlich-Peterson isotherm model is the most appropriate for fitting the equilibrium sorption of alizarin yellow on parent silica with hexagonally arranged mesoporous structure as well as on modified one with chemically immobilized β-cyclodextrin groups. Graphical abstract