Entropy‐Driven Cooperativity in the Guest Binding of an Octaphosphonate Bis‐cavitand

Abstract

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. 1H 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.

Feet‐to‐Feet‐Connected Multitopic Resorcinarene Macrocycles

“…Octaphosphonate biscavitand 11 captures two equivalents of ammonium guests ( Figure 6). [63][64] X-ray crystallographic analysis of the host-guest complex of 11 with two n-butylmethylammonium salts revealed that both cavitand units are filled with the two ammonium salts with the N-methyl groups directed toward the cavities, generating favorable CH-π and ion-dipole interactions. The solvent significantly influences guest binding behaviors.…”

“…Thermodynamic parameters for the molecular association of 11 in methanol and chloroform. [64] Solv. parameter larger than 3.1, whereas a negative cooperative association occurs when the value is less than 0.3.…”

“… Guest molecules for 11 and crystal structure of host‐guest complex. Adapted from Ref [64] . with permission.…”

“…Figure 7. Schematic representation of homotropic positive cooperative guest binding of 11.Reprinted with permission from Ref [64]. Copyright (2020) John Wiley & Sons, Inc.…”

Upper-rim functionalization and supramolecular polymerization of a feet-to-feet-connected biscavitand

“…25 The interaromatic bridges yielded a biscavitand, showing allosteric guest binding. [26][27][28] To expand the biscavitand chemistry, upper rim functionalization is required to deepen the cavities through carbon-carbon bond forming reactions. Octaiodobiscavitand 1 can deepen its cavities through the introduction of various substituents by means of carbon-carbon bond forming reactions.…”