Insertion and Expulsion Mechanism of an Amphiphile in a Membrane Mimetic

A theoretical study, validated with experimental data, on the mechanism of insertion/expulsion of an amphiphile from its aggregate is presented. Using molecular dynamics (MD), the equilibrium of tetradecyltrimethylammonium (TTA+) between the aqueous phase and a bilayer, with TTA+ as the main component, was simulated. In order to be inserted, the first interaction of TTA+ with the bilayer is with the hydrophobic chain, and more importantly, before any interaction, TTA+ has to adopt a stretched conformation along with a perpendicular orientation with respect to the aggregate surface. Otherwise, insertion fails and the amphiphile goes back into the bulk water phase. This conformation and orientation remains unmodified during the insertion and expulsion processes. Thus, this mechanism can be called the “dive in mechanism”.