Diacetylene 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. 

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). 

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... 

Fig. 13 Top CD spectra of tubules of various mixtures of the two enantiomers of di-acetylenic phospholipid 22 (inset variation of the molar ellipticity as a function of enantiomeric excess) prepared from methanol/water. Bottom CD spectra of tubules of diacetylenic phospholipid 22 solid /me), of an achiral analogue dotted line), and of a mixture of the achiral analogue with 6.1% of 22 dashed line). Reprinted with permission from [34] and [102]. Copyrights 1998 American Chemical Society and 2003 National Academy of Sciences (USA)...

Figure 10 Self-assembled nanotubes can be obtained through a rolling mechanism (chiral molecular packing) or packing directly from the monomer. The structures of amphiphilic molecules used in nanotube formation (a) diacetylenic phospholipids, (b) diacetylenic N-aldonamides, (c, d, and e) glucose glycolipids, (f) sphingolipids, (g) glucophospholipid amphiphiles, (h) amphiphile with a serine head. R and R groups represent a variety of alkyl, alkenyl, or alkynyl groups. (Reproduced with permission from Ref. 52. The Chemical...

Pons, M., D.S. Johnston and D. Chapman. A Study of the Spectra of Diacetylenic Phospholipid Polymers in Solvents and Dispersions. 

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