Ion-Pair Amphiphile Vesicles Modified by Native and Oleyl-Substituted Hyaluronan: Colloidal Properties and Interfacial Relaxation Dynamics

Abstract How hydrophobic modification of hyaluronan changes its coupling to cationic ion-pair amphiphile (IPA) membranes beyond electrostatic surface association remains insufficiently resolved. Here, a counterion-depleted carbethopendecinium/dodecylbenzenesulfonate IPA was supplemented with 10 mol % excess carbethopendecinium bromide to form electrostatically stabilized cationic vesicular dispersions and was studied with and without cholesterol, native hyaluronan (HA), and oleyl-modified hyaluronan (oleylHA). Dynamic and electrophoretic light scattering were combined with DPH fluorescence anisotropy, Laurdan generalized polarization (GP), and Laurdan time-resolved emission spectroscopy (TRES) to link colloidal association with membrane-level responses. Both polymers reversed the positive zeta potential, confirming association with the cationic dispersions. Native HA produced only modest changes in DPH anisotropy and a temperature-dependent TRES response. OleylHA produced a more coherent signature, increasing DPH anisotropy while shifting the fitted Laurdan relaxation toward higher asymptotic centroid values and lower relaxation amplitudes, particularly in cholesterol-containing IPA vesicles. These observations are consistent with hydrophobic substitution adding a membrane-associated contribution to the predominantly electrostatic interaction of HA. DPPC liposomes served only as ordered and fluid phospholipid reference states. The results show that combining colloidal measurements with interfacial relaxation analysis can distinguish polymer-membrane interaction modes that are not resolved by surface charge or size measurements alone.