Structural characterization of Di-C12 P-uridine worm-like micelles:: ionic strength dependence

Through a combination of small angle neutron scattering and static light scattering we have investigated the aqueous self-assembly of 1,2-dilauroyl-sn-glycero-3-phosphatidyl-uridine (DLPU). This phospholipid reproduces on its polar head the chemistry and the charge of an RNA monomer. The results indicate that DLPU forms flexible cylindrical micelles. The structural properties of the aggregates have been determined for three fixed surfactant volume fractions as a function of the medium salinity. The desired structural parameters have been inferred from non-linear least-square fitting of the whole scattering curve (SLS + SANS) through a parametrized worm-like chain scattering function. Surfactant concentration and ionic strength affect the contour length and the effective flexibility, leaving the cross section virtually unchanged. DLPU micelles become more flexible upon salt addition since the salt-dependent contribution to the micellar rigidity decreases. The intrinsic contribution is directly coded in the chemistry of molecular subunits, and depends for DLPU, besides on the steric hindrance of the amphiphile, on intermolecular interactions acting between polar heads and triggered by self-assembly. This contribution is invariant with medium conditions and can be considered as a mesoscopic gage of molecular specificity, while the response to ionic strength of ionic surfactant solutions represents a tuneable, responsive property.