Phospholipid films

Formation from Template Surfaces Recently, a new method for the preparation of LUV was reported by Lasic et al. (1988). The method is based on a simple procedure which leads to the formation of homogeneous populations of LUV with a diameter of around L vim. Upon addition of solvent to a dry phospholipid film deposited on a template surface, vesicles are formed instantly without any chemical or physical treatment. The formation of multilamellar structures is prevented by inducing a surface charge on the bilayers. The size of the vesicles is controlled by the topography of the template surface on which the phospholipid film was deposited (Lasic, 1988). 

Generally, the recrystaUization of S-layer protein into coherent monolayer on phospholipid films was demonstrated to depend on (1) the phase state of the hpid film, (2) the nature of the lipid head group (size, polarity, and charge), and (3) the ionic content and pH of the subphase [122,138] (Table 6). 

It is noted that, as is shown in Figure 15, the chemicals with different taste-responses show markedly different effects on the dynamic behavior of the phospholipid film. Detail discussion on the chemical response in relation to the mechanism of taste sensation has already been given in a series of studies from our research group [3,42,43]. 

PFCs have recently been shown to prevent formation of a liquid condensed (semicrystalline) phase upon compression of a phospholipid film (Fig. 15). PFCs can also help dissolve semicrystalline domains after they have already formed. This fluidization effect facilitates the respreading of dimyristoylphosphatidylcho-line (DMPC), the main component of the lung surfactant, on the surface of lung alveoli upon inspiration [59], Experimentation on premature rabbits demonstrated a significant increase in tidal lung volume, allowing survival of the treated animals, while controls were all dead within minutes. PFCs may thus prove... 

T7RNA polymerase within cell-sized giant vesicles formed by natural swelling of phospholipid films... 

Figure 6. Proposed mechanism of dinitrogen reduction catalyzed by octamolybdenum(III) complex incorporated in the phospholipid film on the amalgam surface.

Fluorinated surfactants (or fluorosurfactants, i.e., surfactants with hydrophobic tails comprising a fluorocarbon moiety) provide an alternative means of achieving extremely stable PFC emulsions, as they can provide very low PFC/water interfacial tensions [cr , another factor in Eq. (2)]. d s yet, this option has not been developed, in part because of the added cost involved in the evaluation for approval of a novel active excipient. A further means of effectively increasing the stability of EYP-based PFC emulsion consists of supplementing standard phospholipids with mixed fluorocarbon-hydrocarbon diblock compounds, such as 14 or 15. Such diblocks, which have fluorophilic-lipophilic amphiphilic properties, are expected to improve the adhesion of the phospholipid film onto the PFC droplet. 

Remove the ethanol by low vacuum (58 mbar) rotary (150 rpm) evaporation at 40°C. At the end, a thin phospholipid film will form against the inside of the flask. Remove the condensed ethanol by aerating the flask three times. 

Disperse the phospholipid film in 20 mL clodronate solution (for clodronate liposomes) or 20 mL PBS (for empty liposomes) by gentle rotation (max. 100 rpm) at room temperature. Development of foam should be avoided by reducing the speed of rotation. 

Advised is here to use a round bottom flask of 500 mL. A smaller volume, for instance 100 mL, is also possible. The liquids, however, may boil and come into the bottle neck more easily. The vacuum must be reduced in time to stop the boiling and preventing a phospholipid film in the apparatus. 

Many substances cross biological membranes according to their lipid solubility. Other polar molecules, such as amino acids and glucose, cross the membranes more rapidly than expected according to their solubUity in lipids. Cations, such as Na" and K, also cross membranes rapidly in spite of their hydrophilic nature. This passive transport of substances at higher rates than predicted from their lipid solubility is termed facilitated diffusion. That proteins are directly involved in facilitated diffusion was shown by comparison of experiments with natural membranes and synthetic membranes produced with phospholipid films. With phospholipid films all molecules, except water, diffuse according to lipid solubility and molecular size. Ions are essentially impermeable. The addition of membrane proteins, however, frequently allowed many polar and charged species to penetrate the membrane at rates comparable to natural membranes. 

Since the first attempt of Chapman and co-workers in 1966 [860], IR spectroscopy has become one of the most frequently used tools for elucidating lipid properties and the mutual effects of different lipids and proteins, which are of interest for different aspects of bioscience and biosensor design (see Refs. [333, 748, 861-864] for review). The IR methods used are transmission, ATR (MIR), and IRRAS for model monolayer, bilayer, and multibilayer membranes and biological membranes. To perform in situ measurements on the membranes of intact individual cells (e.g., as a function of cell membrane potential), planar miniature waveguides can be used instead of the ATR optics [865]. PM-IRRAS has been applied to obtain high-performance spectra of model membranes at the AW interface [866-875]. The experimental data focus mainly on the correlation between the structure of the matrix amphiphile or phospholipid film and the structure of the constituent species, the subphase composition, the surface pressure, and other external conditions, as well as the interaction of such monolayers with peptides and proteins (for reviews, see Refs. [332-334, 876, 877]). 

From convective assembly to Landau-Levich deposition of multilayered phospholipid films of controlled thickness. Langmuir, 25 (5), 2554-2557. 

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