Homochiral nanotubes from heterochiral lipid mixtures: a shorter alkyl chain dominated chiral self-assembly.

It is an important topic to achieve homochirality both at a molecular and supramolecular level. While it has long been regarded that "majority rule" guides the homochiral self-assembly from an enantiomer mixture, it still remains a big challenge to manipulate the global homochirality in a complex system containing chiral species that are not enantiomers. Here, we demonstrate a new example wherein homochiral nanotubes self-assembled from a mixture of heterochiral lipids that deviated from the "majority rule". We have found that when two heterochiral lipids with mirror headgroups but a 2-methylene discrepancy in alkyl chain length are mixed, homochiral nanotubes are always formed regardless of their mixing ratio. Remarkably, the helicity of the nanotube is exclusively controlled by the molecular chirality of the lipids with shorter alkyl chains, i.e., the chiral self-assembly was dominated by the lipid with the shorter alkyl chain. MD simulation reveals that the match of both the alkyl chain length and hydrogen-bonding between two kinds of lipids plays an important role in the assembly. This work provides a new insight into the supramolecular chirality of complex systems containing multi chiral species.