| Abstract
| - We investigated the dye-exchange dynamics between rhodamine 123 (R123), a mitochondrial fluorescentdye, and micelles as membrane mimetic systems. In the presence of neutral micelles (Triton X-100 and Brij35) R123 partitions between the aqueous solution and the micellar pseudo-phase, undergoing red shift of theabsorption and the emission spectra. Fluorescence correlation spectroscopy (FCS) was used to study thedynamics of these systems over an extremely wide time range and at the single-molecule level, yieldinginformation in one and the same experiment about the diffusional dynamics of free and bound rhodamineand about the dye-exchange dynamics as well as several photophysical properties of the rhodamine bound tothe micelles. It was found that the entry rate constants are diffusion-controlled, indicating that there are nogeometric or orientational requirements for the association of the dye with the micelle. With respect to thedye-exchange dynamics, micelles are found to behave as soft supramolecular cages in contrast to other rigidsupramolecular cavities, such as cyclodextrins. The exit rate constants depend on the surfactant and determinethe stability of the binding. Single-molecule multiparameter fluorescence detection (MFD) was used to examinethe fluorescence properties of individual molecules in comparison to ensembles of molecules. The MFDhistograms confirm the fast dye-exchange dynamics observed by FCS and yield mean values of fluorescencelifetimes and anisotropies in agreement with those obtained in bulk measurements.
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