Silica Gel Support Research Articles

Fiber-optic glucose biosensor based on glucose oxidase immobilised in a silica gel matrix

A monolithic silica gel matrix with entrapped glucose oxidase was constructed as a bioactive element in an optical biosensor for glucose determination. Physicochemical and biochemical characterizations of the catalytic matrix were performed, and the intrinsic fluorescence of immobilised glucose oxidase (GOD) was investigated in the UV and visible range by performing steady state and time course measurements. In all cases, the silica gel matrix proved to be a suitable support for optical biosensing owing to its superior optical properties (e.g., high transmittance and reliable fluorescence and GOD absorption spectra after immobilisation). From steady state measurements, calibration curves were obtained as a function of glucose concentration. When time course measurements were performed, the silica gel support displayed a larger linear calibration range and higher sensitivity than other immobilisation systems. In addition, a glucose optical biosensor was developed and characterised using as catalytic element GOD immobilised on a gel disk bound to a bundle of optical fibres.

Synthesis, characterization and protein binding properties of supported dendrons

Novel benzylether type aldehyde and acetal terminated dendrons were synthesized and attached to a silica gel support; a linear spacer was also introduced as a control material. The supported dendritic compounds were mainly characterized by solid state 13C CPMAS NMR, elemental analysis and X-ray photoelectron spectroscopy (XPS) and the presence of free aldehydes was determined by the purpald test. Bovine serum albumin (BSA) protein was coupled to the dendronized support by imine bond formation, followed by irreversible reduction of the carbon–nitrogen double bond. A significant positive dendritic effect was observed on the antibody binding capacity of immobilised BSA as measured by fluorescence immunoassay (FIA).

One-Pot Synthesis of α-Aminophosphonates on Silica under Solvent-Free Conditions from Aromatic Aldehydes

α-Aminophosphonates were synthesised under solvent-free conditions on an acidic silica gel support using aromatic aldehydes, diethyl phosphite and anhydrous ammonium acetate as starting materials in moderate yields

Catalytic Dehydrogenation of Isopentane with Iridium Catalysts

Activation by adding PPh3: The catalytic dehydrogenation of isopentane to give isopentene and hydrogen with iridium catalysts on a silica gel support at 450 °C proceeds with impressive conversion when the support is impregnated with PPh3. The active species are proposed to be iridium phosphides which arise by thermal cleavage of phenyl groups.

Conformal ZnO coatings on high surface area silica gel using atomic layer deposition

Silica gel is a mesoporous form of silica with a high specific surface area that is widely used as a support material for heterogeneous catalysis. In this study, we use atomic layer deposition (ALD) methods to deposit ZnO layers onto silica gel supports. ZnO ALD was performed using alternating exposures of diethyl zinc (DEZ) and water to coat 1 g quantities of silica gel in a conventional viscous flow reactor. The coated materials were analyzed using weight gain, X-ray fluorescence, X-ray diffraction, energy dispersive X-ray analysis, and scanning and transmission electron microscopy. These measurements revealed that the silica gel support could be conformally coated using reactant exposure times of ∼ 90 s. The ALD ZnO was amorphous for films deposited using < 5 ALD cycles, but became hexagonal, nanocrystalline ZnO for films deposited using > 5 ALD cycles. In addition to the ZnO films, we also discovered that metallic Zn was deposited in the silica gel using very large DEZ exposures and deposition temperatures > 150 °C. The metallic Zn phase begins to form as soon as the ZnO ALD surface reactions have saturated, indicating that the Zn growth is strongly dependent on the availability of excess DEZ precursor.

Removal of Pertechnetate from Simulated Nuclear Waste Streams Using Supported Zerovalent Iron

The application of nanoparticles of predominantly zerovalent iron (nanoiron), either unsupported or supported, to the separation and reduction of pertechnetate anions (TcO4-) from complex waste mixtures was investigated as an alternative approach to current waste-processing schemes. Although applicable to pertechnetate-containing waste streams in general, the research discussed here was directed at two specific potential applications at the U.S. Department of Energy's Hanford Site: (1) the direct removal of pertechnetate from highly alkaline solutions, typical of those found in Hanford tank waste, and (2) the removal of dilute pertechnetate from near-neutral solutions, typical of the eluate streams from commercial organic ion-exchange resins that may be used to remediate Hanford tank wastes. It was envisioned that both applications would involve the subsequent encapsulation of the loaded sorbent material into a separate waste form. A high surface area (>200 m2/g) base-stable, nanocrystalline zirconia was used as a support for nanoiron for tests with highly alkaline solutions, while a silica gel support was used for tests with near-neutral solutions. It was shown that after 24 h of contact time, the high surface area zirconia supported nanoiron sorbent removed about 50% (Kd = 370 L/kg) of the pertechnetate from a pH 14 tank waste simulant containing 0.51 mM TcO4- and large concentrations of Na+, OH-, NO3-, and CO32- for a phase ratio of 360 L simulant per kg of sorbent. It was also shown that after 18 h of contact time, the silica-supported nanoiron removed >95% pertechnetate from a neutral pH eluate simulant containing 0.076 mM TcO4- for a phase ratio of 290 L/kg. It was determined that in all cases, nanoiron reduced the Tc(VII) to Tc(IV), or possibly to Tc(V), through a redox reaction. Finally, it was demonstrated that a mixture of 20 mass % of the solid reaction products obtained from contacting zirconia-supported nanoiron with an alkaline waste solution containing Re(VII), a surrogate for Tc(VII), with 80 mass % alkali borosilicate based frit heat-treated at 700 °C for 4 h sintered into an easily handled glass composite waste form.

Immobilization of polysaccharide derivatives onto silica gel: Facile synthesis of chiral packing materials by means of intermolecular polycondensation of triethoxysilyl groups

The 3,5-dimethylphenylcarbamates of cellulose and amylose bearing a small amount of 3-(triethoxysilyl)propyl residues were synthesized by a simple process and efficiently immobilized onto a silica gel support by intermolecular polycondensation of the triethoxysilyl groups. The obtained chiral packing materials (CPMs) were evaluated by high-performance liquid chromatography. The polysaccharide derivatives containing about 1–2% of the 3-(triethoxysilyl)propyl residue were efficiently immobilized with a high chiral recognition. The immobilized CPMs could be used with the eluents containing chloroform and tetrahydrofuran, which cannot be used with the conventional coated-type CPMs. By using these eluents, the chiral recognitions for many racemates could be improved.

On the use of solid phase ion exchangers for isolation of amino acids from liquid samples and their enantioselective gas chromatographic analysis

This work focuses on the development of a suitable working procedure for preconcentration of amino acids enantiomers from water samples using a solid phase extraction. The three types of ion exchangers with various capabilities have been used. The effect of experimental conditions in SPE procedure employing strong anion exchange (SAX), weak (WCX) and strong cation exchange (SCX) cartridges (such as sample volume, pH, origin of elution solvent and its volume) on effective preconcentration of the model set of amino acids has been studied in detail. The enantiomers of isolated and preconcentrated amino acids have been analysed by GC on three capillary columns coated with chiral selectors. The different amino acids derivatives have been investigated in order to achieve optimal resolution of biogenic amino acids and their enantiomers. The best separation of amino acid enantiomers has been obtained on a Chirasil- l-Val column analysing their N-TFA methyl esters. It has been shown that SCX-SPE cartridge with sulfonic groups attached on silicagel support is most suitable for isolation and preconcentration of amino acids from water samples. For this sample treatment procedure, the overall recovery of extraction process has been calculated as an average value from three measurements. It has been found, that recoveries are practically identical for both enantiomers of a particular amino acid and varies in the range 75–99% depending on the type of amino acid. The effectivity of this sample preparation and GC method has been verified by preconcentration of amino acids from orange juice fortified by racemic mixture of some selected amino acids.

Efficient Immobilization of Cellulose Phenylcarbamate Bearing Alkoxysilyl Group onto Silica Gel by Intermolecular Polycondensation and Its Chiral Recognition

Cellulose 3,5-dimethylphenylcarbamate bearing a small amount of 3-(triethoxysilyl)propyl residues was synthesized and effectively immobilized onto silica gel support for high-performance liquid chromatography by the polycondensation of triethoxysilyl groups. The immobilized chiral packing material (CPM) showed high chiral recognition as well as the conventional CPM prepared by coating the derivative onto silica gel, and can be used with a variety of eluents.

A comparative study of supported aqueous- and ethylene glycol-phase catalysts in stilbene hydrogenation: Influence of the different modes of dispersion of supported liquids

Supported liquid phase catalysts (SLPC) containing water-soluble Pd complexes were used for hydrogenation of stilbene in toluene. When water is loaded on a silica gel support, the catalytic activity of SLPC increases with the amount of the water. In contrast, when ethylene glycol (EG) is used as the supported liquid, the activity does not depend on the amount of EG loaded. These results can be explained by differences in the mode of dispersion of the supported liquids over the support.

Development of Industrial Reaction Processes Using Fluorous Lewis Acid Catalysts

AbstractWe have developed a series of novel fluorous Lewis acid catalysts, namely the ytterbium(III), scandium(III), tin(IV) or hafnium(IV) bis(perfluoroalkanesulfonyl)amides or tris(perfluoroalkanesulfonyl)methides for waste‐free and environmentally‐benign industrial processes. Our catalysts are not only highly active but also recyclable due to their fluorous properties for acylations of alcohols and aromatics, Baeyer‐Villiger reactions, direct esterifications and transesterifications in a fluorous biphasic system (FBS) and on fluorous silica gel supports.

Development of Fluorous Lewis Acid-Catalyzed Reactions

Organic synthetic methodology in the 21st century aims to conform to the principles of green sustainable chemistry (GSC) and we may expect that in the future, the realization of GSC will be an important objective for chemical industries. An important aim of synthetic organic chemistry is to implement waste-free and environmentally-benign industrial processes using Lewis acids as versatile as aluminum chloride. A key technological objective of our work in this area has been to achieve a "catalyst recycling system that utilizes the high activity and structural features of fluorous Lewis acid catalysts". Thus, we have developed a series of novel fluorous Lewis acid catalysts, namely the ytterbium(III), scandium(III), tin(IV) or hafnium(IV) bis(perfluoroalkanesulfonyl)amides or tris(perfluoro- alkanesulfonyl)methides. Our catalysts are recyclable and effective for acylations of alcohols and aromatics, Baeyer-Villiger reactions, direct esterifications and transesterifications in a fluorous biphasic system (FBS), in supercritical carbon dioxide and on fluorous silica gel supports.

Movement and Diffusion of Paramagnetic Ions in a Magnetic Field

The magnetic movement and thermal diffusion have been studied for Cu(2+) ions in solution. The Cu(2+) ion solution was spotted on the silica gel support and exposed to the magnetic field of 410 kOe(2) cm(-1) intensity x gradient. The Cu(2+) ions were attracted toward the filed center. The moving distance and diffusing distance were observed at various time intervals. It is shown that the Cu(2+) ions move in a large group composed of Cu(2+) ions and H(2)O molecules. The size of the group is approximately estimated to be of 4.6 mum diameter by the analysis of the drift velocity of the group and the Cu(2+) ion concentration in the group.

Retention and selectivity tests of silica‐based and metal‐oxide bonded stationary phases for RP‐HPLC

Chromatographic properties of silica-, zirconia- and alumina-based columns with octadecyl-, polyethylene glycol- and pentafluorophenylpropyl-bonded stationary phases were tested. Selectivities of nine columns for LC were characterized using chromatographic methods including Walters, Engelhardt, Tanaka and Galushko hydrophobicity and silanol activity tests, measurements of methylene selectivity in various aqueous-methanol and aqueous-acetonitrile mobile phases and of gradient lipophilic capacity as a measure of the effect of the sample hydrophobicity on gradient-elution separations. A semi-empirical interaction indices model, assuming a predominant role of the solvophobic interactions of test compounds with different polarities, was compared with the linear free energy relationships approach taking into account selective polar interactions. The interaction indices model was applied to both non-polar stationary phases bonded on silica, alumina and zirconia supports, and to the non-modified adsorbents in the normal-phase LC. The retention data of isomeric naphthalene disulfonic acids were used to compare the attractive and repulsive ionic interactions of the columns in purely aqueous mobile phases. The results of the hydrophobicity and polarity tests were consistent, and allowed column characterization and classification. Silanol activity was important with octadecyl silica columns, but was relatively insignificant with bonded polyethylene glycol and pentafluorophenylpropyl phases on silica gel support. Polar interactions with the alumina and zirconia support materials significantly affect the retention.

Theoretical investigation of novel silsesquioxane-supported Phillips-type catalyst by density functional theory (DFT) method

In spite of great commercial importance of the Phillips CrOx/SiO2 catalyst and long term research efforts, the precise physicochemical nature of active sites and polymerization mechanisms still remains unclear. The difficulties in a clear mechanistic understanding of this catalyst mainly come from the complexity of the surface chemistry of the amorphous silica gel support. In this work, novel silsesquioxane-supported Phillips Cr catalysts are utilized as realistic models of the industrial catalyst for theoretical investigation using the density functional theory (DFT) method in order to elucidate the effects of surface chemistry of silica gel in terms of supporting of chromium compounds and fluorination of the silica surface on the catalytic properties of the Phillips catalyst. Both qualitative and quantitative aspects with respect to various electronic properties and thermodynamic characteristics of the model catalysts were achieved. The future prospects of a state-of-the-art catalyst design and mechanistic approaches for the heterogeneous SiO2-supported Phillips catalyst has been demonstrated.

Microwave‐Assisted One‐Pot Synthesis of α‐Amino Phosphonates via Three Component Coupling on a Silica Gel Support.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Active Silica Gel-Supported Metathesis (Pre)Catalysts

2,3-Disubstituted styrene 1 was immobilized on silica gel support to give 2-iso­propoxy-3-anchored styrene (loading: 0.622 mmol/g). After capping of the free Si-OH groups, the supported 2-isopropoxystyrene group was treated with Grubbs’ catalyst to afford the silica-based Ru complexes 2a and 2b. The silica gel-supported complexes 2a and 2b exhibited high catalytic activity in a variety of metathesis reactions.

Microwave-assisted One-pot Synthesis of α-Amino Phosphonates via Three Component Coupling on a Silica Gel Support

Abstract A fast, highly efficient, general procedure under microwave irradiation, using silica gel-supported reagents for the synthesis of α-aminophosphonates is developed through a one-pot reaction of aldehydes and ketones with amines.

Microwave‐Assisted Claisen Rearrangement on a Silica Gel Support.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chiral separation of beta-adrenergic antagonists, profen non-steroidal anti-inflammatory drugs and chlorophenoxypropionic acid herbicides using teicoplanin as the chiral selector in capillary liquid chromatography

Three groups of structurally diverse chiral compounds were used to study the interaction mechanism responsible for stereoselective recognition with teicoplanin as chiral selector in capillary liquid chromatography. Teicoplanin-based chiral stationary phase (CSP) was used. The effect of the variation of mobile phase composition on retention and enantioselective separation was studied. The mobile phase composition suitable for enantioresolution of the various chiral compounds differed according to the interaction forces needed for chiral recognition. Mobile phases with high buffer portion (70–90 vol.%) were preferred for separation of enantiomers of profen non-steroidal anti-inflammatory drugs and chlorophenoxypropionic acid herbicides that require hydrophobic interactions, inclusion and π–π interactions for stereoselective recognition with teicoplanin. Higher concentration triethylamine in the buffer (0.5–1.0%) increased resolution of these acids. On the other hand, H-bonding and electrostatic interactions are important in stereoselective interaction mechanism of β-adrenergic antagonists with teicoplanin. These interaction types predominate in the reversed phase separation mode with high organic modifier content (95% methanol) and in polar organic mobile phases. For this reason β-adrenergic antagonists were best enantioresolved in the polar organic mode. The mobile phase composed of methanol/acetic acid/triethylamine, 100/0.01/0.01 (v/v/v), provided enantioresolution values of all the studied β-adrenergic antagonists in the range 1.1–1.9. Addition of teicoplanin to the mobile phase, which was suitable for enantioseparation of certain compounds on the CSP, was also investigated. This system was used to dispose of nonstereoselective interactions of analytes with silica gel support that often participate in the interaction with CSPs. Very low concentration of teicoplanin in the mobile phase (0.1 mM) resulted in enantioselective separation of 2,2- and 2,4-chlorophenoxypropionic acids.