was established by the 1987 Nobel Prize for Chemistry which was awarded to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen in recognition of their work in this area. The development of selective "host–guest" complexes in particular, in which a host molecule recognizes and selectively binds a certain guest, was cited as an important contribution. In the 1990s, supramolecular chemistry became even more sophisticated, with researchers such as James Fraser Stoddart developing molecular machinery and highly complex self-assembled structures, and Itamar Willner developing sensors and methods of electronic and biological interfacing. During this period, electrochemical and photochemical motifs became integrated into supramolecular systems in order to increase functionality, research into synthetic self-replicating system began, and work on molecular information processing devices began. The emerging science of nanotechnology also had a strong influence on the subject, with building blocks such as fullerenes, nanoparticles, and dendrimers becoming involved in synthetic systems. Control Thermodynamics 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 HpGq, 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. {| class="wikitable" |+ Log K1,1 values for complexes of medicinal interest in methanol at 25 °C |- ! !! Li+ !! Na+ !! K+ !! Rb+ !! Cs+ |- ! Valinomycin || <0.7 || 0.67 || 4.9 || 5.26 || 4.42 |- ! Enniatin || 1.28|| 2.42||2.92||2.24|| 2.34 |- ! Nigericin || -|| 4.7|| 5.6|| 5.0 || - |- !Monensin || 3.6 || 6.5|| 5.0||4.3|| 3.6 |} 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