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At least 685 records · Page 38Linked to original sources
PubMed2001

Neutron reflection from a dimyristoylphosphatidylcholine monolayer adsorbed on a hydrophobised silicon support.

Neutron specular reflection has been used to study the structure of a monolayer of dimyristoylphosphatidylcholine (DMPC) deposited using the Langmuir-Blodgett technique onto a silicon oxide substrate. A self-assembled monolayer of octadecyltrichlorosilane with a deuterated alkyl chain (d-OTS) had been previously bonded onto this silicon oxide substrate which rendered it hydrophobic. In the system under study, the alkyl chains of the phospholipid were found to penetrate extensively into the d-OTS layer with the mixed chain region (d-OTS and DMPC) having a total thickness of 30.5 A. This mixed region was divided into two halves for analysis; the 'lower half' (nearest to the substrate surface) was found to comprise anchored d-OTS chains mixed with the lipid chains in the volume ratio approx. 0.60:0.35. The corresponding volume ratio in the 'upper half' of this region was determined to be approx. 0.50:0.40. The thicknesses of these regions were found to be 17.9 A (incorporating approx. 6% solvent) and 12.6 A (incorporating approx. 9% solvent) for the lower and upper halves respectively. The DMPC head groups were found to be confined to the most external layer (furthest away from the silicon substrate). This layer was found to have a thickness of 9.4 A and included a small fraction of the lipid alkyl chains with approx. 47% solvent.

Dimyristoylphosphatidylcholine↗
PubMed2002

Mechanics of F-actin characterized with microfabricated cantilevers.

In this report we characterized the longitudinal elasticity of single actin filaments manipulated by novel silicon-nitride microfabricated levers. Single actin filaments were stretched from zero tension to maximal physiological tension, P(0). The obtained length-tension relation was nonlinear in the low-tension range (0-50 pN) with a resultant strain of approximately 0.4-0.6% and then became linear at moderate to high tensions (approximately 50-230 pN). In this region, the stretching stiffness of a single rhodamine-phalloidin-labeled, 1-microm-long F-actin is 34.5 +/- 3.5 pN/nm. Such a length-tension relation could be characterized by an entropic-enthalpic worm-like chain model, which ascribes most of the energy consumed in the nonlinear portion to overcoming thermal undulations arising from the filament's interaction with surrounding solution and the linear portion to the intrinsic stretching elasticity. By fitting the experimental data with such a worm-like chain model, an estimation of persistence length of approximately 8.75 microm was derived. These results suggest that F-actin is more compliant than previously thought and that thin filament compliance may account for a substantial fraction of the sarcomere's elasticity.

Actins↗
PubMed2001

Biocompatibility of silicon-based arrays of electrodes coupled to organotypic hippocampal brain slice cultures.

In this study we examined the passive biocompatibility of a three-dimensional microelectrode array (MEA), designed to be coupled to organotypic brain slice cultures for multisite recording of electrophysiological signals. Hippocampal (and corticostriatal) brain slices from 1-week-old (and newborn) rats were grown for 4-8 weeks on the perforated silicon chips with silicon nitride surfaces and 40 microm sized holes and compared with corresponding tissue slices grown on conventional semiporous membranes. In terms of preservation of the basic cellular and connective organization, as visualized by Nissl staining, Timm sulphide silver-staining, microtubule-associated protein 2 (MAP2) and glial fibrillary acidic protein (GFAP) immunostaining, the slice cultures grown on chips did not differ from conventionally grown slice cultures. Neither were there any signs of astrogliosis or neurodegeneration around the upper recording part of the 47-microm-high platinum-tip electrodes. Slice cultures grown on a separate set of chips with platinum instead of silicon nitride surfaces also displayed normal MAP2 and GFAP immunostaining. The width of the GFAP-rich zone (glia limitans) at the bottom surface of the slice cultures was the same ( approximately 20 microm) in cultures grown on chips with silicon nitride and platinum surfaces and on conventional insert membranes. The slice cultures grown on chips maintained a normal, subfield differentiated susceptibility to the glutamate receptor agonist N-methyl-D-aspartate (NMDA) and the neurotoxin trimethyltin (TMT), as demonstrated by the cellular uptake of propidium iodide (PI), which was used as a reproducible and quantifiable marker for neuronal degeneration. We conclude that organotypic brain slice cultures can grow on silicon-based three-dimensional microelectrode arrays and develop normally with display of normal subfield differentiated susceptibilities to known excito- and neurotoxins. From this it is anticipated that the set-up, designed for recording of electrophysiological parameters, can be used for long-term studies of defined neuronal networks and provide valuable information on both normal, neurotoxicological and neuropathological conditions.

Animals↗
PubMed1989

In vitro effects of fibrous and nonfibrous silicon nitride on bovine pulmonary macrophages.

Bovine pulmonary macrophages were exposed in vitro to 0.3, 0.1, 0.03, or 0.01 mg/ml of a fibrous silicon nitride, nonfibrous (milled) silicon nitride comminuted from the fibrous powder, alpha-quartz (an active control), or glass beads (an inert control). Functional evaluation of the exposed cells indicated that the fibrous silicon nitride was as cytotoxic as quartz, while the nonfibrous silicon nitride was relatively inert. To further evaluate the mechanisms of cytotoxicity, the cells were exposed to 1 mg/ml of the control and test materials and biochemical studies were performed. Quartz increased release of both the cytoplasmic enzyme, lactate dehydrogenase (LDH), and the lysosomal enzyme, acid phosphatase (AP), consistent with both cell membrane and lysosome lysis. In addition, total protein levels were significantly depressed, suggesting significant impairment of cellular synthetic processes. LDH, but not AP, values were increased with fibrous silicon nitride treatment, but not with the nonfibrous silicon nitride. In contrast to quartz, which increased LDH levels by 65%, the fibrous silicon nitride only increased LDH levels by 11%. Scanning electron micrographs further indicated that the fibrous silicon is cytotoxic and poorly tolerated by macrophages. These studies provide further evidence of morphology as a primary determinant of cytotoxicity since the milled powder test article was comminuted from the fibrous material.

Acid Phosphatase↗
PubMed2000

Speciation of selenium compounds with ion-pair reversed-phase liquid chromatography using inductively coupled plasma mass spectrometry as element-specific detection.

For selenium speciation analysis, the hyphenation of chromatographic separation with element-specific detection has proved a useful technique. A powerful separation system, which is capable of resolving several biologically and environmentally important selenium compounds in a single column, is greatly needed. However, that has been difficult to achieve. In this paper eight selenium compounds, namely, selenite [Se(IV)], selenate [Se(VI)], selenocystine (SeCys), selenourea (SeUr), selenomethionine (SeMet), selenoethionine (SeEt), selenocystamine (SeCM) and trimethylselenonium ion (TMSe+), were separated by using mixed ion-pair reagents containing 2.5 mM sodium 1-butanesulfonate and 8 mM tetramethylammonium hydroxide as a mobile phase. The separation of these anionic, cationic and neutral organic selenium compounds on a LiChrosorb RP18 reversed-phase column took only 18 min at a flow-rate of 1.0 ml/min with isocratic elution, and baseline separation among the six organic Se compounds was achieved. Inductively coupled plasma mass spectrometry (ICP-MS) was employed as element-specific detection. A comparison of ICP-MS signal intensity obtained with a Barbington-type nebulizer and with an ultrasonic nebulizer (USN) was made. Different signal enhancement factors were observed for the various selenium compounds when a USN was used. The speciation technique was successfully applied to the study on chemical forms of selenium in a selenium nutritional supplement. Selenomethionine was found to be the predominant constituent of selenium in the supplement.

Chromatography, High Pressure Liquid↗
PubMed1976

Forensic aspects of high-pressure liquid chromatography.

This paper reviews the applications of high-pressure liquid chromatography (HPLC) to forensic problems, and discusses some of the developments that have taken place in the use of the technique in the Metropolitan Police Laboratory. Preparation of octadecyltrichlorosilane-modified silica is described and some of the chromatographic characteristics of this material are investigated. Applications of HPLC to the analysis of cannabis, opium alkaloids, amphetamine-related materials, LSD and polynuclear hydrocarbons are described.

Alkaloids↗
PubMed1986

Gas-liquid chromatography and mass spectral analysis of mono-, di- and tricarboxylates as their tert.-butyldimethylsilyl derivatives.

A gas-liquid chromatographic (GLC) procedure is described which permits the baseline separation and quantitation of twenty saturated monocarboxylates, sixteen dicarboxylates (both alkanedioic and alkenedioic), and the tricarboxylates citrate and aconitate in a single GLC analysis. The carboxylic acids, as their tert.-butyldimethylsilylated derivatives, are readily separable on a SPB-1 (bonded) capillary column. Separation data on an OV-17 (bonded) capillary column and a SP-2250 packed column of these carboxylates, in addition to fifteen unsaturated carboxylates, are also given. The tert.-butyldimethylsilylation of carboxylic acids in their free or ammonium salt forms is accomplished in a single derivatization step with N-methyl-N-(tert.-butyldimethylsilyl)-trifluoroacetamide. Retention data and responses for all mono-, di- and tricarboxylic acids are given. Mass spectral analysis of all tert.-butyldimethylsilylated carboxylic acids is presented and each displays a prominent and characteristic [M-57] fragment ion.

Carboxylic Acids↗
PubMed1987

Analysis of amino acids by gas-liquid chromatography as tert.-butyldimethylsilyl derivatives. Preparation of derivatives in a single reaction.

The effect of temperature, solvent and reagents on the formation of the N(O)-dimethyl-tert.-butylsilyl derivatives of proteic amino acids has been studied. Quantitative silylation is achieved using dimethyl-tert.-butylsilyltrifluoroacetamide with 1% tert.-butyldimethylchlorosilane in dimethylformamide by heating at 75 degrees C for 30 min. Two peaks were obtained for arginine under these conditions. However, most of the standard proteic amino acids can be assayed. The N(O)-dimethyl-tert.-butylsilyl derivatives of the proteic amino acids have been analysed by gas chromatography-mass spectrometry using the methane chemical ionization mode. The spectral data are presented and have been used to confirm the structures of the amino acid derivatives.

Amino Acids↗
PubMed1985

Liquid chromatographic retention behavior of organometallic compounds and ligands with amine-, octadecylsilica- and beta-cyclodextrin-bonded phase columns.

Effects of solvent composition and ligand variation on the retention of organometallic compounds have been studied using an amino, an octadecylsilica (ODS) and a beta-cyclodextrin (beta-CD) bonded phase column in either a normal-phase or a reversed-phase mode. The retention behavior for the organometallic compounds with the amino column can be rationalized using the displacement model. The "apparent" molecular areas are greater for compounds capable of strong hydrogen bonding. The retention in the ODS column roughly follows an argument based on the expected solubility behavior while mixed retention mechanisms are involved for the solubility behavior while mixed retention mechanisms are involved for the beta-CD column, i.e. both inclusion process and solubility or solvophobic interactions are possibly operative.

Amines↗
PubMed2002

Fast ion chromatography of common inorganic anions on a short ODS column permanently coated with didodecyldimethylammonium bromide.

Fast ion-exchange chromatography has been developed and applied to the separation of common inorganic anions. Using a didodecyldimethylammonium bromide (DDAB) coated short (30 mm x 4.6 mm) ODS analytical column (3-microm particle size) and a 5 mM phthalate eluent (pH 7.5) the isocratic separation of nine common anions in 160 s was possible, with the first seven anions, including phosphate, chloride and sulphate, separated within 65 s. Detection was achieved using indirect UV at 279 nm. The high capacity, highly hydrophobic ion-exchange coating demonstrated excellent stability over time, even at elevated temperatures (45 degrees C) and exhibited unusual selectivity for common anions (retention order=fluoride, carbonate, phosphate, chloride, bromate, nitrite, sulphate, bromide and nitrate). The developed chromatography was successfully applied to the rapid analysis of river water and seawater samples.

Anions↗
PubMed1997

Description and prediction of retention in normal-phase high-performance liquid chromatography with binary and ternary mobile phase.

The suitabilities of several earlier reported models for description and prediction of retention in normal-phase systems with mobile phases comprised of two organic solvents-a polar and a non-polar one-were tested on the chromatographic behaviour of phenylurea herbicides and alkyl-, aryl- and nitrophenols as sample solutes with a silica-gel column and 2-propanol, n-heptane and dioxane as mobile phase components. With few exceptions, the data obtained from the best-fit three-parameter retention equation differ from the experimental capacity factors at less than 0.1, or 2%, and for most compounds the fit is better than 1%. Of the two two-parameter equations derived from theoretical models, one failed to describe the retention behaviour. The fit of the other two-parameter equation to the retention data of phenols is slightly inferior than with the three-parameter equation. The differences between the fitted data and the experimental capacity factors of substituted phenylureas were < or = 0.2, or 5%. Three-parameter equations were suggested to describe the retention behaviour in three-component mobile phases either at a constant sum or at a constant ratio of the two stronger solvents in ternary mobile phases. To fit the three-component data at any combination of concentrations of the three solvents with the error comparable to that in binary mobile phases, a nine-parameter equation is necessary. Suitability of these equations to describe the experimental behaviour of substituted phenylureas and phenols was verified in ternary mobile phases with various concentrations of 2-propanol, dioxane and n-heptane. Finally, a method was suggested for the prediction of retention in ternary mobile phases with varying concentration ratios of the two polar solvents from the parameters of best-fit equations in binary mobile phases and a single experimental capacity factor in a ternary mobile phase. For most capacity factors, the error of prediction was lower than 0.2, or 5%. Dried solvents were used to improve the reproducibility of the results and the temperature was controlled to +/-0.1 degree C in all experiments. With these precautions, differences between the original retention volumes and the data from repeated experiments measured after ten months of use of the column in the system tested were less than 0.2 ml for 85% of the values compared.

1-Propanol↗
PubMed2001

Regeneration of N, P and Si near the sediment/water interface of lakes from Southwestern China Plateau.

Lake water, pore water, and sediments were sampled in both polluted and unpolluted lakes from Southwestern (SW) China Plateau. The results show that although the mechanisms of nutrient regeneration were similar in the polluted and unpolluted lakes, the processes, however, were much stronger in the polluted lakes. Nitrogen regeneration was mainly of organic process. Phosphorus regeneration was essentially controlled by iron redox cycling near sediment/water interface. Nutrient upward fluxes were in the order SiO2 > NH4+ > PO4(3-). This study has significance for further investigating the response of nutrient biogeochemistry to the increasing nutrient levels in aquatic environments.

China↗
PubMed2003

A method for preparing silica-containing iron(III) oxide adsorbents for arsenic removal.

A method for preparing iron(III)-based binary oxide adsorbents in a granulated form for arsenic removal was studied. The key step in the method was the simultaneous generation of hydrous ferric oxide (FeOOH) sol and silica sol in situ in one reactor. This eventually led to the formation of Fe-Si complexes. The addition of silica enhanced the granulated adsorbent strength but reduced the arsenic adsorption capacity. An optimum Si/Fe molar ratio in the balance of adsorbent strength and arsenic adsorption capacity was found to be approximately 0.33. The effects of aging time, drying temperature and process pH on adsorbents were also evaluated in the study. X-ray diffraction analysis confirmed that the iron(III) oxide in the Fe-Si binary oxide adsorbents was amorphous, largely due to the retardation of the iron oxide crystallization by the presence of silicate species. The surface area of the Fe-Si adsorbents and the particle size of Fe-Si complexed suspensions were determined as well. The batch strength testing procedure introduced in this study can provide a simple and quick evaluation of granulate strength in a wet status. Generally, this developed method can prepare granulated Fe-Si binary oxide adsorbents for column adsorption of arsenic from water.

Adsorption↗