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The chromatographic selectivities of polystyrene-coated zirconia (PS-ZrO2) have been investigated in detail by means of homologue series retention studies and studies of a variety of nonpolar aromatic positional isomers. This material has been compared to polybutadiene-coated zirconia, octadecyl- and phenyl-bonded silica, and polymer-based reversed phases. In addition, the separations of a wide variety of compound classes on PS-ZrO2 were compared with those on other aromatic and aliphatic RPLC phases. The PS-ZrO2 material exhibits substantial differences in selectivity toward nonpolar and polar analytes as compared to other phases, especially with respect to polybutadiene-coated zirconia (PBD-ZrO2). On PS-ZrO2, polynuclear aromatic hydrocarbons (PAHs) are retained much more than are alkylbenzenes, whereas on PBD-ZrO2 the opposite is observed. In addition, PS-ZrO2 has much greater selectivity than does PBD-ZrO2 for the separation of structural isomers which differ in the position of phenyl groups. In general, even though the carbon content of PS-ZrO2 is much lower than that of conventional reversed-phase materials, such as octadecyl-bonded silica (C18-SiO2), polar analytes exhibit sufficient retention and differential selectivity on PS-ZrO2 that resolution comparable to that on C18-SiO2 can be obtained but with substantially improved analysis times.
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PMID:A comparative study of the chromatographic selectivity of polystyrene-coated zirconia and related reversed-phase materials. 1065 23

A novel zirconia-based HPLC packing material, ZrO2/SiO2, which consists of micrometer-sized silica spheres as core and nanometer-sized zirconia particles as surface coating, was prepared by a layer-by-layer self-assembly technique. The material exhibits favorable characteristics for HPLC applications, including high surface area and pore volume, good pore structure, narrow particle size, and pore size distribution. Not only the support ZrO2/SiO2 but also the stationary-phase C18 bonded ZrO2/SiO2 exhibits excellent chemical stability. In addition, good permeability was observed for both of them. High specific area surface and good permeability of ZrO2/SiO2 permit a high loading amount of chiral polymer on it and greatly improved the enantioselectivity and resolution for some chiral separations.
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PMID:Layer-by-layer self-assembly of multilayer zirconia nanoparticles on silica spheres for HPLC packings. 1537 36

Quantitative Structure-Retention Relationships of benzoylphenylureas and similar compounds have been studied on a new type of stationary phase (polystyrene-octadecene-encapsulated zirconia) in reversed-phase high performance liquid chromatography. Using stepwise regression analysis, the relationships between the structural descriptors of the compound and its chromatographic retention were examined. It was confirmed that the retention of the dihalogenobenzoylphenylureas is mainly governed by the dipole moment (DM), the calculated molar refractivity (CMR), and the hydrophobicity parameter (C log P) of the compounds. The predicting equations for the 18 dihalogenobenzoylphenylureas and similar compounds were also established; there is a good agreement between the observed k values and the predicted k values. In addition, a typical ODS (Kromasil-C18-SiO2) was compared with C18-PS-ZrO2. The results showed that there were some differences between the two stationary phase for the separation of the compounds investigated, which are certainly related to surface characteristics of the two different supports.
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PMID:Quantitative structure-retention relationships of benzoylphenylureas on polystyrene-octadecene-encapsulated zirconia stationary phase in reversed-phase high performance liquid chromatography. 1568 34

Two types of novel reversed-phase packing materials were made by adding TiO2/ SiO2 (or ZrO2/SiO2) and octadecyltrichlorosilane into toluene with stirring and refluxing for 36 h. TiO2/SiO2 and ZrO2/SiO2 particles were prepared by a layer-by-layer self-assemble technique and consist of micrometer-sized silica spheres as cores and nanometer-sized zirconia or titania as surface coating. The carbon loading of C18-bonded TiO2/SiO2 was 11.51% and that of C18-bonded ZrO2/SiO2 was 9.62%. The hydrophobic selectivity and sensitivity were studied respectively and compared in details; the results showed that the packing supports both acted as true reversed chromatographic stationary phase with similar hydrophobic selectivity. The chromatographic behaviors of the two types of novel reversed-phase packing material were evaluated with nine aromatic compounds. The chromatographic studies showed that either of the packing materials would be a good choice to separate aromatic compounds, however, the selectivity of C18-bonded TiO2/SiO2 was a little better than that of C18-bonded ZrO2/SiO2.
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PMID:[Comparison in hydrophobic selectivity for two types of reversed-phase high performance liquid chromatography packing material]. 1701 64

X-ray photoelectron spectra (XPS) are reported from a series of buried titanium/organic monolayer interfaces accessed through sample delamination in ultrahigh vacuum (UHV). Conventional characterization of such buried interfaces requires ion-mill depth profiling, an energetic process that frequently destroys bonding information by chemically reducing the milled material. In contrast, we show that delaminating the samples at the metal/organic interface in vacuum yields sharp, nonreduced spectra that allow quantitative analysis of the buried interface chemistry. Using this UHV delamination XPS, we examine titanium vapor deposited onto a C18 cadmium stearate Langmuir-Blodgett monolayer supported on Au, SiO2, or PtO2 substrates. Titanium is widely used as an adhesion layer in organic thick film metallization as well as a top metal contact for molecular monolayer junctions, where it has been assumed to form a few-atoms-thick Ti carbide overlayer. We establish here that under many conditions the titanium instead forms a few-nanometers-thick Ti oxide overlayer. Both TiO2 and reduced TiOx species exist, with the relative proportion depending on oxygen availability. Oxygen is gettered during deposition from the ambient, from the organic film, and remarkably, from the substrate itself, producing substrate-dependent amounts of Ti oxide and Ti carbide "damage". On Au substrates, up to 20% of the molecular-monolayer carbon formed titanium carbide, SiO2 substrates approximately 15%, and PtO2 substrates <5%. Titanium oxide formation is also strongly dependent on the deposition rate and chamber pressure.
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PMID:Oxide and carbide formation at titanium/organic monolayer interfaces. 1831 37

Very severe reaction conditions are required in the conventional synthesis of molecularly imprinted polymers (MIPs), which is unfavorable to their applications in chemical separation and analysis. A simple surface molecular imprinting approach was developed to synthesize MIP-coated SiO2 micro-particles in aqueous solutions. The 1H NMR and UV-vis spectroscopic analysis indicated that via hydrogen bonding, the functional monomer (o-phenylenediamine) can associate with the target (template) 2,4-dinitrophenol (2,4-DNP), as a model compound of organic pollutants, to form a precursor in aqueous solution. The copolymerization of this precursor and the free monomer was performed in the aqueous suspension of surface modified SiO2 particles, leading to the formation of MIP-coated SiO2 micro-particles. The MIP-coated silica particles were characterized with FT-IR, TGA, and UV-vis solid-state reflection spectroscopy, and were further demonstrated to have high adsorption capacity, excellent selectivity and site accessibility for 2,4-DNP. The new absorbent was successfully used in solid-phase extraction (SPE) to selectively enrich and determine 2,4-DNP in aqueous samples. The experimental results indicated that the MIP-SPE column yielded recoveries higher than 92% with R.S.D. <2.8%, much better than the commercial C18-SPE column, which produced a recovery less than 30% with R.S.D. <3.0%.
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PMID:Synthesis of surface molecularly imprinted silica micro-particles in aqueous solution and the usage for selective off-line solid-phase extraction of 2,4-dinitrophenol from water matrixes. 1851 36

A two-dimensional liquid chromatographic system (NPLC x RPLC) has been developed. Normal phase liquid chromatography (NPLC) with a Hypersil SiO2 column (50 mm x 4.6 mm) was used as the first dimension, and reversed-phase liquid chromatography (RPLC) with a Kromasil C18 column (250 mm x 4.6 mm) was used as the second dimension. The interface was a ten-port, two-position valve with two storage loops. As to improve the compatibility of the two dimensional mobile phase and be good for adjusting the selectivity of separation, 1,4-dioxane was used in the mobile phase of the first dimension, and isopropyl alcohol was used in the mobile phase of the second dimension based on the characters of the organic solvents. By raising the temperature of the second dimension, the incompatibility of the two dimensional mobile phases was avoided. A Chinese potent medicine, Zhengtian Wan, was analyzed by this system. The total peak capacity reached 1 220.
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PMID:[Establishment and application of a two-dimensional liquid chromatographic system (NPLC x RPLC)]. 1872 80

A comprehensive orthogonal two-dimensional liquid chromatography (2D-LC) based on the modification of mobile phases was developed with a sample loop-valve interface. To improve the compatibility of mobile phases and analysis speed, some special solvents were chosen as the mobile phases, and the column temperature was elevated to decrease the viscosity of mobile phases of reversed-phase liquid chromatography (RPLC). Based on this principle, the first dimension was normal-phase liquid chromatography (NPLC) with a SiO2 column, and the second dimension was reversed-phase liquid chromatography containing two tandem C18 columns. 1,4-Dioxane was used in the NPLC mobile phase, and isopropyl alcohol was employed in the RPLC mobile phase. Moreover, the elevated column temperature enabled the reduction of the backpressure and using tandem C18 columns to improve the resolving power in RPLC. The new comprehensive 2D-LC system and applied strategy offered a novel idea for construction of 2D-LC system. A traditional Chinese medicine, Zhengtian pill, was used as the test sample to evaluate the constructed 2D-LC system. 876 peaks were detected, and the peak capacity reached 1740.
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PMID:A comprehensive two-dimensional normal-phase x reversed-phase liquid chromatography based on the modification of mobile phases. 1971 35

Nonporous monodispersed silica spheres of 1.3 microm were coated with gold nanoparticles (AuNPs) and subsequently coated with n-octadecanethiol. By transmission electron microscopy analysis, the average diameter of the AuNPs on the silica spheres was determined to be 12 nm. The chromatographic and electrochromatographic properties of self-assembled n-octadecanethiol AuNP-coated silica microspheres (C18-AuNPs-SiO2) were investigated using a group of nonpolar PAHs. The stationary phase appears to display a characteristic reversed-phase behavior. Higher separation efficiency and shorter separation times were obtained using pressurized CEC (pCEC) compared with capillary LC (CLC). A maximum column efficiency of about 2.5x10(5) plates per meter and less than 18 min separation time for benzene were obtained in pCEC while only 66 507 plates per meter and an analysis time of nearly 100 min were observed in CLC mode. A chemical stability test of the C18-AuNPs-SiO2 stationary phase under extremely high and low pH conditions demonstrated that it is stable at pH 12 and 1 for at least 60 h. The results confirm that C18-AuNPs-SiO2 possesses a high rigidity to withstand high packing pressures and can be used as a good stationary phase for CLC and pCEC.
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PMID:Silica spheres coated with C18-modified gold nanoparticles for capillary LC and pressurized CEC separations. 2011 65

Silica has been widely used as HPLC column packing material. However, the fact that base can attack the silanol and dissolve the silica embarrasses the utilization of silica stationary phase in high pH mobile phases (pH >8). In our previous research, the use of porous spherical silicon oxynitride (sph-SiON) material from high temperature nitridation of silica microspheres as stationary phase for HPLC has been explored, and the sph-SiON is stable to alkaline mobile phases and demonstrates excellent separation of a variety of polar compounds in hydrophilic interaction liquid chromatography (HILIC) mode. Herein, the degree of nitridation was studied as a function of temperature of nitridation at 750-1 050 degrees C, yielding the silicon oxynitride with 0.40%-12.0% (mass fraction) nitrogen from elemental analysis. At the temperature of 1 050 degrees C, the nitrogen content increased from 12.0% to 24.5% with the nitridation time increasing from 20 h to 120 h. The sph-SiON is stable when disposed in different pH aqueous solutions for one week. The sph-SiON material can be modified to give hydrophobic surface through the reaction of surface Si-NHx with dimethyloctadecylchlorosilane. Elemental analysis and 13C cross-polarization magic-angle spinning (CP/MAS) NMR spectrum of C18-sph-SiON prove the integration of C18 alkyl groups attached onto the sph-SiON surface. The chromatographic evaluation of C18-sph-SiON in reversed-phase separation mode was performed with alkylbenzenes as hydrophobic probes. Three alkylbenzene compounds can be separated and retained well on C18-sph-SiON even in the mobile phase of methanol/H2O (70/30, v/v) with 78 507 plates/m, and an excellent tailing factor (0.95) can be obtained for ethylbenzene. In comparison with C18-SiO2, C18-sph-SiON shows distinct differences with respect to different classes of analytes, i. e. neutral analyte naphthalene, acidic analyte ibuprofen, and basic analyte amitriptyline.
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PMID:[Synthesis of porous spherical silicon oxynitride material and evaluation of its properties in reversed-phase chromatographic separation]. 2389 32


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