Bolaamphiphiles unsymmetrical

Masuda, M., and Shimizu, T. (2004), Lipid nanotubes and microtubes experimental evidence for unsymmetrical monolayer membrane formation from unsymmetrical bolaamphiphiles, Langmuir, 20(14), 5969-5977. 

There are, for example synkinons for the synkinesis of micelles, vesicles, pores, fibres and planar mono- or multilayers. A given synkinon can also be applied for another synkinetic target if the conditions are changed or if the synkinon is chemically modified. The most simple example is stearic acid. At pH 9, it is relatively well-soluble in water and forms spherical micelles. If provided with a hydrogen bonding chiral centre in the hydrophobic chains (12-hydroxystearic acid), it does not only form spherical micelles in water but also assembles into helical fibres in toluene. At pH 4, stearic acid becomes water-insoluble but does not immediately crystallize out spherical vesicles form. A second type of synkinon, which produces perfectly unsymmetrical vesicle membranes, consists of bolaamphiphiles with two dififerent head groups on both ends of a hydrophobic core. Such bolaamphiphiles are also particularly suitable for the stepwise construction of planar multilayered assemblies. 

The immisdbility of CF2- and CHi-chains was also utilized for the preparation of unsymmetric vesicle membranes. The hydrophobic parts of bolaamphiphile 5 with fatty acid and fluorocarbon sulfonate halves do not mix and all the fluorosulfonate halves were on the outer side of the monolayered vesicle membrane (Figure 4.7). The sulfonate head group was once more localized by the metachromatic effect, the hydrophobic parts with F- and H-substituted spin labels. 

A macrocyclic and unsymmetrical bolaamphiphile with a large succinic acid headgroup on one end and a smaller sulfonate headgroup on the other is also water soluble at pH >8 and forms vesicles upon acidification to pH 4.5. In this case, however, the precipitated large succinic acid headgroups are located on the outer surface, all small sulfonate headgroups on the inner surface. This has been... 

Bixin, a bolaamphiphile with one methylester and one carboxylate end group, appears in the waxy cover of seed granules of the South American and African tree Bixa orellana. This lively colored coating of the seed proteins may protect them against attack by microorganisms. Why is an unsymmetrical bolaamphiphile needed, if the protective role can presumably also be played by P-carotene Why is a cw-double bond introduced at one end ... 

Access to unsymmetrical derivatives was envisaged, especially to study symmetrical or dissymmetrical organization of bolas in lipid membranes. They are usually prepared by selective reactions of one functional group of the unprotected symmetrical hydrophobic core, Shimizu and Masuda [68] developed the synthesis of bolaamphiphiles 15a-g containing an oligomethylene chain connected with a sugar at one end and a free carboxylic acid... 

Figure 7.31 Unsymmetrical bolaamphiphiles possessing a single polymethylene bridging chain.

Figure 14 Structure of several bolaamphiphiles used in nanotube formation. At the bottom, model of the four possible types of monolayer lipid manbranes (MLMs) from unsymmetrical bolaamphiphiles is shown.

Fuhrhop, J.-H. and Fritsch, D. (1986) Bolaamphiphiles form ultrathin, porous, and unsymmetric monolayer Upid membranes. Acc. Chem. Res., 19,130-137. 

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