Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of "High-Energy" Water

作者：Metherell Alexander J.; Cullen William; Williams Nicholas H.; Ward Michael D.^*

来源：Chemistry - A European Journal, 2018, 24(7): 1554-1560.

DOI：10.1002/chem.201704163

• coordination cage
• host-guest systems
• hydrophobic effect
• molecular recognition
• supramolecular chemistry

The cavity of an M8L12 cubic coordination cage can accommodate a cluster of ten water molecules in which the average number of hydrogen bonds per water molecule is 0.5H-bonds less than it would be in the bulk solution. The presence of these hydrogen-bond frustrated or high-energy water molecules in the cavity results in the hydrophobic effect associated with guest binding being predominantly enthalpy-based, as these water molecules can improve their hydrogen-bonding environment on release. This contrasts with the classical form of the hydrophobic effect in which the favourable entropy change associated with release of ordered molecules from hydrophobic surfaces dominates. For several guests Van't Hoff plots showed that the free energy of binding in water is primarily enthalpy driven. For five homologous pairs of guests related by the presence or absence of a CH2 group, the incremental changes to Delta Delta H and T Delta Delta S for guest binding-that is, Delta Delta H and T Delta Delta S, the difference in contributions arising from the CH2 group-are consistently 5(+/- 1) kJ mol(-1) for H and 0(perpendicular to) kJ mol(-1) for TS. This systematic dominance of H in the binding of hydrophobic guests is consistent with the view that guest binding is dominated by release of high energy water molecules into a more favourable solvation environment, as has been demonstrated recently for some members of the cucurbituril family.

• 出版日期2018-2-1