An effective simulation of aqueous micellar aggregates by computational models

We have computationally studied the interaction modes, localization and orientation of a benzene (Bz) molecule on the surface of micelles formed by cetyltrimethylammonium salts CTAX. Experimental 1HNMR data on complexation shifts induced by Bz on the polar head hydrogens and on the adjacent methylene hydrogens of CTAX have been interpreted using a computational approach that combines an automatic molecular docking procedure with a calculation module that accounts for NMR complexation shifts due to ring current diamagnetic anisotropy. Three different models were used to reduce the complexity of the micellar system. Computational results, in good agreement with available experimental data, point to a preferential localization of the Bz molecule along the CTAX alkyl tail, about 3.9 A ˚ away from the charged nitrogen. The Bz molecular plane is predicted perpendicular to the CAH bonds of the alkyl tail. The good results obtained with the simplest model suggest that it could be used to study more complex systems involving surfactants endowed with molecular recognition or catalytic abilities.