Aggregational process of the positively charged surfactants CTAC and CAT16 in the presence of starburst dendrimers: an electron paramagnetic resonance spectroscopic study

The aggregation process of positively charged surfactants (CAT16 alone and mixed CAT16-CTAB) in the presence of half generation polyamidoamine starburst dendrimers (n.5-SBDs) was analyzed by means of a computer-aided analysis of the electron paramagnetic resonance (EPR) spectra. The partition of the probes in different environments was evaluated from the relative intensities of the corresponding EPR signals, which superimposed on each other to form the overall EPR line shape. Mobility and polarity parameters were evaluated for CAT16 monomers under the following conditions: (i) free in solution below the critical micellar concentration (cmc) of the surfactants; (ii) free in solution in equilibrium with surfactant aggregates (above their cmc); (iii) interacting as monomers with the n.5-SBDs (primary interactions). A parameter related to the local concentration (or the structural packing) of CAT16 was evaluated under the following conditions: (i) CAT16 aggregates; (ii) mixed CTAB-CAT16 aggregates. It was hypothesized that the formation of different supramolecular structures — SBDs/surfactants — varied as a function of the dendrimer size (generation) and the concentrations of both the dendrimer and the surfactant.