A silicon analogue of vinyllithium: structural characterization of a disilenide.
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Lithium↗
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Palygorskite as a feasible amendment to stabilize heavy metal polluted soils.
The sorption behaviour of palygorskite has been studied with respect to lead, copper, zinc and cadmium in order to consider its application to remediate soils polluted with these metals. The Langmuir model was found to describe well the sorption processes offering maximum sorption values of 37.2 mg/g for lead, 17.4 mg/g for copper, 7.11 mg/g for zinc and 5.83 mg/g for cadmium at pH 5-6. In addition the effect of palygorskite amendment in a highly polluted mining soil has been studied by means batch extractions and leaching column studies. The soluble metal concentrations as well as the readily-extractable metal concentrations were substantially decreased at any concentration of palygorskite applied to soil (1, 2, 4%), although the highest decrease is obtained at the 4% dose. The column studies also showed a high reduction in the metal leaching (50% for lead, 59% for copper, 52% for zinc and 66% for cadmium) when a palygorskite dose of 4% was applied.
Cadmium↗
One-dimensional filtration of pharmaceutical grade phyllosilicate dispersions.
The filtration behaviour of some clay-water dispersions was studied. Two Spanish fibrous phyllosilicates (sepiolite from Vicálvaro and palygorskite from Turón) and a commercial bentonite (Bentopharm UK) with similar sizes and different morphologies (fibrous and/or laminar) were selected as model clays. Sepiolite from Vicálvaro is an almost pure fibrous sample, Bentopharm presents a high amount of laminar particles and palygorskite from Turón is made up of similar percentages of laminar and fibrous particles. The disperse systems were made up using a rotor-stator mixer working at two different mixing rates (1000 and 8000 rpm), for periods of 1 and 10 min. Filtration measurements were taken and the corresponding filtration curves obtained. Finally, the desorptivity (S) of the filtration cakes was calculated and correlated to the textural characteristics of the materials, the solid fraction and mixing conditions. Filtration behaviour of the dispersions depended on all three of these factors. Laminar dispersions presented lower S values than fibrous dispersions. In the 2% w/v dispersions the bridging forces between particles did not permit formation of an interconnected network as in 10% w/v dispersions and, consequently, filtration times increased with the solid fraction (i.e. S values decreased). Regarding stability to pH changes, the results showed that filtration behaviour was highly sensitive to basic pH in the fibrous clay dispersions and almost insensitive in the laminar clay dispersions.
Aluminum Silicates↗
Pharmaceutical grade phyllosilicate dispersions: the influence of shear history on floc structure.
The effect of mixing conditions on the flow curves of some clay-water dispersions was studied. Two Spanish fibrous phyllosilicates (sepiolite from Vicálvaro and palygorskite from Turón) and a commercial bentonite (Bentopharm Copyright, UK) were selected as model clays. The disperse systems were made up using a rotor-stator mixer working at two different mixing rates (1000 and 8000 rpm), for periods of 1 and 10 min. Rheological measurements were taken and the corresponding flow curves obtained immediately after interposition and then after a period of 24 h under low shear caused by a roller apparatus. Aqueous sepiolite dispersions showed the highest viscosity and were easily interposed, whereas palygorskite dispersions were more difficult to obtain, resulting in low to medium viscosity gels. Bentonite dispersions provided medium viscosity systems, which greatly increased their viscosity after the low shear treatment (as a result of swelling), whereas the viscosity of the fibrous clays stayed at approximately the same values or even decreased. A linear relation was found between mixing energy and apparent viscosity in the bentonite systems, while apparent viscosity in the sepiolite samples was related to mixing power, with minor influence of mixing times. All the systems studied had thixotropic behaviour, changing from clearly positive to even negative thixotropy in some palygorskite systems. Finally, we studied the effect of drastic pH changes on the system structure. Results showed that rheological properties were highly sensitive to pH in the fibrous dispersions, but less sensitive behaviour was found in the laminar clay systems.
Aluminum Silicates↗
Groundwater discharge: potential association with fecal indicator bacteria in the surf zone.
Short-lived radium isotopes (223Ra and 224Ra) are used to investigate the potential association between groundwater discharge and microbial pollution at Huntington Beach, CA. We establish the tidally driven exchange of groundwater from the surficial beach aquifer across the beach face. Groundwater is found to be a source of nutrients (silica, inorganic nitrogen, and orthophosphate) to the surf zone, and these nutrients could possibly provide an environment for enhanced growth or increased persistence of fecal indicator bacteria (FIB). Ammonium and ortho-phosphate explain up to 12-20% of the variance in FIB levels in the surf zone. Elevated levels of FIB were only found in 1 of the 26 groundwater samples. However, FIB in the surf zone covary with radium at fortnightly, diurnal, and semi-diurnal tidal periods. In addition, radium accounts for up to 38% of the variance in log-FIB levels in the surf zone. A column experiment illustrates that Enterococcus suspended in Huntington Beach saline groundwater is not significantly filtered by sand collected from the field. This work establishes a mechanism for the subterranean delivery of FIB pollution to the surf zone from the surficial aquifer and presents evidence that supports an association between groundwater discharge and FIB.
California↗
Observation of iron silicide formation by plan-view transmission electron microscopy.
The formation and the phase transitions of iron silicide by solid-phase epitaxy have been investigated by means of plan-view transmission electron microscopy, which enables us to observe a clean interface between Fe and Si. Layers of Fe were deposited on Si (100) at room temperature in an ultrahigh vacuum chamber. The sample was annealed in the electron microscope at a temperature between 673 and 1073 K. After annealing at 673 K, FeSi crystallites were formed with various orientations. When the annealing temperature was increased to 973 K, we found that the crystallites suddenly started to coalesce into grains of several hundreds of nanometers in size and polycrystalline beta-FeSi2 was formed. These phase transitions were also confirmed with electron energy-loss spectroscopy.
Crystallography↗
Characterisation of palygorskite specimens from different geological locales for health hazard evaluation.
Palygorskite, a fibrous clay mineral, is being used as a substitute for asbestos in some applications. Nine specimens obtained from different geological locales were studied for mineral purity, elemental composition, fibre size distribution, and surface binding characteristics. The membranolytic activity of each was determined using a human erythrocyte model. The membranolytic behaviour and surface binding characteristics were compared with three chrysotile specimens employed as positive controls. The palygorskite specimens derived from the different geological locales display a range of physicochemical properties. This study shows the importance of selecting several mineral specimens for a health hazard evaluation. The current carcinogenic classification of the mineral may be limited due to the number of specimens used for that particular evaluation.
Asbestos↗
[Optimization of the process of culturing yeast in the presence of the dispersed mineral palygorskite].
A positive effect from introduction of the highly dispersed mineral palygorskite in the nutrient medium for aerobic batch cultivation of the yeast Saccharomyces cerevisiae, the Kyivsky strain, used in production of champagne has been established experimentally. An adequate mathematical model describing the process of growth has been constructed. Optimal cultivation conditions have been determined which provided for the achievement of such yeast cell concentration in the culture fluid as 116 mln/ml, palygorskite concentration in the nutrient medium being 0.37 g/l and sucrose 2.0 +/- 0.2%. The yeast obtained possess higher fermentation activity.
Culture Media↗
[Studies of a new adsorbent cross-linked agar beads entrapped attapulgite clay for hemoperfusion].
The preparation and properties of a new adsorbent cross-linked agar beads entrapped attapulgite clay (CAA) are reported in detail. Medicinal attapulgite clay made in China was encapsulated with agar, shaped in organic solvent, and cross-linked by epichlorohydrin. The products withstood autoclaving at 121 degrees C for half an hour with no breakage, and had a good selective adsorption ability for some model compounds and medicaments such as methylene blue and phenothiazine drugs. Preliminary investigations and SEM photographs indicate that the CAA as an adsorbent is relatively hemocompatible for hemoperfusion.
Agar↗
[Studies of adsorbents for hemoperfusion--preparation and in vitro studies of cross-linked agar beads entrapped Attapulgite clay].
A new method for preparation of cross-linked agar beads entrapped Attapulgite clay (CAA) is reported. Attapulgite clay was coated with agar and shaped in organic solvent, as well as cross-linked by epichlorohydrin. The products withstood autoclaving at 121 degrees C for 30 minutes and had a good adsorption ability for model compounds and medicines. The results of preliminary investigation indicate that CAA is relatively hemocompatible.
Adsorption↗
Determination of attapulgite and nifuroxazide in pharmaceutical formulations by sequential digital derivative spectrophotometry.
A new method for the sequential determination of attapulgite and nifuroxazide in pharmaceutical formulations by first- and second-derivative spectrophotometry, respectively, has been developed. In order to obtain the optimal conditions for nifuroxazide stability, studies of solvent, light, and temperature effects were performed. The results show that a previous hydrolysis of 2 h in 1.0 x 10(-1)M NaOH solution is necessary in order to obtain stable compounds for analytical purposes. Subsequently, the first- and second-derivative spectra were evaluated directly in the same samples. The sequential determination of the drugs can be performed using the zero-crossing method; the attapulgite determination was carried out using the first derivative at 278.0 nm and the nifuroxazide determination, using the second derivative at 282.0 nm. The determination ranges were 5.7 x 10(-6)-1.0 x 10(-4) and 3.7 x 10(-8) -1.2 x 10(-4)M for attapulgite and nifuroxazide, respectively. Repeatability (relative standard deviation) values of 1.2 and 3.0% were observed for attapulgite and nifuroxazide, respectively. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets. Further, infrared spectroscopy and cyclic voltammetry studies were carried out in order to obtain knowledge of the decomposition products of nifuroxazide.
Anti-Infective Agents↗
[Anti-endotoxin therapy in liver diseases].
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Aluminum Silicates↗
Attapulgite in the treatment of acute diarrhoea: a double-blind placebo-controlled study.
A double-blind placebo-controlled study was carried out to assess the therapeutic effects of Attapulgite, a purified hydrated aluminium magnesium silicate, as an additional agent to oral rehydration solutions in 30 adults with mild-to-moderate acute diarrhoea where no bacterial or protozoal causes could be identified. The study subjects were give 600 mg tablets of Attapulgite or placebo in a random order and followed up for 72 hours. Attapulgite was observed to be significantly better than placebo in reducing the severity and duration of diarrhoea in terms of frequency of motion and consistency of stools (p < 0.01), severity of dehydration (p < 0.01) and in reducing the amount of ORS consumed (p < 0.05). Attapulgite was also well-tolerated. Attapulgite, therefore, merits attention as an additional safe agent besides ORS for the treatment of mild-to-moderate acute diarrhoea.
Acute Disease↗
Electron impact and chemical ionisation mass spectrometry in the characterisation of organometallic silicon, germanium, tin and lead compounds
The electron impact and chemical ionisation mass spectra of a number of organometallic derivatives of silicon, germanium, tin and lead, incorporating inter alia 2-bis(trimethylsilyl)methylpyridyl or cyclopentadienyl ligands have been recorded. Representative spectra are presented and illustrate the utility of these mass spectrometric techniques in the characterisation of such compounds, particularly so in light of the highly informative nature arising from their fragmentation patterns and the numerous isotopes of the nuclei involved. Copyright 2000 John Wiley & Sons, Ltd.
Journal Article↗
Hypothalamo-pituitary portal development in the ovine fetus.
The ontogeny of the hypothalamo-pituitary portal system was studied in six ovine fetuses, 48-67 days of gestation (term = 147 days) after infusion of the vascular system with a silicone rubber compound. In all of these fetuses, a marked orange blush of silicone rubber could be seen, under the dissecting microscope, extending down the stalk from the hypothalamus to the pituitary. On microscopic examination, extensive and well-developed capillary connections between the median eminence, the pituitary stalk, and pituitary gland were seen in all fetuses. In an additional fetus, aged 45 days, which was not perfused with silicone rubber, portal capillary loops had penetrated the median eminence. These findings suggest that, in the ovine fetus, hypothalamic releasing factors can be transported directly via a portal vascular route to the pituitary gland as early as 45 days of gestation.
Animals↗
Spiking of performance reference compounds in low density polyethylene and silicone passive water samplers.
A method for spiking performance reference compounds (PRCs) into low density polyethylene (LDPE) and silicone polymers is described. This method is based on equilibration of the polymers in aqueous/methanolic solutions of PRCs. Equilibration times range from minutes to hours for perdeuterated polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) with a hydrophobicity in the range 3.9 < logKow < 7.7. Best results were obtained for methanol-water ratios of 80/20 (v/v). The method allows for the use of PRCs for in situ calibration of the uptake kinetics of these solvent-free sampling phases in a similar way as for semipermeable membrane devices (SPMDs).
Calibration↗
WETTABILITY OF POLY-(METHYL METHACRYLATE) TREATED WITH SILICON TETRACHLORIDE.
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Acrylic Resins↗
Biomineralization of calcium disilicide in porous polycaprolactone scaffolds.
The incorporation of CaSi(2) grains within a polycaprolactone (PCL) framework results in bioactive and biodegradable scaffolds which may be used in bone tissue regeneration. Porous PCL scaffolds were prepared via a combination of salt-leaching and microemulsion methods. To provide markedly different structural environments for the inorganic phase, calcium disilicide powder was either added to a mixed-composition porogen during a given scaffold preparation, or alternatively added to pre-formed scaffolds. Selective fluorescent labeling, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis were employed to assess scaffold calcification in vitro. The process of CaSi(2)/PCL scaffold calcification under zero bias, during which calcium phosphate growth is significantly dependent on the structural degradation of CaSi(2) grains, has a similar mechanism as the calcium phosphate growth on bioactive glasses/ceramics. The biomineralization of these scaffolds is initiated solely by the silicide phase and can be accelerated by the degradation of the polymer matrix.
Body Fluids↗