Polymerized lipids

Elbert R, Laschewsky A and Ringsdorf H 1985 Hydrophilic spacer groups in polymerizable lipids— formation of biomembrane models from bulk polymerized lipids J. Am. Ohem. Soc. 107 4134-41... 

The UV absorption of the aqueous vesicular systems, which provides information on the relative concentration of lipids in aqueous system, also proved the enhanced stability of the polymerized vesicles. The absorptions at 238 nm of the unpolymerized vesicles showed a sharp decrease, as seen in Figure 5, as a result of the precipitation of the lipid in the system. However, the absorptions at the same wavelength of the polymerized system showed a relatively steady trend that meant the polymerized lipid had a longer suspension life in the aqueous system. 

The polymerized system gives similar results. The IR spectrum of the polymerized lipid shows two absorption peaks at 1805 cm-1 and 1735 cm"1 which correspond to the lactone carbonyl and ester groups, respectively. After the polymerized vesicle had been allowed to stand in an aqueous system for 2 weeks, the lactone carbonyl absorption peak at 1805 cm"1 disappeared as seen in Figure 3, which indicates the hydrolysis of the connecting acetal linkages has been completed. 

This polymeric lipid can first be polymerized by free radical initiator in organic solutions before making the vesicles. The proton NMR spectrum of the polymerized lipid shows that vinyl protons of the cyclic acrylate between 85.00 ppm and 86.00 ppm disappeared from the spectrum, compared with that of monomeric lipid. Also in the IR spectrum (Figure 6) the absorption peak at 1670 cm"1 for the cyclic acrylate carbon carbon double bond disappeared as the result of polymerization. The carbonyl absorptions of the esters at 1740 cm 1 and the lactone at 1805 cm"1 still remain in the spectrum. 

Figure 6. IR spectra of Lipid 2, (a) monomeric lipid, (b) polymerized lipid, (c) hydrolyzed lipid.

The procedure for the formation of vesicles from this prepolymerized lipid was similar to that for the monomeric lipid. However, the concentration of the lipid in this system was lower than in the case of the monomeric lipid. Also the time of sonication for this polymerized lipid was longer than that for the monomeric lipid because of the decreased freedom of motion of the amphiphilic structure in the polymerized system. The electron microscope pictures (Figure 7) show the formation of tiny and very homogeneous vesicles. 

The DSC spectra confirm that the fluid phase of the polymerized vesicles remains and the phase transitions are retained with the introduction of the spacer group. As can been seen in Figure 8 of the DSC spectrum of the monomeric lipid, there is a peak around 28°C which corresponds to the phase transition of monomeric lipid. As the result of the presence of the spacer group, a similar phase transition can also be observed clearly in the spectrum of the polymerized lipid as shown in Figure 9, but the transition temperature is increased to 36°C by the presence of the polymer chains. 

Figure 7. Electron micrographs of the vesicles of the polymerized Lipid 2 (stained by 1% uranyl acetate).

Figure 9. DSC spectrum of the polymerized Lipid 2 in an aqueous system.

The chromatic transition was completely blocked by a-methyl sialoside, a soluble competitive inhibitor of the influenza virus, demonstrating that binding of the virus to the film was due to a specific carbohydrate-protein recognition event. This experiment demonstrated that the chromatic transition of the PDA backbone could be triggered by molecular recognition of a membrane surface ligand that was covalently attached to the polymerized lipid. 

Film penetration studies show unequivocally that lecithin-cholesterol mixtures containing from 0 to 50 mole % cholesterol and lecithin—lactoside mixtures containing from 0 to 80 mole % Ci6-dihydroceramide lactoside have the same effect as pure lecithin. This suggests the presence of a lipid complex in which lecithin prevents the interaction of the cholesterol or ceramide lactoside with globulin. Over these ranges of composition the lipid film would consist of a mixture of the lecithin-cholesterol or the lecithin-lactoside complex with excess lecithin. One may picture two models in which the protein contact is restricted to molecules of lecithin. In one, individual polar groups of the protein interact with the excess lecithin molecules as well as with the lecithin portions of the complex. In the other model, the protein as a whole interacts with the lecithin sites of polymeric lipid structures. The latter, which could be referred to as surface micelles (I), are visualized also through the term "mono-... 

Miscibility of a natural lipid (DMPC) and the monomeric and polymeric lecithin analogue (26) was studied in large unilamellar vesicles using freeze-fracture electron microscopy and photobleaching by H. Gaub 100>. Before polymerization the two lipids appear miscible at all compositions in the fluid state and at DMPC concentrations at or below 50 mol/o in the solid state. After polymerization a two-dimensional solution of the polymer in DMPC is obtained at T > T (T phase transition temperature of polymeric 26) while lateral phase segregation into DMPC-rich domains and patches of the polymer is observed T < T. The diameter of the polymerized lipid domains was found to average 400 A. 

The two major polymeric lipid components found in plant cuticles are cutin and cutan. Whereas cutin is the polyester biopolymer that is solubilized upon saponification treatment, cutan is a nonsaponifiable and nonextractable polymeric substance... 

We report here on the structure and gas transport properties of asymmetric membranes created by the Langmuir-Blodgett deposition of ultra-thin polymeric lipid films on porous supports. Transmission and grazing angle FTIR spectroscopy provide a measure of the level of molecular order in the n-alkyl side-chains of the polymeric lipid. The level of orientational order was monitored as a function of the temperature. Gas permeation studies as a function of membrane temperature are correlated to the FTIR results. 

We report here on the structure and gas transport properties of asymmetric membranes produced by the LB deposition of a polymeric lipid on porous supports. The effects of temperature on the structure and gas transport is described. The selectivity of CO2 over N2 permeation through the LB polymer films is determined. The polymerized lipid used in this study contains tertiary amines which may influence the CO2 selectivity over N2. The long term objective of our work is to understand how structure and chemistry of ultrathin films influence the gas permeation. 

Materials and Film Preparation. The molecular structure of the polymerized lipid referred to as CO-1.5 is shown in Figure 1. The material is a co-polymer of a double 18-carbon alkyl chain lipid with a side-group spacer and five main-chain spacer groups. The purpose of the spacer chains is to allow more free volume for the lipid chains to orientationally order normal to the polymer backbone. The lipid chain contains an amide, and the main-chain spacer groups contain tertiary amines. The polymer was synthesized following the general procedures given by Laschewsky et al. (10). 

Infrared Spectroscopy. The GO RE-TEX substrate was chosen for its complete fluorocarbon composition. As it contains no hydrocarbon, we are able to investigate the IR spectra of the polymerized lipid coating, free from substrate band interference. The GORE-TEX is opaque near 1200 cm l due to absorptions of the CF2 and CF3 groups. 

Hydrophobically modified polybetaines combine the behavior of zwitterions and amphiphilic polymers. Due to the superposition of repulsive hydrophobic and attractive ionic interactions, they favor the formation of self-organized and (micro)phase-separated systems in solution, at interfaces as well as in the bulk phase. Thus, glasses with liquid-crystalline order, lyotropic mesophases, vesicles, monolayers, and micelles are formed. Particular efforts have been dedicated to hydrophobically modified polyphosphobetaines, as they can be considered as polymeric lipids [5,101,225-228]. One can emphasize that much of the research on polymeric phospholipids was not particularly focused on the betaine behavior, but rather on the understanding of the Upid membrane, and on biomimicking. So, often much was learnt about biology and the life sciences, but little on polybetaines as such. 

Phospholipid polymers having a 2-methacryloylox-yethyl phosphorylcholine (MPC) were investigated as a solubilizer for paclitaxel. The paclitaxel solubility was observed to increase up to 5.0mg/ml in the presence of a copolymer of MPC and Ai-butyl methacrylate (BMA), poly(MPC-co-BMA), with 70mol% of the BMA unit. The MPC polymer forms a polymer aggregate with the diameter of 23 nm, called a polymeric lipid nanosphere, in aqueous media by hydrophobic interaction, which may solubilize hydrophobic drugs. 

Polymerized lipids do not occur in natural cell membranes. Nature tends to support fragile membrane structures with polymeric skeletons, i.e. protein cytoskeletons, polysaccharide cell walls etc. Analogous synthetic polymeric nets are simply constructed from polymerizable counterions. Negatively charged dihexadecyl phosphate vesicles can be neutralized with choline methacrylate polymerization of the latter produces a polycationic vesicle coat which is not inserted into the membrane (Figure 4.30). A cytoskeleton at the... 

Lipids are bioorganic substances related to fatty acid esters and include a variety of compounds such as glycerol esters, waxes, phosphoglycerides, sphingolipids, natural hydrocarbons, some vitamins, etc. This diversity of compounds is explained by the fact that initially the term lipids was used to describe natural bioorganic substances soluble in hydrocarbons and insoluble in water. Lipids include both small molecules and polymeric materials. Because some simple lipids are not polymeric, their pyrolysis will be discussed only to the extent of being associated with the pyrolysis of complex lipids. However, non-polymeric lipids are commonly associated with polymeric ones, and pyrolytic techniques were frequently applied on the whole lipid without separation for purposes such as classification or identification of microorganisms based on the pyrolysis pattern of their lipids [1]. 

This article is organized primarily on the geometry of the supramolecular structure (e.g., vesicle, planar supported film, etc.). Functionalization of poly(lipid) structures and their technological applications are presented in a separate section as these have expanded greatly as the field has matured. The analytical techniques available for characterization of substrate-supported, thin organic films have advanced considerably since polymerized lipid films were first reported in the early 1980s, and examples of the use of these techniques to study poly(lipid) membranes are presented throughout this review. 

Fig. 3 Schematic illustration of the procedure for chemically grafting a polymerized lipid mono-layer onto a silicon catheter surface. Reprinted with permission from [60]. Copyright 2005,...

Fig. 12 Schematic representation of polymerized lipid patterning in a capillary, a SUVs prepared using bis-SorbPC are fused to the inner capillary surface to create a uniform supported bilayer, b The bilayer is polymerized via UV irradiation through a photomask placed over the capillary, c Unpolymerized lipid is removed from the capillary to yield a poly(lipid) pattern, d SUVs composed of other lipids are then fused into the bare silica regions between poly(bis-SorbPC) structures, generating chemically functionalized patterns. Reprinted with permission from [96]. Copyright 2007, American Chemical Society...

Recent studies that reported incorporation of pore-forming peptides and proteins into BLMs composed of poly(lipids) were discussed in Sect. 3. In both of these examples, a conformational change was not required for channel activity, and the bilayer was not completely polymerized. Reconstitution of TMPs into solid- and polymer-supported membranes composed solely of polymerized lipids has been reported by two groups in recent years. 

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