Hydrophobically driven hosting - What about the guest?

The hosting of cyclic and linear aliphatic moieties by cucurbit[7]uril and 8-cyclodextrin was investigated by means of ITC, 2D ROESY NMR spectroscopy, and by classical MD simulations. The cyclodextrin complexation thermodynamics at 298 K revealed classical hydration of the investigated guests. The results of the comparative calorimetric study clearly pointed out that the dehydration of cucurbituril cavity is accompanied with lower entropy changes compared to the analogous process involving cyclodextrin. A pronounced temperature depen-dence of & UDelta;rH degrees (hence & UDelta;rS degrees) unaccompanied by changes in product structure was observed for all studied systems. The effect was primarily due to temperature-induced disordering of the guest-hydrating water, i.e. gradual change from classical-towards non-classical hydration of the aliphatic moieties. The study thus reveals the effect of the guest and the cavity dehydration on the complexation thermodynamics while simultaneously providing rationale bridging the classical and non-classical hydrophobic effect. The obtained results also indicate that closer examination of the temperature influence on the corresponding complexation equilibria could further enhance the utilisation of the thermodynamic potential of hydrophobically driven association and result in a better understanding of water solvation properties.