RESUMEN
An equilibrium phase belonging to the family of bilayer liposomes in ternary mixtures of dimyristoylphosphatidylcholine (DMPC), water, and geraniol (a biological alcohol derived from oil-soluble vitamins that acts as a cosurfactant) has been identified. Electron and optical microscopy reveal the phase, labeled Ltv, to be composed of highly entangled tubular vesicles. In situ x-ray diffraction confirms that the tubule walls are multilamellar with the lipids in the chain-melted state. Macroscopic observations show that the Ltv phase coexists with the well-known L4 phase of spherical vesicles and a bulk L alpha phase. However, the defining characteristic of the Ltv phase is the Weissenberg rod climbing effect under shear, which results from its polymer-like entangled microstructure.
Asunto(s)
Dimiristoilfosfatidilcolina/química , Membrana Dobles de Lípidos/química , Liposomas/química , Terpenos/química , Monoterpenos Acíclicos , Microscopía Electrónica , Dispersión de Radiación , Temperatura , Difracción de Rayos X , Rayos XRESUMEN
The association of lipid molecules into spherical vesicles in solution as a result of non-specific intermolecular forces constitutes a primary self-assembly process. Such vesicles can undergo a secondary self-assembly into higher order structures in a controlled and reversible manner by means of site-specific ligand-receptor (biotin-streptavidin) coupling. Cryoelectron microscopy shows these structures to be composed of tethered, rather than adhering, vesicles in their original, unstressed state. In contrast, vesicles aggregated by nonspecific, such as van der Waals, forces are deformed and stressed, producing unstable structures. Vesicle association by site-specific binding provides a practical mechanism for the production of stable, yet controllable, microstructured biomaterials.
Asunto(s)
Liposomas/química , Adhesividad , Proteínas Bacterianas/química , Biotina/análogos & derivados , Biotina/química , Coloides , Técnica de Fractura por Congelación , Membrana Dobles de Lípidos , Matemática , Microscopía Electrónica , Fosfatidilcolinas/química , Fosfatidiletanolaminas/química , Estreptavidina , Propiedades de SuperficieRESUMEN
Rapid freezing is the most important step in sample preparation for freeze-fracture and other cryotechniques for electron microscopy. We present the design and operation of a simple environmental chamber coupled to a plunger-driven freezing device that has provided simple and reliable freezing from temperatures and humidities other than ambient. The chamber can be constructed and operated with equipment and techniques common to most electron microscopy labs. Temperature control of +/- 0.1 degree C and relative humidities of greater than 90% were provided over the range -5-60 degrees C. Typical electron micrographs showing well preserved structures comparable to jet-freezing are presented.