NMR Evidence of Slow Monomer-Micelle Exchange in a Calixarene-Based Surfactant

The self-aggregation of amphiphilic p-sulfonatocalix[4]arene was studied by fluorescence and NMR techniques. Pyrene fluorescence spectra were used to determine the critical micelle concentration and the value obtained was confirmed using Diffusion-Ordered NMR Spectroscopy (DOSY). It was found from the H-1 NMR spectra that exchange between the monomers in the bulk and in the micelles is slow on the NMR time scale. This finding was confirmed by 2D EXSY experiments and the rate constants of the process at different temperatures were extracted using the latter technique.