Galactose oxidase immobilized on silica in an analytical determination of galactose-containing carbohydrates.

Galactose oxidase from Fusarium graminearum IMV-1060 adsorbed on, and covalently bound to, silica carriers has been used for analytical determinations of D-galactose and galactose-containing sugars. Using a flowing oxygen electrode of the Clark-type, sensor system for enzymatic analysis of water solutions of galactose-containing carbohydrates was made. Measurements were taken both in the pulse and continuous modes of a substrate flowing through a column with an immobilized biocatalyst. The linear measurement ranges for galactose-containing carbohydrates concentrations were determined.     

Mesoporous Titanium-containing Silicas. Synthesis and geometrical characteristics

Mesoporous titanium-containing silicas with TiO₂ contents from 1 up to 70 mol% were prepared. The obtained samples have been characterized by the powder X-ray diffraction data, the diffuse reflectance infrared Fourier transform method, and nitrogen adsorption at 77 K. Specific surface area, total pore volume, distribution pore volume on pore sizes were determined from nitrogen adsorption isotherm for synthesized titanosilicas. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cobalt complex with immobilized porphyrin in hydrazine oxidation

Porphyrin immobilized on silica and its complex with cobalt have been prepared and identified. Oxidation kinetics is described by the Michaelis-Menten equation.

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Morphology control of mesoporous silicas and their template synthesis in silica gel pores

Structure-related adsorption characteristics of ordered mesoporous silicas with spherical particles were studied depending on the conditions of their synthesis, including pH of the medium, the type of the alcohol, and the concentrations of the initial components of micelle solutions. The special features of the template synthesis of mesoporous silica in large silica gel pores were studied. The synthesized silicas were characterized by low-temperature nitrogen sorption-desorption, X-ray diffraction, and scanning electron microscopy measurements.     

Behaviour of pure water and water mixture with benzene or chloroform adsorbed onto ordered mesoporous silicas

Structural characteristics of synthesized ordered mesoporous silicas MCM-41, MCM-48 and SBA-15 were studied using XRD, nitrogen adsorption and FTIR methods. Pure water and mixtures with water/benzene and water/chloroform-d adsorbed onto silicas were studied by ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial liquids. Concentrated aqueous suspensions of MCM-48 and SBA-15 were studied by thermally stimulated depolarization current (TSDC) method. Benzene and chloroform-d can displace a portion of water to broad pores from the pore walls and from narrower pores, especially in the case of a large excess of an organic solvent. This process is accompanied by diminution of both interaction energy of water with an adsorbent surface and freezing temperature depression of adsorbed water. The effect of nonpolar benzene on pore water is much stronger than that of weakly polar chloroform-d. Modifications of the Gibbs-Thomson relation to describe the freezing point depression of mixtures of immiscible liquids confined in pores allow us to determine distribution functions of sizes of structures with unfrozen pore water and benzene. Former address: Pisarzhevskii Institute of Physical Chemistry, 31 Prospect Nauki, Kiev, Ukraine     

Role of ionene in composition of porous structure of template-synthesized silicas

Effect of the presence of I-4 Me-Ph ionene in the supramolecular template (cetyltrimethylammonium bromide) on formation of porous structure of silicas has been studied. As-synthesized nanocomposites were characterized by using thermal analysis. Nitrogen adsorption–desorption measurements, X-ray diffraction and scanning electronic microscopy were applied to determine adsorption-structural characteristics and morphology of particles of the mesoporous templated silicas prepared in basic media.     

Complex investigations of structural and thermal properties of silica-titania adsorbents

Mesoporous titanium-containing silicas with different Titania contents were investigated. The structural parameters of the materials were characterized by low-temperature adsorption/desorption of nitrogen and X-ray diffraction analysis. The thermodesorption of water using the quasi-isothermal thermogravimetry as well as the differential scanning calorimetry were used to characterize thermal and surface properties of these materials. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent/water interfaces were calculated. It was stated that the increase of Titania content causes a gradual decrease of specific surface area and formation of biporous structure inside the tested materials. The water thermodesorption from the surface proceeds in two or three stages, which is connected mainly with pore distribution and TiO₂ content. One can observe the increase of the total surface free energy (??G _??) with the increasing TiO₂ content, but the largest ??G _?? value at the adsorbent/strongly bound water interface is exhibited by the adsorbent of intermediate content (30%) of TiO₂. Freezing temperature of water contained in the pores of the studied materials is connected largely with their porous structure. Due to the well developed porous structure, the water freezing process is a multi-stage one.     

Potentialities of silane-modified silicas to regulate palladium nanoparticles sizes

A promising approach to control palladium nanoparticle sizes by application of silane modified silicas was suggested. The combination of reductive properties of silicon hydride groups and hydrophobic properties of alkylsilyl groups which act as agglomeration limiters for metal nanoparticles gives an opportunity to synthesize uniformly distributed particles with a specified size. Silicas modified with triethoxysilane (TES) and diisopropylchlorosilane (DIPCS), as well as, the combination of hexamethyldisilazane (HMDS) and triethoxysilane were applied for formation of such bifunctional matrices. Properties of the silane-modified silica samples and changes occurred during the formation of palladium nanoparticles were studied by IR spectroscopy. Thermal stability of surface chemical compounds was investigated by thermogravimetric analysis (TGA); low-temperature nitrogen adsorption was used to study structural properties of the applied materials. With the use of transmission electron microscopy (TEM) the dependence of palladium nanoparticle size on the nature of support surface layer was found.     

Immobilization of Optically Active Olefins on the Silica Surface by Combined Hydrosilylation and Sol–gel Technology

By means of hydrosilylation reactions between functional olefins and triethoxysilane in the presence of Speier's catalyst and sol-gel transformations of the reaction products, a number of optically active and complexing alkenes (quinine, quinidine, cinchonine, cinchonidine, alprenolol, N-allylrhodanine and hemin) were immobilized on the surface of silica. The structures of the compounds formed and the nature of their bonding with the surface were studied by DRIFT and NMR spectroscopies. The concentrations of olefins anchored to the surface layer of the silica matrix were estimated by UV spectroscopy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Covalent Attachment of Some Phenol Derivatives to the Silica Surface by Use of Single-stage Aminomethylation

The reaction conditions and component ratios were established for the attachment of 4-(2-pyridylazo)resorcinol (PAR), 1-(2-pyridylazo)-2-naphthol (PAN) and 8-hydroxyquinoline (8-HQ) to the silica surface by means of a single-stage Mannich reaction. The modified sorbents that were synthesized were characterized by an adsorption method, and DRIFT and UV spectroscopies. The concentrations of PAR, PAN and 8-HQ grafted to the silica surface that were attained were 2.8×10⁻⁵, 8.5×10⁻⁵ and 2.7×10⁻⁴ mol g⁻¹, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.