Phosphatidylcholine diacetylenic

The realization that tubules may be formed on temperature reduction of polymerized SUVs, prepared from polymerizable diacetylenic phosphatidylcholines (21 where n = 7-16 and m = 5-11), represented a major breakthrough in obtaining the desired supramolecular structure [355-360]. In the initial experiments, 0.4- to 1.0-pm-diameter and 10- to 1000-pm-long tubules were prepared by the gradual lowering of the temperature (to about 38 °Q of 21 (m = 8, n = 9) SUVs [358]. The walk of the tubules had thickness of 10-40 nm and were coated by spiral ripples and helical bilayer strips. Many tubules contained trapped SUVs. Polymerization of the acetylenic moieties greatly enhanced the mechanical and thermal stabilities of the tubules [355-360]. 

Tubules 2D 0.2-1.0 pm diameter, 10-1,000 pm long Precipitation of diacetylenic phosphatidylcholines, dissolved in organic solvents, by water below the phase transition temperature Weeks Interior and exterior could be metallized or coated by substrates or particles 361... 

The storage and reactivity of electroactive molecules in polymerized diacetylene vesicles was the subject of studies reported by Stanish, Singh, and coworkers [109, 110], They entrapped ferricyanide in large unilamellar vesicles of photopolymerized PCg PC (1 - palmitoyl - 2 - (tricosa - 10,12-diynoyl)-OT-glycero-3-phosphocholine). Cyclic voltammetry was used to demonstrate that the ferricyanide was electrochem-ically isolated by the poly(lipid) bilayer [110]. At pH7 and 25°C, an anomalously long half-life of 2.4 weeks was calculated for Fe (CN)g- retention in polymerized vesicles. In a subsequent study [109], vesicles with entrapped ferricyanide were prepared from 2-bis(10,12-tricosadiynoyl)-OT-glycero-3-phosphatidylcholine (DCs.gPC) doped with a disulfide-capped lipid (Af-3-(pyridyl-2-dithio)propionyl-2-... 

Chiral phospholipid molecules aggregate spontaneously to form tubes with diameters of 500 nm and lengths of 50-100 pm. Diacetylenic phosphatidylcholine structures were first coated in 1993 by Baral and Schoen [72] with silica nanoparticles. The tubule dispersion was mixed with Ludox (a silica sol with a particle diameter of 10-15 nm and negative surface charge at pH 8.2) and allowed to stand for up to 9 days, during which time a white precipitate formed. TEM analysis of the collected precipitate showed a film with a thickness of about 50 nm, composed of silica particles, on the hollow cylindrical templates. The adsorption of the nanoparticles to the headgroups of the phospholipid is believed... 

Figure 9.41 Visible spectra of suspensions of C25-diacetylenic phosphatidylcholine liposomes irradiated at various temperatures. Insert shows the effect of temperature of irradiation on the absorbance at 482 nm. Irradiation time was 5 min. Lipid concentration 1 mg/ml. Light path 0.2 cm. C non-irradiated suspension. (Leaver et al., 1983.)...

The various relations that can be established between molecular chirality and fiber handedness are worth a detailed presentation. The general rule is that the handedness of a chiral self-assembled fiber is controlled by the stereochemistry of the molecule. One enantiomer gives a right-handed fiber and the other enantiomer a left-handed fiber. However, there are some rare cases where a pure enantiomer of a chiral molecule assembles into a mixture of right- and left-handed helices. This is the case for the phosphonate analogues of diacetylenic lipid 22 (Fig. 8) [98-100], for cholesteryl anthryloxy-butanoate [83], or for a mixture of a bile salt, a phosphatidylcholine, and cholesterol (Fig. 9) [101]. In the latter case, in addition to the fact that both right- and left-handed helical ribbons are observed, two or three different and well-defined helical pitches coexist (Fig. 9) [101]. 

Phospholipids, phosphatidylcholines, have been synthesized which contain the diacetylene group in their acyl chains. These lipids may be dispersed in water or deposited in Langmuir-Blodgett multilayers and their polymerisation initiated with ultraviolet light. The polymers are optically active and thermochromic. A similar polymerisation can be initiated in the membranes of microorganisms which have been grown in the presence of diacetylenic fatty acids. 

In common with other surfactants containing the diacetylene group, diacetylene containing phosphatidylcholines only polymerise in the solid state, in this case when they are cooled below Tc. 2) Polymerisation occurs either when the lipid is dispersed in water in the form of liposomes or compressed in KBr discs. That di acetylene containing phosphatidylcholines dispersed in water do form closed... 

There are two ways in which membranes of diacetylenic lipids containing intrinsic membrane proteins can be obtained either proteins extracted from natural membranes with detergent can be reconstituted into synthetic diacetylenic phosphatidylcholines or the growth medium of micro-organisms incapable of synthesizing their own fatty acids can be enriched with diacetylenic fatty acid. In this laboratory, Ca2+-ATPase from sarcoplasmic reticulum and bacteriorhodopsin from the purple membrane of Halobacterium halobium have been reconstituted into diacetylenic phosphatidylcholines. Provided the more reactive mixed-chain lipids are used polymerisation can be achieved before the protein is denatured by the UV irradiation. Both proteins remain active within polymeric bilayers. 

Influence of Short Chain Phospholipid Spacers on the Properties of Diacetylenic Phosphatidylcholine Bilayers 239... 

Diacetylenes in phospholipid bilayers have been the subject of extensive studies in our laboratory, not only because of the highly conjugated polymers they form, but also because of their ability to transform bilayers into interesting microstructures. Consequent to our synthesis and characterization of several isomeric diacetylenic phospholipids, we have found that the polymerization in diacetylenic bilayers is not complete. In order to achieve participation of all diacetylenic lipid monomer in the polymerization process, diacetylenic phospholipid was mixed with a spacer lipid, which contained similar number of methylenes as were between the ester linkage and the diacetylene of the polymerizable lipid. Depending upon the composition of the mixtures different morphologies, ranging from tubules to liposomes, have been observed. Polymerization efficiency has been found to be dependent on the composition of the two lipids and in all cases the polymerization was more rapid and efficient than the pure diacetylenic system. We present the results on the polymerization properties of the diacetylenic phosphatidylcholines in the presence of a spacer lipid which is an acetylene-terminated phosphatidylcholine. 

Table 1. Effect of short chain phosphatidylcholine (spacer) on the diacetylenic phosphatidylcholine polymerization. Samples were polymerized at -5 C for 120 seconds. Monomer polymer ratio remain unchanged after 5 minute of UV irradiation.

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