Dynamics of 7-Azatryptophan and Tryptophan Derivatives in Micellar Media. The Role of Ionic Charge and Substituent Structure

We have investigated the motional and population relaxation dynamics of several derivatives of 7-azatryptophan (7AT) and tryptophan (TRP), and N -acetyl-tryptophanamide (NATA), in anionic, cationic, and neutral surfactant solutions above the surfactant critical micelle concentrations. We chose the specific derivatives of 7AT and TRP used previously, along with NATA, to elucidate the roles of chromophore charge and side group structure in mediating interactions with micelles. Fluorescence lifetime data are sensitive to local environment, revealing significant differences in the ability of different chromophores to interact with the micelles. Reorientation dynamics of these chromophores indicate persistent probe/micelle interactions that are determined by a balance between ionic charge(s) and dispersion interactions.