Two schematics of the proposed pathways from the bilayer to the inverted monolayer tube transition.

<p>On the left hand side, the classical vesicle fusion route is depicted. The formation of pores is widely believed to be the prerequisite for the formation of bicontinuous cubic (Q<sub>2</sub>) nanostructures <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002072#pone.0002072-Shearman1" target="_blank">[87]</a>, which upon further curvature frustration may transform into self-assembled monolayer tubes (H<sub>2</sub> phase). On the right hand side, the direct formation of an inverse lipid nanotube between two opposed bilayers is illustrated. For better understanding of the structural conversions, the headgroups of opposed monolayers are shown in light blue whereas the rest are depicted in blue (for further details see text).</p>