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  • ASTROPHYSICS  (4)
  • INORGANIC AND PHYSICAL CHEMISTRY  (1)
  • formation clearance  (1)
  • 1985-1989  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Inhibition of epoxidation of carbamazepine by valproic acid in the isolated perfused rat liver (1985)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 13 (1985), S. 453-466 
    Details
    ISSN: 1573-8744
    Keywords: carbamazepine ; valproic acid ; carbamazepine epoxide ; formation clearance ; perfused rat liver
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of valproic acid on carbamazepine epoxidation in the perfused liver was investigated in two separate studies. In study I, significant decreases were observed both in the intrinsic clearance of carbamazepine and the intrinsic formation clearance of carbamazepineepoxide in the presence of therapeutic concentrations of valproate. The same inhibitory effect of valproate was also observed in liver preparations from a group of animals pretreated with carbamazepine. Study II focused on the effect of valproate and carbamazepine on the apparent Michaelis-Menten parameters (V max,m,Km,m)associated with the intrinsic formation clearance of carbamazepineepoxide in the perfused liver. Valproate had no statistically significant effect on either the V max,morthe Km,m of epoxidation, although the Km,m value was 43% higher in the presence of valproate. However, the ratio of V max,m and Km,m (intrinsic formation clearance) was significantly reduced by valproate. The V max,m and Km,m values obtained in study II predicted a significant decrease in the intrinsic formation clearance of carbamazepineepoxide, consistent with the results of study I. Carbamazepine pretreatment was associated with significant increases in apparent V max,m and Km,m of epoxide formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01059329
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    Paper (German National Licenses)
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  • 2
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    Organic chemistry of Murchison meteorite: Carbon isotopic fractionation (1986)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington Second Symposium on Chemical Evolution and the Origin and Evolution of Life; p 40
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Laser microprobe characterization of C species in Interplanetary Dust Particles (IDP) (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Preliminary results of a study whose aim is the characterization of carbon (C) species in microvolumes of materials by means of laser ionization mass spectrometry (LIMS) are presented. The LIMS instrument employs a pulsed UV laser to produce nearly instantaneous vaporization and ionization of materials, followed by acceleration and time-of-flight analysis of the ions produced. LIMS provides a survey technique with nearly simultaneous acquisition of mass spectra covering the entire elemental range. The main limitation of the LIMS technique at present is its limited ability to perform quantitative analysis, due in part to insufficient knowledge of the mechanism of laser-solid interaction. However, considerable effort is now being directed at making LIMS a more quantitative technique. A variety of different C samples, both natural and man made were analyzed to establish the ability of LIMS to differentiate among the various C phases. The results of preliminary analyses performed on meteoritical and interplanetary dust samples are also presented. The C standards selected for the LIMS characterization range from essentially amorphous soot to diamond, which exhibits the highest degree of ordering.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst. Trajectory Determinations and Collection of Micrometeoroids on the Space Station; p 77-79
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    The carbon chemistry of meteorites: Relationships to comets (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The carbonaceous meteorites exhibiting alteration by liquid water bear a strong relationship to comets. Not only is their elemental composition closer to solar in relative abundances than other meteorites, they are water rich; and they contain isotopic compositions among refractory and volatile elements indicative of presolar components. Some of these isotopic anomalies occur in organic compounds and carbonaceous grains signifying the presence of discrete and identifiable carbon components derived from interstellar and circumstellar matter. Insofar as comets and meteorites are ultimately formed from interstellar gas and dust, and comets have been subjected to considerably less aqueous and thermal evolution than carbonaceous meteorites, the interstellar imprint should be much stronger and better preserved in comets.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Workshop on Analysis of Returned Comet Nucleus Samples; p 13-14
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Adsorption and recombination of hydrogen atoms on a model graphite surface (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The adsorption and recombination of atomic hydrogen on a model graphite grain have been examined in a series of calculations in which a modified, iterative, extended Hueckel program was used. The hydrogen atom is found to be chemisorbed at a site with a zero-point binding energy of 0.7 eV and at an equilibrium distance of 2.25 A above the site. Despite a barrier of about 0.4 eV between adjacent sites, calculations suggest that at temperatures as low as 10 K, an H atom will tunnel through to adjacent sites in less than one nanosecond. However, a potential barrier to the recombination of two hydrogen atoms has been found which displays high sensitivity to the mutual arrangement of the two hydrogen atoms with respect to the graphite surface. Results show that at very low temperatures, recombinations can occur only by tunneling. Consistent with experiment, the region in which H2 begins to form exhibits a repulsive potential with respect to possible chemisorption of the incipient H2 entity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 243-250
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Hot hydrogen atom reactions moderated by H2 and He (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Photolysis experiments were performed on the H2-CD4-NH3 and He-CD4-NH3 systems. The photolysis (1849 A) involved only NH3. Mixtures of H2:CD4:NH3 included all combinations of the ratios (200,400,800):(10,20,40):4. Two He:CD4:NH3 mixtures were examined where the ratios equalled the combinations 100:(10,20):4. Abstraction of a D from CD4 by the photolytically produced hot hydrogen from ammonia was monitored by mass spectrometric determination of HD. Both experiment and semiempirical hot-atom theory show that H2 is a very poor thermalizer of hot hydrogens with excess kinetic energy of about 2 eV. Applications of the hard-sphere collision model to the H2-CD4-NH3 system resulted in predicted ratios of net HD production to NH3 decomposition that were two orders of magnitude smaller than the experimental ratios. On the other hand, helium is found to be a very efficient thermalizer; here, the classical model yields reasonable agreement with experiments. Application of a semiempirical hot-atom program gave quantitative agreement with experiment for either system.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Journal of Physical Chemistry (ISSN 0022-3654); 90; 9; p. 1806-1811.
    Format: text
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    NASA TECHNICAL REPORTS
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