Dynamics of 7-azatryptophan derivatives in micellar media. Elucidating the interactions between peptide oligomers and micelles

We have investigated the motional and population relaxation dynamics of the nonnatural amino acid 7-azatryptophan (7AT) in free (zwitterionic) form and bonded to polyvaline oligomers in aqueous micelles. We have studied the oligomers in solutions of anionic, cationic, and neutral surfactants above their critical micelle concentrations. The use of these peptide oligomers enables the study of charge and structure on interactions with aqueous micelles. The 7AT fluorescence population decay and reorientation dynamics are monitored in aqueous and micellar solutions as a function of micellar headgroup charge and oligopeptide chain length. The lifetime data on 7AT are discussed in terms of its local environment, and the data point to partitioning of probes into micelles mediated by ionic and dispersion interactions with the micelles. The reorientation dynamics are indicative of persistent 7AT-micelle interactions and can be understood in the context of the hindered rotor model.