Catanionic Tubules with Tunable Charge

The tuning of the particle charge allows the regulation of phenomena that are crucial in nanotechnology, such as the ability of the particle to load molecules (drugs, DNA, proteins, etc.), to aggregate and to penetrate membranes. The application of the charge tuning to tubular structures is particularly interesting because of the growing nanotechnological interest of these morphologies. Here, a catanionic mixtures is described that allows the preparation of surfactant tubules with controlled charge. In particular, an aqueous solution of mixed anionic and cationic bile salt derivatives was identified that forms catanionic tubules in the whole range of the investigated anionic/cationic surfactant molar ratio (from 19/1 to 1/19) up to very low total surfactant concentration (0.023-0.030 wt%). Tubules with charge ranging from negative to positive values can be obtained depending on the surfactant molar ratio of the solution. Mixtures of anionic and cationic surfactants in water have been the fascinating subject of extensive investigations for many years. Generally, at low concentrations of the catanionic components, vesicles and micelles are formed, in these systems, accompanied by two-phase regions and precipitates around the equimolar composition. For their phase behavior, the catanionic mixtures have been mainly studied so far, to provide stable and spontaneously formed anionic or cationic rich vesicles. The reported results are completely new. They demonstrate that catanionic mixtures with new behaviours and potential technological employments can be prepared by using anionic and cationic forms of rigid non conventional amphiphiles. The reported findings join others data recently shown for pure solutions of this kind of molecules, demonstrating a general peculiarity of their self assembly properties.