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At least 253 records · Page 14Linked to original sources

PubMed2005

Anchored metal-to-metal charge-transfer chromophores in a mesoporous silicate sieve for visible-light activation of titanium centers.

Binuclear metal-to-metal charge-transfer (MMCT) moieties consisting of a Ti and a Cu(I) or a Ti and a Sn(II) center were obtained in a MCM-41 silicate sieve along with isolated metal centers when exposing Ti-grafted MCM-41 to Cu(I) or Sn(II) precursors featuring highly labile CH3CN ligands. Fourier transform infrared (FT-IR) spectroscopy revealed complete removal of the labile CH3CN ligands of the metal precursor and the formation of Cu(I)-O-Ti, Cu(I)-O-Si, and corresponding Sn(II) linkages on the pore surface. Optical and FT-IR difference spectroscopy upon oxidation of Cu(I) (Sn(II)) allowed assignment of the Cu(I)-O (642 cm(-1)) and Sn(II)-O (610 cm(-1)) bond modes of the MMCT moiety. The visible-light-absorbing Ti(IV)-O-Cu(I) MMCT chromophore extends from the UV to 600 nm, the corresponding Ti(IV)-O-Sn(II) absorption to 470 nm. Electron paramagnetic resonance monitoring of the TiSn(II)-MCM-41 sieve following photoexcitation of the MMCT transitions at cryogenic temperature confirmed that Ti is reduced to Ti(III) under visible light. Assembly of inorganic MMCT sites inside high-surface-area mesoporous silicates with each metal in a preselected oxidation state opens up activation of catalytically important metal centers under visible light.

Light↗

PubMed2006

Adsorption and activity of a domoic acid binding antibody fragment on mesoporous silicates.

The adsorption of an anti-domoic acid single-chain Fv (scFv) antibody fragment onto a range of mesoporous silicate supports was investigated. The scFv fragment adsorbed to all materials investigated, and pI had an apparently large effect on coating, with the greatest-and fastest-adsorption found on the most negatively charged silicates. Maximal coating levels attainable did not reflect the pore diameters of the materials. The immobilized antibody was functional on all materials and bound its antigen, a naturally occurring neurotoxin produced by shellfish, in a rapidly saturating manner that suggested the antibody adsorbed in a multilayer on the mesoporous particles. The antigen:antibody ratio decreased from 1:1.3 to <1:10 with increasing concentration of immobilized antibody, and the immobilized scFv exhibited no detectable reduction in domoic acid binding over a 42-day incubation period.

Adsorption↗

PubMed2006

Photoluminescent layered Y(III) and Tb(III) silicates doped with Ce(III).

The synthesis and structural characterization of new layered rare-earth silicates K(3)[M(1-a)Ce(a)Si(3)O(8)(OH)(2)], M = Y(3+), Tb(3+), a << 1 (AV-22 materials), have been reported. These materials combine the properties of layered silicates, such as intercalation chemistry, and photoluminescence and may find applications in new types of sensor devices. For mixed Tb/Ce-AV-22, evidence has been found for the energy transfer from the large Ce(3+) 4f( 1) --> 5d(1) broad band to the sharp Tb(3+) 4f (8) lines. This energy transfer allows the fine-tuning of the color emission in the blue-green region of the chromaticity diagram. Upon Ce(3+) excitation (342 nm), the radiance of Tb/Ce-AV-22 is approximately 2 times higher than that measured under direct Tb(3+) excitation, which reinforces the existence of effective room-temperature Ce(3+)-to-Tb(3+) energy transfer.

Cerium↗

PubMed2004

Palladium-catalyzed cross-coupling of aryl triethylammonium bis(catechol) silicates with aryl bromides using microwave irradiation.

The scope of the palladium-catalyzed cross-coupling reaction of aryl bis(catechol) silicates has been extended to include the coupling of aryl bromides by employing microwave irradiation. This new set of coupling conditions is tolerant of electron-rich and -deficient aryl bromides. In addition, a variety of substituted aryl bis(catechol) silicates have been successfully cross-coupled.

Bromides↗

PubMed1998

Fluctuating silicate:nitrate ratios and coastal plankton food webs.

Marine diatoms require dissolved silicate to form an external shell, and their growth becomes Si-limited when the atomic ratio of silicate to dissolved inorganic nitrogen (Si:DIN) approaches 1:1, also known as the "Redfield ratio." Fundamental changes in the diatom-to-zooplankton-to-higher trophic level food web should occur when this ratio falls below 1:1 and the proportion of diatoms in the phytoplankton community is reduced. We quantitatively substantiate these predictions by using a variety of data from the Mississippi River continental shelf, a system in which the Si:DIN loading ratio has declined from around 3:1 to 1:1 during this century because of land-use practices in the watershed. We suggest that, on this shelf, when the Si:DIN ratio in the river decreases to less than 1:1, then (i) copepod abundance changes from >75% to <30% of the total mesozooplankton, (ii) zooplankton fecal pellets become a minor component of the in situ primary production consumed, and (iii) bottom-water oxygen consumption rates become less dependent on relatively fast-sinking (diatom-rich) organic matter packaged mostly as zooplankton fecal pellets. This coastal ecosystem appears to be a pelagic food web dynamically poised to be either a food web composed of diatoms and copepods or one with potentially disruptive harmful algal blooms. The system is directed between these two ecosystem states by Mississippi River water quality, which is determined by land-use practices far inland.

Animals↗

PubMed1998

Simultaneous sulfur dioxide and nitrogen dioxide removal by calcium hydroxide and calcium silicate solids.

At conditions typical of a bag filter exposed to a coal-fired flue gas that has been adiabatically cooled with water, calcium hydroxide and calcium silicate solids were exposed to a dilute, humidified gas stream of nitrogen dioxide (NO2) and sulfur dioxide (SO2) in a packed-bed reactor. A prior study found that NO2 reacted readily with surface water of alkaline and non-alkaline solids to produce nitrate, nitrite, and nitric oxide (NO). With SO2 present in the gas stream, NO2 also reacted with S(IV), a product of SO2 removal, on the exterior of an alkaline solid. The oxidation of S(IV) to S(VI) by oxygen reduced the availability of S(IV) and lowered removal of NO2. Subsequent acidification of the sorbent by the removal of NO2 and SO2 facilitated the production of NO. However, the conversion of nitrous acid to sulfur-nitrogen compounds reduced NO production and enhanced SO2 removal. A reactor model based on empirical and semi-empirical rate expressions predicted rates of SO2 removal, NO2 removal, and NO production by calcium silicate solids. Rate expressions from the reactor model were inserted into a second program, which predicted the removal of SO2 and NOx by a continuous process, such as the collection of alkaline solids in a baghouse. The continuous process model, depending upon inlet conditions, predicted 30-40% removal for NOx and 50-90% removal for SO2. These results are relevant to dry scrubbing technology for combined SO2 and NOx removal that first oxidizes NO to NO2 by the addition of methanol into the flue duct.

Air Pollutants, Occupational↗

PubMed2006

Iron-magnesium silicate bioweathering on Earth (and Mars?).

We examined the common, iron-magnesium silicate minerals olivine and pyroxene in basalt and in mantle rocks to determine if they exhibit textures similar to bioweathering textures found in glass. Our results show that weathering in olivine may occur as long, narrow tunnels (1-3 microm in diameter and up to 100 microm long) and as larger irregular galleries, both of which have distinctive characteristics consistent with biological activity. These weathering textures are associated with clay mineral by-products and nucleic acids. We also examined olivine and pyroxene in martian meteorites, some of which experienced preterrestrial aqueous alteration. Some olivines and pyroxenes in the martian meteorite Nakhla were found to contain tunnels that are similar in size and shape to tunnels in terrestrial iron-magnesium silicates that contain nucleic acids. Though the tunnels found in Nakhla are similar to the biosignatures found in terrestrial minerals, their presence cannot be used to prove that the martian alteration features had a biogenic origin. The abundance and wide distribution of olivine and pyroxene on Earth and in the Solar System make bioweathering features in these minerals potentially important new biosignatures that may play a significant role in evaluating whether life ever existed on Mars.

Earth, Planet↗

PubMed1975

Adaptation of silicate and Adaptic to the margins of cavities. A scanning electron microscope study.

The effects of etching of the enamel, on the adaptation of silicate and Adaptic to the cavity walls was examined with the scanning electron microscope. Replica methods were utilized to ensure that no shrinkage of the filling materials was caused by the vacuum in the instrument. It was shown that following etching of the cavity margins, Adaptic adhered to the enamel with absent, or minimal, fissure formation on one side of the filling, and some on the opposite side. The adaptation of silicate to the margins of the cavities was not improved by etching.

Composite Resins↗

PubMed1985

Biochemical studies in paraplegic renal stone patients. 2. Urinary excretion of citrate, inorganic pyrophosphate, silicate and urate.

The urinary excretions of citrate, inorganic orthophosphate and pyrophosphate, silicate and urate were measured in 17 paraplegic patients with renal calculous disease associated with urinary infection, in 16 paraplegics with no history of urinary calculus and in 14 healthy control subjects. The paraplegics excreted less citrate, orthophosphate and pyrophosphate than the control subjects. The stone-formers excreted more urate than the paraplegics without stone disease, but less than the control subjects. There were significant positive correlations between urinary orthophosphate and pyrophosphate and between urinary silicate and 24-h urine volume. The possible roles of increased urate and diminished excretion of citrate and inorganic pyrophosphate in the aetiology of renal calculosis in paraplegic patients deserve further investigation.

Adult↗

PubMed1976

Root caries: distribution and uptake of elements in lesions adjacent to silicate or amalgam restorations.

In carious lesions adjacent to silicate or amalgam restorations outer lesions of the cementum showed the same content and distribution of Ca, P, Mg, and S as did primary lesions in this area, but differed from these in having an increased content of Zn, Al, and probably F (silicate cases) and Zn, Sn, and Cu (amalgam cases). The cementum walls showed an uptake of ions largely similar to that previously described in dentinal walls.

Aluminum↗

PubMed1977

Pulp reactions to silicate cement in teeth with healing pulpitis.

Unlined silicate restorations were placed in intact and experimentally altered monkey, teeth. Pulpitis had been induced experimentally by sealing soft carious human dentin in Class V cavities with amalgam for 7 d. These fillings were then removed and healing allowed by inserting zinc oxide/eugenol cement. A protective effect of the secondary dentin in teeth with healing pulpitis could be demonstrated in short-term experiments. After a 1-month observation period no difference in response to silicate cement could be found between intact and experimentally altered pulps, both groups exhibiting no or slight pulp reactions and secondary dentin formations.

Animals↗

PubMed1982

Heat treatment of glass ionomer, silicate, zinc phosphate and zinc polycarboxylate cements.

The compressive strength and erosion resistance of glass ionomer, silicate, zinc phosphate or zinc polycarboxylate cements, submitted to heat treatments at 50 degrees or 70 degrees C after mixing, have been assessed. Zinc phosphate cement specimens showed a marked reduction in compressive strength properties and erosion resistance, while minor improvements in compressive strength were observed for various brands of the other types of cements. For silicate cement a considerable improvement in erosion resistance was noted. One brand showed a reduction in the release of phosphate amounting to approximately a factor of 20. The various improvements observed may be clinically exploited by exposing the restoration after insertion to radiation from an external heat source which deposits radiation energy in the surface or bulk of the restoration.

Chemical Phenomena↗

PubMed2004

Discovery of ancient silicate stardust in a meteorite.

We have discovered nine presolar silicate grains from the carbonaceous chondrite Acfer 094. Their anomalous oxygen isotopic compositions indicate formation in the atmospheres of evolved stars. Two grains are identified as pyroxene, two as olivine, one as a glass with embedded metal and sulfides (GEMS), and one as an Al-rich silicate. One grain is enriched in 26Mg, which is attributed to the radioactive decay of 26Al and provides information about mixing processes in the parent star. This discovery opens new means for studying stellar processes and conditions in various solar system environments.

Aluminum↗

PubMed1980

Pulmonary disease from occupational exposure to an artificial aluminium silicate used for cat litter.

All available workers engaged in bagging an artificial crystalline aluminium silicate--the kiln-dried residue from the calcining and water extraction of alunite (a hydrated sulphate of aluminium and potassium) that is currently classified as a nuisance dust--were studied after a complaint of respiratory and systemic symptoms, including arthritis, by an employee of the factory, who showed physiological and radiographic evidence of diffuse pulmonary fibrosis and in whom lung biopsy showed diffuse fibrosis with granulomas. Inhalation challenge produced a transient decrease in transfer factor and transfer factor standardised for alveolar volume. Twenty-five subjects were known to have been exposed at some time to the dust of alunite-residue. Of the 17 who could be contacted, all agreed to attend for respiratory questionnaire and occupational history, pulmonary function testing (spirometry, lung volumes, gas transfer), and posteroanterior chest radiograph. Six subjects considered that occupational exposure to the dust was responsible for respiratory symptoms. Three subjects had abnormality of the chest radiograph consistent with pulmonary fibrosis. The mean percentage of predicted transfer factor standardised for effective alveolar volume was 71.1% in subjects with abnormal chest radiographs and 86.6% in subjects with normal radiographs (p = 0.10). There was a trend in the correlation between the percentage of predicted transfer factor standardised for effective alveolar volume and total dust exposure (sum of the products of grade of severity of each exposure period and duration of each exposure period in months) (r = 0.40 p = 0.10). This study suggests that there may be a relation between inhalation of the dust of this form of aluminium silicate and pulmonary fibrosis.

Adolescent↗

PubMed1993

Dialysis-associated arthropathy: secondary ion mass spectrometry evidence of aluminum silicate in beta 2-microglobulin amyloid synovial tissue and articular cartilage.

The role of aluminum accumulation in articular tissues of patients affected by dialysis-associated arthropathy (DAA) is questioned. The aim of this work is to identify the nature of these aluminum accumulations by the use of secondary ion mass spectrometry (SIMS). Al/Si ratios of about 1, measured by SIMS, strongly suggest for the first time the presence of aluminum silicates and possibly aluminum hydroxides in amyloid synovial tissue and articular cartilage of 1 patient with DAA and aluminum intoxication. This is thermodynamically consistent with the total dissolved Al and Si contents and pH measured in the synovial fluids. These results are similar to the abnormal Al distribution recently found by SIMS in the forebrain of chronic renal dialysis patients and to the amorphous aluminum silicates identified in the core of senile plaques in Alzheimer's disease.

Aluminum Silicates↗

PubMed1986

Induction of IgE antibody production to aerosolized ovalbumin in mice treated intratracheally with aluminum silicate.

Induction of IgE antibody production was studied in mice with aerosolized antigen exposure and intratracheal instillation of adjuvants. BALB/c mice were immunized intratracheally with 10 micrograms ovalbumin (OA) adsorbed with or without aluminum silicate as an adjuvant. A primary IgE antibody production was observed in mice immunized with OA plus adjuvant, but not with OA alone. In mice immunized with OA plus adjuvant, a secondary IgE antibody production was observed after a booster of OA aerosol exposure on day 28. Mice were instilled intratracheally with aluminum silicate or aluminum hydroxide (alum) and subsequently exposed to aerosolized OA for 30 min. Primary and secondary anti-OA IgE antibody productions were obtained in the groups instilled with the adjuvants. After the intratracheal instillation of alum, aluminum remained in the mice for a long period. These results suggest that the intratracheal instillation of adjuvants is effective in the induction of IgE antibody production by aerosolized antigen exposure.

Adjuvants, Immunologic↗

PubMed2002

New poly(butylene succinate)/layered silicate nanocomposites: preparation and mechanical properties.

New poly(butylene succinate) (PBS)/layered silicate nanocomposites have been successfully prepared by simple melt extrusion of PBS and octadecylammonium modified montmorillonite (C18-mmt) at 150 degrees C. The d-spacing of both C18-mmt and intercalated nanocomposites was investigated by wide-angle X-ray diffraction analysis. Bright-field transmission electron microscopic study showed several stacked silicate layers with random orientation in the PBS matrix. The intercalated nanocomposites exhibited remarkable improvement of mechanical properties in both solid and melt states as compared with that of PBS matrix without clay.

Bentonite↗

PubMed2005

Approaches for functional characterization of diatom silicic acid transporters.

A major component of the diatom cell wall is silica, derived from silicon taken up from the environment. Due to limiting environmental concentrations of silicon, and a substantial requirement during cell wall synthesis, diatoms must transport silicon into the cell against a steep concentration gradient. This is accomplished through the silicic acid transporters (SITs). The SITs were first identified in the marine pennate diatom Cylindrotheca fusiformis. Five distinct SITs were found and have been classified as a novel family of transporters. This review covers our current understanding of silicon transport in diatoms with a focus on the SITs. Approaches for in-depth functional characterization of the SITs are discussed, including (1) isolating SITs from evolutionarily distant diatom species to identify conserved amino acids that may be important for function, (2) developing expression systems to assay the function of selected SITs, and (3) determining the cellular location and membrane topology of the C. fusiformis SITs to further clarify their roles in diatom silicon metabolism. Because of the specificity of interaction between the SITs and silicon, and the ability of the SITs to transport silicic acid across lipid bilayers, the SITs may have applications in nanotechnology.

Amino Acid Sequence↗