Entropy–driven Cooperativity in the Guest Binding of an Octaphosphonate Biscavitand
2019
Uncommon entropy-driven cooperativity is reported in the guest binding of an octaphosphonate bis-cavitand. Isothermal titration calorimetry determined the thermodynamic parameters for the 1:2 host-guest binding of bis-cavitands with ammonium guests in methanol, ethanol, 2-propanol, and chloroform. Chloroform drove uncommon entropy-driven cooperative binding, whereas the alcohols resulted in enthalpy-driven noncooperative binding. (1) H NMR studies revealed that each cavity contained six water molecules in chloroform, which were liberated on guest binding. The enthalpy-entropy compensation relationship produced a large positive intrinsic entropy in chloroform, which implies that water desolvation causes a considerable entropic gain by paying an enthalpic penalty due to breaking the hydrogen-bonding networks of the water clusters.
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