Calorimetric Analysis of the 1:1 Complexes Formed between a Water-soluble Deep-cavity Cavitand, and Cyclic and Acyclic Carboxylic Acids

A water-soluble cavitand was shown to form 1:1 complexes with a series of acyclic and cyclic aliphatic carboxylic acids. Isothermal titration calorimetry was used to determine the standard molar enthalpy change (ΔH°) and binding constant (K a), and hence the Gibbs free energy (ΔG°) and entropy (ΔS°) change for the different complexes. The thermodynamic determinations were carried out from 288 to 318 K, allowing the standard molar heat capacity changes ( ) also to be derived. Typical of the processes driven by the hydrophobic effect, was observed to be proportional to the accessible (non-polar) surface area of the guest. The cyclic and acyclic guests displayed opposite trends; the heat capacity penalty upon binding increased with longer aliphatic chains, while the opposite was observed with the cyclic guests.

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