AGGREGATE MORPHOLOGY AND INTERMEMBANE INTERACTION OF SYNTHETIC PEPTIDE LIPIDS BEARING VARIOUS HEAD GROUPS

Article abstract of DOI:10.1021/ja00293a055

Peptide lipids bearing thre different head groups, cationic N⁺C5Ala2C_n, anionic (SO3^-)C5Ala2C_n, and nonionic QC5Ala2C_n, were prepared for the investigation of their aggragate morpholiogy and intermembrane interaction between the ionic and nonionic lipid aggragates in aqueous media.Anionic lipids bearing the sulfonate head group, (SO^-)C5Ala2C_n, form primarily lamellar aggregates in the aqueous dispersion state, which are converted into double-walled bilayer vesicles upon sonication.In contrast with the ionic lipids, nonionic lipids bearing the quinoyl head group, QC₅Ala2C_n, form highly ordered network assemblies in the dispersion state in the neutral pH range, and the sonication of such aggregation afforded scattered cloudlike assemblies without formation of small bilayer vesicles.QC₅Ala2C_n behaves as a normal anionic lipid under conditions that the hydroxyl groups of the quinoyl moiety are deprotonated and forms multiwalled bilayer vesicles in the dispersion state.The morphological change of the nonlamellar network aggregates of QC₅Ala2C_n is induced by intermembrane interaction with ionic lipids to afford the normal bilayer membranes, The present results obtained by turbidity and differential scanning calorimetry measurements strongly indicate that the morphological change is induced by the one-way intermembrane transfer of the ionic lipid molecules through the intervening aqueous phase and the rate-determining step is the diffusion of the ionic lipid molecules from the bilayer phase to the bulk aqueous phase.