Bola-amphiphiles

Willibald J, Rennebaum S, Breukers S, Abdel Hafez SH, Patel A, Opstad CL, Schmid R, Nalum Naess S, Sliwka HR, and Partali V. 2009. Hydrophilic carotenoids Facile synthesis of carotenoid oxime hydrochlorides as long-chain, highly unsaturated cationic (bola)amphiphiles. Chemistry and Physics of Lipids 161(1) 32-37. 

Symmetric amphiphilic molecules, in which two hydrophilic residues are linked by hydrophobic segments, are generally known as bola-lipids based on their resemblance to an old South American hunting weapon. Well-characterized bola amphiphiles are archaebacterial lipids, which usually consist of two glycerol backbones connected by two hydrophobic... 

Figure 6 (Top) Chemical structure of dequalinium (bottom) possible conformations of single-chain bola amphiphiles. Amphiphiles in a stretched conformation (bola) would form monolayers, while amphiphiles in a bended conformation (horseshoe) would form bilayers.

The lipids used in the syntheses of neoglycolipids are often commercially available most of the long-chain carboxylic acids, n-alcanols, n-alcanethiols or -alkylamines are readily available as well as a,o)-dicarboxylic acids, diols or diamines useful for the syntheses of bola-amphiphiles. 

Munoz, S. Mallen, J. V. Nakano, A. Chen, Z. Echegoyen, L. Gay, I. Gokel, G. W., (1992) Lariat ether bola-amphiphiles formation of crown ether based bola-amphisomes Chem. Commun. 520-522. 

FIGURE 7.12. Structures of the bola-amphiphiles 20-24. Scanning force micrographs of the aggregates formed by 22 and 24. 

TABLE 7.2. Peptide-based bola-amphiphiles synthesized by Furhrhop etal., and their assembling... 

In nature, asymmetry is achieved through membrane dissolved proteins. In lipid membrane systems without proteins, only monolayers made of bola-amphiphiles allow a totally asymmetric arrangement of head groups. The simplest asymmetry to be achieved is dependent on the one-sided precipitation of bolaamphiphiles. a,to-Dicarboxylic acids, for example, are often soluble at pH > 8 and spontaneously form vesicles upon acidification to pH 5. At a lower pH, all carboxyl groups become protonated and one usually observes ill-defined precipitates . 

Photolabelling experiment of a vesicle bilayer membrane with bola-amphiphile DIPEP. The light green areas indicate the membrane portions which would be photolabelled by the diazirine (white circles) upon UV irradiation, if the bolaamphiphile stretched through the membrane was inwardly or outwardly U-shaped. Labelling experiments of the amino groups on the outer surface shows that all three conformations occurred in a statistical ratio. ... 

Fig. 3 Classification of CD ICs type I hydrophobic guest, insoluble channel IC, type II amphiphilic guest, solubilization of a guest, type III bola-amphiphilic guest, homogenous IC formation, type IV charged CD derivative, solubilization of a hydrophobic guest...

Fig. 4 Energy diagram for the dissociation of the IC of a bola-amphiphile, E hydrophilic end group, AG jss activation free energy of dissociation, AG iss = —AG° free energy of dissociation (reprinted with permission from [31], copyright of the American Chemical Society)...

Fig. 6 Binding free energies -AG° as a function of the lengths of the hydrophobic binding sites, quantified by the number of methylene groups n(CH2), for (filled circle) bola-amphiphiles, a, co-diaminoalkanes, and (open circle) poly-bolaamphiphiles, poly(imino-oligomethylene)s at pH 6.7 and 25°C, determined by ITC [119]...

Fig. 7 Recognition of bola-amphiphiles by a-CD (Reprinted with permission of [40], copyright of Wiley)...

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