Showing papers on "Silica gel published in 2001"

Molecular confinement influences protein structure and enhances thermal protein stability.

Abstract: The sol-gel method of encapsulating proteins in a silica matrix was investigated as a potential experimental system for testing the effects of molecular confinement on the structure and stability of proteins. We demonstrate that silica entrapment (1) is fully compatible with structure analysis by circular dichroism, (2) allows conformational studies in contact with solvents that would otherwise promote aggregation in solution, and (3) generally enhances thermal protein stability. Lysozyme, α-lactalbumin, and metmyoglobin retained native-like solution structures following sol-gel encapsulation, but apomyoglobin was found to be largely unfolded within the silica matrix under control buffer conditions. The secondary structure of encapsulated apomyoglobin was unaltered by changes in pH and ionic strength of KCl. Intriguingly, the addition of other neutral salts resulted in an increase in the α-helical content of encapsulated apomyoglobin in accordance with the Hofmeister ion series. We hypothesize that protein conformation is influenced directly by the properties of confined water in the pores of the silica. Further work is needed to differentiate the steric effects of the silica matrix from the solvent effects of confined water on protein structure and to determine the extent to which this experimental system mimics the effects of crowding and confinement on the function of macromolecules in vivo.

Fluorous Reverse Phase Silia Gel. A New Tool for Preparative Separations in Synthetic Organic and Organofluorine Chemistry

Abstract: Fluorous reverse phase silica gel, or silica gel with a fluorocarbon bonded phase, can be readily prepared by standard techniques, but shows unusual separation features. This silica gel separates primarily by fluorine content. Uses of fluorous reverse phase silica gel in both synthetic organic chemistry and organofluorine chemistry are introduced. Solid phase extraction can be used to separate fluorous or fluorous-tagged compounds from organic compounds. Fluorous chromatography can be used to purify mixtures of compounds with differing fluorine content as well as for "demixing" in the new technique of fluorous mixture synthesis.

Surface modification of inorganic oxide particles with silane coupling agent and organic dyes

Abstract: The silane coupling agent 3-glycidoxypropyl trimethoxylsilane (GPS) was grafted onto the surface of silica gel, P2 glass beads and TiO2 oxide particles. FT-IR, thermogravimetric and elemental analysis were used to characterize the modified particles. The effects of various factors on the GPS grafting efficiency such as catalyst, GPS concentration, reaction temperature and time were studied. After modification with GPS, the xanthene dye rhodamine B and azo dyes 4-phenylazophenol and 4-phenylazoaniline, respectively, were grafted on to the particles, which were then used as pigment fillers. The colors of the pigments were adjusted by changing the kind of dyes, the concentration, the pH and the reaction solvents. Copyright © 2001 John Wiley & Sons, Ltd.

Preparation and characterization of surface bond-conjugated TiO2/SiO2 and photocatalysis for azo dyes

Abstract: Surface bond-conjugated TiO2/SiO2 was prepared by means of the impregnation method. Based on the results of XRD, FTIR, XPS and BET measurements, the growth of titania (predominantly anatase) on the silica substrate seems to occur by anchoring of the TiO2 phase through Ti-O-Si cross-linking bonds. The structure model of TiO2/SiO2 was proposed. Compared to B-TiO2, the most efficient catalyst is 30 wt.% TiO2/SiO2 (Ims30), which showed three times higher photoactivity for the degradation of reactive 15 (R15). In addition, the catalyst had a higher photoactivity on a silica of smaller particle size than on the silica of larger particles. Silica gel plays the basic role of dispersion and support for power TiO2. The isoelectric point of the catalyst was 3.0 pH units by the measurement of zeta-potential, indicating the presence of the surface acidity of the: catalyst. The photodegradation and the adsorption of R15 and cationic blue X-GRL (CBX) were investigated with the change of initial aqueous pH. (C) 2001 Elsevier Science B.V. All rights reserved.

Silica sol-gel for the controlled release of antibiotics. I. Synthesis, characterization, and in vitro release.

Abstract: Room temperature processed silica sol-gel (xerogel) was investigated as a novel controlled release carrier of antibiotics (vancomycin). Xerogel characteristics, in vitro release properties, and bactericidal efficacy of the released antibiotic were determined. The xerogel/vancomycin composite showed a long-term sustained release (up to 6 weeks). In addition, bactericidal efficacy of released vancomycin was retained. The kinetics of release and the amount released were dose dependent. The initial, first-order release was followed by a near-zero-order release. The time to transition from the first- to zero-order release increased with vancomycin load (from 2 to 3 weeks with load increase from 2.2 to 11.1 mg/g). Regardless of the load, about 70% of the original vancomycin content was released by the transitional point, and the cumulative release after 6 weeks of immersion was about 90%. This study, combined with other reports documenting biocompatibility and controlled resorbability of the xerogel/drug composite in vivo, suggests that silica xerogel is a promising controlled release material for the treatment of bone infections.

Novel Electrochemical Interfaces with a Tunable Kinetic Barrier by Self-Assembling Organically Modified Silica Gel and Gold Nanoparticles

Abstract: A simple strategy is presented for the construction of an electrochemical interface with a tunable kinetic barrier by self-assembling organically modified silica gel and gold nanoparticles. Self-assembly of an organically modified silica layer is carried out from the hydrolyzed sol of the precursor mercaptopropyltrimethoxysilane. The kinetic barrier of this self-assembled silicate film is modified by gold nanoparticles that are self-assembled into the silicate network. The electrochemistry of ferricyanide redox reaction is used as a marker to probe the interface.

Coating and fusing cell membranes onto a silica surface and their chromatographic characteristics

Abstract: A new cell membrane stationary phase (CMSP) consisting of porous silica coated with active cell membranes is presented for affinity chromatography. By immersing, silica into a suspension of cell membranes, the whole surface of silica was covered by the cell membranes due to the irreversible adsorption of silanol groups (Si−OH) on the silica surface and the self-fusion of the cell membranes. CMSP can be used directly as a chromatographic packing material without any additional chemical modification. The surface characteristics, enzymatic activity, and chromatographic behavior of CMSP were investigated. The results obtained from scanning electron microscope, surface energy spectrometer, enzyme assay, and liquid chromatography showed that the surface characteristics of CMSP were very different from that of normal and reversed stationary phases. CMSP was found to have the characteristics of both cell membrane activity and chromatographic separation. Moreover, CMSP, as a chiral stationary phase, could be used for the enantiomeric separation of (±) Bay-K8644. The capacity factor of some calcium antagonists on CMSP was found to have a good correlation with their pharmacological actions. It is concluded that CMSP may be used not only as a kind of packing material in bio-affinity chromatography, but also as a tool for studying the interactions between a drug and its receptor.

Voltammetric detection of copper(II) at a carbon paste electrode containing an organically modified silica

Abstract: A carbon paste electrode modified with aminopropyl-grafted silica gel (APS) was evaluated as an electrochemical sensor for copper species in aqueous medium. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the voltammetric quantification. During the preconcentration step, copper(II) was accumulated on the APS surface by complexation with the amine groups. In the detection step, copper(II) was desorbed in acidic medium, then cathodically electrolyzed at −0.5 V for 60 s, and detected by anodic stripping square wave voltammetry. The influence of various experimental parameters on the sensor response was investigated (i.e. pH of the detection and accumulation media, electrolysis time, carbon paste composition, silica gel porosity, accumulation time). Reproducible results were obtained, giving after optimization a linear calibration in the 5×10 −8 –2×10 −7 M concentration range, with a detection limit of 3×10 −9 M. This new sensor was applied to copper analysis in laboratory tap water.

Silica sol‐gel for the controlled release of antibiotics. II. The effect of synthesis parameters on the in vitro release kinetics of vancomycin

Abstract: Room temperature-processed silica sol-gel (xerogel) was investigated as a novel controlled release carrier of vancomycin for the treatment of osteomyelitis. Vancomycin-loaded xerogels were fabricated with varying water/alkoxysilane molar ratios and vancomycin concentrations. The goal of this study was to determine the effect of varying the aforementioned synthesis parameters on the daily in vitro release kinetics of vancomycin from the xerogel disks. A controlled, load-dependent, long-term release of vancomycin was observed for all of the molar ratios that were used in the study (4, 6, and 10). Variations in the water/alkoxysilane molar ratio affected the release process extensively. A cumulative release of about 90% of the original amount of vancomycin was found for molar ratios 6 and 10 by 21 and 14 days, respectively. Only about 30% was released from xerogels with a molar ratio of 4 after 21 days of immersion. A first-order release stage was followed by a steady release stage for xerogels with molar ratios of 6 and 10, whereas zero-order release was observed for xerogels with a molar ratio of 4. The findings of this study indicate that the release kinetics of vancomycin from xerogel can be tailored by varying the xerogel synthesis parameters.

Strengthening of silica gels and aerogels by washing and aging processes

Abstract: Gels were prepared from a polyethoxydisiloxane precursor by using HF as a catalyst. During washing in water solution a significant increase in the permeability of the gels was observed, showing that dissolution-reprecipitation occurs. After washing, the gels were further soaked in a solution of polyethoxydisiloxane precursor to strengthen and stiffen the gel. As expected, a significant enhancement of the mechanical properties of the wet gels was observed. It is also interesting to note, however, that the permeability does not decrease below the value for the as-prepared gels. Hence, a promising process has been developed where both the stiffness and the strength have been increased as well as the permeability. The increase in permeability is of importance to facilitate the supercritical drying process. Reasonably successful scaling up of the supercritical drying of these gels to laboratory scale has been achieved, and monolithic and transparent gels are obtained. Optical properties have been measured on laboratory scale aerogels. The corresponding results have been correlated with structural characteristics measured by small-angle X-ray scattering (SAXS).

Measurements of Equilibrium Pressures and Temperatures for Propane Hydrate in Silica Gels with Different Pore-Size Distributions

Abstract: Equilibrium pressures for the dissociation of propane hydrate confined in silica gel pores of nominal radii 7.5, 5.0, 3.0, and, 2.0 nm were measured across a wide temperature range, and were higher...

Reactions of Organosilanes with Silica Surfaces in Carbon Dioxide

Abstract: Silylation reactions using liquid and supercritical CO2 as the solvent were performed on both single surface (silicon wafers) and nanoporous (silica gel) silica samples. The alkylsilyl monolayers formed on single surfaces were characterized by wettability, ellipsometry, and X-ray photoelectron spectroscopy. Modified nanoporous silica samples were analyzed by chemical analysis. A range of different silanes including monochloro-, dichloro-, trichloro-, and dimethylamino-silanes was examined. The results indicate that dense carbon dioxide is a good solvent for silylation reactions, comparable or better than most solvents. Compared with the optimum conditions for silylation at solid−liquid interfaces, reactions in carbon dioxide are faster, although maximum bonding densities are slightly lower.

Matrix‐assisted laser desorption/ionization mass spectrometry using porous silicon and silica gel as matrix

Abstract: Porous silicon powder and silica gel particles have been applied as inorganic matrices for the analysis of small molecules in matrix-assisted laser desorption/ionization mass spectrometry (maldi-tofms). in contrast to conventional maldi-tofms, the signal interference of low-molecular analytes by the matrix has been eliminated. almost no fragmentations of the analytes were observed. effects of various factors, such as the particle and pore size, the suspending solution, and sample preparation procedures, on the intensity of mass spectra have been investigated. the pore structure of the inorganic matrix and penetration of the analytes into the pores must be optimized for effective desorption and ionization of the analytes. matrices (dhb and hcca) were covalently bound to silica gel for improvement of spectrum intensity. copyright (c) 2001 john wiley & sons, ltd.

FTIR Thermal Analysis on Organofunctionalized Silica Gel

Abstract: Silica gel modificada com grupos orgânicos tem sido muito utilizada como fase estacionaria para cromatografia liquida. Reacoes de enxerto podem ser usadas na obtencao de superficies modificadas estaveis de silica gel. Neste trabalho a silica gel (10 nm de diâmetro de poro e 320 m 2 g -1 de area superficial) foi modificada quimicamente com 3-cloropropiltrimetoxisilano ou com 3-aminopropiltrimetoxisilano e posteriormente com anilina, p-anisidina, benzilamina e 3-fenilpropilcloreto a fim de se obter grupos aromaticos imobilizados na superficie de silica gel. A espectroscopia no infravermelho foi utilizada para a caracterizacao dos grupos aromaticos enxertados, usando-se uma cela de quartzo. Os solidos foram aquecidos a varias temperaturas em alto vacuo sendo que as areas sob as bandas dos grupos orgânicos obtidas no infravermelho foram usadas para estimar a estabilidade termica. Silica gel modified with organic groups is widely used as a stationary phase for liquid chromatography. Grafting synthesis can be used to obtain stable modified silica gel surfaces. In this work, silica gel (10 nm of pore diameter and surface area of 320 m 2 g -1 ) was chemically modified with 3-chloropropyltrimethoxysilane or 3-aminopropyltrimethoxysilane and reacted with aniline, p-anisidine, benzylamine and 3-phenylpropylchloride in order to yield aromatic groups immobilized on the silica gel surface. Infrared spectroscopy was utilized for characterization of the aromatic groups grafted on the silica gel surface, using a quartz cell. The solids were heated at several temperatures in high vacuum and the infrared band areas of the organic groups were used to evaluate the thermal stability.