Biomedical subjects

K Desmet

Publications and source records attributed to K Desmet.

7 recordsLinked to original sources

PubMed2002

Evaluation of reversible and irreversible models for the determination of the enantiomerization energy barrier for N-(p-methoxybenzyl)-1,3,2-benzodithiazol-1-oxide by supercritical fluid chromatography.

It has been found that the interconversion of enantiomers on a chromatographic column during the separation process can be studied by the first-order kinetic equations derived both for reversible and irreversible reactions in a stationary system if the extent of interconversion is not too high. The equation derived for irreversible reactions gives, however, results also for higher degrees of enantiomerization while that derived for reversible interconversion failed. The irreversible equation was used to determine the enantiomerization barrier of N-(p-methoxybenzyl)-l,3,2-benzodithiazol-l-oxide enantiomers by supercritical fluid chromatography. The racemate of N-(p-methoxybenzyl)-l,3,2-benzodithiazol-l-oxide was separated by supercritical fluid chromatography on the (R,R)-Whelk-Ol column with supercritical carbon dioxide containing 20% methanol as a mobile phase. Peak areas of enantiomers prior to and after the separation used for the calculation of the enantiomerization barrier were determined by computer-assisted peak deconvolution of peak clusters registered on chromatograms using commercial software.

Chromatography↗

PubMed2002

Stir bar sorptive extraction-thermal desorption-capillary GC-MS applied to biological fluids.

A new sample preparation method, stir bar sorptive extraction (SBSE), has been evaluated for the enrichment of organic solutes from biological fluids such as urine and blood. In SBSE, a stir bar coated with a polydimethylsiloxane layer is stirred for a given time in the sample. After sampling the stir bar is placed in a thermal desorption unit coupled on-line to capillary gas chromatography-mass spectrometry (SBSE-TD-CGC-MS). The principle and operation of SBSE are presented. Total profiling and target compound analysis have been selected as applications to illustrate the performance of SBSE-TD-CGC-MS (MSD). It is demonstrated that a variety analytes ranging from biological markers (phenols, hormones, fatty acids) to artificial contaminants (recreational drugs, plasticizers) can be enriched with high sensitivity. For polar solutes, in-situ derivatization can enhance both recovery into the polydimethylsiloxane (PDMS) layer and chromatographic analysis. Two types of derivatization have been applied, derivatization with ethyl chloroformate and with acetic acid anhydride. Linearity, detectability, and repeatability are illustrated by the determination of 1-hydroxypyrene in a urine sample from a smoker.

Body Fluids↗

PubMed2001

Asymmetric induction in intramolecular meta photocycloaddition: cyclodextrin-mediated solid-phase photochemistry of various phenoxyalkenes.

[reaction: see text]. An approach to the asymmetric intramolecular meta photocycloaddition of phenoxyalkenes is described. The beta-cyclodextrin complexes of several phenoxyalkenes have been synthesized and irradiated in the solid phase. The effect of the CD-hosting on the regio- and enantioselectivity is discussed. Values of ee up to 17% were obtained.

Alkenes↗

PubMed2001

Prevalence of genotypic resistance among antiretroviral drug-naive HIV-1-infected patients in Belgium.

OBJECTIVES: To estimate the prevalence and the evolution over time (1995-1998) of genotypic resistance to antiviral drugs in antiretroviral drug-naive HIV-1-infected patients in Belgium. DESIGN: Belgian Aids Reference Laboratories provided retrospective samples and clinical data from antiretroviral drug-naive HIV-1-infected patients who visited the hospital for the first time in 1995 (n=45), 1997 (n=75) and 1998 (n=111). Genotypic resistance to the three available classes of drugs was monitored using the Line Probe Assay (Innogenetics, Gent, Belgium). Additionally, ARMS-151 was performed for scoring multinucleoside resistance. RESULTS: The prevalence of genotypic resistance at baseline to nucleoside analogue reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) were each between 10% and 20% for 1995, 1997 and 1998 without an increasing trend over time. For NRTIs, resistance mutations were mainly related to zidovudine in 1995, whereas in 1997 and 1998 baseline resistance was scored for zidovudine, lamivudine or for both drugs simultaneously. No patients displayed the multi-nucleoside resistance Q151M mutation. Baseline resistance mutations to protease inhibitors (PIs) did not rise significantly: 4.4% in 1995, 8% in 1997 and 9.9% in 1998. When scoring any resistance-related mutation, 26.6% displayed genotypic baseline resistance in 1995, 26.6% in 1997 and 31.5% in 1998. DISCUSSION: The prevalence of genotypic baseline resistance to any drug, as scored with LiPA, in naive HIV-1 patients in Belgium is 29%, with baseline resistance mutations to one or several drugs from all available classes of antiviral drugs. The ability of LiPA to pick up minor variants could be an explanation for the higher overall prevalence we observe, when compared to recent estimates in other countries of 16.3% and 22%, which were based on sequencing methods. According to the European guidelines for resistance testing, resistance testing in Belgium before starting antiviral therapy should be considered.

Acquired Immunodeficiency Syndrome↗

PubMed1997

Inhibition of acetylcholine esterase and choline esterase by benzethonium chloride and avoidance of the benzethonium chloride carry-over inhibitory effect.

It has been shown that benzethonium chloride produces linear mixed-type inhibition of choline esterase and acetylcholine esterase. These enzymes also show-reagent-carry-over inhibition if the enzyme activities are measured in plastic cuvettes in which previously protein has been determined by the alkaline benzethonium chloride method. Choline esterase is about 10-fold more sensitive to benzethonium chloride than acetylcholine esterase. With acetylthiocholine as substrate Michaelis-Menten constants for choline esterase and acetylcholine esterase are 85 mumol/l and 102 mumol/l, respectively. Carry-over inhibitory effect of benzethonium chloride can be avoided by washing the cuvettes, after protein determination by the benzethonium chloride method, with 5 ml/l Triton X-100, 5 ml/l Tween 20 or 10 g/l sodium dodecyl sulphate. The latter has a disadvantage in that it precipitates out at low temperatures. The dry slide method (Johnson & Johnson) for serum choline esterase is free of the inhibitory effect until the concentration of benzethonium chloride in the sample reaches about 200 mumol/l.

Acetylcholinesterase↗

PubMed1993

Diminished sedation during diazepam treatment for chloroquine intoxication.

We report a case of a woman hospitalized after chloroquine overdose whose whole blood concentration on admission was 7.87 micrograms/ml. High blood concentrations of chloroquine induce cardiotoxicity and have been associated with death when they exceed 3.0 micrograms/ml. Early administration of massive doses of diazepam has been described to reduce the mortality due to chloroquine toxicity, but the protective mechanism has remained unknown. This patient was treated with diazepam (2.0 mg/kg over 30 min followed by a dosage of 1.0 to 2.0 mg/kg over 24 h), yet she remained awake despite the high plasma concentrations of diazepam and nordiazepam which would normally be associated with sedation. This suggests an antagonistic effect of chloroquine on the benzodiazepine-induced sedation due to an interaction between these drugs at their site of action.

Adult↗

PubMed1993

Quantitation of paraquat in serum by HPLC.

An HPLC method for the quantitation of paraquat in urine was applied to serum. Sample preparation consisted of ion-pair extraction on disposable cartridges of end-capped octadecyl silica. The paraquat thus extracted, was quantitated by HPLC using 1,1'-diethyl-4,4'-dipyridyl dichloride as an internal standard. Relatively small sample volumes (1 mL serum) were required. Within- and between-assay coefficients of variation for the HPLC technique were 2.9% and 4.0%, respectively, at low paraquat serum concentration (0.4 microgram/mL), and 2.4% and 3.2% at high paraquat serum concentration (4.0 micrograms/mL). The between-assay coefficient of variation for the total procedure, including the extraction, was 5.6% at low concentration (0.4 microgram/mL). Serum concentration levels down to 0.025 microgram/mL could be quantitated. The technique was checked for interference from muscle relaxants (pancuronium bromide and vecuronium bromide) and from anticoagulants (heparin and K2EDTA). No interference was observed.

Chromatography, High Pressure Liquid↗