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Molecular tweezers as synthetic receptors: the effect of pressure and temperature on the formation of host–guest complexes
Author(s) -
Ruloff Robert,
Seelbach Uta P.,
Merbach André E.,
Klärner FrankGerrit
Publication year - 2002
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.477
Subject(s) - chemistry , supramolecular chemistry , enthalpy , molecule , molecular tweezers , entropy (arrow of time) , nuclear magnetic resonance spectroscopy , volume (thermodynamics) , thermodynamics , stereochemistry , organic chemistry , physics
For the formation of the supramolecular complexes between the molecular tweezers 1 and 2 and the aromatic guests 3 – 5 the volumes of reaction Δ V were determined from the pressure dependence of the association constants K by the use of high‐pressure 1 H NMR spectroscopy and the enthalpy Δ H and entropy Δ S of reaction from the temperature dependence of K . The small pressure dependence of K and, hence, the small variation of the reaction volumes around the zero value (Δ V ≈ 0 cm 3 mol −1 ) clearly indicate that the contraction in volume resulting from the host–guest association is compensated for by the expansion in volume resulting from the desolvation of the free host and guest which has to proceed during the complexation. The association and desolvation are expected to have similar effects on Δ S compensating each other. The significant deviations of Δ S from the zero value are, however, good evidence that the size of Δ S not only depends on the processes mentioned above but moreover is influenced by other factors such as the conformational mobility of the guest molecule inside the receptor cavity. Copyright © 2002 John Wiley & Sons, Ltd.