LIPOSOMES OF CONTROLLABLE SIZE IN THE RANGE OF 40 TO 180 nm BY DEFINED DIALYSIS OF LIPID/DETERGENT MIXED MICELLES

OTMAR ZUMBUEHL and HANS GEORG WEDER

Biochimica et Biophysica Acta, 640 (1981) 252-262

Liposomes, in the size range of 40--180 nm, are formed when lipid and additives are solubllized with detergent, yielding defined mixed micelles, and the detergent is subsequently removed by controlled dialysis. Their most important properties are that they are indeed unilamellar with usefully large encapsulated volumes and are homogeneous in size. Liposomes have been formed from both natural and synthetic phospholipids with cholesterol and charged molecules added. This relatively simple technique may be particularly useful for encapsulating drugs, enzymes and other macromolecules and in studies of reconstitution of membrane proteins.

Direct formation of mixed micelles in the solubilization of phospholipid liposomes by Triton X-100

FEBS Letters 426 (1998) 314-318

The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant with phosphatidylcholine vesicles was studied by means of dynamic light scattering (at different reading angles) and by freeze-fracture electron microscopy techniques. Vesicle solubilization was produced by the direct formation of mixed micelles without the formation of complex intermediate aggregates. Thus, vesicle to micelle transformation was mainly governed by the progressive formation of mixed micelles within the bilayer. A subsequent separation of these micelles from the liposome surface (vesicle perforation by the formation of surfactant-stabilized holes on the vesicle surface) led to a complete solubilization of liposomes.

Temperature Dependence of Triton X-100 Micelle Size and Hydration

Kiril Streletzky and George D. J. Phillies

Langmuir 1996,11, 42-47

Quasi-elastic light scattering spectroscopy was used to measure the mutual diffusion coefficient, D of Triton X-100 micelles in aqueous solution and the translational diffusion coefficient, D, of mesoscopic probes in the same solutions. We apply conventional hydrodynamic treatments of diffision under the assumption that Triton X-100 minimal micelles are adequately represented as hard spheres. Dm and D, measured at a series of surfactant concentrations are used to infer the micelle radius, am, aggregation number, N, and degree of hydration, 6, for temperatures 10 5 T 5 50 "C. As T is increased toward the cloud point, am and N increase, the increase in N being especially dramatic above 40 "C, 6 at first increases but then tends to saturate with increasing T.

The Size, Shape, and Hydration of Nonionic Surfactant Micelles. Triton X-100

Robert J. Robson and Edward A. Dennis
The Journal of Physical Chemistry, Vol. 81, No. 11, 1977

Calculations of the size, shape, and hydration of micelles composed of the nonionic surfactant Triton X-100 were performed based on molecular weight and intrinsic viscosity data. Geometrical considerations show that if the hydrophobic core as well as the whole micelle is spherical, then its structure cannot contain the distinctpolar and apolar regions that are classically assumed for micelles. On the other hand, ellipsoids of revolution would be consistent with a classical micellar structure and an oblate rather than a prolate ellipsoid would be most consistent with intrinsic viscosity measurements and volume calculations.

Thermodynamic and Structural Studies of Triton X-100 Micelles in Ethylene Glycol-Water Mixed Solvents

C. Carnero Ruiz, J. A. Molina-Bolfvar, and J. Aguiar

Langmuir 2001, 17, 6831-6840

Micellar properties of p-tert-octyl-phenoxy (9.5) polyethylene ether (Triton X-100) in aqueous mixtures of ethylene glycol (EG) were determined using such techniques as surface tension, static and dynamic light scattering, and fluorescence spectroscopy. Thermodynamics of micellization was obtained from the temperature dependence of critical micelle concentration values. The differences in the Gibbs energies of micellization of Triton X-100 between water and binary solvent systems were calculated to evaluate the influence of cosolvent on the micellization process. From this study, it can be concluded that the structurebreaking ability of EG and its interaction with the oxyethylene groups of the surfactant are dominating factors in the micellization process. Thermodynamics of adsorption of the solution-air interface was also evaluated. It was found that the surface activity of the surfactant decreases slightly with increasing concentration of EG at a given temperature. By a combination of static and dynamic light scattering measurements, a reduction of the micelle size was observed, mainly due to a decrease of the micellar aggregation number, whereas the micellar solvation was not substantially modified in magnitude with EG addition. However, the change of the surface area per headgroup of the surfactant suggested an alteration in the nature of its solvation layer, produced probably by a certain participation of cosolvent in the micellar solvation layer. This point was corroborated from the fluorescence polarization studies of several luminescent probes, including coumarin 6, merocyanine 540, and rhodamine B. These experiments revealed a slight increase of the micellar microviscosity. Finally, the proposed mechanism was also supported by the increase observed in the cloud point of Triton X-100, induced by the EG addition.

Protection and Promotion of UV Radiation-Induced Liposome Leakage via DNA-Directed Assembly with Gold Nanoparticles

Neeshma Dave and Juewen Liu

Adv. Mater. 2011, 23, 3182–3186

Mind over myocardium

Shailaja Neelakantan
S16 | NATURE | VOL 493 | 31 JANUARY 2013
Mental factors beyond stress trigger physiological changes that can cause heart disease.