Supramolecular complexes are formed by non-covalent interactions between two chemical moieties, which can be described as an host and a guest. Most commonly, the interacting species are held together by hydrogen bonds.  The definition excludes compounds formed by electrostatic interactions, which are called ion pairs.
In solution, the host H, guest G, and complexes HG, will be in equilibrium with each other. In the simplest case, p=q=1, the equilibrium can be written as
The value of the equilibrium constant, K, for this reaction can, in principle, be determined by any of the techniques described below. Some examples are shown in the following table.
The Gibbs free energy change, , for this reaction is the sum of an enthalpy term,  and an entropy term .
Both  and  values can be determined at a given temperature, , by means of Isothermal titration calorimetry. For an example, see Sessler. et.al. In that example a macrocyclic ring with 4 protonated nitrogen atoms encapsulates a chloride anion; illustrations of ITC data and a titration curve are reproduced in Steed&Atwood. (pp 15–16) The value of the equilibrium constant and the stoichiometry of the species formed were found to be strongly solvent-dependent. With nitromethane solutions values of ΔH = 8.55 kJmol and ΔS = -9.1 JKmol were obtained.