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At least 397 records · Page 22Linked to original sources
PubMed2000

Delayed-hypersensitivity granulomatous reaction induced by blepharopigmentation with aluminum-silicate.

Blepharopigmentation has been introduced during the last decade as a technique for creating a permanent line along the eyelid margin, thus simulating a cosmetic eyeliner. Complications related to this procedure are mostly reported in the opthalmologic literature describing infectious, allergic, or technical problems. We report a case of a woman who underwent blepharopigmentation with aluminum-silicate and in whom a delayed hypersensitivity granulomatous reaction developed.

Aluminum Silicates↗
PubMed1997

Effect of 1H-decoupling in two-dimensional multiple-quantum MAS NMR spectroscopy of 23Na in a hydrous layered silicate.

In order to check the efficiency of high-power 1H decoupling when used with the two-dimensional multiple-quantum MAS method recently proposed to obtain isotropic spectra from quadrupolar nuclei, we applied this new technique to 23Na NMR for a hydrous layered silicate compound, makatite, with and without 1H decoupling. A remarkable improvement of the spectral resolution in the isotropic dimension was observed by the decoupling, showing that it is effective in the 2D MQ-MAS method and suggesting that proton decoupling should be generally applied in 23Na experiments concerning these kinds of compound.

Chemical Phenomena↗
PubMed1997

29Si chemical shift tensors of silyl silicate cages.

Static and 29Si CP MAS spectra (spinning rates of 2000 and 500 Hz) of six silyl silicate cages are analyzed by deconvolution and simulation. The principal values of the various 29Si chemical shift tensors provide information about the point symmetry of the Si sites. The intensities of the signals correspond sufficiently well with the stoichiometries.

Isotopes↗
PubMed2004

Measurement of femtogram quantities of protactinium in silicate rock samples by multicollector inductively coupled plasma mass spectrometry.

We describe a new method for the chemical separation and analysis of Pa in silicate rock samples by isotope dilution. Our new technique has the following advantages over previous methods: (a) The initial separation of Pa from the rock matrix is carried out using anionic exchange resin and HCl-HF mixtures, avoiding the need to remove F(-) quantitatively from the sample solution prior to this step, (b) Efficient ionization of Pa is achieved using a multicollector inductively coupled plasma mass spectrometer, so that smaller sample sizes and shorter measurement times are required, compared to previous methods using thermal ionization mass spectrometry or alpha spectrometry. (c) Plasma ionization requires less efficient separation of the high field strength elements from Pa, thus reducing reagent volumes, blanks, and sample preparation times. Instrumental mass fractionation can be corrected for using admixed U of known isotopic composition. Using this method, Pa concentrations can be measured to a precision of approximately 0.5% and an accuracy of approximately 1% using only a few tens of femtograms of Pa.

Protactinium↗
PubMed2004

Real-time measurements of dissolved oxygen inside live cells by organically modified silicate fluorescent nanosensors.

Optical PEBBLE (probes encapsulated by biologically localized embedding) nanosensors have been developed for dissolved oxygen using organically modified silicate (ormosil) nanoparticles as a matrix. The ormosil nanoparticles are prepared via a sol-gel-based process, which includes the formation of core particles with phenyltrimethoxysilane as a precursor followed by the formation of a coating layer with methyltrimethoxysilane as a precursor. The average diameter of the resultant particles is 120 nm. These sensors incorporate the oxygen-sensitive platinum porphyrin dye as an indicator and an oxygen-insensitive dye as a reference for ratiometric intensity measurement. Two pairs of indicator dye and reference dye, respectively, platinum(II) octaethylporphine and 3,3'-dioctadecyloxacarbocyanine perchlorate, and platinum(II) octaethylporphine ketone and octaethylporphine, were used. The sensors have excellent sensitivity with an overall quenching response of 97%, as well as excellent linearity of the Stern-Volmer plot (r(2) = 0.999) over the whole range of dissolved oxygen concentrations (0-43 ppm). In vitro intracellular changes of dissolved oxygen due to cell respiration were monitored, with gene gun injected PEBBLEs, in rat C6 glioma cells. A significant change was observed with a fluorescence ratio increase of up to 500% after 1 h, for nine different sets of cells, which corresponds to a 90% reduction in terms of dissolved oxygen concentration. These results clearly show the validity of the delivery method for intracellular studies of PEBBLE sensors, as well as the high sensitivity, which is needed to achieve real-time measurements of intracellular dissolved oxygen concentration.

Animals↗
PubMedDate not supplied

Plasmid DNA purification by selective calcium silicate adsorption of closely related impurities.

The selective adsorption of supercoiled plasmid, open-circular plasmid, and genomic DNA to gyrolite, a compound from the class of crystalline calcium silicate hydrates, is investigated and exploited for purification purposes. Genomic DNA and open-circular plasmid bind to gyrolite adsorbents with greater affinity than the more conformationally constrained supercoiled plasmid. As such, the gyrolite adsorbents are an economical and scaleable alternative to chromatographic purification for the removal of DNA impurities from solutions containing supercoiled plasmid. The advantage of gyrolite adsorbents is their lower unit price and ability to selectively adsorb DNA impurities without binding supercoiled plasmid under certain conditions. The effects of ionic strength, temperature, chelating agent, divalent cation, and lyotropic salts on adsorption of highly purified plasmid are studied to understand the forces that bind DNA to gyrolite, a structure with hydrophilic and hydrophobic characteristics. The results indicate that DNA binding is governed by hydrogen bonding, electrostatic bridging with divalent cations, shielding of electrostatic repulsion, hydrophobic adsorption, and disruption of integral surface water layer on gyrolite. On the basis of results from a range of Hofmeister series salts, strongly hydrated anions may enhance DNA adsorption by promoting hydrophobic interactions between DNA and gyrolite. Conversely, the very weakly hydrated chaotrope I(-) may enhance adsorption by strongly associating with hydrophobic siloxanes of gyrolite, thereby disrupting an integral water layer, which competes for hydrogen bonding sites.

Adsorption↗
PubMedDate not supplied

Endotoxin removal using a synthetic adsorbent of crystalline calcium silicate hydrate.

A synthetic adsorbent of crystalline calcium silicate hydrate, the product LRA by Advanced Minerals Corp., has been studied for endotoxin removal from aqueous solutions. This adsorbent removes endotoxin effectively, and the removal is greatly enhanced by the presence of an electrolyte such as NaCl, Tris-HCl, or Na2HPO4. It has an endotoxin removal capacity as high as 6 million endotoxin units (EU) per gram. Its endotoxin removal kinetics is fast, and for instance, over 99.9% endotoxin in a 5000 EU/mL solution was removed by mixing for 2 min at an adsorbent usage of 10 g/L. Using the chromatographic column method to treat a 5000 EU/mL solution, an endotoxin log-reduction factor of 6.2 was achieved with a single pass. This adsorbent also demonstrated significantly better performance when compared to many commonly used endotoxin removal agents, such as ActiClean Etox Endotoxin Removal Resin, Affi-Prep Polymyxin Support, Detroxi-Gel Endotoxin Removing Gel, Q Sepharose Fast Flow Media, and Sigma Endotoxin Removal Solution. Furthermore, it demonstrated a high selective removal of endotoxin from a solution of lambda DNA. This adsorbent provides opportunities for developing disposable, scaleable, and cost-effective methods for endotoxin reduction in many biotechnological and pharmaceutical processes.

Adsorption↗
PubMedDate not supplied

Characteristics of a mesoporous silicate immobilized trypsin bioreactor in organic media.

Mesoporous silicates (MPS) materials are attractive materials for immobilizing proteins/enzymes because of their well ordered structures, large surface areas (up to 1000 m(2) g(-1)), narrow pore size distributions, large pore diameters, and pore volumes. MPS with average pore diameters ranging from 28 to 300 Angstroms were prepared using cationic and nonionic surfactants. The influence of water content, pH, storage, and thermal treatment on the activity of trypsin immobilized onto MPS was investigated. In a range of solvents, the amidolytic activity of immobilized trypsin was higher than that of the lyophilized preparation. Significant increases in k(cat)/K(M) occurred in propanol, ethanol, methanol, and formamide of 90, 62, 45 and 26, respectively. The observed increases were primarily a result of substantial increases in k(cat).

Alcohols↗
PubMed2001

Sorption mechanisms of zinc to calcium silicate hydrate: sorption and microscopic investigations.

Knowledge of the binding mechanisms of heavy metals to cement minerals is essential for the prediction of the long-term leachability of secondary building materials and cement-stabilized wastes containing heavy metals. In this study, the sorption of Zn(II) to calcium silicate hydrate (C-S-H(I)) in pre-equilibrated aqueous suspensions has been investigated as a function of time (up to 87 d), pH (11.7, 12.48, and 12.78) and Zn(II) concentration (4.8-4800 microM). Electron probe microanalysis (EPMA) was performed in order to determine where Zn(II) was bound. At high Zn(II) concentrations (>1000 microM), the precipitation of beta2-Zn-(OH)2 (< pH 12) and calcium zincate (Zn2Ca(OH)6 x 2H2O, > pH 12) was observed. Surface precipitation could not be discerned. At lower concentrations, it was found that the sorption process was initially very rapid with over 50% sorbed within 30 min but that the sorption continued more slowly to at least 87 d. The data could be interpreted in terms of the Freundlich isotherm up to a Si:Zn(II)sorbed atomic ratio of approximately 6:1. Zinc was observed by EPMA to incorporate into the C-S-H(I) particles but did not appear to substitute for Ca or Si. The incorporation of Zn(ll) in the interlayer of C-S-H(I) or sorption to internal surfaces of crystalline appear to be the most probable mechanisms for the observed Zn(II) sorption to C-S-H(I).

Adsorption↗
PubMed2003

EXAFS study of Sn(IV) immobilization by hardened cement paste and calcium silicate hydrates.

In this study, the immobilization mechanisms of Sn(IV) onto calcium silicate hydrates (C-S-H) and hardened cement paste (HCP) have been investigated by combining wet chemistry experiments with X-ray absorption spectroscopy (XAS). Evidence is presented which demonstrates the formation of a Sn(IV) inner-sphere surface complex on C-S-H with a CaO/SiO2 weight ratio of 0.7. Two possible structural models, implying a corner sharing between the Sn octahedra and Q1 or Q2b Si tetrahedra, have been developed based on the experimentally determined structural parameters. In HCP, the formation of a different type of Sn(IV) inner-sphere complex has been observed, indicating that C-S-H may not be the uptake-controlling phase for Sn(IV) in the cement matrix. An alternative structural model for Sn(IV) binding in HCP has been developed, assuming that ettringite is the uptake-controlling phase. At high Sn(IV) concentrations, Sn(IV) immobilization in HCP occurs due to the formation of CaSn(OH)6.

Calcium Compounds↗
PubMed2003

Uptake of Cm(III) and Eu(III) by calcium silicate hydrates: a solution chemistry and time-resolved laser fluorescence spectroscopy study.

The interaction of the two chemical homologues [Cm(III) and Eu(III)] with calcium silicate hydrates (CSH phases) at pH 13.3 has been investigated in batch-type sorption studies using Eu(III) and complemented with time-resolved laser fluorescence spectroscopy (TRLFS) using Cm(III). The sorption data for Eu(III) reveal fast sorption kinetics and a strong uptake by CSH phases with distribution ratios of (6 +/- 3) x 10(5) L kg(-1). Three different Cm(III) species have been identified: A nonfluorescing species, which was identified as a curium hydroxide (surface) precipitate, and two fluorescing Cm(III)/CSH-sorbed species. The fluorescing sorbed species have characteristic emission spectra with main peak maxima at 618.9 and 620.9 nm and fluorescence emission lifetimes of 289 +/- 11 and 1482 +/- 200 micros, respectively. From the fluorescence lifetimes, it was calculated that the two fluorescing Cm(III) species have one or two and no water molecules left in their first coordination sphere, suggesting that these species are incorporated into the CSH structure. A structural model for Cm(III) and Eu(III) incorporation into CSH phases is proposed based on the substitution for Ca at two different types of sites in the CSH structure.

Calcium Compounds↗
PubMed2004

Mechanism of europium retention by calcium silicate hydrates: an EXAFS study.

The uptake of Eu by calcium silicate hydrate (C-S-H) phases as a function of Eu/sorbate ratio (from 37 to 450 micromol g(-1) C-S-H), C-S-H Ca/Si mole ratio (1.3, 1.0, and 0.7), and initial supersaturating conditions was probed by solution kinetics experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy, to shed light on the retention mechanism of trivalent radionuclides under waste repository conditions. The rates of Eu (9.7 x 10(-10) M) uptake in C-S-H suspensions and in solutions at equilibrium with C-S-H were rapid. Uptake of more than 90% of dissolved Eu was generally observed within 15 min. Europium LIII-edge EXAFS spectra collected on samples of Eu sorbed on, or coprecipitated in, C-S-H differed from that of Eu(OH)3(s) expected to precipitate under the pH conditions of C-S-H waters, ruling out compelling precipitation of pure hydroxide phases. Fourier transforms for EXAFS spectra for Eu in sorption/coprecipitation samples displayed comparable features at distances typical of neighboring cationic shells, pointing to similar crystallochemical environments. Optimal spectral simulations were obtained by assuming the presence of Si, Si/Ca, and Ca cationic shells surrounding Eu at distances of 3.2, 3.7-3.8, and 3.8-3.9 A, respectively. The nearly continuous distribution of (Si, Ca) backscattering shells parallels the distribution in Ca-(Ca, Si) interatomic distances in structural models of C-S-H. Discernible effects of experimental parameters on the Eu local environment were observed by comparison of Fourier transforms, but could not be confirmed by EXAFS quantitative analysis. These results indicate that sorbed or coprecipitated Eu is located at Ca structural sites in a C-S-H-like environment. Kinetics and spectroscopic results are consistent with either Eu diffusion within C-S-H particles or precipitation of Eu with Ca and Si creating a C-S-H-like solid phase.

Absorptiometry, Photon↗
PubMed2005

Solvation dynamics of DCM in a DPPC vesicle entrapped in a sodium silicate derived sol-gel matrix.

Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl) 4H-pyran (DCM) has been studied in a dipalmitoyl-phosphatidylcholine (DPPC) vesicle entrapped in a sodium silicate derived sol-gel glass. Solvation dynamics in DPPC in a sol-gel glass is described by two components of 350 +/- 50 ps (50%) and 2300 +/- 200 ps (50%) with a total dynamic Stokes shift of 1300 cm(-1). The fast component (350 ps) is similar to the fast component in a DPPC vesicle in bulk water (320 +/- 50 ps). This component may be ascribed to the dynamics of the water molecules inside the water pool of the vesicle. However, the slow component (2300 +/- 200 ps) is about 2.5 times slower compared to the slow component of solvation dynamics of DCM in a DPPC vesicle in bulk solvent (900 +/- 100 ps). The anisotropy decay of DCM in a DPPC vesicle both in sol-gel glass and in bulk water exhibits a very fast initial decay with a large residual anisotropy, which does not decay in approximately 10 ns. The time scale of anisotropy decay is very different from that of solvation dynamics.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2006

Characterization of the structural and electronic properties of crystalline lithium silicates.

Density functional theory (DFT) calculations within the generalized gradient approximation (GGA) were performed to study the atomic and electronic structure of lithium silicate crystals that were fully optimized within the theory. It is found that the relative stability of two crystalline forms of lithium disilicate agrees well with experimental results. The calculated electronic density of states shows distinguishable contributions to the oxygen 2s and upper valence bands associated with bridging (BO) and nonbridging oxygen (NBO) atoms. Bond ionicity, characterized by determining the relative atomic charges, is used to distinguish BO and NBO atoms as well as the corresponding Si-BO and Si-NBO bonds. Results from this work reveal that atomic charges obtained by using population analysis methods based on electron deformation density rather than total electron density provide an accurate description of bond ionicity consistent with chemical intuition.

Crystallography, X-Ray↗
PubMed2006

Ab initio molecular dynamics study of 45S5 bioactive silicate glass.

Bioglass 45S5, the prototype of bioactive melt-quenched silicate glasses, was modeled by means of Car-Parrinello molecular dynamics (CPMD) simulations. Although long-range structural properties cannot be modeled by using this ab initio approach, the accuracy of CPMD simulations is exploited here to provide insight into the short-range structure and to analyze vibrational and electronic properties of this biomaterial. Detailed structural analysis in the short-range scale provided insight into the local environment of modifier Na and Ca ions: a possible key role of these cations in organizing the glass network by connecting different chains and fragments into specific, rather flexible geometries was proposed. The individual contributions of different species to the vibrational density of states were separated and discussed, allowing the identification of specific features in the vibrational spectrum, such as those related to phosphate groups. The components of the electronic density of states were also analyzed, enabling us to identify correlations between the electronic structure and the structural properties, such as the different bonding character of Si-O bonds involving bridging or nonbridging oxygen atoms.

Glass↗
PubMed2006

Silicon oxide nanoparticles reveal the origin of silicate grains in circumstellar environments.

A synergistic effort combining experiments in beams and first principles theoretical investigations is used to propose mechanisms that could lead to the formation of silicates and nanoparticles with silicon-rich cores through agglomeration of SiO, an abundant oxygen-bearing species in space. The silicon oxygen species involved in the transformation have optical excitations that could contribute to extended red emissions and blue luminescence. Apart from resolving an outstanding astronomical problem, we demonstrate novel silicon architectures.

Computer Simulation↗
PubMed2004

Pre-mineralisation of starch/polycrapolactone bone tissue engineering scaffolds by a calcium-silicate-based process.

This work describes a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other degradable polymeric biomaterials. As an alternative to the more typical bioactive glass precursors, a calcium silicate gel is being employed as a nucleating agent, for inducing the biomimetic formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3-D architectures aimed at being used on tissue replacement applications and as bone tissue engineering scaffolds. This treatment is also very effective in reducing the incubation periods, being possible to observe the formation of an apatite-like layer, only after 12 h of immersion in a simulated body fluid (SBF). The apatite coatings formed on the compact surfaces or along the fibres of a fibre mesh scaffold structure made from a starch/polycrapolactone blend (SPCL) were analysed and compared in terms of morphology, chemical composition and structure. After the first days of SBF immersion, the apatite-like films exhibit the typical cauliflower like morphology. With increasing immersion times, these films exhibited a partially amorphous nature and the Ca/P ratios became very closer to the value attributed to hydroxyapatite (1.67). It was possible to fully pre-mineralise the SPCL scaffolds and simultaneously to keep the porous morphology of the fibre-bonded scaffold.

Absorption↗
PubMed1992

Quantification of the disorder in network-modified silicate glasses.

Local order in silicate glasses has been observed by many experimental techniques to be similar to that in crystalline materials. Details of the intermediate-range order are more elusive, but essential for understanding the lack of long-range symmetry in glasses and the effect of composition on glass structure. Two-dimensional 17O dynamic-angle-spinning nuclear magnetic resonance experiments reveal intermediate-range order in the distribution of inter-tetrahedral (Si-O-Si) bond angles and a high degree of order in the disposition of oxygen atoms around the network-modifying cations.

Glass↗