Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: KEGG:D06522 (Silica)
2,396 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of pore size and alkyl chain length of silica- and polymer-based packing materials in the elution of polypeptides with an acetonitrile gradient in the presence of trifluoroacetic acid were studied. Considerable differences were found in the performance of alkylsilylated phases prepared from various wide-pore silica particles assumed to have 30-50-nm pores. The pore size of such silica gels was found to be the critical factor in determining the efficiency for high-molecular-weight polypeptides. Silica C18 phases having small pore volumes below 20 nm pore diameter showed comparable performances to C4 and C8 phases for polypeptides with molecular weights of up to 80,000, and were more stable. Polymer-based packing materials with adequate pore size provided excellent column efficiencies and recoveries for polypeptides with higher chemical stabilities than silica-based materials.
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PMID:Performance of wide-pore silica- and polymer-based packing materials in polypeptide separation: effect of pore size and alkyl chain length. 196 93

A rapid technique (5-10 min) has been developed for fractionating nucleotides from base and nucleoside contaminants in acid extracts of cells, by adsorption to silica gels. Silica gels (1-mL bed volume) were washed with 5 mL of water then with 5 mL of acetonitrile/water (90/10 by vol). After applying 3-mL samples, adjusted to 900 mL/L acetonitrile content, we washed the gel with an additional 10 mL of the acetonitrile/water solvent. More than 95% of the amounts of bases and nucleosides prsent, except for cytidine (92%), did not adsorb to silica under these conditions. Nucleotides were then quantitatively eluted with 9 mL of water. The retention volumes for positive, negative, and neutral nucleic acid components have been determined, to investigate the discriminatory properties of nucleic acid components on silica. Compounds (bases, nucleosides) that are not ionized at pH 7 do not bind to silica. However, negative, positive, and zwitterionic compounds are tightly adsorbed to the silica gels. This procedure has been used to purify nucleotides from several normal and transformed cell lines.
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PMID:Rapid preparation of nucleotides from acid-soluble pools by chromatography on silica, as exemplified with acid extracts of cultured cells. 625 Jul 40

We developed a procedure for trace enrichment of benzo[a]pyrene (BP) in extracts of smoked food products, and an HPLC-fluorescence detection (FL) method for determination of BP in the enriched extracts. The procedure consists in extraction/sonication of the lyophilized product in hexane, clean-up of the hexane extract by passage through a Sep-Pak Silica Plus cartridge and, subsequently, by partitioning between hexane and dimethyl sulphoxide, and concentration of the BP using a Sep-Pak C18 Plus cartridge. HPLC-FL and quantification limits were 0.049 microgram/l in acetonitrile (< 0.0067 microgram/kg of smoked food) and 0.089 microgram/l in acetonitrile (< 0.012 microgram/kg), respectively. Recovery (94.1%) and RSD (< 8.65%) were satisfactory. When applied to 15 types of sausage, mean BP content was 0.022 microgram/kg, and all but two samples (both treated with wood smoke) had BP contents below the 0.03 microgram/kg limit imposed in EU legislation for smoking-flavour agents.
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PMID:Enrichment of benzo[a]pyrene in smoked food products and determination by high-performance liquid chromatography-fluorescence detection. 896 9

We prepared continuous porous silica rods that had silica skeletons with sizes of 1.0-1.7 microns and through-pores of 1.5-1.8 microns, and evaluated their performance as a column in reversed-phase liquid chromatography. The mesoporous silica monoliths (mesopore size: 14 or 24 nm) were derivatized to C18 phase by on-column reaction with octadecyldimethyl-N,N-diethylaminosilane. The C18 silica rods gave minimum plate heights of 10-15 microns for aromatic hydrocarbons in 80% methanol and of 20-30 microns for insulin in acetonitrile-water mixtures in the presence of trifluoroacetic acid. The performance of the silica rods at a high flow-rate was much better than that of conventional columns packed with 5 microns C18 silica particles with pores of 12 or 30 nm, especially for high-molecular-mass species. Silica rods with the smaller sized silica skeletons resulted in Van Deemter plots showing a minimum plate height linear velocity of the mobile phase and a smaller dependence of plate height on the linear velocity. Separation impedance of less than 1000 was achieved with the continuous silica columns. The higher performance and lower pressure drop of silica rods at high flow-rates compared with particle-packed columns is provided by the small silica skeletons and large through-pores.
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PMID:Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography. 909 72

A practical and reproducible high-performance liquid chromatographic method using normal solid-phase extraction has been developed for the simultaneous analysis of twelve non-steroidal anti-inflammatory drugs (NSAIDs) in human urine. A urine specimen mixed with acetate buffer pH 5.0 was purified by solid-phase extraction on a Sep-Pak Silica cartridge. The analyte was chromatographed by a reversed-phase Inertsil ODS-2 column using a phosphate buffer-acetonitrile at pH 5.0 as the mobile phase, and the effluent from the column was monitored at 230 or 320 nm. Absolute recoveries were greater than 73% for all of the twelve NSAIDs. The present method enabled simple manipulation and isocratic HPLC with UV analysis as well as high sensitivity of 0.005 microg/ml for naproxen, and 0.05 microg/ml for sulindac, piroxicam, loxoprofen, ketoprofen, felbinac, fenbufen, flurbiprofen, diclofenac, ibuprofen and mefenamic acid as the quantitation limit in human urine using indomethacin as an internal standard.
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PMID:Simultaneous analysis of several non-steroidal anti-inflammatory drugs in human urine by high-performance liquid chromatography with normal solid-phase extraction. 918 27

A specific, sensitive and fully automated coupled-column LC method for the determination of the anthracycline cytostatic epirubicin and four metabolites in the biological materials human plasma, liver homogenate and liver tumour homogenate has been developed. System-integrated sample processing was achieved using a new restricted access silica precolumn packing. This porous Alkyl-Diol Silica (ADS) was specially designed for the direct and repetitive injection of proteinaceous samples. It consists of a hydrophilic and electroneutral external particle surface (glyceryl-residues) and a hydrophobic reversed-phase internal surface (butyryl-, octanoyl- or octadecyl-residues). These bimodal chromatographic properties allow retention of low molecular analytes by classical RP-chromatography exclusively at the lipophilic pore surface. Macromolecular constituents of the sample matrix (e.g. proteins) are size-excluded by 5 nm pores and quantitatively eliminated in the interstitial void volume. On-line analysis was performed by coupling a C4-Alkyl-Diol precolumn (20 x 4 mm i.d., particle size 25 microns) and LiChrospher RP Select B analytical column (250 x 4 mm i.d., particle size 5 microns) via an electrically driven six-port valve. Separation of the parent compound and its metabolites was achieved with a mobile phase consisting of water (0.1% triethylamine, v/v, pH 2.0 adjusted with trichloroacetic acid)-acetonitrile (70:30, v/v) at a flow rate of 1 ml min-1. The analytes were detected using their natural fluorescence (excitation 445 nm, emission 560 nm). The method described is used for the determination of pharmacokinetics of epirubicin and its metabolites in order to evaluate and optimize treatment regimen of liver cancer chemoembolization therapy.
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PMID:Coupled-column liquid chromatographic analysis of epirubicin and metabolites in biological material and its application to optimization of liver cancer therapy. 969 77

Hydrophilic interaction chromatography (HILIC) is described as a useful alternative to reversed-phase chromatography for applications involving polar compounds. In the HILIC mode, an aqueous-organic mobile phase is used with a polar stationary phase to provide normal-phase retention behavior. Silica and amino columns with aqueous-acetonitrile mobile phases offer potential for use in the HILIC mode. An examination of the retention and separation of several pyrimidines, purines, and amides on silica and amino columns from three manufacturers revealed that mobile phases should contain a buffer or acid for pH control to achieve similar and reproducible results among columns from different sources. Amino columns may also be used in an anion-exchange mode, which provides an advantage for some applications. In some cases, silica can provide different selectivity and better separation than an amino column. Example applications include: low-molecular-mass organic acids and amides as impurities in non-polar drug substances, 5-fluorouracil in 5-fluorocytosine, guanine in acyclovir, and different selectivity for polar basic compounds compared to an ion-pairing system.
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PMID:Hydrophilic interaction chromatography using amino and silica columns for the determination of polar pharmaceuticals and impurities. 1135 3

The simplicity and flexibility of solid-phase microextraction have been combined with the selectivity of molecularly imprinted polymers (MIPs). Silica fibers were coated reproducible with a 75-microm layer of methacrylate polymer either nonimprinted or imprinted with clenbuterol to compare their extraction characteristics under various conditions. Although the template molecule could be removed effectively from the imprinted polymer, structural analogues of clenbuterol were used for evaluation. The influence of pH on the extractability of brombuterol was investigated. Extraction yields up to approximately 80% were obtained when both types of fibers were used to extract brombuterol from phosphate buffer (pH 7.0). In contrast, yields of about 75 and <5% were obtained when extraction was performed from acetonitrile with imprinted and nonimprinted polymers, respectively, which demonstrates the selectivity of the MIP-coated fiber. Time sorption profiles were measured for the extraction of brombuterol from buffer and acetonitrile at the 10 and 100 ng/mL level with both types of fibers in order to compare extraction characteristics. Equilibrium times of about 30 and 90 min were found for the extraction of brombuterol from acetonitrile and buffer, respectively. The MIP-coated fibers were capable of extracting five structural analogues of clenbuterol from both buffer and acetonitrile, which suggests that the amine alcohol part of these molecules is responsible for interaction with the imprinted polymer. To achieve selective extraction of brombuterol from human urine, MIP-coated fibers were washed with acetonitrile after the extraction. Clean extracts and yields of approximately 45% were obtained, demonstrating the suitability of MIP-coated fibers for the analysis of biological samples.
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PMID:Fibers coated with molecularly imprinted polymers for solid-phase microextraction. 1146 65

We report the validation of a quantitative method for paraquat in plasma and urine using high-performance liquid chromatography (HPLC) with ultraviolet detection (260 nm). Furthermore, we illustrate the use of this method in the clinic (over five years), in conjunction with a qualitative urine paraquat screen. Urine or plasma sample (1 mL) preparation was performed in duplicate using C18 solid-phase extraction. Chromatographic separation was achieved on a Zorbax RX-Silica column (250 x 4.6-mm i.d.). The mobile phase consisted of 96% sodium chloride (5 g/L) and 4% acetonitrile (pH 2.2) pumped at 1.0 mL/min. Using a single-point calibration (1.0 mg/L), the method was found to be linear from 0.1 to 5.0 mg/L. The accuracy and imprecision of the method, over the linear range and for plasma and urine, were 94.7-104.9% and < 12.2%, respectively. The limit of quantitation for both matrices was 0.1 mg/L. The absolute recovery of paraquat from plasma and urine was 79.9 +/- 5.3% and 88.2 +/- 5.3%, respectively. From January 1995 to February 2000, 47 qualitative urine paraquat screens were requested throughout Australia. Nine screens were positive, and eight were confirmed to have paraquat present by our HPLC method. One sample was not analyzed by HPLC because the patient died prior to analysis. Thus, no false-positive results were reported for the qualitative urine screen. An additional 11 samples were referred for patients with positive screens from other sites for HPLC confirmation. The presence of paraquat was confirmed in nine of these samples. In conclusion, a qualitative urine screen combined with our validated HPLC confirmation is an effective protocol for assessing suspected cases of paraquat poisoning.
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PMID:A detection scheme for paraquat poisoning: validation and a five-year experience in Australia. 1155 Aug 20

Acyclovir (ACV) is an antiviral drug, which selectively inhibits replication of members of the herpes group of DNA viruses with low cell toxicity. Valaciclovir (VACV), a prodrug of ACV is usually preferred in the oral treatment of viral infections, mainly herpes simplex virus (HSV). Also other analogues such as ganciclovir and penciclovir are discussed here. The former acts against cytomegalovirus (CMV) in general and the latter against CMV retinitis. The action mechanism of these antiviral drugs is presented briefly here, mainly via phosphorylation and inhibition of the viral DNA polymerase. The therapeutic use and the pharmacokinetics are also outlined. The measurement of the concentration of acyclovir and related compounds in biological samples poses a particularly significant challenge because these drugs tend to be structurally similar to endogenous substances. The analysis requires the use of highly selective analytical techniques and chromatography methods are a first choice to determine drug content in pharmaceuticals and to measure them in body fluids. Chromatography can be considered the procedure of choice for the bio-analysis of this class of antiviral compounds, as this methodology is characterised by good specificity and accuracy and it is particularly useful when metabolites need to be monitored. Among chromatographic techniques, the reversed-phase (RP) HPLC is widely used for the analysis. C18 Silica columns from 7.5 to 30 cm in length are used, the separation is carried out mainly at room temperature and less than 10 min is sufficient for the analysis at 1.0-1.5 ml/min of flow-rate. The separation methods require an isocratic system, and various authors have proposed a variety of mobile phases. The detection requires absorbance or fluorescence measurements carried out at 250-254 nm and at lambdaex=260-285 nm, lambdaem=375-380 nm, respectively. The detection limit is about 0.3-10 ng/ml but the most important aspect is related to the sample treatment, mainly when body fluids are under examination. The plasma samples obtained from human blood are pre-treated with an acid or acetonitrile deproteinization and the supernatant after centrifugation is successively extracted before RP-HPLC injection. Capillary Electrophoresis methods are also discussed. This new analytical approach might be the expected evolution, in fact the analyses are improved with regard to time and performance, in particular coated capillary as well as addition of stabilisers have been employed. The time of analysis is shortened arriving at less than half a minute. Furthermore by using an electrochemical detection, and having a calibration linearity in the range of 0.2-20.0 ng/ml, the detection limit is 0.15 microg/ml. The measurements of acyclovir and penciclovir have been presented but in the future other related drugs will probably be available using CE methods.
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PMID:Separation methods for acyclovir and related antiviral compounds. 1181 33


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