Diacetylenic phospholipids

Relatively little work on chiral assemblies was reported over the next 15 years until a resurgence in activity in the mid-1980s with nearly simultaneous reports of chiral morphologies in gluconamides,22 amino acid amphiphiles,23,24 and diacetylenic phospholipids 25,26 These systems will be discussed in... 

There are two reasons to think this situation might occur. The first reason is experimental. As discussed in Sections 2-5, in most experiments on chiral materials, tubules and helical ribbons are observed with only one sense of handedness. However, there are a few exceptions in experiments on diacetylenic phospholipids,144 diacetylenic phosphonate lipids,145 146 and bile.162 In these exceptional cases, some helices are observed with the opposite sense of handedness from the majority. In the work on diacetylenic phospholipids, the minority handedness was observed only during the kinetic process of tubule formation at high lipid concentration,144 which is a condition that should promote metastable states. Hence, these experiments may indeed show a case of biased chiral symmetry-breaking in which the molecular chirality favors a state of one handedness and disfavors a mirror image state. 

Glycolipid incorporated liposomes have found extensive use as sensors for the detection of Escherichia coli bacteria. Liposomes prepared using a diacetylene and a glucosyl lipid underwent a chromatic transition upon the addition of E. coli (Ma et al. 1998). The chromatic transition is sensitive to the diyne and glycolipid stmc-ture (Ma et al. 2000). An optimized vesicle assembly, consisting of a maltotriosyl lipid, phospholipid, and diyne, detected E. coli at a concentration of 2x10 cells/mL... 

Tubules prepared from diacetylenic phospholipids (21) Copper and nickel films Electron microscopy and X-ray fluorescence measurements indicated 20- to 30-nm metallic coatings on the interiors and exteriors of the tubules 356... 

A decrease in occupied area of the head group results in an increase in packing density of the molecules (45) exhibits only an expanded phase, (46) both a liquid and a solid-like phase, and (47) forms only a condensed film. Monolayer properties of many natural phospholipids and synthetic amphiphiles are described in the literature37 38. Especially the spreading behaviour of diacetylenic phospholipids at the gas-water interface was recently described by Hupfer 120). 

First, a mixture of synthetic or natural phospholipids, polymerizable lipids, and proteins can be converted to liposomes and then be polymerized. Second, polymerizable lipids are introduced into e.g. erythrocyte ghost cells by controlled hemolysis and subsequent polymerization as described by Zimmermann et al.61). This hemolysis technique is based on a reversible dielectric breakdown of the cell membrane. Dielectric breakdown provides a third possible path to the production of bi omembrane models. Zimmermann et al. could show that under certain conditions cells can be fused with other cells or liposomes61). Thus, lipids from artificial liposomes could be incorporated into a cell membrane. A fourth approach has been published by Chapman et al.20). Bacterial cells incorporate polymerizable diacetylene fatty acids into their membrane lipids. The diacetylene units can be photopolymerized in vivo. The investigations discussed in more detail below are based on approaches 1. and 3. 

Since cholesterol is an important component of many biological membranes mixtures of polymerizable lipids with this sterol are of great interest. In mixed monolayers of natural lipids with cholesterol a pronounced condensation effect , i.e. a reduction of the mean area per molecule of phospholipid is observed68. This influence of cholesterol on diacetylenic lecithin (18, n = 12), however, is not very significant (Fig. 32). Photopolymerization indicates phase separation in this system. Apparently due to the large hydrophobic interactions between the long hydrocarbon chains of... 

As an example of an asymmetric membrane integrated protein, the ATP synthetase complex (ATPase from Rhodospirillum Rubrum) was incorporated in liposomes of the polymerizable sulfolipid (22)24). The protein consists of a hydrophobic membrane integrated part (F0) and a water soluble moiety (Ft) carrying the catalytic site of the enzyme. The isolated ATP synthetase complex is almost completely inactive. Activity is substantially increased in the presence of a variety of amphiphiles, such as natural phospholipids and detergents. The presence of a bilayer structure is not a necessary condition for enhanced activity. Using soybean lecithin or diacetylenic sulfolipid (22) the maximal enzymatic activity is obtained at 500 lipid molecules/enzyme molecule. With soybean lecithin, the ATPase activity is increased 8-fold compared to a 5-fold increase in the presence of (22). There is a remarkable difference in ATPase activity depending on the liposome preparation technique (Fig. 41). If ATPase is incorporated in-... 

The physical properties of diacetylene-containing phospholipid liposomes (25) have been investigated by D. Chapman 102 103 104> by means of UV/VIS and 13C-NMR spectroscopy. They found that short linear segments of polymer are interconnected through the glycerol backbone of the lipid in identical-chain phosphatidyl cholines, but the molecular weights of the polymers are still unknown. 

Hydroxy stearic acid and polybenzylglutamate were the classical cases of relatively simple molecules that produced twisted fibers, till the burst of reports on other examples, viz. amino acid amphiphiles, diacetylenic phospholipids, and gluconamides started in the mid-1980s. The handedness of chiral assemblies can be determined from electron micrographs, provided that care is taken to manipulate grids, specimens, films, and image scanners in a consistent way. It was not till the... 

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