Lipid thin films

Sucrose changes the dynamic structure of water molecules, which, in turn, affects the manner of aggregation of the DPPE. Citric acid changes the degree of dissociation of the head group of the DPPE molecules. It becomes, therefore, apparent that each chemical species affects the viscoelastic behavior of the lipid thin film in a characteristic manner. 

Figure 23. Schematic representation of the repetitive formation and reconstruction of the lipid thin film.

Kumar A, Ramakrishnan V, Gonnade R, Ganesh KN, Sastry M (2002) Electrostatically entrapped DNA molecules in lipid thin films as templates for the in situ growth of silver nanoparticles. Nanotechnology 13 597... 

We have studied the viscoelastic behavior of lipid thin films at an air/water interface from surface pressure (tt) vs. surface area (A) curves, since an observation of the k-A curve of a monolayer is one of the most convenient methods to elucidate the viscoelastic behavior of the monolayer. Recently, in spite of compression process, we observed an overshoot-hump, a zero surface pressure, and a flat plateau in the rt-A curve of a synthetic fatty acid [3]. These characteristic features in the curve were explained by using a kinetic model representing the formation of aggregates of the fatty-adds molecules at an air/water interface. 

The overshoot-hump in the n-A curve of DNP DPPE monolayer was foimd with constant-speed compression. From the absorption spectra of the lipid thin film, the hump reflected the formation of condensed layers at the critical surface pressure. A computer simulation was carried out on the basis of a cooperative aggregation process between the DNP-DPPE molecules at the air/water interface, the characteristic feature in the n-A curve was able to be reproduced. 

Lipid thin films have been used in many applications, such as permeation control, drug delivery, and other medical applications because of their... 

FIGURE 1. Supramolecular objects consist of inorganic building blocks mainly based on soft supramolecular assemblies, (a) Hybrid lipid thin films, (b) Layer-by-layer assemblies, (c) Structure transcription, (d) Functional mesoporous hybrid. 

In this volume we have collected 10 review chapters from distinguished scientists who have contributed extensively to the study and development of supramolecular assemblies that contain metals and metal-like elements with unusual structures and morphologies and possess potentially useful (and applicable) physical and biological properties. The first chapter by K. Ariga et al. is a general discussion of supramolecular structures that contain inorganic building blocks for hybrid lipid thin films, layer-by-layer assemblies, structure transcription, and functional mesoporous hybrids. This is followed by two chapters, the first by M. L. Kistler et al., who describe the self-assembly of hydrophilic polyoxometalate (POM) macro-anions and examine the structure and behavior of POM macro-ions in solution. This is followed by a chapter by S. K. Das, who provides an overview of the supramolecular features of POM-supported transition metal complexes, POM-crown ether complexes with supramolecular cations, and supramolecular water clusters associated with POMs. 

As a point of interest, it is possible to form very thin films or membranes in water, that is, to have the water-film-water system. Thus a solution of lipid can be stretched on an underwater wire frame and, on thinning, the film goes through a succession of interference colors and may end up as a black film of 60-90 A thickness [109]. The situation is reminiscent of soap films in air (see Section XIV-9) it also represents a potentially important modeling of biological membranes. A theoretical model has been discussed by Good [110]. 

Seitz M ef al 1998 Formation of tethered supported bilayers via membrane-inserting reactive lipids Thin Solid Films 327-9 767-71... 

Mueller et al. [6] discovered in 1962 that when a small quantity of a phospholipid (2% wt/vol alkane solution) was carefully placed over a small hole (0.5 mm) in a thin sheet of Teflon or polyethylene (10-25 pm thick), a thin film gradually forms at the center of the hole, with excess lipid flowing towards the perimeter (forming a Plateau-Gibbs border ). Eventually, the central film turns optically black as a single (5 nm-thick) bilayer lipid membrane (BLM) forms over the hole. Suitable lipids for the formation of a BLM are mostly isolated from natural sources, e.g.,... 

In the experiments on the Jt-A characteristics, it has been usually assumed that thermal equilibrium will be attained easily if the experiment is performed using a slow rate of compression of thin film at the interface. Measurements under thermal equilibrium are, of course, the necessary condition to obtain the physico-chemical properties of the individual "phase" of the lipid ensemble. 

Next, we discuss the mechanism of the characteristic features observed in the Jt-A curve. When the PhDA2-8 thin film is compressed with relatively high speed, there will be a non-negligible effect of the special inhomogeneity over the lipid film, i.e., the surface pressure in the region near the blade becomes larger than that in the other region. 

In the above subsection it was demonstrated that the inclusion of electrostatic interactions into the pressure-area-temperature equation of state provides a better fit to the observed equilibrium behavior than the model with two-dimensional neutral gas. Considering this fact, we would like to devote our attention now to the character of the lipid film under the dynamical, nonequilibrium conditions. In the following we shall describe the dynamical behavior of the phospholipid(l,2-dipalmitoyl-3-sn-phosphatidylethanolamines DPPE) thin films in the course of the compression and expansion cycles at air/water interface. 

Liposome Formation. The pioneering investigations of Bang-ham (5) have shown that thin films of natural phospholipids form bilayer assemblies if they are lyophilized in excess water by simple handshaking above the phase transition temperature. While this procedure results in the formation of large, multibilayered spherical structures, by ultrasonication of such lipid dispersions small unilamellar liposomes are formed (16), which are schematically shown in Figure 10. Additional metTiods for liposome preparation are described in a number of reviews (17,44,45,46). 

A thin film of oil-like material was visible after 28 d on the exterior surfaces of the SPMD membrane. Analysis of this film indicated that the triolein impurities, oleic acid and methyl oleate, were the major constituents. This external lipid film (Petty et al., 1993) appeared to contain imbibed particulates. Although the film was removed from the SPMDs by solvent rinsing and analyzed separately, some lipid-mediated desorption of particle-associated PCBs and subsequent diffusion into the SPMD may have occurred prior to solvent-removal of the film. This observation suggests the potential for SPMD concentrations to reflect both vapor phase concentrations and to a lesser extent, lipid-extracted particulate-associated residues (see Section 3.9.2.). Unfortunately, concentrations of more chlorinated congeners in particulates collected on GFFs from the NIOSH method were often below quantitation limits, because only a small volume of air was sampled (1 m ) using this active method. 

In both of these cases, the ligand (sialic acid) for the analyte of interest (influenza vims) was covalently linked to the PDA backbone generated upon photopolymerization. Functional sensors based on ligands that are noncovalently incorporated into liposomes have also been reported (Charych et al. 1996 Pan and Charych 1997). Mixed liposomes as well as mixed thin films on glass containing a combination of the ganglioside GMl and diacetylene lipids detect the presence of cholera toxin, a protein that binds to GMl. 

Tubules have also been prepared by swelling thin films of polymerizable diacetylenic phosphatidylhydroxyethanol (choline functionally in 21 is replaced by hydroxyethanol) in aqueous metal ion solutions above the phase transition temperature of the lipid. Various cylindrical structures were observed upon swelling the lipid in the presence of mono- and divalent cations. In contrast, no definable microstructures were noted in the absence of cations [362],... 

In the past, mica has been the material of choice for the interacting surfaces because of the ease of handling and since molecularly smooth surfaces can be fabricated mica surface coated with a thin film of other materials (e.g., lipid monolayers or bilayers, metal films, polymer films, or other macromolecules such as proteins) can also be used. The use of alternative materials such as molecularly smooth sapphire and silica sheets and carbon and metal oxide surfaces is also being explored. 

Even closer to cell membranes than monolayers and bilayers are organized surfactant structures called black lipid membranes (BLMs). Their formation is very much like that of an ordinary soap bubble, except that different phases are involved. In a bubble, a thin film of water — stabilized by surfactants — separates two air masses. In BLMs an organic solution of lipid forms a thin film between two portions of aqueous solution. As the film drains and thins, it first shows interference colors but eventually appears black when it reaches bilayer thickness. The actual thickness of the BLM can be monitored optically as a function of experimental conditions. Since these films are relatively unstable, they are generally small in area and may be formed by simply brushing the lipid solution across a pinhole in a partition separating two portions of aqueous solution. 

---