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1997 (1)
1996 (1)
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    C. Margheritis, C. SinistriRequires cookie*
 Title    /?-cyclodextrine and Water: Semiempirical Calculations  
 Abstract    AMI and PM3 calculations were carried out on ß-cyclodextrine (ß-CD) undecahydrate in the experimental conformation at 120 K. The calculated /TCD/water interaction energies are very small and indicative for each water molecule of an unfavorable condition in respect to that of pure water. The conformationally optimized system was also studied: ß-CD appears highly symmetrical with negligible dipole moment, mainly because of the circular arrangement of the single vectors. Primary hydroxyls can easily rotate, while the secondary ones are stabilized by heteroannular hydrogen bonds and homoannular electrostatic interactions due to the consequent increase of the atomic charges. The ß-CD/water interaction energies in the optimized hydrated system are not significantly different from the experimental ones. This almost hydrophobic character is also shown by MM equilibrated solutions: all water molecules are rejected beyond 2.4 A; between 2.4 and 2.9 A highly structured water is present. From a purely enthalpic standpoint the molecule hydration appears highly improbable, thus the formation of ß-CD 11 H 2 0 must involve a compensation mechanism. 
  Reference    Z. Naturforsch. 51a, 950—956 (1996); received May 13 1996 
  Published    1996 
  Keywords    ß-cyclodextrine hydrate, Semiempirical calculations, Water interactions 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0950.pdf 
 Identifier    ZNA-1996-51a-0950 
 Volume    51