Dynamics of supramolecular association monitored by fluorescence correlation spectroscopy

Supramolecular binding is a key process in many biological systems and in newly developed supramolecular assemblies. Most of the scientific work on these systems is focused on their structural properties and on the thermodynamics of the association process. However, the underlying dynamics are usually much less known, in spite of the great importance they have during the binding process in these highly dynamic systems. Understanding supramolecular binding in biological systems and controlling the functionality of new synthetic supramolecular systems can only be achieved through knowledge of the structure-dynamics relationship. There is a strong need for suitable techniques which cover the typically wide time interval of the association dynamics and which do not need a perturbation of the system. We briefly review high-resolution fluorescence correlation spectroscopy (FCS) as a technique to monitor supramolecular dynamics and to give information on how structure determines the dynamics of host-guest association. The comparison of hosts and guests with different structures shows that geometrical and orientational requirements determine the association rate constant, whereas the dissociation is defined by the strength of specific interactions. As model hosts cyclodextrins and micelles are studied.