Monte Carlo calculations of ion distributions around micelles

The Monte Carlo (MC) method was used to calculate the distribution of ions around static all-atom models of dodecyl sulfate and cetyl trimethylammonium micelles with solvent represented as a dielectric continuum. The highest concentration of counterions was found around the charged headgroups with some ion penetration into micelle interior, in agreement with studies where the solvent was modeled explicitly. The effects of ion size and micelle aggregation number on the shape of distribution functions were investigated. The MC results were compared with the predictions of the Poisson–Boltzmann equation for a uniformly charged sphere. MC-calculated hydroxide ion concentration profiles were used to model the kinetics of the basic hydrolysis of crystal violet in the presence of cetyl trimethylammonium micelles. The MC method of estimating reactive ion concentration around a micelle enables a simple and consistent description of the observed dependence of the reaction rate on the detergent concentration. Our results also suggest that changes in the shape and polydispersity of micelles caused by increasing added salt concentration have an effect on micellar catalysis.