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Background: Paraquat (PQ) has been implicated as a risk factor for the Parkinson disease phenotype (PDP) in humans and mice using epidemiologic or experimental approaches. The toxicokinetics (TK) and toxicodynamics [...]

The disappearance of 9-hydrooxy-methylanthracene with UV/vis absorption spectroscopy is followed to determine the rate of the Diels-Alder reaction between N-ethylmalleimide and 9-hydroxymethylanthracene in supercritical carbon dioxide.

Animal models, consistent with the hypothesis of direct interaction of paraquat (PQ) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) with specific areas of the central nervous system have been developed to study Parkinson’s disease (PD) in mice. These models have necessitated the creation of an analytical method for unambiguous identification and quantitation of PQ and structurally similar MPTP and 1-methyl-4-phenylpyridinium ion (MPP+) in brain tissue. A method for determination of these compounds was developed using microwave-assisted solvent extraction (MASE) and liquid chromatography–mass spectrometry. Extraction solvent and microwave conditions such as power and time were optimized to produce recoveries of 90% for PQ 78% for MPTP and 97% for its metabolite MPP+. The chromatographic separation was performed on a C8, column and detection was carried out using an ion trap as an analyzer with electrospray ionization. Mass spectrometer parameters such as heated capillary temperature, spray voltage, capillary voltage and others were also optimized for each analyte. Analysis was done in selective ion-monitoring (SIM) mode using m/ z 186 for PQ, m/ z 174 for MPTP, and m/ z 170 for MPP+. The method detection limit for paraquat in matrix was 100 pg, 40 pg for MPTP, and 20 pg MPP+. [ABSTRACT FROM AUTHOR]

The rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthracene in supercritical carbon dioxide (scCO2) was determined by following the disappearance of 9-hydroxymethylanthracene with in situ UV/vis absorption spectroscopy. The reaction conditions were 45-75 °C and 90-190 bar, which correspond to fluid densities (based on pure carbon dioxide) ranging between approximately 340 and 730 kg m-3. The measured reaction rate at low scCO2 fluid densities was nearly 25× faster than that reported in acetonitrile at the same temperature (45 °C). An inverse relationship between reaction rate and fluid density/pressure was observed at all temperatures in scCO2. The apparent activation volumes were large and positive (350 cm3 mol-1) and only a weak function of reduced temperature. A solvophobic mechanism analogous to those observed in conventional solvents is postulated to describe (a) the rate acceleration observed for this reaction in scCO2 relative to that in acetonitrile, (b) the observed relationship between reaction rate and pressure/temperature/density, and (c) the large, positive activation volumes. Solubility measurements in scCO2, rate measurements in conventional solvents, and an empirical correlation are used to support this theory. Our results advance the general understanding of reactivity in supercritical fluids and provide a rationale for selecting reactions which can be accelerated when conducted in scCO2. [ABSTRACT FROM AUTHOR]