Microscopic Observation of Nanofibers and Helical Nanoribbons Composed of Tetraether Cyclobolaphile

In this paper, we describe the microscopic observation, using transmission electron microscopy and scanning probe microscopy, of self-assembled lipid nanostructures composed of a cyclic amphiphilic compound containing four ether bonds as a hydrophilic-hydrophobic linker, referred to as “tetraether cyclobolaphile”. Cyclobolaphiles mimic naturally occurring cyclic lipids found in archaea that exhibits extreme resistance to harsh environments. The general structural features of such artificial lipids include (i) a cyclic framework, (ii) two diacetylene units, and (iii) two hydrophilic groups. Our previous work has indicated that tetraether cyclobolaphile self-assembles into microtubules and sheet like aggregates in water. Our principle results, which are reported herein, show the self-organization of the lipid into nanofibers and helical nanoribbons in a dry form, which is likely triggered by electron beam and UV irradiation, respectively. In essence, the examination by transmission electron microscopy at a higher magnification indicated that the planar self-assembled lipid aggregates contain fibrous nanostructures with a width of approximately 4 nm. The scanning probe microscopic observation of the irradiated aggregates revealed the presence of fibers that exhibit right-handed helicity with an apparent width and pitch of 25 nm and 130 nm, respectively.