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At least 19 recordsLinked to original sources
PubMed2004

Extraction of heavy metals by 2-mercaptoethoxy groups attached to silica gel.

Silica gel is currently being used as a support for various straight chain mono- and bifunctional compounds such as amines, thiols (mercaptans), and mercaptoalochols. The current study reports the results of an investigation of a 2-mercaptoethoxy moiety covalently attached to silica gel. The condensation was effected by acid-catalyzed condensation of toluene solution of 2-mercaptoethanol and silica gel and azeotropically removing the water using a Dean-Stark tube. As a coordinating agent, this bifunctional compound was used in the removal of copper(II), cadmium(II), and lead(II) from standard aqueous solutions. Using silica gel support, the removal percentages were 91-93% for the three metals.

Cadmium↗
PubMed1996

Preconcentration of Pb(II), Cd(II), Cu(II) and Hg(II) with 2-mercapto-5-phenylamino-1,3,4-thiadiazole impregnated on silica gel.

Silica gel modified by the addition of 2-mercapto-5-phenylamino-1,3,4-thiadiazole (MPATD) was developed for the preconcentration of Pb(II), Cd(II), Cu(II) and Hg(II) at trace levels. A "series" experimental procedure permitted the determination of the optimal working conditions (time and pH) and an "on-column" experimental method permitted the determination of the quantity of MPATD retained on silica gel, the uptake capacity, the most suitable eluent and the minimum volume of eluent for which the maximum quantity of metal cations is recovered. The maximal retention capacity on the impregnated silica gel columns was obtained at pH 7.5-8 and was 1500 micrograms g-1 for Pb(II) and about 1000 micrograms g-1 for Cd(II), Cu(II) and Hg(II). The effect of preconcentration is relevant; on passing 1 l of solution containing 1 microgram ml-1 of cation through a column containing 5 g of impregnated silicagel, after elution with 30-50 ml of the appropriate eluent the cation concentration increased about 15-20-fold. The determination of cations by flame AAS was statistically evaluated and showed recoveries higher than 96% for Pb(II), 98.5% for Cd(II) and 97.95% for Cu(II) after elution with 4 M HNO3 and about 99.15% for Hg(II) after elution with thiourea.

Cadmium↗
PubMed1977

Production of aflatoxin B1 and G1 by Aspergillus parasiticus on silica gels.

Silica gels were prepared by acidifying alkaline silicate solutions with phosphoric or tartaric acid. Various combinations of glucose, sucrose, yeast extract, and salts were included in the gels an nutrients. Maximum production of aflatoxins B1 and G1 occurred when silica gel (0.4 to 0.5 cm deep in a petri dish) containing 20% sucrose and 2% yeast extract, and gelled with tartaric acid, was inoculated with approximately 120 to 12000 spores of Aspergillus parasiticus per plate; and plates were incubated at 28 degrees C for 10 days.

Aflatoxins↗
PubMed2001

"Cap-Tag"-Novel Methods for the Rapid Purification of Oligosaccharides Prepared by Automated Solid-Phase Synthesis Financial support from the donors of the Petroleum Research Fund, administered by the ACS (ACS-PRF 34649-G1), Merck (Predoctoral Fellowship for E.R.P.), Boehringer-Ingelheim (Predoctoral Fellowship for E.R.P.), and the NIH (Biotechnology Training Grant for M.C.H.) is gratefully acknowledged. Funding for the MIT-DCIF Inova 501 was provided by the NSF (Award CHE-9808061). Funding for the MIT-DCIF Avance (DPX) 400 was provided by the NIH (Award 1S10RR13886-01). We thank Silicycle (Quebec City, Canada) for the generous gift of fluorous silica gel and isocyanate silica gel scavenger resin. We thank Dr. O. Plante for helpful discussions and help with the automated oligosaccharide synthesizer.

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Journal Article↗
PubMed2003

Inner-sphere complexation of cobalt(II) 2,9-dimethyl-1,10-phenanthroline ([Co(neo)]2+) with commercial and sol-gel derived silica gel surfaces.

[Co(2,9-dimethyl-1,10-phenanthroline)(solvent)4]2+ ([Co(neo)]2+) undergoes a significant decrease in symmetry to form an inner-sphere surface complex when grafted directly on performed silica or introduced during the sol-gel process. The visible and X-ray absorption spectra of the surface adducts are interpreted in terms of a binding mode in which the Co(II) center has a highly distorted pseudo-C2v symmetry. The interaction of [Co(neo)]2+ with the silica surface was analyzed using an acid-base equilibrium relationship. Half-maximal surface binding was observed at pH ca. 6. Linear fits to the pH dependence data are consistent with inner-sphere binding of a single silanol group to the cobalt center. The formation of the surface species in tetramethoxyorthosilicate (TMOS) sol-gels required approximately 2 equiv of hydroxide anion per cobalt center, suggesting a two-proton-dependent binding event to form a species such as [Co(neo)(SiO)2]. Both sol-gel and silica samples showed essentially identical visible and X-ray absorption spectra, indicating formation of very similar surface adducts when the different synthesis procedures were employed. The maximal binding of [Co(neo)]2+ on three silica samples with different pore diameters and surface areas was compared. Increased binding was found to be inversely proportional to surface area and proportional to pore diameter, indicating a preference for less sterically demanding surface sites.

Cobalt↗
PubMed2000

Solid dosage form preparations from oily medicines and their drug release. Effect Of degree of surface-modification of silica gel on the drug release from phytonadione-loaded silica gels.

A surface-modified silica gel was produced to improve the surface affinity to an oily medicine, phytonadione (VK1). The effect of the degree of surface modification of the silica gel on the drug release behavior from the silica porous matrix was investigated. The silica gels were surface-modified using the silan coupling agent, 3-methacryloxypropyltrimethoxysilane (C7), octadecyltriethoxysilane (C18), or 3,3,3-trifluoropropyltrimethoxysilane (F3). A mixture of VK1 solution and surface-modified silica gel was evaporated under reduced pressure at room temperature, then the resulting powder was dried in vacuo. The degree of surface modification was evaluated based upon elementary analysis. The dissolution profiles of the samples were investigated in Japanese Pharmacopoeia XII, 1st fluid buffer (pH 1.2, 37+/-0.5 degrees C) containing 1.5% sodium lauryl sulfate. The FT-IR spectra of VK1-loaded surface-modified silica gels suggested that the amount of hydrogen-bonded VK1 with the silanol group on the gel surface decreased with increasing hydrophobicity of the silica gel. Since the modified group was rotating on the silica gel surface, and inhibited the adsorption of VK1 to the surface, the attractive molecular interaction between VK1 and the silica gel surface might decrease with increasing length of the modified functional group. However, the characteristics of the affinity of VK1 to the functional groups significantly differed among the groups. The VK1 release from the modified silica gels was initially rapid, slowed markedly after 1 h, and continued for more than 24 h. The amount of VK1 released from the modified surface silica gels by C7, C18 or F3 increased with increasing density of the surface modification group. The mean drug release moment (MDT) decreased with an increase in surface-modified group density.

Adsorption↗
PubMed2000

In vitro evaluation of sol-gel processed spray dried silica gel microspheres as carrier in controlled drug delivery.

The objective of this study was to evaluate sol-gel-derived spray dried silica gel microspheres as carrier material for dexmedetomidine HCl and toremifene citrate. The drug was dissolved in sol-gel processed silica sol before spray drying with Büchi laboratory scale equipment. Microspheres with a low specific surface area were spherical by shape with a smooth surface without pores on the external surface. The particle size distribution was quite narrow. The in vitro release of toremifene citrate and dexmedetomidine HCl showed a dose-dependent burst followed by a slower release phase, that was proportional to the drug concentration in the concentration range between 3.9 and 15.4 wt.%. The release period for toremifene citrate was approximately 10 days and for dexmedetomidine HCl between 7 and 50 days depending on drug concentration. Spray drying is a promising way to produce spherical silica gel particles with a narrow particle size range for controlled delivery of toremifene citrate and dexmedetomidine HCl.

Delayed-Action Preparations↗
PubMedDate not supplied

Multiresidue screen for organophosphorus insecticides using gel permeation chromatography--silica gel cleanup.

A multiresidue screen for quantitative determination of 43 organophosphorus insecticides in 5 g of plant and animal tissues is described. The organophosphorus insecticides are extracted with methanol-dichloromethane (10 + 90, v/v) and cleaned up using automated gel permeation chromatography with hexane-ethyl acetate (60 + 40) eluant and in-line silica gel minicolumns. Concentrated extracts are analyzed by gas chromatography with flame photometric detection. The method recovers 43 organophosphorus insecticides in the range of 72 to 115%. Analysis of fortified bovine liver (n = 5) shows an average 95.9 +/- 4.8% recovery at the 0.05 micrograms/g level and 93 +/- 3.8% at the 0.5 micrograms/g level. Analysis of fortified bovine rumen content (n = 5) shows an average 98 +/- 4.2% recovery at the 0.1 micrograms/g level and 98.7 +/- 2.8% at the 1 micrograms/g level. Method detection limits ranged from 0.01 to 0.05 micrograms/g for the compounds studied using a nominal 5 gram sample.

Animals↗
PubMed1996

Apatite formation on silica gel in simulated body fluid: its dependence on structures of silica gels prepared in different media.

It has been shown that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of a layer of biologically active bonelike apatite on their surfaces. The hydrated silica formed on the surfaces of glasses and glass-ceramics plays an important role in nucleating the apatite. In the present study, the structure of the hydrated silica responsible for the apatite nucleation was investigated in an accellular simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Three kinds of porous silica gels were prepared by hydrolysis and polycondensation of tetraethoxysilane in pure water or in aqueous solution containing polyethylene glycol or polyacrylic acid. The silica gels prepared in aqueous solution containing polyethylene glycol or polyacrylic acid had micron-size interconnected pores, whereas the gel prepared in pure water did not. All the gels contained a large volume of nanometer-size pores, almost the same amounts of silanol groups and D2 defect, and showed a high dissolution rate of the silica. Despite this, only the gel prepared in the solution containing polyethylene glycol formed the apatite on its surface in the simulated body fluid. This indicates that only a certain type of structural unit of the silanol group is responsible for the apatite nucleation.

Acrylates↗
PubMed1977

[Thin layer chromatographic detection of aflatoxins on ready-made silica gel plates].

Silica gel instant plates with an aluminium reflection foil as the carrier material (Silufol) were tested for their suitability for the thin-layer chromatographic separation of aflatoxins in comparison with conventiol silica gel G coated glass plates. Besides the well-knwon merits of instant plates, the Silufol plates offer remarkable analytical advantages; increased sensibility and shorter time of development. For this reason, the Silufol plates may be recommended for routine examinations of foods for aflatoxins.

Aflatoxins↗
PubMed1992

Separation of oligogalacturonic acids by high-performance gel filtration chromatography on silica gel with diol radical.

Oligogalacturonic acids (OLGAs) ranging from two to nineteen residues in length were separated using high-performance gel filtration chromatography on a silica gel with diol radical. The optimum conditions (eluent, column temperature) for separation of OLGAs by high-performance gel filtration chromatography were investigated. The column used in this experiment allowed a high pressure of 4900 p.s.i. and a flow-rate of 2 ml/min. The stationary phase of silica gel stabilized the separation of OLGAs. The peaks of OLGAs separated using this column were assigned by comparing retention times with standards, and the molecular weights of the corresponding OLGAs were determined by fast atom bombardment mass spectrometry.

Chromatography, Gel↗
PubMed2002

Preparation and in vitro evaluation of porous silica gels.

Porous silica gels with high surface areas were prepared from tetraethylothosilicate and polyacrylic acid (PAA) of high molecular weight in acidic media by a sol-gel method. PAA content and ageing temperatures were varied in order to obtain different microstructures. Samples were sintered at temperatures up to 400 degrees C, and subjected to in vitro evaluation by soaking them in acellular inorganic solutions at 37 degrees C and pH 7.3. Surface precipitation of carbonate-apatite on some of the gels was observed by FTIR spectroscopy, scanning electron microscopy and EPMA. Silica dissolution and re-precipitation phenomena were also observed. The relationship between both phenomena during the in vitro test is discussed mainly in terms of structural and microstructural features of the gel.

Acrylic Resins↗
PubMed2006

Trypsin immobilization by direct adsorption on metal ion chelated macroporous chitosan-silica gel beads.

Silica gel bead coated with macroporous chitosan layer (CTS-SiO(2)) was prepared, and the metal immobilized affinity chromatographic (IMAC) adsorbents could be obtained by chelating Cu(2+), Zn(2+), Ni(2+) ions, respectively on CTS-SiO(2), and trypsin could be adsorbed on the IMAC adsorbent through metal-protein interaction forces. Batch adsorption experiments show that adsorption capacity for trypsin on these IMAC adsorbent variated with change of pH. The maximal adsorption reached when the solution was in near neutral pH in all three IMAC adsorbents. Adsorption isothermal curve indicated that maximal adsorption capacity could be found in the Cu(2+)-CTS-SiO(2) with the value of 4980+/-125 IUg(-1) of the adsorbent, while the maximal adsorption capacity for trypsin on Zn(2+) and Ni(2+) loaded adsorbent was 3762+/-68 IUg(-1) and 2636+/-53 IUg(-1), respectively. Trypsin immobilized on the IMAC beads could not be desorbed by water, buffer and salt solution if the pH was kept in the range of 5-10, and could be easily desorbed from the IMAC beads by acidic solution and metal chelating species such as EDTA and imidazole. The effect of chelated metal ions species on CTS-SiO(2) beads on the activity and stability of immobilized trypsin was also evaluated and discussed. Trypsin adsorbed on Zn-IMAC beads retained highest amount of activity, about 78% of total activity could be retained. Although the Cu-IMAC showed highest affinity for trypsin, only 25.4% of the calculated activity was found on the beads, while the activity recovery found on Ni-IMAC beads was about 37.1%. A remarkable difference on stability of trypsin immobilized on three kinds of metal ion chelated beads during storage period was also found. Activity of trypsin on Cu-IMAC decreased to 24% of its initial activity after 1-week storage at 4 degrees C, while about 80% activity was retained on both Ni-IMAC and Zn-IMAC beads. Trypsin immobilized on Zn-CTS-SiO(2) could effectively digest BSA revealed by HPLC peptide mapping.

Adsorption↗
PubMed1985

[High performance liquid chromatography of peptide bioregulators, their fragments and derivatives. II. Sorption of peptides from aqueous-organic eluents on octadecylsilylsilica gel and unmodified silica gel].

Dependence of the peptide retention upon the organic component concentration in eluent has been studied. A parabolic dependence has been found in a wide range of acetonitrile concentrations. The effect observed with ODS- and unmodified silica as stationary phases extends analytical and preparative potentialities of HPLC of peptides.

Chromatography, High Pressure Liquid↗
PubMed2002

Effect of synthesis parameters of the sol-gel-processed spray-dried silica gel microparticles on the release rate of dexmedetomidine.

The objective of this study was to evaluate the possibilities to control the release rate of dexmedetomidine (DMED) from different spray-dried silica gel microparticle formulations. Microparticles were prepared by spray drying a silica sol polymer solution containing the drug. Drug release was investigated both in vitro and in vivo. The influence of sol-gel synthesis parameters, like pH and the water/alkoxide ratio (r) of the sol, on the release behaviour of the drug was studied. Silica gel microparticles had a smooth surface. Microparticles prepared from diluted sol, however, were more aggregated and clustered. The drug release conformed to zero order release from microparticles prepared near the isoelectric point of silica (pH 2.3 and pH 3) and to the square root of time kinetics from microparticles prepared at pH 1 and pH 5. The release also showed a dual-phasic profile with an initial burst and after that a slower release period. The dexmedetomidine release conformed to zero order kinetics from microparticles prepared at water/ alkoxide ratios between r = 6 and r = 35 (at pH 2.3). The release rate was the slowest from microparticles prepared with water/ alkoxide ratio 35. The bioavailability of dexmedetomidine in dogs showed that the release was sustained from silica gel microparticles as compared with a subcutaneously administered reference dose of 0.1 mg.

Analgesics, Non-Narcotic↗