Dynamics of Supramolecular Association Monitored by Fluorescence Correlation Spectroscopy

Abstract

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.

Exchange-dynamics of a neutral hydrophobic dye in micellar solutions studied by Fluorescence Correlation Spectroscopy

“…The necessary theory has been described in more detail elsewhere and only a brief overview will be given here [3,4,18].…”

“…FCS analyzes spontaneous fluorescence intensity fluctuations that may be caused by various processes at the molecular level [4,[22][23][24]. The normalized autocorrelation function GðsÞ of the intensity fluctuations dFðtÞ ¼ FðtÞ À hFi is given by:…”

“…Recently we have shown how the typically very fast dye exchange dynamics can be conveniently studied with Fluorescence Correlation Spectroscopy (FCS), using micelles as membrane mimetic systems and a typical mitochondrial fluorescence marker, Rhodamine 123 (R123), as probe [3,4]. We also demonstrated the advantages of FCS to determine the association/dissociation rate constants of fluorescent dyes with cyclodextrins [5].…”

Single-molecule approaches to characterizing kinetics of biomolecular interactions

“…Colocalization [38] and FRET-based [39] strategies can be used in combination with this fluorescence correlation spectroscopy (FCS) method to obtain accurate information on the kinetic and thermodynamic properties of supramolecular complex formation or ligand binding [40 ].…”

Host-Guest Complexation Studied by Fluorescence Correlation Spectroscopy: Adamantane–Cyclodextrin Inclusion

“…FCS is used in a wide range of fields, but surprisingly few applications to the study of host-guest complexation can be found. We studied recently by FCS host-guest dynamics and determined the fast entry/exit rate constants of fluorescent dyes within cyclodextrins [4,5]. In this contribution we will study by FCS the stoichiometry and the stability of the inclusion complex formed between the host β-cyclodextrin (βCD) and the nonfluorescent guest adamantane labelled with Alexa 488 as fluorescent probe (see Figure 2).…”