Search

A comparative study of the relative antioxidant activity (RAA) of fullerene С60 and its amino acid derivatives is performed via amperometry and fluorimetry. The sizes of nanoparticles in the corresponding colloidal solutions are determined via dynamic light scattering (photon correlation spectroscopy) to study the effect the steric factors of the investigated compounds have on the magnitude of the RAA. Data are subjected to statistical correlation regression analysis using results obtained for the RAA dependence of fullerene С60 and salt forms of its acid derivatives on the corresponding sizes of nanoparticles in colloidal aqueous solutions. A close negative (inverse) correlation is identified between the size of nanoparticles in a solution and their antioxidant properties, with a pronounced synergic effect related to the influence of both chemical structure of the studied compounds and their structural organization in colloid solution. It is found that the structure of a substituent in a molecule of amino acid derivative of fullerene С60 also influences the size of the forming nanoparticles. At the same time, reductive properties of amino acid derivatives of fullerene С60 are generally determined by the electron effects of substituents. [ABSTRACT FROM AUTHOR]

Means of synthesis are developed and a physicochemical study of ligands based on 2,3,6-О-cellulose derivatives for asymmetric hydrogenation catalysts is performed. [ABSTRACT FROM AUTHOR]

Aluminum oxide was modified by sulfuric acid using the adsorption method under static and dynamic conditions, as well as through impregnation. The areas occupied by a molecule in a saturated monolayer on hydro- and dehydroxylated aluminum oxide were equal to 0.44 and 0.36 nm, respectively. The dependence of the surface and adsorption properties and porosity characteristics of aluminum oxide on its thermal treatment and the modifying sulfo-groups content has been demonstrated. On aluminum oxide with a sulfo-group content close to that of the monolayer, the pyridine sorption proceeds on both Lewis and Brønsted acid sites. The increase of the contribution of specific interactions on the sulfated aluminum oxide was shown using the adsorption of saturated and aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Esterification of 3-hydroxy-2-naphthoic acid with homologous primary and secondary alkenyl alcohols with different chain lengths in the presence of N,N'-carbonyldiimidazole (CDI) and 1,8-diazabicyclo[ 5.4.0]undec-7-ene (DBU) in N,N-dimethylformamide gave the corresponding esters. [ABSTRACT FROM AUTHOR]

Amino acid derivatives of C60 fullerene were studied by solid-state NMR spectroscopy. The spectroscopic data given in this work suggest that the compounds under study are derivatives of C60 fullerene and corresponding amino acids. The fullerene core is attahced to the amino acids via the amino group. [ABSTRACT FROM AUTHOR]

Ferromagnetic γ-FeO was modified with stearic and oleic acids. Diffuse reflection spectra show that modification occurs both via the interaction with free surface hydroxyl groups and by forming bidentate carboxylates with iron atoms. Surface modification enhances adsorption of water-soluble organic dyes (orange acid and methylene blue dyes, cytochrome C enzyme) due to contribution of hydrophobic interaction to adsorption. Differences in adsorption of dyes onto the modified γ-FeO caused by different structures of hydrocarbon chains in stearic and oleic acids were revealed. The effect of electrolyte concentration and pH of a solution on adsorption of cytochrome C was studied. The activated iron(III) oxide can be used as a magnetic carrier for immobilized enzymes in bioreactors and for targeted drug delivery. [ABSTRACT FROM AUTHOR]

The adsorption of HAuCl chloroauric acid on silica modified with γ-aminopropyltriethoxysilane (aminosilica) and on aluminum oxide is studied. Diffuse-scattering spectra of these Au(III) composite materials and their reduced Au(0) composites are recorded in the visible and infrared spectral ranges. Au(III) composites are selective with respect to the adsorption of phenylacetylene (PA) from octane due to the formation of π-complexes with Au(III). Au(III)-aluminum oxide composite material has a much larger capacity for PA adsorption than does aminosilica composite with the same gold content. The formation of coordination bonds between free aminopropyl groups of the silica carrier and gold atoms prevents PA adsorption. The formation of such bonds is manifested in a shift in λ of the spectral line from 408 to 522 and 546 nm with a decrease in [Au(III)] concentration from 400 to 120 and 60 μmol/g. The decrease in the intensity and the red shift of the absorption bands of NH stretching vibrations in the infrared spectra of the specimen upon modification also confirms the supposition. There are absorption bands of free hydroxyl radicals, but no band of bound radicals in the infrared spectra of Au(0) composites. The electronic spectra (λ = 511, 504, and 512 nm) are close for all three specimens that differ in gold content, which means that the sizes of immobilized Au(0) nanoparticles are similar. Upon the sorption of HAuCl on a Au(III)-aluminum oxide specimen, the absorption band of surface OH groups disappears, however, in Au(0) composite, it appears again near 3105 cm. [ABSTRACT FROM AUTHOR]

The paper reports the immobilization of Ag cations on alumina and silica and AuCl anions on amino silica and alumina. The method of inverse gas chromatography have demonstrated that Ag(I)-silica is selective for the separation of alkanes, alkenes, alkines, and arenes. The dependence of the capacitance of Ag(I) and Au(III) composites with regard to phenylacetylene (PHA) on the nature of the carriers, surface concentration, and technique of immobilizing ion metals has been considered. The isotherms of the adsorption of PHA from solutions in octane have been measured. It has been revealed that the capacitance of composites with regard to toward PHA prepared by the immobilization of ammoniates of silver nitrate on silicon dioxide is several times higher than for composites based on alumina with the same silver concentration and composites prepared by the immobilization of silver nitrate on silicon dioxide. The capacitance of the Au(III) composite based on alumina for PHA is significantly higher than for that based on aluminum oxide. The highest capacitance for PHA (0.83 and 0.88 molecules per metal ion) is observed for Ag(I) silica and the Au(III) alumina composite. In the visible region, the diffuse reflection spectra of amino silica Au(III) composites have a significant shift of the maximum of adsorption band along with the decrease in the concentration of immobilized anions of AuCl, which evinces the formation of coordination bonds between free aminîpropyl groups of the silica carrier and gold atom. The formation of these bonds prevents the adsorption of PHA on amino silica Au(III) composites with low gold concentrations. [ABSTRACT FROM AUTHOR]

The chemistry of the surface and structural and adsorption properties of fluorinated carbon fiber were studied by IR spectroscopy, gas chromatography, and static adsorption of vapors and dyes from aqueous solutions. Also, the quantitative characteristics of the influence of a binder (polytetrafluoroethylene) used to prepare a granulated adsorbent on the basis of the fiber were determined. The functional properties of the adsorbent were found to be largely determined by the properties of the initial fluorocarbon fiber. Fluorocarbons were shown to possess a developed porous structure and highly hydrophobic chemically homogeneous nonpolar surface for the adsorption of most of the organic compounds studied. [ABSTRACT FROM AUTHOR]

Certain possibilities of scanning electron microscopy and cryoporometry based on nuclear magnetic resonance (NMR) have been evaluated to determine pore sizes in porous silicon. The results obtained by these methods have been compared. NMR cryoporometry has been shown to be promising in the investigation of porous materials. [ABSTRACT FROM AUTHOR]

Catalytic systems containing mainly mononuclear (CuCl) or dinuclear (Cu2Cl) tributylbenzylammonium chlorocuprates are prepared by adsorption on silica surfaces of different structures (Aerosil and Silokhrom). Using ESR, XANES, and electronic spectroscopy, the CuCl ions are shown to be reduced rapidly under conditions of C-Cl bond metathesis, whereas the dinuclear chlorocuprates are relatively stable. A correlation between the number of copper ions in the chlorocuprate anion and its catalytic activity is established: the mononuclear complexes are several times more active than their dinuclear counterparts. [ABSTRACT FROM AUTHOR]

The surface properties of fully fluorinated samples of natural graphite (FG) and carbon fiber (FCF) were studied by gas chromatography, IR spectroscopy, and static adsorption. It was found that for fluorocarbons, the contributions from the O atom (for ethers) and the OH group (for alcohols) are comparable with the contribution from the methylene unit to the retention parameters, which is typical only of highly homogeneous, hydrophobic, and nonpolar surfaces. Unusual properties of fluorocarbons compared to known hydrophobic adsorbents include weaker adsorption of secondary alcohols than ketones, their dehydrogenation products. An analysis of the retention parameters of isomeric propanols and butanols revealed that the FCF surface is accessible to the adsorption of these molecules, and is mainly formed by planar homogeneous fragments. In contrast, the FG structure is porous; the pore width is comparable with the molecule size, which makes the adsorption equilibrium more difficult to reach. [ABSTRACT FROM AUTHOR]

The adsorption of the vapors of a number of oxygen-containing compounds (alcohols, ketones, acids, and other functional derivatives of hydrocarbons) on fluorinated carbon (FC) was studied by the gas chromatography method at low surface coverages. The Henry law constants, heats of adsorption, standard entropies of adsorption, and retention indices were determined. An analysis of adsorption and IR-spectroscopy measurements suggests that FC contains no surface active sites capable of forming hydrogen bonds. It was established that the adsorption of oxygen-containing compounds on a FC surface is primarily governed by dispersion interactions. The adsorbent under study was found to exhibit a high selectivity in separation of isomeric alcohols. [ABSTRACT FROM AUTHOR]

The influence of the metal content on the support, the conditions of the preparation of the catalysts, and the reaction conditions on the enantioselectivity of the liquid-phase hydrogenation reaction of ethyl acetoacetate in the presence of Ni and Ni-Co catalysts supported on AlO and SiO, and modified by RR(+)-tartaric acid, was investigated. The maximal optical yield (66-76%) was obtained for the 20% Ni/AlO catalyst. [ABSTRACT FROM AUTHOR]

A study was carried out on the effect of the nature of the catalysts, additives, and solvents on the stereoselectivity of the liquid-phase hydrogenation of an equilibrium menthone-isomenthone mixture to give menthols. Neoisomenthol, which is the least stable of all the menthol isomers, was predominantly formed on a cobalt catalyst modified by (+)-tartaric acid in ethyl acetate at 130°C and 10 MPa. [ABSTRACT FROM AUTHOR]

Thermal-desorption and isotope methods were used to investigate the state of hydrogen found on the surface of ruthenium framework catalysts. The possibility of the migration of chemisorbed hydrogen from the ruthenium was demonstrated. [ABSTRACT FROM AUTHOR]

An effect of modification conditions of powdered nickel-cobalt catalysts on enantioselectivity of hydrogenation of ethyl acetoacetate has been studied. Addition of NaBr to the modifying solution of RR-(+)-tartaric acid does not improve enantioselectivity of the catalyst. When the Ni-Co catalysts are modified with amino acids, the best results are obtained with L-β-phenylalanine (17% ee). [ABSTRACT FROM AUTHOR]

Competitive complexation in the copper(II) chloride-N,N-dimethylformamide (DMF)-Aerosil system was studied by IR spectroscopy. It was found that adsorption from organic solutions containing copper(II) chloride and DMF resulted in the formation of the following three types of DMF complexes: self-associates of DMF, DMF complexes with surface hydroxyl groups, and DMF complexes with Cu(II) ions. The removal of DMF resulted in the sequential degradation of, initially, self-associates; next, complexes with silanol groups; and, finally, complexes with copper ions. [ABSTRACT FROM AUTHOR]

LinC60 fullendes were prepared by high-pressure solid-state reactions and characterized by IR spectroscopy and x-ray diffraction. The results are interpreted in terms of a sequence of phase transformations induced by Li incorporation. At low Li contents, 2 < n < 3, a one-dimensional polymer with an orthorhombic structure is formed. Higher Li contents give rise to the formation of a mixture of dimeric and polymeric phases. At n = 5.7, only a dimeric phase with a triclinic structure is formed. In the range 7.1 < n < 10.1, the size of Li clusters increases and a dimeric monoclinic phase forms. [ABSTRACT FROM AUTHOR]

For Raney Cu-Ru and Cu-Pd catalysts non-additive changes in the strength of the catalyst-hydrogen bond and in the catalytic activity and enantioselectivity were found to occur with changing composition, indicating the presence of a ligand effect in these systems. [ABSTRACT FROM AUTHOR]

The complexes of Co, Ni, Fe, and Cu with dimethyl- and diphenylglyoxime inhibit the initiated oxidation of cumene by reacting with the peroxide radicals. [ABSTRACT FROM AUTHOR]

Enantioselective hydrogenation of ethyl acetoacetate was carried out for the first time on unsupported 1∶1 Cu-Ni catalysts obtained by precipitation. The highest optical yield (50%) was obtained with a catalyst obtained by reduction of oxides at 250°C in a 1∶10 H∶N atmosphere. [ABSTRACT FROM AUTHOR]

Skeletal ruthenium catalyst, modified with D-(+)-tartaric acid, leads to the asymmetric hydrogenation of the carbonyl group in acetoacetic ester. [ABSTRACT FROM AUTHOR]