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At least 631 records · Page 35Linked to original sources
PubMed1996

Ion-pair chromatography of methotrexate in a column-switching system using an alkyl-diol silica precolumn for direct injection of plasma.

The retention behaviour of methotrexate as an ion-pair with tetrabutylammonium in a column-switching system, based on an alkyl-diol silica C8 precolumn, combined with an analytical column, LiChrospher RP 18, was studied. Methotrexate is mainly present as a divalent anion at pH 7.4, however, the retention data was consistent with the formation of a 1 + 1 ion pair with the counter ion. The concentration of the tetrabutylammonium and the acetonitrile in the mobile phase could be used to regulate the retention in the system. Relevant chromatographic parameters to estimate the enrichment effect in the column-switching system are also identified and discussed. The column-switching system was applied to direct injection of plasma (100 microliters) giving a limit of detection of 10 ng/ml for methotrexate using UV detection at 307 nm.

Acetonitriles↗
PubMed1988

A comparison of the rates of methylation of mercury(II) species in aquatic media by various organotin and organosilicon moieties.

Metals can be methylated in environmental aqueous media by a variety of organotin and organosilicon compounds. Main group metals and metalloids were surveyed for the identification of species that can either donate or accept methyl groups. The methylation of mercury(II) by trimethyltin cation was found to be a bimolecular reaction, the reaction rate of which decreased with increasing chloride concentration. Kinetic investigations using NMR techniques showed that the most important pairs of reactants were (CH3)3Sn+ + HgCl2, (CH3)3SnCl + HgCl2, and (CH3)3SnCl + HgCl-3. Sodium 2,2,3,3-tetradeutero-3-(trimethylsilyl)propionate (TSP) and sodium 2,2-dimethyl-2-silapentane-5-sulfonate (DSS) were found to methylate mercury(II). Organylsilatranes were found to transfer their organic groups readily to mercury(II) to produce organomercury compounds.

Magnetic Resonance Spectroscopy↗
PubMed1991

Passage time measurement of individual red blood cells through arrayed micropores on Si3N4 membrane.

A new system has been developed for determining the deformability of individual red blood cells (RBCs), simulating the passage of RBCs in capillaries. The kernel of this system was the micropore array filter with an accurately defined pattern made by semiconductor microprocessing techniques. Individual microscopic RBC images were processed in parallel through a microcomputer and its interfacing circuit. An experiment with a normal RBC from a human donor demonstrated that it could pass the circular pore filter with a diameter as small as 1.0 micron at 2 cm H2O pressure difference. Deformability of RBCs treated with diamide or acetylphenylhidralazine was also measured, showing that the system was sufficiently sensitive to detect the deformability loss due to membrane damage or to polymerization of the cytoplasma.

Adult↗
PubMed1995

Surface modifications of a glass and a glass-ceramic of the MgO-3CaO.P2O5-SiO2 system in a simulated body fluid.

A glass of nominal composition (wt%) 17.25 MgO-52.75 3CaO.P2O5-30 SiO2 and a glass-ceramic obtained from it showed surface modifications when immersed in an acellular medium having a composition similar to that of human blood plasma. A (Ca, P)-rich layer, with an approximate Ca/P atomic ratio of 1.7, identified as hydroxyapatite, developed on both samples. The precipitated film on the glassy sample was weakly bonded, whereas that formed on the glass-ceramic was strongly adherent. The apatite precipitated during the in vitro tests on both samples grew as a needle-like structure with crystals about 150-200 nm long and 50-70 nm thick, as measured on specimens soaked for 1 month in the simulated body fluid (SBF). The presence of calcium and phosphate ions in the SBF contributed to the precipitation of the (Ca, P)-rich layers on both specimens.

Binding Sites↗
PubMed1995

Sister-chromatid exchanges in lymphocytes of workers at a phosphate fertilizer factory.

The frequencies of sister-chromatid exchange (SCE) in peripheral blood lymphocytes of 40 workers at a phosphate fertilizer factory in North China were studied. HF and SiF4 are main air pollutants in the factory, there is also some dust containing fluoride, phosphate fog, NH3 and SO2. It was shown that the chemicals caused an increase in SCE, and also induced cell mitotic delays. The mean SCEs/cell of the workers and the non-exposed controls were 7.47 +/- 0.31 and 4.94 +/- 0.14 (p < 0.01) respectively. SCEs/cell in 75% of 40 workers were higher than 6 while 40 controls all had values lower than 6. SCE frequencies of the workers increased with length of the chemical exposure period up to 10 years. Smoking enhanced the SCE frequencies induced by the chemicals.

Air Pollutants, Occupational↗
PubMed1995

27Al magic-angle spinning nuclear magnetic resonance satellite transition spectroscopy of glasses in the system K2O-Al2O3-SiO2.

27Al magic-angle spinning nuclear magnetic resonance satellite transition spectroscopy at 78 MHz has been applied to determine (true) chemical shift and quadrupole coupling parameters of glasses in the system K2O-Al2O3-SiO2 with 60-80 mol% SiO2 and K2O concentrations between 0 and 24 mol%. The powdered crystalline aluminosilicates andalusite and sillimanite have also been examined. In the glasses, all Al appears to be tetrahedrally bound in the aluminosilicate network unless x = mol% K2O:mol% Al2O3 becomes extremely small. Upon decreasing x the distortion of the tetrahedral Al(OSi)4 units increases in steps, and possible explanations are discussed. Six-coordinated aluminum observed for x < 0.2 is connected with the occurrence of interstitial Al3+ ions which charge-compensate the AlO4 units in addition to K+.

Aluminum↗
PubMed1995

Nuclear magnetic resonance investigation of the structures of phosphate and phosphate-containing glasses: a review.

This paper presents a review of the nuclear magnetic resonance (NMR) data for phosphate and phosphate-containing glasses obtained primarily within the past 10 years and of the structural interpretations based on those data. Compositions discussed include P2O5, alkali and alkaline earth phosphates, aluminophosphates, borophosphates, fluorophosphates, and phosphate-containing silicate and aluminosilicate glasses. 31P NMR data, in conjunction with 27Al, 29Si, 11B, 7Li, and 23Na data if appropriate, have proven very powerful in providing direct evidence about the local structural environments present in the these materials and in many cases have allowed interpretation of the physical and chemical behavior of these glasses in terms of polyhedral structures.

Alkalies↗
PubMed1996

Femtomolar sensitivity using a channel-etched thin film waveguide fluoroimmunosensor.

A dual channel, evanescent fluoroimmunoassay format is used to detect femtomolar analyte concentrations (i.e. less than 1 part per trillion [w/w]) on an etched channel siliconoxynitride thin film integrated optical waveguide. Two assays are used to demonstrate the dose-response behaviour of the sensor: (1) a direct assay of a fluorescently-labeled protein ligand binding to an immobilized protein receptor, and (2) an indirect sandwich assay of a non-fluorescent protein ligand binding to an immobilized protein receptor, as detected by the binding of a fluorescently-labeled secondary receptor protein. A red-emitting cyanine dye (Cy-5), which minimized background fluorescence and scatter losses of the waveguide, was used in both assays. To our knowledge, this is the first report of femtomolar sensitivity in an immunosensing instrument.

Biosensing Techniques↗
PubMed2005

A surface modification strategy on silicon nitride for developing biosensors.

A surface modification strategy for the use of giant magnetoresistive materials in the detection of protein-protein interactions is developed. This modification strategy is based on silanization of semiconductive materials. A native silicon nitride surface was treated with concentrated hydrofluoric acid to improve surface homogeneity. Nano-strip was used to oxidize silicon nitride to form a hydrophilic layer. Aminopropyltriethoxysilane was subsequently used to functionalize the treated surfaces to form amine groups, which were further activated with glutaraldehyde to introduce a layer of aldehyde groups. The effectiveness of this modification strategy was validated by chemiluminescence immunoassays of purified 6x His-HrpW of Pseudomonas syringae pv. tomato DC3000 and human transferrin. Signals with intensities related to concentrations of these two immobilized model proteins were observed. The modified surface was also validated by a more complex system: intercellular proteins secreted by DC3000. HrpW in these protein mixtures was successfully recognized by anti-HrpW antibodies when mixed proteins were immobilized onto activated surfaces. This surface modification strategy provides a platform onto which proteins can be directly immobilized for biosensor and protein array applications.

Biosensing Techniques↗
PubMed2006

Polymerase chain reaction of 2-kb cyanobacterial gene and human anti-alpha1-chymotrypsin gene from genomic DNA on the In-Check single-use microfabricated silicon chip.

The microfabricated chip is a promising format for automating and miniaturizing the multiple steps of genotyping. We tested an innovative silicon biochip (In-Check Lab-on-Chip; STMicroelectronics, Agrate Brianza, Italy) designed for polymerase chain reaction (PCR) analysis of complex biological samples. The chip is mounted on a 1x3-in(2). plastic slide that provides the necessary mechanical, thermal, electrical, and fluidic connections. A temperature control system drives the chip to the desired temperatures, and a graphical user interface allows experimenters to define cycling conditions and monitor reactions in real time. During thermal cycling, we recorded a cooling rate of 3.2 degrees C/s and a heating rate of 11 degrees C/s. The temperature maintained at each thermal plateau was within 0.13 degrees C of the programmed temperature at three sensors. From 0.5 ng/microl genomic DNA, the In-Check device successfully amplified the 2060-bp cyanobacterial 16S rRNA gene and the 330-bp human anti-alpha(1)-chymotrypsin gene. The shortest PCR protocol that produced an amplicon by capillary electrophoresis comprised 30 cycles and was 22.5 min long. These thermal cycling characteristics suggest that the In-Check device will permit future development of a genotyping lab-on-a-chip device, yielding results in a short time from a limited amount of biological starting material.

Cyanobacteria↗
PubMed2005

Circular dichroism of the peripheral chlorophylls in photosystem II reaction centers revealed by electrochemical oxidation.

Visible absorption spectra and circular dichroism (CD) of the red absorption band of isolated photosystem II reaction centers were measured at room temperature during progressive bleaching by electrochemical oxidation, in comparison with aerobic photochemical destruction, and with anaerobic photooxidation in the presence of the artificial electron acceptor silicomolybdate. Initially, selective bleaching of peripheral chlorophylls absorbing at 672 nm was obtained by electrochemical oxidation at +0.9 V, whereas little selectivity was observed at higher potentials. Illumination in the presence of silicomolybdate did not cause a bleaching but a spectral broadening of the 672-nm band was observed, apparently in response to the oxidation of carotene. The 672-nm absorption band is shown to exhibit a positive CD, which accounts for the 674-nm shoulder in CD spectra at low temperature. The origin of this CD is discussed in view of the observation that all CD disappears with the 680-nm absorption band during aerobic photodestruction.

Chlorophyll↗
PubMed2006

Functional atomic force microscopy investigation of osteopontin affinity for silicon stabilized tricalcium phosphate bioceramic surfaces.

Resorbable silicon stabilized tricalcium phosphate (Si-TCP)-based bioceramics are characterized from a biological perspective by measuring the intermolecular interaction force between osteopontin (OPN) protein and the material surface using atomic force microscopy (AFM). OPN protein was covalently bound to silicon nitride AFM tips and adsorption and adhesion forces were measured in an electrolyte with a composition similar to that of physiological fluids. A strong relationship exists between the adhesion force of OPN on the material surface, the number of adherent osteoclasts (OC) and the resorption of the material. OPN adhesion is strongest on hydroxyapatite (HA) surfaces, or in samples that induce a HA-like surface through a precipitation reaction in electrolytic media. It is proposed that the increased biological response of the Si-TCP phase can be attributed in part to its reactivity in a physiological electrolyte, which involves a rapid conversion to a calcium deficient HA phase with a corresponding increase in the adhesion strength of OPN to the material, with a consequentially higher OC resorption response.

Adsorption↗