The Binding of Sulfate Anions by Guanidinium Receptors is Entropy-Driven.

Clear trends in the molecular recognition of guest species by artificial hosts in solution are often observed by intrinsic enthalpy-entropy compensation, which requires the dissection of these free-energy components. Contrary to common belief, it is not the enthalpic electrostatic attraction that makes guanidinium hosts such as 1 strong binders for sulfate anions. Isothermal titration calorimetry has now allowed this molecular recognition to be characterized as an entropy-driven association.