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'Thermodynamics' in keywords Facet   Publication Year 1997  [X]
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1997[X]
1Author    C. Margheritis, A. Marini, C. SinistriRequires cookie*
 Title    Thermodynamics of /J-cyclodextrine/water Interactions  
 Abstract    From a purely enthalpic standpoint, the ß-CD hydration, as studied by semiempirical calcula-tions, appears improbable, in contrast to experiment. For the spontaneous hydration process, a compensation mechanism, connected with substrate stabilization and/or entropy increase, is sug-gested on the basis of simple thermodynamic considerations. The analysis is done on the basis of a single parameter £ w (> 0), which represents the energy needed to transfer a mole of water from the liquid to the ß-CD absorbed phase. The model, although simple, allows predictions largely consistent with the experimental results, while suggesting possible interpretations. 
  Reference    Z. Naturforsch. 52a, 348—350 (1997); received January 3 1996 
  Published    1997 
  Keywords    ß-cyclodextrine, Water interactions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0348.pdf 
 Identifier    ZNA-1997-52a-0348 
 Volume    52 
2Author    M. Sandmann, F. Hamann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4-/i-Pentyl-4'-Cyano-Biphenyl (5CB) and trans-4-(4'-Octyl-Cyclohexyl)-Benzonitrile (8PCH) up to 300 MPa  
 Abstract    Specific volumes are presented for 4-n-pentyl-4'-cyanobiphenyl (5CB) and trans-4-(4'-octyl-cyclo-hexyl)-benzonitrile (8PCH) for temperatures between 300 and 370 K up to 300 MPa. The p,V m ,T data were determined for the liquid crystalline and isotropic phases, and partly also for the solid phase adjacent to the melting curve. Stable and metastable crystal phases can be distinguished. The density and melting temperature of the metastable form are lower than for the stable one. Volume and enthalpy changes accompanying the phase transitions are reported as well. The p,V m ,T data allow to calculate the entropy change for a hypothetical transition at constant volume. The molar volumes along the nematic-isotropic phase transition T NI (p) allow to determine the molecular field parameter y = S In T NI /0 In F N ,. 
  Reference    Z. Naturforsch. 52a, 739—747 (1997); received August 13 1997 
  Published    1997 
  Keywords    5CB, 8PCH, High pressure, pVT, Phase transitions, Thermodynamics, DTA 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0739.pdf 
 Identifier    ZNA-1997-52a-0739 
 Volume    52 
3Author    Masahisa KakiuchiRequires cookie*
 Title    Hydrogen Isotope Fractionation in Aqueous Alkali Halide Solutions  
 Abstract    The D/H ratios of hydrogen gas in equilibrium with aqueous alkali halide solutions were deter-mined at 25 °C, using a hydrophobic platinum catalyst. The hydrogen isotope effect between the solution and pure water changes linearly with the molality of the solution at low concentrations, but deviates from this linearity at higher concentration for all alkali halide solutions. The magnitude of the hydrogen isotope effect is in the order; Kl > Nal > KBr > CsCl ^ NaBr > KCl > NaCl > LiCl, at concentrations up to a molality of 4 m. The sign and trend of the hydrogen isotope effect is different from that of oxygen. In aqueous alkali halide solutions, the hydrogen isotope effect is influenced by both the cation and the anion species, while the oxygen isotope effect is mainly caused by the cation species. This suggests that the mechanism of hydrogen isotope fractionation between the water molecules in the hydration spheres and the free water molecules differs from the mechanism of the oxygen isotope fractionation. The hydrogen and oxygen isotope effects for alkali halides, except LiCl and NaCl, may be influenced by changes in energy of the hydrogen bonding in free water molecules. 
  Reference    Z. Naturforsch. 52a, 811—820 (1997); received April 15 1997 
  Published    1997 
  Keywords    Hydrogen Isotope, Alkali halide, D/H fractionation, Thermodynamics, Isotope effect 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0811.pdf 
 Identifier    ZNA-1997-52a-0811 
 Volume    52