title: Spontaneous vesicles, disks, threadlike and spherical micelles found in the solubilization of DMPC liposomes by the detergent DTAC.
abstract: The spontaneous colloidal nanostructures formed in water by the zwitterionic phospholipid DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) with the cationic detergent DTAC (n-dodecyltrimethylammonium chloride) were investigated at a fixed DMPC concentration and variable detergent:lipid total molar ratios (D:L). Apparent (neutral-sphere-equivalent) hydrodynamic diameters (Φ(e)) of liposomes and micelles were obtained by dynamic light scattering (DLS). Fluorescence lifetime imaging microscopy (FLIM), using chlorophyll-a as a probe, showed the morphology of giant vesicles and threadlike micelles. Micro-differential scanning calorimetry (micro-DSC) detected the presence of bilayers, in vesicles and discoidal micelles (disks). Pure DMPC liposomes are multilamellar and polydisperse (Φ(e)≈100-10,000 nm). As D:L increased, smaller vesicles were found, due to the bigger spontaneous curvature of the bilayer: at D:L=1, ULVs (unilamellar vesicles; Φ(e)≈100 nm) appeared and, at D:L=2-10, ULVs coexisted with disks (Φ(e)≈30 nm). Bilayers totally disappeared at D:L≥15, giving rise to spheroidal (Φ(e)≈2-16 nm) and threadlike (Φ(e)≈100-10,000 nm) micelles. A quasi-equilibrium structural diagram for the DMPC-DTAC-water system shows equivalent diameters of the scattering nanoparticles as a function of D:L. The results obtained herein for the system DMPC-DTAC show the role of electrostatic interactions in the formation of the mixed structures.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Lisboa, Portugal.
authors.forename: Raquel F
authors.initials: RF
authors.lastname: Correia
authors.forename: Maria Isabel
authors.initials: MI
authors.lastname: Viseu
authors.forename: Telmo J V
authors.initials: TJ
authors.lastname: Prazeres
authors.forename: José M G
authors.initials: JM
authors.lastname: Martinho
mesh_terms: D003902:Detergents / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008823:Micelles; D010316:Particle Size; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012995:Solubility; D013499:Surface Properties
chemical_list: D003902:Detergents; D008081:Liposomes; D008823:Micelles; D000644:Quaternary Ammonium Compounds; C022806:dodecyltrimethylammonium; D004134:Dimyristoylphosphatidylcholine