Showing papers on "Silica gel published in 1969"

Microbial culture preservation with silica gel.

Abstract: Cessation of cellular metabolism is a prerequisite for the preservation and longterm storage of a microbial culture in a state essentially free from the accumulation of morphological and physiological variants (Reusser, I 963). The method of lyophilization (Heckley, 1961) is the most universally used procedure for stock culture preservation. Hunt, Gourevitch & Lein (1958) and Perkins (1962) described methods for preserving microbial cultures by dehydration with anhydrous silica gel. The method of Hunt et al., where silica gel and culture are held apart, has been used to preserve fungi (Lange & Boyd, 1968) and a range of bacterial species (Hunt et al. 1958; Norris, 1963). The technique reported by Perkins, in which a suspension of the micro-organism in skim-milk is added directly to the anhydrous silica gel, has been applied to stocks of the fungi Neurospora crassa, Ustilago maydis, strains of yeast (Perkins, 1962), cystforming slime moulds (Reinhardt, 1966) and Claviceps paspali (Mizrahi & Miller, 1968). This technique is inexpensive, rapid, extremely simple to use and, as reported in this communication, can also be applied to micro-organisms other than fungi.

Transformation of aflatoxin B1 by steroid-hydroxylating fungi.

Abstract: Numerous organisms were examined to find a fungal system capable of catalyzing aflatoxin transformations. Some fungi, particularly Dactylium dendroides, Absidia repens, and Mucor griseo-cyanus, transform about 50–60% of aflatoxin B1 in shake cultures to a new fluorescent-blue compound (R0), with a lower Rf (0.57) than B1 (0.69) on silica gel thin-layer chromatographic plates (acetone:CHCl3, 20:80). In a separate assay, washed fungal mycelium suspended in 0.02 M PO4 buffer catalyzed a 25–30% conversion in 20 h. The new fluorescent compound was separated from the unchanged B1 by column chromatography on silica gel G with washed CHCl3 containing 6% acetone and 0.75% ETOH as solvent. The ultraviolet spectrum showed maxima of 325, 261, and 254 mμ. Its infrared spectrum, showing a shift in absorption peaks at 1760 and 1685 cm−1, indicated a change in the functional carbonyls of B1; in addition, a broad band at 3400 cm−1 indicated a hydroxylated compound.

Electronic properties of transition-metal complex ions adsorbed on silica gel. Part II. Cobalt(II) and cobalt(III)

Abstract: The electronic spectra and magnetic moments of a series of complexes of the cobalt(II) and cobalt(III) ions, adsorbed on silica gel by an exchange process, have been examined. The Co(H2O)62+ cation reacts with the hydrated surface to form a blue tetrahedral species which probably involves a CoO3′O1″ chromophore on the surface, but a pink octahedral species is formed when the hydrated gel is allowed to stand. With nitrogen chelate ligands (en and dien) partial reaction occurs on the hydrated gel depending on the ratio of ligand to cobalt(II) ion; more extensive reaction occurs upon dehydration. The electronic properties suggest the formation of four-, five-, and six-co-ordinate species depending on the conditions. In the presence of air, extensive oxidation to cobalt(III) occurs. These results suggest that the cobalt(II) ion reacts much more strongly with the gel surface than does the nickel(II) ion. With cobalt(III) complexes no reaction occurs with the hydrated gel, but dehydration results in the reduction of the cobalt(III) complexes to the corresponding cobalt(II) surface species. Possible mechanisms for this reaction are discussed.

Electronic properties of transition-metal complex ions adsorbed on silica gel. Part I. Nickel(II) complexes

Abstract: The electronic spectra of a series of multidentate nitrogen ligand complexes of the nickel(II) ion adsorbed on silica gel in the sodium form by ion exchange have been examined as a function of the degree of hydration of the silica gel surface The results show that, on adsorption, the nickel(II) species produced are generally similar to those present in the parent aqueous solution The removal of physically adsorbed water has a marked effect on the electronic spectra of the adsorbed ion; with high ligand: nickel ratios a cis-octahedral chromophore is suggested, but with low ratios a five-co-ordinate chromophore is formed These processes can be reversed by the readmission of water vapour The results are interpreted in terms of a competition of the ligands for co-ordination sites on the nickel(II) ion, with the competing ligands being water surface donors and the nitrogen ligands The surface seems capable of acting as both a bidentate or a terdentate ligand towards the nickel(II) ionPossible implications to related heterogeneous catalytic systems are considered

Thin-layer chromatography of some c21, c19 and c18 steroids

Abstract: The resolution of 30 different C21, C19 and C18 steroids by various solvent systems on silica gel chromatoplates was reported. Effective resolution of Δ4-pregnene, 5α, axial-equatorial hydroxyl epimers and positional isomers was successfully achieved. The differentiation between these compounds by using four different colour reagents has been also reported.

Production of insulating materials having low specific gravity

Abstract: Heat-insulating compositions are made by mixing porous plastic particles with an inorganic binder consisting of a suspension of water-containing particles of alkali metal silicate and inorganic fillers in an aqueous solution of an alkali metal silicate, and solidifying at a temperature above >0 DEG C. but below that at which the plastic sinters. Solidification can be assisted by extracting water down to a content of 20%, by treatment with carbon dioxide, or by the application of pressure. The porous plastic may be polyurethane, polystyrene, copolymers of styrene and acrylonitrile, acrylic acid, or butadiene, vinyl chloride, or copolymers of vinyl chloride and vinylidene chloride. Flame retardants such as inorganic halogen compounds or mixtures of chloroparaffins and antimony trioxide may be included. The alkali metal silicate powder is preferably sodium silicate containing 16-20% water and having an Na2O/SiO2 ratio of 1:2.0 to 1:4.0. The solution is of 15-60 DEG Be1 concentration, and the total water content varies between 25 and 75% of the weight of the silicate. Magnesia, talc, calcium carbonate, powdered asbestos, glass, quartz, zinc carbonate, sodium silicofluoride, or silica gel can be used as fillers in the ratio of 1:1 to 4:1 relative to the anhydrous silicate.

The Surface Structure of Silica Gel Studied by Dielectric Dispersion

Abstract: The effect of water adsorption and heat treatment at various temperatures between 200 and 1100°C on the dielectric dispersions of silica gel was measured in the frequency range from 50 to 3×106 Hz and 9.81 GHz and in the temperature range from −196°C to 180°C. Two anomalous dispersions (Dispersion I and II) and one anomaly (Anomaly III) were found. The mechanisms of those anomalies were discussed in relation to some physical properties and silica crystal structures. Dispersion I, having activation energy ΔE equal to 11 to 14 kcal/mol, can be ascribed to the monomolecular layer of adsorbed water. Dispersion II, with activation energy of about 5 to 7 kcal/mol, can be attributed to proton diffusion through hydrogen-bond chain of surface silanol groups. Anomaly III, having activation energy of about 3 kcal/mol, may be assigned to dipolar rotation of free silanol.

Influence of properties of adsorbent, and of the surface and bulk solutions on adsorption from solution

Abstract: To elucidate the effect of the molecular field of surface solution on adsorption equilibrium the experimental adsorption isotherms of toluene from solutions in n-heptane on the hydroxylated surface of silica gel and on weakly oxidized and non-oxidized channel carbon blacks were analyzed using expressions following from the model of monolayer adsorption and the thermodynamics of adsorption from solutions. Assuming an ideal surface solution, the thermodynamic equation approximately describes the experimental isotherm only for strong specific adsorption of toluene on the hydroxylated silica gel. It completely fails to describe the isotherm (having an azeotropic point) for weak non-specific adsorption on the non-oxidized carbon black. The calculated activity coefficients in the surface solutions and equilibrium constants reflect the decrease in the specific interaction of toluene with the adsorbents in passing from the hydroxylated silica gel surface through weakly oxidized carbon black to non-oxidized carbon black.

Nature of Acid Sites on the Surface of Silica-alumina. I. The Relation between the Acid Property of Sites and the Heat of Immersion

Abstract: The acidity and the acid strength of the sites of such solid catalysts as silica gel, alumina, and silica-alumina were determined by the n-butylamine titration method using the Hammett indicators. The distribution of the acid sites on the surfaces of these catalysts was found to vary with the outgassing temperature, and also with the alumina content in the case of silica-alumina. The heats of immersion of these catalysts in water and in an aqueous solution of n-butylamine were measured. The heat value corresponding to the difference between these two cases, as well as the number of acid sites, showed a maximum at contents of 10–20%. These phenomena are discussed with reference to the results of the diffuse reflection measurements.

Mössbauer Spectral Observation of α-Fe2O3 Supported on Silica Gel during Activation

Abstract: Mossbauer spectral studies were made of samples of α-Fe2O3 highly dispersed on silica gel before and after activation, which consisted of evacuated heating at 475°C. The spectra gave Ividence that Fe2+ ions were produced from α-Fe2O3 during the activation process. Reduction was impossible after the activation and oxidation had been repeated three times. However, the inactivated sample came to be again reduced by activation after having been exposed to water vapor at room temperature. In order to explain these facts, a working hypothesis was advanced that the hydroxyl groups near the surface of the particles play a principal role in reacting with organic contamination from the vacuum system, as a result bringing about the partial reduction of α-Fe2O3.

Electron Spin Resonance Studies of the Formation of Anion Radicals on γ-Irradiated Silica Gel

Abstract: The ESR spectra assigned to the anion radicals of SO2−, (TCNE)− (tetracyanoethylene), and O2− were obtained for, respectively, sulfur dioxide, TCNE, and oxygen when these gases were adsorbed on γ-irradiated silica gel. As regards sulfur dioxide, a characteristic change in the concentration of the SO2− radical was observed during the post-irradiation with high-energy UV light. In the case of carbon dioxide, the CO2− radical was produced only when UV post-irradiation was added to γ-irradiation. The assignments were principally made in comparison with the reported g-values. Especially, the identification of the CO2− radical was ascertained by using 13C. The analyses of the g-factor for the O2− radical and of 13C hyperfine constants for the CO2− radical gave information on the interaction of the radicals on a solid surface with the cations in the adsorption center. In view of the fact that each of these molecules possesses a different degree of electron affinity, the results described above indicate that the ...

Adsorption from binary liquid mixtures on chromatographic silica gel

Abstract: Adsorption equilibria of binary solutions of cyclohexane, benzene and dioxane on chromatographic silica gel at 20°C have been determined. The thermodynamic treatment outlined by Everett and by Schay and Nagy have been applied. The results obtained by the alternate methods show a fair agreement in the nσ/m and xσi values, but differences are observed in the log fσi values.

[74] Stereospecifically labeled citric acid cycle intermediates

Abstract: Publisher Summary The chapter presents lists of labelled citric acid cycle intermediates and discusses the general procedures for separation, purification, isolation, and analysis of these intermediates. The separation of citric acid cycle intermediates and other organic acids are achieved by partition chromatography on silica gel or similar media and by elution chromatography on anion exchange resins, such as Dowex 1-formate or Dowex 1-acetate. In preparation for isotope analysis, samples of deuterated compounds are generally diluted with their protonated counterparts to contain between 0.5 and 1.0 atom percent excess deuterium. For deuterium analysis, the samples are oxidized in liquid-air oxygen, and the water is converted to hydrogen by passage through a uranium converter connected in series with a mass spectrometer. Samples of deuterated succinate can be analyzed for their content of normal, mono-, di-, tri-, and tetradeuteratcd succinate molecules. The isolated succinic acid is converted to succinic anhydride by refluxing with acetyl chloride, evaporating the reagent and washing the crystals with ether.

Manufacture of silica-rich zeolites

Abstract: ZEOLITES OF THE Y CRYSTAL TYPE ARE PRODUCED BY DIGESTING AN QUEOUS REACTION MIXTURE COMPRISING SILICAL GEL SYNERIZED AT A PH BETWEEN ABOUT 5.5 AND 10, PREFERABLY BETWEEN ABOUT 6 AND 9, AND SODIUM ALUMINATE AT AN ELEVATED TEMPERATURE. THE PARTICULAR SILICA GEL EMPLOYED PERMITS THE PRODUCTION OF GOOD YIELDS OF Y-TYPE ZEOLITES HAVING A SILICA TO ALUMINA MOLE RATIO OF ABOVE 3.9 UNDER MILDLY ALKALINE CONDITIONS HERETOFORE CONSIDERED POSSIBLE ONLY IN CONJUNCTION WITH SILICA HYDROSOLS AND REACTIVE AMORPHOUS SOLID SILICAS.