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The Anatomy of the Energetics of Molecular Recognition by Calorimetry: Chiral Discrimination of Camphor by α ‐Cyclodextrin
Author(s) -
Schmidtchen Franz P.
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020802)8:15<3522::aid-chem3522>3.0.co;2-x
Subject(s) - chemistry , supramolecular chemistry , enantiomer , enthalpy , molecular recognition , cyclodextrin , solvent , molecular binding , molecule , stereochemistry , thermodynamics , organic chemistry , physics
The molecular recognition of both camphor enantiomers 2 with the chiral α ‐cyclodextrin ( α ‐CD) 1 in water and D 2 O was examined by calorimetry. On the basis of statistically supported determinations the thermodynamics of 2:1 host–guest binding and chiral discrimination was evaluated. The energetic signature strongly supports hydrophobic interaction as the dominant driving force for camphor encapsulation by α ‐CD in water. The solvent isotope effect on the binding equilibrium served to dissect the experimental enthalpy Δ H ass into direct interaction (Δ H intr ) and solvent reorganization (Δ H solv ) terms. From this analysis the mutual interaction of two cyclodextrin and one camphor molecules contributes only 25 % to the observed enthalpy of binding Δ H ass , all the rest is attributed to solvent restructuring. Furthermore, the dramatic change in the pattern of thermodynamic state functions on solvent transfer from water to D 2 O is taken as compeling evidence for the involvement of water as a structural tectone in the supramolecular architecture of the 2:1 complex. As a corollary, bilateral host–guest interactions as conveyed by the lock‐and‐key metaphor of molecular recognition provide an inadequate description of this seemingly simple artificial host–guest system.