Vesicles multilayer

Fig. 11 Left Changes in / and D measured at = 3, 5, and 7 upon subsequent formation of multiple lipid vesicle layers provided via hybridization of vesicles modified with complementary DNA sequences. Right Cartoon illustrating the lipid vesicle multilayer formation...

Abstract Screened electrostatic interactions are commonly employed in colloid and polymer science for stabilization in aqueous solutions to avoid macroscopic phase separation, but these are equally versatile as driving force for complexation (or microscopic phase separation) into micelles, vesicles, multilayers and other nanostructured materials. In this introductory chapter, we present an overview of the field of electrostatically driven assembly of polyelectrolytes into nanometresized association colloids focusing in particular on the fundamentals followed by a discussion of selected application areas. 

Cationic quaternary ammonium compounds such as distearyldimethylammonium-chloride (DSDMAC) used as a softener and as an antistatic, form hydrated particles in a dispersed phase having a similar structure to that of the multilayered liposomes or vesicles of phospholipids 77,79). This liposome-like structure could be made visible by electron microscopy using the freeze-fracture replica technique as shown by Okumura et al. 79). The concentric circles observed should be bimolecular lamellar layers with the sandwiched parts being the entrapped water. In addition, the longest spacings of the small angle X-ray diffraction pattern can be attributed to the inter-lamellar distances. These liposome structures are formed by the hydrated detergent not only in the gel state but also at relatively low concentrations. 

Grliner, S. M., Lenk, R. P., Janoff, A. S., and Ostro, M. J. (1985). Novel multilayered lipid vesicles Comparison of physical characteristics of multilamellar liposomes and stable plurilamellar vesicles, Biochemistry. 24. 2833-2842. 

In oriented, partially dehydrated multilayers, under conditions suitable for X-ray diffraction studies, the sarcoplasmic reticulum vesicles retain much of their ATP energized Ca transport activity [200-202], The Ca transport can be initiated by flash-photolysis of P -l(2-nitro)phenyl-ethyladenosine-5 -triphosphate, caged ATP [203-208], The flash-photolysis of caged ATP rapidly releases ATP and effectively synchronizes the Ca transport cycle of the ensemble of Ca -ATPase molecules [190-192,201,209],... 

Pidgeon, C., Hunt, A.H., and Dittrich, K. (1986) Formation of multilayered vesicles from water/organic-solvent (W/O) emulsions theory and practice. Pharm. Res. 3, 23-34. 

A standard procedure for manufacturing liposomes is the film-forming method where the phospholipids are dissolved in an organic solvent. By rotational evaporation of the solvent a thin, multilayered film of phospholipids arises at the inner wall of the vessel. Redispersion of this film in water or aqueous buffer results in the formation of vesieles. The size of these vesicles and the number of bilayers vary. Henee further manufaeturing steps have to follow to obtain defined vesieular dispersions with a suffieiently long shelf life. 

Most of the above membrane-oriented studies were carried out for peptides in multilayer systems that were collapsed or transferred onto a sample cell surface. An alternative and very interesting way to study membrane systems is by IRRAS (infrared reflection absorption spectroscopy) at the air-water interface. In this way, unilamellar systems can be studied as a function of surface pressure and under the influence of various membrane proteins and peptides added. Mendelsohn et al.[136] have studied a model series of peptides, [K2(LA) ] (n = 6, 8, 10, 12), in nonaqueous (solution), multilamellar (lipid), and unilamellar (peptide-IRRAS) conditions. In the multilamellar vesicles these peptides are predominantly helical in conformation, but as peptide only monolayers on a D20 subphase the conformation is (1-sheet like, at least initially. For different lengths, the peptides show variable surface pressure sensitivity to development of some helical component. These authors further use their IR data to hypothesize the existence of the less-usual parallel (i-sheet conformation in these peptides. A critical comparison is available for different secondary structures as detected using the IRRAS data for peptides on H20 and D20 subphasesJ137 ... 

Surfactants provide several types of well-organized self-assembhes, which can be used to control the physical parameters of synthesized nanoparticles, such as size, geometry and stability within liquid media. Estabhshed surfactant assembles that are commonly employed for nanoparticie fabrication are aqueous micelles, reversed micelles, microemulsions, vesicles [15,16], polymerized vesicles, monolayers, deposited organized multilayers (Langmuir-Blodgett (LB) films) [17,18] and bilayer Upid membranes [19](Fig. 2). 

Description of the different mimetic systems will be the starting point of the presentation (Sect. 2). Preparation and characterization of monolayers (Langmuir films), Langmuir-Blodgett (LB) films, self-assembled (SA) mono-layers and multilayers, aqueous micelles, reversed micelles, microemulsions, surfactant vesicles, polymerized vesicles, polymeric vesicles, tubules, rods and related SA structures, bilayer lipid membranes (BLMs), cast multibilayers, polymers, polymeric membranes, and other systems will be delineated in sufficient detail to enable the neophyte to utilize these systems. Ample references will be provided to primary and secondary sources. 

Multilayered vesicles (liposomes) formed from sonically dispersed phosphatidylcholine in the presence of 10% diacetylphosphate and 2% potassium phosphotungstate. Each vesicle has a trilaminar structure consisting of two dark layers separated by a light layer. The dark layers contain the electron-dense phosphotungstate ion the light layer corresponds to the hydrophobic interior of the bilayer. 

Molecular organization and self-assembly into layers, membranes, vesicles etc., construction of multilayer films [7.1-7.5], generation of defined aggregate morphologies [4.74, 4.75, 7.6-7.8J etc., make it possible to build up specific supramolecular architectures. The polymerization of the molecular components has been a major step in increasing control over the structural properties of such assemblies [7.9-7.13]. 

The liposomes prepared by this method are usually MLVs, but the structure inside the vesicles can be highly formulation dependent. MLVs composed entirely of neutral lipids tend to be very tightly packed multilayer assemblies with the adjacent bilayers stacked closely on one another, with very little aqueous space between them. The presence of negatively charged lipids in the membram tends to push the bilayers apart from each other and increase the aqueous volume of entrapmer signiLcantly for water-soluble compounds. 

FIGURE 7.38. Computer generated model of a liposome-streptavidin conjugate (a), a schematic representation of a liposome-streptavidin (Sav)-concanavalin A (Con A)-streptavidin multilayer (b) and of streptavidin crosslinked vesicles (c). 

In THE PAST DECADE, IMPROVEMENTS IN infrared spectroscopic instrumentation have contributed to significant advances in the traditional analytical applications of the technique. Progress in the application of Fourier transform infrared spectroscopy to physiochemical studies of colloidal assemblies and interfaces has been more uneven, however. While much Fourier transform infrared spectroscopic work has been generated about the structure of lipid bilayers and vesicles, considerably less is available on the subjects of micelles, liquid crystals, or other structures adopted by synthetic surfactants in water. In the area of interfacial chemistry, much of the infrared spectroscopic work, both on the adsorption of polymers or proteins and on the adsorption of surfactants forming so called "self-assembled" mono- and multilayers, has transpired only in the last five years or so. 

Chifen AN, Forch R, Knoll W et al (2007) Attachment and phospholipase A2-induced lysis of phospholipid bilayer vesicles to plasmapolymerized maleic anhydride/Si02 multilayers. Langmuir 23 6294-6298... 

Michel M, Izquierdo A, Decher G et al (2005) Layer-by-layer self-assembled polyelectrolyte multilayers with embedded phospholipid vesicles obtained by spraying integrity of the vesicles. Langmuir 21 7854-7859... 

When water is added to certain dry phospholipids with long hydrocarbon chains, the phospholipids swell, and when they are dispersed in more water, structures known as liposomes are formed. Liposomes are vesicles with multilayers of phospholipid. See Fig. 6-5. When subjected to ultrasonic vibration (sonication), liposomes are transformed into vesicles that have only a single bilayer of phospholipid. 

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