Interaction of Tyrosine Analogues with Quaternary Ammonium Head Groups at the Micelle/Water Interface and Contrasting Effect of Molecular Folding on the Hydrophobic Outcome and End-Cap Geometry.

The surface property of the cationic micelles of cetyltrimethylammonium bromide (CTAB) in an aqueous medium is highly modified in the presence of tyrosineoctyl ester (TYOE) and tyrosinedodecyl ester (TYDE), the models for aromatic amino acid side chains of transmembrane proteins. While the synergistic interaction between the quaternary ammonium head group of CTAB and the π-electron cloud of aromatic amino acid ester is influenced by the relative orientation and the unusual molecular geometry of the latter, this eventually triggers a morphology transition of the spherical micelle to cylindrical/wormlike micelles and imparts a strong viscoelasticity in the medium. Physical characteristics of the elongated micelles have been investigated by high resolution transmission electron microscopy (HRTEM) and the small angle neutron scattering (SANS) technique; the complex fluidic nature of the system is investigated by a dynamic rheological measurement. The intermolecular interactions have been recognized via 1H NMR and 2D nuclear Overhauser effect spectroscopy (NOESY), and the unambiguous geometry of the end-caps of the rods has been ascertained for the first time. While the interplay between lipids and transmembrane proteins is thought to be crucial in controlling the membrane shape of the cells during many vital events such as cellular fission, fusion, and virus entry, the observed tuning of the micellar surface curvature via the cation-π interaction involving tyrosine analogues is thought provoking and opens up an avenue for new physical chemistry research on a vital biological phenomena.