Light scattering and cryo-transmission electron microscopy investigation of the self-assembling behavior of...

Aggregates formed from freshly prepared and annealed samples of dilauroyl-phosphatidyl-adenosine, dilauroyl-phosphatidyl-uridine, and their 1:1 mixture have been investigated by dynamic light scattering, cryo-transmission electron microscopy (cryo-TEM) observations, and circular dichroism. The two surfactants differ only for the nucleoside at the phospholipid polar headgroup and self-assemble in solution to form supramolecular structures that behave dissimilarly. The uridine derivative forms long wormlike aggregates that are invariant with the aging of the solution, while the wormlike aggregate of the adenosine derivative undergoes, as the sample ages, a subsequent self-assembling process forming giant helicoidal aggregates that coexist with the smaller wormlike aggregates. Dynamic light scattering and cryo-TEM show that the large helicoidal structures are formed at the expense of the small wormlike micelles. The 1:1 mixture behaves as the adenosine derivative and evolves to form giant superstructures for all the lipid concentrations investigated. Circular dichroism measurements suggest that the formation of the supramolecular helicoidal structure might not be driven by a purely chiral effect, but rather stacking and hydrogen bonding, present at the phospholipid headgroups of the self-assembled nucleosides, contribute to the final supramolecular structure.