Giant polymerlike micelles formed by nucleoside-functionalized lipids

We report an investigation on the aggregation of 1,2-dilauroyl-sn-glycero-3-phosphatidyluridine (DLPU), a surfactant molecule that merges the self-assembling properties of lecithins with the molecular recognition characteristics of nucleic bases in a phosphate-buffered aqueous solution at physiological pH and as a function of lipid concentration. Because spontaneous self-assembly and interfacial properties are the result of a delicate balance between hydrophobic interactions and polar-head interactions, a structural characterization is essential for a complete and full understanding of base-base properties in the aggregates, as observed by spectroscopic techniques. Small-angle neutron scattering, static light scattering, and quasi-elastic light scattering have been employed to assess the structural evolution of the binary system as the lipid concentration is increased. The data indicate the presence of rather flexible elongated aggregates, whose local structure is cylindrical and remains essentially unchanged during micellar growth. Scattering data are fully supported by cryo-TEM analysis. The results are consistent with micellar unidimensional growth to giant wormlike aggregates that eventually entangle to form a transient network with a response to mechanical stress that is similar to that of polymer solutions in the semidilute range. Such aggregates are known as polymerlike micelles to stress the similarity with the behavior of macromolecules in good solvents. In our case, the correspondence is not limited to a mesosocopic structural scale because from a chemical point of view each monomer contains a nucleic acid functionality that is also expressed in the polymerlike aggregates whose biopolymeric counterpart is in fact a polynucleotide. Therefore, these new aggregates can be considered to be the first example of an "associative polynucleotide".