Time evolution of the thermotropic behavior of spontaneous liposomes and disks of the DMPC-DTAC aqueous system.
In this work, solubilization of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) by the cationic detergent n-dodecyltrimethylammonium chloride (DTAC) was studied in aqueous solution, at a fixed DMPC concentration and variable detergent:lipid (D:L) molar ratios. The colloidal nanostructures present in different stages of the solubilization process were characterized using micro-differential scanning calorimetry (DSC) and dynamic light scattering (DLS) techniques. For total (analytical) D:L molar ratios below approximately 1, DTAC monomers incorporate into the DMPC liposome bilayers, forming smaller and more fluid vesicles than pure DMPC liposomes. At D:L approximately 1-2, vesicles begin to rupture, coexisting with intact vesicles and bilayer fragments. At D:L approximately 2-12.5, discoidal and spherical micelles are formed and coexist with vesicles; a slow structural rearrangement of the system, monitored in successive DSC heating/cooling cycles, was observed, and is reported for the first time. Finally, for D:L above approximately 15-20, the bilayers are completely dissolved, and the main aggregates in solution become spherical micelles, which slowly evolve to cylindrical (threadlike) micelles. Based on the dependence of the temperature and enthalpy of transitions on the total D:L molar ratio, at constant DMPC concentration, a schematic model, showing the different colloidal nanostructures present in the solubilization process, is proposed.
Viseu
Maria Isabel
MI
Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. isabelviseu@ist.utl.pt
Correia
Raquel F
RF
Fernandes
Anabela C
AC
D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008823:Micelles; D008958:Models, Molecular; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012995:Solubility; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
D008081:Liposomes; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D014867:Water; C022806:dodecyltrimethylammonium; D004134:Dimyristoylphosphatidylcholine