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Abstract  

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.

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Abstract  

Differential scanning calorimetry (DSC) and isothermal calorimetric batch technique were used to monitor the heat-induced structural changes and adsorption properties of human immunoglobulin G (IgG), in native and hydrophobized states. The transition temperature (T max) and enthalpy of heat-induced conformational changes ( cal H) of IgG in solution as well as the enthalpy change accompanying the adsorption of IgG onto hydrophilic silica ( ads H), were shown to depend on the degree of the protein hydrophobicity (number of covalently attached alkyl chains). The adsorption enthalpy for all forms of IgG at all surface concentrations was found to be endothermic, that is the process is entropy driven. Factors affecting the IgG adsorption onto silica are discussed.

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Abstract  

In order to optimize the infrared extinction of a SiC-powder in a silica powder matrix, Mie scattering calculations for spherical SiC-particles have been performed. A single oscillator-model was applied to calculate the optical constants of SiC. Taking into account the particle size distribution of a commercially available SiC-powder, its wavelength dependent extinction coefficient was calculated. The result is in very good agreement with the extinction spectrum of the powder derived by infrared optically measurements. Mie scattering theory also was used to find the optimum mean SiC-particle diameter of a mixture of 20% SiC-powder and 80% silica powder.

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Abstract  

The diffusion coefficients of Sr in gelled silica gel layers have been measured at various porosities. They decreased with the second power of porosity. At constant porosity, the diffusion coefficients of Sr and Co were measured at various pHs. They were dependent on the distribution coefficients (K) of the species between silica gel and pore water as a function of 1/(1+K). Gelation of the porous layer enables a stable measurement of diffusion coefficients under various conditions and facilitates the analysis of the distribution of ions after the diffusion experiments.

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Abstract  

The isotherms of adsorption-desorption of the vapour of benzene, cyclohexene and n-hexane on different porous silica gels were measured gravimetrically. For all the adsorbates, the amount of vapour condensed in the adsorbent pores is significantly greater than the amount adsorbed. The isotherms of all the adsorbates are linear in a wide range of relative pressures.

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The chromatographic behavior of eight pesticides has been examined on cationic-micelles impregnated silica layers using mixed organic solvent (different combinations of hexane-acetone, v/v) systems. The chromatographic system constituting 0.01% CTAB (N-cetyl-N,N,N-trimethyl ammonium bromide) impregnated silica gel as stationary phase, and hexane-acetone in 1:1 ratio (v/v) as mobile phase was most favorable for on-plate identification of pesticides with preliminary separation. Surface modification of silica gel on impregnation, as indicated by SEM and FTIR studies was responsible for improved chromatographic performance. The results obtained on 0.01% CTAB impregnated silica layers were compared with those achieved on 0.01% CTAB impregnated kieselguhr, cellulose, or alumina layers. With selected chromatographic system, fivecomponent mixtures of pesticides (glyphosate, acephate, chlorpyrifos, malathion/methyl parathion, and isoproturon) were successfully resolved. The interference of metal cations as impurities on separation of pesticides from their mixtures was also examined. The developed method was successfully applied to the identification of pesticides in cereals, vegetables, and fruit grains. The applicability of the proposed method for the identification of five-component mixture of pesticides present in maize grains was also tested after separation on TLC plates. The limit of detection of glyphosate, acephate, chlorpyrifos, malathion, methyl parathion, and isoproturon was ≈20 μg per zone. For validation and reproducibility of the developed method, standard deviation (SD), ΔR F, and separation factor (α) were calculated.

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Correlation of R F values for pairs of chromatographic systems has been used for practical separation of a mixture of eight cephalosporins by two-dimensional thin-layer chromatography on silica gel layers. Plates were scanned and videoscanned to show the real picture of separation.

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Abstract  

Matrix isolation of ferroelectric BaTiO3 nanoparticles was executed by formation of protective silica shell (via hydrolysis and polycondensation of tetraethyl orthosilicate) on particles of precursor—barium titanyl oxalate. Synthesized BaTiO3–SiO2 composites have been characterized by IR spectroscopy, XRD, TEM, DTA/DTG methods.

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Abstract  

The promotion of radioanalysis as an elegant, predominantly instrumental, analytical method is a major achievement of Vincent P. Guinn. As an example the sequential analysis for trace elements in the mm-range of small “pure” silica components from the electronic industry of various, often irregular, shapes is presented here. The idea reaches back to our discussions in the early seventies.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: J. Jones, A. Sharratt, S. Jackson, R. Griffiths, L. Gladden, F. Robertson, and G. Webb

Abstract  

Details of a novel temperature-programmed reduction technique are described, which allowed nickel oxide/silica catalysts to be reduced with [3H]-hydrogen. In addition to obtaining characteristic reduction profiles for the catalysts it was possible to study hydrogen isotope exchange over the catalysts during the reduction process.

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