Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Silicates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24Linked to original sources
PubMed2004

Channel formation and intermediate range order in sodium silicate melts and glasses.

We use inelastic neutron scattering and molecular dynamics simulation to investigate the interplay between the structure and the fast sodium ion diffusion in various sodium silicates. With increasing temperature and decreasing density the structure factors exhibit an emerging prepeak around 0.9 A(-1). We show that this prepeak has its origin in the formation of sodium rich channels in the static structure. The channels serve as preferential ion conducting pathways in the relative immobile Si-O matrix. On cooling below the glass transition this intermediate range order is frozen in.

Diffusion↗
PubMed1979

The effect of silicate cement on the mitochondria and lysosomes of cultured cells assessed by quantitative enzyme histochemistry.

The cytotoxic effect of the silicate cement "Silicap" was evaluated in an in vitro system which simulates the clinical usage of the material. BHK-21 (C-13) cells on cover slips were exposed to the freshly mixed material for 1h, and stained for the demonstration of succinic dehydrogenase and acid phosphatase. The mean stain density for succinic dehydrogenase and acid phosphatase in the experimental cells was 77% and 153% of the control values respectively. The mechanism of cytotoxicity of "Silicap" is discussed.

Acid Phosphatase↗
PubMed1979

Toxic elements in silicate cements.

Six brands of silicate cements have been characterized by means of optical emission spectrography with respect to the contents of elements in minor or trace quantities in a search for presence of possible toxic elements. Beryllium was observed in two powders at levels of 1.3 and 1.6% Cadmium was found in two powders at levels of 0.02 and 0.03%. Lead was measured in three powders at levels of 0.001-0.003%. Bismuth, boron, copper, gallium, iron, manganese, titanium, tin and zirconium were found in various brands in either powder or liquid at levels of 0.001-0.1%. Upper limits of the amounts of the various elements that might be transferred to the gastrointestinal tract after dissolution of the cement matrix in the oral cavity have been calculated.

Beryllium↗
PubMed1982

Improvement of erosion resistance of a silicate cement by infrared radiation.

Silicate cement specimens have been exposed to infrared radiation for the purpose of improving the erosion resistance. Exposure for periods of 3-10 min, corresponding to a surface temperature of about 60-70 degrees C, resulted in a reduced phosphate release of about 3-5 times that of a non-exposed group. The temperature distributions on the surface, as well as in a position 5 mm beneath the surface, were measured with thermocouples during irradiation. A difference in temperature of about 20 degrees C was registered between the surface and interior positions. The technique may be clinically exploited by exposing the restoration after insertion to a small infrared radiation source, available on the commercial market.

Chemical Phenomena↗
PubMed1996

A silicate inclusion in Puente del Zacate, a IIIA iron meteorite.

The IIIA and IIIB iron meteorites are considered to have formed in the cores of asteroids. A silicate inclusion within the IIIA meteorite Puente del Zacate consisting of olivine (Fa4), low-calcium pyroxene (Fs6Wo1), chromium diopside (Fs3Wo47), plagioclase (An14Or4), graphite, troilite, chromite, daubreelite, and iron metal resembles inclusions in IAB iron meteorites. The oxygen isotopic composition of the Puente del Zacate inclusion is like chromite and phosphate inclusions in other IIIA and IIIB irons. The Puente del Zacate inclusion may have been derived from the lower mantle of the IIIAB parent asteroid.

Meteoroids↗
PubMed1998

High-temperature silicate volcanism on Jupiter's moon Io.

Infrared wavelength observations of Io by the Galileo spacecraft show that at least 12 different vents are erupting lavas that are probably hotter than the highest temperature basaltic eruptions on Earth today. In at least one case, the eruption near Pillan Patera, two independent instruments on Galileo show that the lava temperature must have exceeded 1700 kelvin and may have reached 2000 kelvin. The most likely explanation is that these lavas are ultramafic (magnesium-rich) silicates, and this idea is supported by the tentative identification of magnesium-rich orthopyroxene in lava flows associated with these high-temperature hot spots.

Extraterrestrial Environment↗
PubMed1999

Stable five- and six-coordinated silicate anions in aqueous solution.

Addition of aliphatic polyols to aqueous silicate solutions is shown to yield high concentrations of stable polyolate complexes containing five- or six-coordinated silicon. Coordinating polyols require at least four hydroxy groups, two of which must be in threo configuration, and coordinate to silicon via hydroxy oxygens at chain positions on either side of the threo pair. The remarkable ease by which these simple sugar-like molecules react to form hypervalent silicon complexes in aqueous solution supports a long-standing supposition that such species play a significant role in the biological uptake and transport of silicon and in mineral diagenesis.

Anions↗
PubMed1996

A food-grade process for isolation and partial purification of bacteriocins of lactic acid bacteria that uses diatomite calcium silicate.

Bacteriocins, including nisin, pediocin PO2, brevicin 286, and piscicolin 126, were extracted from fermentation media by adsorption onto Micro-Cel (a food-grade diatomite calcium silicate anticaking agent) and subsequent desorption. The optimal conditions for desorption of piscicolin 126 were determined and applied to other bacteriocins, and the relative purities of the desorbed preparations were compared. Piscicolin was not successfully desorbed from Micro-Cel at pH 1.0 to 12.0, with organic solvents, or by increase of ionic strength up to 1 M NaCl. However, 25 and 75% of the bacteriocin activity was desorbed by using 1% sodium deoxycholate and 1% sodium dodecyl sulfate (SDS), respectively. Higher levels (up to 100%) of desorption were achieved by repeated elution or by an increase in surfactant concentration. Desorption of piscicolin with 1/10 volume of SDS solution resulted in a preparation with 10 times concentration in activity, equivalent to that of ammonium sulfate preparations (409,600 to 819,200 activity units/ml). Determination of organic nitrogen (N) content revealed that the desorbed piscicolin preparations were substantially free of proteinaceous substances (approximately 92 to 99%) compared with original culture supernatants and ammonium sulfate preparations. Nisin, pediocin, and brevicin were also desorbed with 1% SDS with a similar level of purification.

Bacteriocins↗
PubMed1991

Continental-pelagic carbonate partitioning and the global carbonate-silicate cycle.

A carbonate-silicate geochemical cycle model is developed and used to explore dynamic and climatic consequences of constraints on shallow-water carbonate burial and possible carbon loss to the mantle associated with sea-floor subduction. The model partitions carbonate deposition between shallow-water and deep-water environments and includes carbon fluxes between the mantle and lithosphere. When total lithospheric carbonate mass is constant, there are two stable steady states, one in which the carbonate burial flux is mostly continental and another in which it is mostly pelagic. The continental steady state is characterized by a low metamorphic CO2 flux to the atmosphere and predominantly shallow-water carbonate burial. The pelagic steady state is characterized by a high metamorphic CO2 flux and predominantly deep-water carbonate burial. For reasonable parameter values, when total lithospheric carbonate mass is allowed to vary, the model oscillates between predominantly continental and predominantly pelagic modes. Model results suggest that carbonate deposition patterns established during the Cenozoic may be pushing the Earth system from the continental to the pelagic mode on a time scale of 10(8) yr, with a possible consequent order-of-magnitude increase in the metamorphic CO2 flux to the atmosphere.

Carbon Dioxide↗
PubMed1993

Hypersensitivity pneumonitis and exposure to zirconium silicate in a young ceramic tile worker.

We describe a nonsmoking ceramic tile worker 25 yr of age who developed a worsening dry cough and dyspnea after 3.5 yr as a sorter and glazer of tiles. Open lung biopsy revealed an intense granulomatous interstitial pneumonia with mild fibrosis, compatible with hypersensitivity pneumonitis, and numerous very small birefringent crystals around the terminal airways and occasionally in granulomas. Pulmonary particle analysis revealed an inhaled dust burden nearly 100-fold the normal background level, mainly consisting of clay minerals and zirconium silicate. The patient had no history or clinical or laboratory findings suggesting any organic etiologic agent. A sarcoid granulomatosis type of chronic pulmonary hypersensitivity reaction is known after long-term exposure to zirconium, but this case demonstrates that zirconium can also cause an acute and fulminant allergic alveolitislike hypersensitivity reaction.

Adult↗
PubMed2005

Microscopy and quantitative morphology of aluminum silicate nanoparticles grown on organic templates.

Biomimetic synthesis of ceramic materials is increasing in popularity because it offers many advantages. In this work, aluminum silicate nanoparticles were obtained on a self-assembled organic multilayer at near room temperature (30 < or = T < or = 50 degrees C) and at atmospheric pressure. Morphological and microanalytical characterization was carried out by means of transmission electron microscopy and subsequent image analysis. The roles of some process parameters such as template type, reactant concentration, [Al]:[Si] molar ratio, number of initiation steps (IS) of mineralization, and reaction time (rt) were assessed by comparing images, diffraction patterns, and EDX spectra. Generally, the Si-rich phase exhibited higher crystallinity, whereas the Al-rich phase was mostly amorphous. Crystal structure resulted with rt > or = 4 days for template-grown materials. Images of materials obtained at T = 50 degrees C, rt = 3 days, and 1 < or = IS < or = 4 were further analyzed by "spectrum enhancement," an algorithm based on the Fourier transform. Morphological indicators were extracted from suitably processed power spectral densities, a correlation matrix was formed, and multivariate statistics was carried out. Visual differences in nanoaggregate morphology were quantitatively translated. Materials were ranked by the spatial uniformity of nanoparticle distribution: the most uniform aggregates were those grown on templates by IS > or = 2. Univariate statistics validated the conclusion: the particles of those same materials had a narrower size distribution and sharper edges. This last property has been ascribed to crystalline structure, independently demonstrated by diffraction patterns.

Aluminum↗
PubMed1979

Studies of prophylaxis pastes containing sodium-potassium aluminum silicate and fluoride.

A sodium-potassium aluminum silicate cleaning and polishing agent was compared with conventional prophylaxis abrasives and was found to be highly compatible with fluoride. When formulated into a fluoride prophylaxis paste, especially with stannous fluoride, a larger reduction in enamel solubility and greater fluoride uptake were obtained with representative commercial prophylaxis pastes.

Aluminum Silicates↗
PubMedDate not supplied

Colloidal silicic acid for the treatment of psoriatic skin lesions, arthropathy and onychopathy. A pilot study.

In a randomized, double-blind study, patients with chronic plaque-type psoriasis were either treated with 30 ml colloidal silicic acid gel, orally, daily, and topically with the same gel (n = 15), or were treated identically with placebo gel (n = 15) for 3 months. One stable psoriatic lesion on the knee or elbow was treated topically and followed throughout the study. Five patients in the treated group and seven controls had psoriatic arthropathy and 11 treated patients and 12 controls had psoriatic onychopathy. Three treated patients and six controls withdrew because of skin irritation or lack of efficacy. In the treated group there were clear improvements in scaling, induration and erythema after treatment. The nail changes were cured in five of 10 evaluable patients in the treated group and joint pain was reduced by almost half in the four evaluable patients with arthropathy. There were no such improvements in the placebo group.

Administration, Oral↗
PubMed1997

Reduced tetracycline bioavailability caused by magnesium aluminum silicate in liquid formulations of bismuth subsalicylate.

RATIONALE: Bismuth subsalicylate, tetracycline hydrochloride, and metronidazole are widely used in combination for the treatment of Helicobacter pylori infections. As a result, there is renewed interest in the interaction between tetracycline and bismuth subsalicylate. OBJECTIVE: To determine whether the observed decrease in tetracycline bioavailability is due to the active drug bismuth subsalicylate via complexation, or to magnesium aluminum silicate (Veegum), an inactive excipient present only in the liquid formulation of bismuth subsalicylate, which might adsorb the tetracycline, rendering it unavailable for systemic absorption. METHODS: Eleven healthy volunteers participated in a randomized three-period, three-treatment complete crossover study with a 7-day washout interval between treatments. After an overnight fast, subjects received a 500-mg capsule of tetracycline hydrochloride with either tap water, 30 mL of bismuth subsalicylate (525 mg) liquid containing Veegum (Pepto-Bismol), or 30 mL of a specially formulated bismuth subsalicylate (525 mg) liquid without Veegum. Blood was collected for 24 hours after each dose of tetracycline. Serum was assayed for tetracycline concentration by HPLC. In addition, standard in vitro ultraviolet spectrophotometric methods were used to determine the capacity for complexation of bismuth with tetracycline and for adsorption of tetracycline to Veegum. RESULTS: Compared with the reference treatment of tetracycline hydrochloride with water, the liquid formulation of bismuth subsalicylate containing Veegum decreased the maximum serum concentration (Cmax) of tetracycline by 21% and the serum tetracycline AUC by 27% (p < 0.001). The bismuth subsalicylate formulation without Veegum resulted in decreases in Cmax and AUC of 11% and 13%, respectively (p > 0.05 vs. tetracycline hydrochloride with water). Multiple linear regression analysis of the spectral absorbance data demonstrated a calculated recovery of tetracycline of 100.9% and, therefore, a lack of in vitro complexation with bismuth. At pH 1.2, the amount of tetracycline adsorbed to Veegum ranged from 91.5% to 97.2% over the concentration range of 0.25 to 2 mg/mL. At pH 7.0, the values ranged from 82.9% to 83.9% over the concentration range of 0.25 to 1 mg/mL. CONCLUSIONS: In vitro and in vivo data from this study indicate that Veegum, a suspending agent, and not the active agent bismuth subsalicylate, is the primary ingredient in liquid formulations of bismuth subsalicylate responsible for a decrease in tetracycline bioavailability. In addition, the mechanism of interaction is not likely due to complexation between tetracycline and bismuth subsalicylate, as previously postulated, but rather is caused by adsorption of tetracycline to the excipient Veegum, which is present only in the liquid formulation of bismuth subsalicylate. The clinical relevance of this interaction has not been determined.

Adolescent↗
PubMed2005

Adsorption of meloxicam on porous calcium silicate: characterization and tablet formulation.

The purpose of the present study was characterization of microparticles obtained by adsorption of poorly water soluble drug, meloxicam, on a porous silicate carrier Florite RE (FLR) and development of a tablet formulation using these microparticles, with improved drug dissolution properties. The study also reveals the use of FLR as a pharmaceutical excipient. Meloxicam was adsorbed on the FLR in 2 proportions (1:1 and 1:3), by fast evaporation of solvent from drug solution containing dispersed FLR. Drug adsorbed FLR microparticles were evaluated for surface topography, thermal analysis, X-ray diffraction properties, infrared spectrum, residual solvent, micromeritic properties, drug content, solubility, and dissolution studies. Microparticles showed bulk density in the range of 0.10 to 0.12 g/cm(3). Dissolution of drug from microparticles containing 1:3, drug:FLR ratio was faster than microparticles containing 1:1, drug:FLR ratio. These microparticles were used for formulating directly compressible tablets. Prepared tablets were compared with a commercial tablet. All the prepared tablets showed acceptable mechanical properties. Disintegration time of prepared tablets was in the range of 18 to 38 seconds, and drug dissolution was much faster in both acidic and basic medium from prepared tablets as compared with commercial tablet. The results suggest that FLR provides a large surface area for drug adsorption and also that a reduction in crystallinity of drug occurs. Increase in surface area and reduction in drug crystallinity result in improved drug dissolution from microparticles.

Adsorption↗
PubMed2005

Influence of magnesium aluminium silicate on rheological, release and permeation characteristics of diclofenac sodium aqueous gels in-vitro.

The effect of magnesium aluminium silicate (MAS) on rheological, release and permeation characteristics of diclofenac sodium (DS) aqueous gels was investigated. DS aqueous gels were prepared using various gelling agents, such as 15% w/w poloxamer 407 (PM407), 1% w/w hydroxypropylmethylcellulose (HPMC), and 1% w/w high and low viscosity grades of sodium alginate (HV-SA and LV-SA, respectively). Different amounts of MAS (0.5, 1.0 and 1.5% w/w) were incorporated into the DS gels. Incorporation of MAS into the DS gels prepared using SA or PM407 caused a statistical increase in viscosity (P<0.05) and a shift from Newtonian flow to pseudoplastic flow with thixotropic property. The DS release rates of these composite gels were significantly decreased (P<0.05) when compared with the control gels. This was due to an interaction between MAS and PM407 or SA, and adsorption of DS onto MAS particles. Moreover, a longer lag time and no change in DS permeation flux were found when MAS was added to the gels. The findings suggest that the rheological characteristics of gels prepared using PM407 or SA could be improved by incorporating MAS. However, the use of MAS could retard the DS release and extend the lag time of DS permeation.

Alginates↗
PubMed1998

Absorption of ibuprofen coated by anhydrous silicic acid.

We studied the dissolution and absorption of ibuprofen (IB) from a three-layer tablet: the 1st layer (CIB layer) consisted of IB which was coated with anhydrous silicic acid (CIB), the 2nd layer was bromovalerylurea and anhydrous caffeine, and the 3rd layer was bromovalerylurea and ethenzamide. Differential scanning calorimetry and powder X-ray diffraction studies showed that the crystallinity of IB was not influenced by the preparation of CIB. The dissolution and absorption of IB from the CIB layer of the three-layer tablet were compared with those of a commercial tablet. In a test solution at pH 1.2, the dissolution rate of IB from the CIB layer was higher than that from the commercial tablet; moreover, the time for peak concentration (Tmax) after administration of the CIB layer was significantly shorter. The Tmax of the CIB layer tablet was about 52 min, while that of the commercial tablet was about 103 min. The rapid dissolution and absorption of IB in the CIB layer may be due to enhanced permeation, disintegration and disaggregation of CIB.

Biological Availability↗
PubMed2004

Quantitative determination of amorphous nicardipine hydrochloride in long acting formula (NIC-LA) using light anhydrous silicic acid.

We investigated a method to quantitatively determine amorphous nicardipine hydrochloride (NIC) in the NIC-long acting formula (LA) model formulas prepared using NIC, light anhydrous silicic acid (LASA) and carboxymethylethylcellulose (CMEC). Consequently, since the quantity of total NIC in the formula can be determined by means of HPLC and crystal NIC can be determined by the differential scanning calorimetry (DSC) method because the heat of fusion (85.08 J/g) of NIC is constant and unaffected by excipients, we developed the HPLC-DSC method by which the quantity of amorphous NIC is calculated as the difference between the quantity of total NIC determined by HPLC and the quantity of crystal NIC determined by DSC. This practical HPLC-DSC method was confirmed to have good accuracy and reproducibility.

Calcium Channel Blockers↗