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At least 973 records · Page 54Linked to original sources
PubMed2005

Effect of surface coverage on the conformation and mobility of C18-modified silica gels.

C18-modified silica gels with surface coverages of 2 to 8.2 micromol m(-2), were prepared by different synthetic pathways and characterized by Fourier Transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR) spectroscopy, and chromatographic measurements. The effects of temperature and bonding density on the conformational order of C18-modified silica gels were studied in detail by FTIR spectroscopy. The silane functionality and degree of cross-linking of silane ligands on the silica surface were evaluated by 29Si cross-polarization magic-angle spinning (CP/MAS) NMR and the structural order and mobility of the alkyl chains were investigated by 13C CP/MAS NMR spectroscopy. CH2 symmetric and anti-symmetric stretching bands and CH2 wagging bands were used as IR probes to monitor the conformational order and flexibility of the alkyl chains in the C18 phases. Qualitative information about the conformational order was obtained from frequency shifts of the CH2 symmetric and anti-symmetric stretching bands. The relative amounts of kink/gauche-trans-gauche, double-gauche, and end-gauche conformers in the alkyl chains were determined by analysis of CH2 wagging bands. These results indicate that surface coverage plays a dominant role in the conformational order of C18-modified silica gels. The FTIR and NMR data are discussed in the context of the chromatographic shape-selectivity differences.

Journal Article↗
PubMed2001

Retention behavior of large polycyclic aromatic hydrocarbons on metalloprotoporphyrin-silica stationary phases.

The retention behavior of large polycyclic aromatic hydrocarbons (LPAHs) (> or = 7 rings) on newly developed metalloplotoporphyrin (MProP)-silica stationary phases is examined and the results are compared to previously reported data for retention of the same solutes on commercially available phases. HPLC columns packed with FeProP-silica are shown to exhibit unique shape selectivity for LPAH retention, with the planar LPAHs always retained much longer than corresponding non-planar solutes. Solute planarity, length to breadth ratio (L/B value), and number of carbon atoms within the LPAHs are all demonstrated to contribute to the retention sequence observed. Further, the retention of LPAH solutes on FeProP-silica phases is shown to be more predictable than on other reversed-phase columns, with the elution sequence constant regardless of the mobile phase composition. Due to the extremely high planar selectivity of FeProP-silicas with respect to LPAH retention, it is envisioned that columns packed with these phases could be used in conjunction with existing commercial columns to devise Inethods for more efficient separation of complex mixtures of LPAHs in environmental and other samples.

Chromatography, High Pressure Liquid↗
PubMed2002

Microbial silica deposition in geothermal hot waters.

A combined use of molecular ecological techniques and geochemical surveys revealed that thermophilic or hyperthermophilic microorganisms living in geothermal environments are likely to be implicated in the formation of biogenic siliceous deposits. Electron microscopic observations indicated that numerous microorganism-like fabrics were preserved in naturally occurring siliceous deposits such as siliceous sinter, geyserite, and silica scale, which suggests microbial contribution to silica precipitation. Molecular phylogenetic analyses suggested that extreme thermophilic bacteria within the genera Thermus and Hydrogenobacter are predominant components among the indigenous microbial community in siliceous deposits formed in pipes and equipment of Japanese geothermal power plants. These bacteria seem to actively contribute to the rapid formation of huge siliceous deposits. Additionally, in vitro examination suggested that Thermus cells induced the precipitation of supersaturated amorphous silica during the exponential growth phase, concomitant with the production of a specific cell envelope protein. Dissolved silica in geothermal hot water may be a significant component in the maintenance of position and survival of microorganisms in limited niches.

Bacteria↗
PubMed2002

Rheumatoid syndrome associated with lung interstitial disorder in a dental technician exposed to ceramic silica dust. A case report and critical literature review.

Exposure to silica minerals is associated with silicosis and autoimmune disorders, especially systemic scleroderma. Evidence of this association has been increasingly reported in the last decade. The aim of this paper is to discuss, on the basis of a literature review, the case of a 28-year-old female dental technician who suffered from episodes of weakness, arthralgia, pain, swelling and stiffness of the fingers, dyspnoea with cough, a positive Waaler-Rose reaction, increased rheumatoid factor and normal ESR. She was a non-smoker. A rheumatoid syndrome with lung interstitial disorder, associated with silica exposure from dental ceramic products, was diagnosed. The patient had the HLA-A2-A31, HLA-B51-B18 and HLA-DR3-DR11 haplotypes, some of which are associated with autoimmune disease susceptibility. A 6-month follow-up, with adequate protection and without treatment, showed disappearance of the symptomatology and negative tests for Waaler-Rose reaction and rheumatoid factor. Exposure to silica should, therefore, be sought in the history of any patient with autoimmune or lupus-like syndrome and pulmonary changes. Symptoms associated with silica dust exposure from dental ceramic products should be recognised as being due potentially to an occupational disease, and dental technicians should be protected as workers at risk.

Adult↗
PubMed2004

Crystallization behavior of silica-calcium phosphate biocomposites: XRD and FTIR studies.

Silica and calcium phosphates (CaP) are the most important ingredients in bioactive materials that bond to bone and enhance bone tissue formation. In this study, silica-calcium phosphate (SiO2-CaP) composites were developed by powder metallurgy method, using silica (SiO2) and anhydrous dicalcium phosphate (CaHPO4) powders (CaP) in the ratios (wt%): 20/80, 40/60, 60/40 and 80/20. The effects of temperature and chemical composition on crystallization and phase transformation of the SiO2-CaP composites were evaluated by XRD and FTIR. Thermal treatment of the starting material suggested that CaHPO4 transforms into: gamma-Ca2P2O7 at 800 degrees C; beta-Ca2P2O7 at 1000 degrees C and alpha-Ca2P2O7 at 1200 degrees C. On the other hand, beta-quartz was the only detected phase after thermal treatment of silica in the temperature range 800-1200 degrees C. For all SiO2-CaP composites, SiO2 and CaP did not modify the crystallization behavior of each other when sintered in the temperature range 800-1000 degrees C. However, at 1200 degrees C, CaP promoted the transformation of gamma-quartz into alpha-cristobalite. Moreover, SiO2 stabilized beta-Ca2P2O7. The modifications in the crystallization behavior were related to ion substitution and formation of solid solutions.

Bone Substitutes↗
PubMed2006

In vitro apatite forming ability of type I collagen hydrogels containing bioactive glass and silica sol-gel particles.

Type I collagen hydrogel containing bioactive glass (CaO-P2O5-SiO2) and silica sol-gel micrometric particles were prepared and their in vitroapatite-forming ability in simulated body fluid assessed. X-ray diffraction and scanning electron microscopy analysis showed that bioactive glass particles entrapment in collagen matrix did not inhibit calcium phosphate formation and induced morphology variations on the crystalline phase precipitated on the hydrogel surface. The silica--collagen hydrogel composite precipitated calcium phosphate whereas silica particles and collagen hydrogel alone did not, indicating a possible synergetic effect between collagen and silica on the apatite-forming ability. Mechanisms of calcium phosphate precipitation and its relevance to biomaterial development are discussed.

Apatites↗
PubMed1989

High-performance liquid affinity chromatography with phenylboronic acid, benzamidine, tri-L-alanine, and concanavalin A immobilized on 3-isothiocyanatopropyltriethoxysilane-activated nonporous monodisperse silicas.

Nonporous, microparticulate, monodisperse silicas with particle diameters between 0.7 and 2.1 microns are introduced as stationary phases in high-performance affinity chromatography. The immobilization of m-aminophenylboronic acid, p-aminobenzamidine, tri-L-alanine, and concanavalin A onto these silicas was successfully achieved using 3-isothiocyanatopropyl-triethoxysilane as an activation reagent. Immobilized phenylboronic acid was applied to the isolation of nucleosides, nucleotides, and glycoprotein hormones such as bovine follicotropin and human chorionic gonadotropin, while immobilized benzamidine was employed for the isolation of the serine proteases thrombin and trypsin, immobilized tri-L-alanine for the separation of pig pancreatic elastase and human leukocyte elastase, and immobilized concanavalin A for the isolation of horseradish peroxidase. In all affinity chromatographic systems studied, the nonporous monodisperse silicas showed improved chromatographic performance compared to results obtained with porous silica supports using identical activation and immobilization procedures. Furthermore, frontal analysis was used as a method to evaluate the influence of experimental parameters on biological activity and accessible ligand densities. Only minor changes in bioactivity were found with the nonporous affinity supports, where accessibilities were typically higher than ca. 60%. The immobilization of affinity ligands onto porous supports as used in this and associated papers thus represents a successful general procedure for the preparation of stable matrices with fast kinetics for use in high-performance affinity chromatography.

Alanine↗
PubMed1989

Diffuse reflectance infrared Fourier transform spectroscopic characterization of a silica-immobilized N-hydroxysuccinimide active ester crosslinking agent and its precursors.

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to characterize the product of each step in the preparation of a silica-immobilized N-hydroxysuccinimide (NHS) active ester. The preparation of this NHS active ester linkage was based on a literature procedure for the immobilization of proteins. The DRIFT method was used to guide modification of this literature procedure. The DRIFT method also was used to indicate an impurity entrapped in the 60-A diameter pores of the silica support during the formation of the immobilized active ester. Degradation of the immobilized NHS active ester, stored under either argon or dioxane, can be followed by the DRIFT method. Myoglobin and glycine were allowed to react with the active ester, and the result for this silica support was evaluated by the DRIFT method. Elemental analysis was used to provide information on the loading of the silica-immobilized moieties that were presented for DRIFT analysis.

Cross-Linking Reagents↗
PubMed1987

Effect of mouse peritoneal macrophages of orally administered very high dilutions of silica.

The activity of very high dilutions of silica, a substance cytotoxic for macrophages, was tested on the synthesis by mouse peritoneal macrophages of the inflammatory ether-lipid paf-acether and its precursor lyso paf-acether. C57Bl6 female mice received for 25 days either 1.66 X 10(-11) M silica (11 sil) or 1.66 X 10(-19) M (19 sil) (final concentration) in the tap-water they were given to drink while control mice remained untreated. Isolated macrophages from mice treated with 11 sil produced 44.2 and 30.8% more paf-acether than cells from untreated mice in the presence of 50 and 200 micrograms zymosan (Z)/ml respectively. When 19 sil was given to the mice, the respective increases were 67.5 and 38%. In an experiment with a blind design, the mice were either untreated or received 19 sil or saline submitted to the same dilution procedure (19 sal). After administration of 19 sil, paf-acether synthesis was 55.5 and 33.5% higher upon stimulation with 50 and 200 micrograms Z/ml, respectively, than in the 19 sal group. In a third blind experiment, macrophages from mice that received 19 sil formed 61.3 and 28.6% more paf-acether upon stimulation with 50 and 200 micrograms Z/ml respectively, as compared to mice receiving 19 sal or lactose submitted to the same dilution procedure (19 lac). There was no difference between the 19 sal and the 19 lac groups. The differences between control and silica-treated mice were highly statistically significant in all experiments. There was no effect on the synthesis of lyso paf-acether. These results demonstrate clear ex vivo cellular effect of high dilutions of silica, that cannot be explained in our present state of knowledge.

Administration, Oral↗
PubMed1991

Immobilization of Fv antibody fragments on porous silica and their utility in affinity chromatography.

Recent advances in molecular biology have allowed antibody binding domains to be cloned and expressed in Escherichia coli. The use of Fv antibody fragments as ligands in immunoaffinity chromatography is reported. Fv fragments specific for hen-egg lysozyme were immobilized on porous silica and used to recover antigen from spiked serum in a single step. Comparison with a conventional immunoadsorbent (whole antibodies immobilized on silica) showed the Fv-silica to have a fivefold superior capacity. Analysis of sectioned Fv-silica particles by immunoelectron microscopy indicated that captured antigen was evenly distributed throughout the internal porous structure of the particle.

Animals↗
PubMed1994

Development of dihydrazide-activated silica supports for high-performance affinity chromatography.

A method of preparing dihydrazide-activated silica was developed for use in high-performance affinity chromatography (HPAC). This support was made by oxidizing diol-bonded silica and reacting it with oxalic or adipic dihydrazide. The steps involved in this synthesis were studied and confirmed by FTIR. Items considered in optimizing the preparation of the support included the amount of dihydrazide added and the reaction time or pH used. Control of dihydrazide bifunctional attachment was obtained by varying the extent of diol-bonded silica oxidation. This support was successfully used in the immobilization of oxidized antibodies, horse radish peroxidase (a glycoenzyme) and transfer RNA. In each case, data indicated that immobilization was through site specific coupling rather than non-specific adsorption. Dihydrazide-activated silica was found to be stable for 2-6 weeks after preparation when stored at 5 to 25 degrees C. The linkage between oxidized biomolecules and this support was stable for at least one month in the presence of various solvents commonly used in HPAC.

Adipates↗
PubMed1994

Phosphorimetry and its potential for the study of surface heterogeneity of chromatographic silica-based stationary phases.

Phosphorimetry was applied to the study of silica-based chromatographic phase surface heterogeneity by determining the phosphorescence response of a phenanthrene probe as a function of loading on underivatized silica and reversed and ion-exchange phases. The phosphorescence response was used to "titrate" and estimate the number of strong adsorption sites on underivatized silica. By incorporating covalent vs. ionic heavy atom/ion enhancers onto derivatized silicas, it was demonstrated that the probe molecules adsorb at residual silanols at lower loadings but associate with alkyl chains at higher loadings. Suggestions for further phosphorimetric studies are given.

Adsorption↗
PubMed1996

Effects of organic modifiers on the chiral recognition by different types of silica-immobilized bovine serum albumin.

We prepared three columns containing bovine serum albumin immobilized on silica by different means and the effects of organic modifiers in the eluent on chiral separation were studied using N-substituted amino acids. Adsorption on silica, covalent immobilization to diol-silica with carbonyldiimidazole (CSP-II) and covalent immobilization to amino-silica with glutaraldehyde were studied. CSP-II had the highest stereoselectivity and was the most affected by organic modifiers in the eluent. The hydrophobicity of amino acid moiety affected the chiral recognition of N-benzoylamino acids and the aromaticity of the N-substituted group was important.

Chromatography, High Pressure Liquid↗
PubMed1987

Selective removal of antigen-complexed IgG from cat plasma by adsorption onto a protein A-silica matrix.

The binding of normal cat IgG, heat-aggregated cat IgG and specific immune complexes (IC) containing cat IgG to a silica matrix containing covalently bound Staphylococcus aureus protein A was evaluated. The amounts of serum relative to protein A-silica, the flow rates and the perfusion times were representative of those existing when protein A-silica columns are used for therapeutic extracorporeal immunoadsorption of IgG and IC from humans and animals. When cat IgG was present in a large excess, approximately one molecule was bound to the matrix per molecule of solid-phase protein A with a KA of 1.5 X 10(6) 1/mol. Aggregated and immune complexed IgG bound to the matrix with relatively higher affinity. IC prepared in vitro between the purified envelope glycoprotein of the feline leukemia virus (FeLV gp70) and affinity-purified cat antibodies bound to the matrix even though normal IgG was present in greater than 10,000-fold excess. Once bound, IC were not eluted from columns upon further perfusion with normal serum. However, bound IgG was eluted from columns by further perfusion of normal serum or IC. IC were at least five-fold more efficient than normal IgG in exerting this effect. The results suggest that protein A-silica columns can be used for preferential removal of IC from plasma in a clinical or experimental setting.

Adsorption↗
PubMed1993

Silica-ELISA method improves detection and quantitation of minor glycolipid components in lipid mixtures and of other antigens.

This paper describes a new type of ELISA plate in which the reaction wells have been coated with silica gel. ELISA using these prototype silica-ELISA plates is markedly more sensitive for glycolipid antigens in lipid mixtures than ELISA using polystyrene plates without silica. Silica-ELISA plates also improve the analysis of certain protein and carbohydrate antigens. This technology may be of considerable benefit in the analysis of minor lipids and other antigens from human brain, cerebrospinal fluid or blood.

Animals↗
PubMed1988

Changes in the fatty acid profile of lung, liver and serum of rats intratracheally given silica.

The esterified (E) and nonesterified (NE) fatty acid level and profile in the lung, serum, and liver of rats are significantly altered after intratracheal administration of silica. The changes include a silica-specific increase of the total long chain (C16-C20:4) fatty acid content in the lung, and a decrease in the serum and liver of both groups of rats intratracheally given silica and/or saline. In the silicotic lung, arachidonate and palmitate accumulated at the highest rate. A heat-labile, high-molecular weight component from lung homogenates increases lipogenesis in isolated hepatocytes in vitro. These findings, taken together with evidence indicating increased lipogenesis in the liver of rats treated with silica under identical conditions, suggest a lung-liver communication mechanism which coordinates lipid uptake by the lung and lipid synthesis and release by the liver. The stimulatory factor identified in lung homogenates might play an important regulatory role-for hepatic lipogenesis in rats developing silicotic lungs.

Animals↗
PubMed1985

The effects of silica on lymph nodes and vessels--a possible mechanism in the pathogenesis of non-filarial endemic elephantiasis.

Non-filarial tropical elephantiasis, which occurs in certain volcanic areas of the world, has been postulated to be an obstructive lymphopathy due to the fibrogenic effects of silica absorbed through the plantar skin of bare-footed people. Animal experiments involving the direct intralymphatic injection of fine silica particles have been carried out in order to assess the extent to which this substance can engender lymphatic obstruction and to determine its main site of action. Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes.

Animals↗
PubMed1987

Plasma membrane glycoproteins covalently bound to silica beads as a model for molecular studies of cell-cell interactions in culture.

In previous studies, we have shown that plasma membrane glycoproteins are of major importance in the density-dependent regulation of growth of normal diploid fibroblasts. Due to the hydrophobic portions of these molecules, functional studies in cell culture are often difficult to perform and to interpret. Specifically, the addition of these molecules in soluble form to cell culture, after depletion of detergents needed for their solubilization, leads to aggregation and internalization. Therefore, we developed a method for the covalent immobilization of the solubilized plasma membrane proteins to derivatized silica beads for further investigations on the molecular nature of the active molecules. The addition of immobilized plasma membrane glycoproteins to sparsely seeded human fibroblasts resulted in cellular reactions similar to those found in confluent cell cultures (strongly reduced cell proliferation; high collagen type III synthesis). The method consists in the derivatization of silica beads (Lichrosphere Si 500, 10 microns) with isothiocyanatopropyltriethoxysilane. Amino-groups react with the SCN group under physiological conditions, resulting in a stable linkage of amino-group bearing molecules with the silica beads. Due to the easy handling of the silica beads (e.g. washing by short centrifugation steps), the mild coupling conditions, and the stable bondings this system is highly suited for functional studies of molecules involved in cell-cell interactions.

Cell Division↗