Bolaamphiphile formation

Jorgenson et al. reported [125] the synthesis of bolaamphiphile 46 in which a tetrathiafulvalene (TTF), a substrate currently of importance in fields such as organomagnetism and molecular electronics, was incorporated within the central lipophilic region. Gel formation of 46 (Fig. 20) in either DMF-water or ethanol-water solution was noted which bear similarities with the above findings of Newkome and coworkers. 

Auer et al. [134] presented an example for multilayer formation and controlled deposition of functionalized nanoparticles on SAM of mercaptohexadecanoic acid (MHA) using electrostatic interactions. As a pH-sensitive switchable linker between the SAM of MHA and negatively charged gold nanoparticles, bis-benzami-dine bolaamphiphiles having different alkyl spacers were used [135]. This strategy resulted in a potentially tunable and switchable property of the entire assembly. For example, the kinetics of adsorption as well as the final particle layer thickness can be controlled by the kind of bis-benzamidine used as the linker (Fig. 9.16). 

Figure 19. (A) Monensin modified channel forming unit 15, negatively charged a,(o-bifunctional amphiphile 16a and neutral one 16b, capable of forming monolayered membrane and positively charged bolaamphiphiles 17 as a sealing agent of the channel. (B) Model of channel formation by 15 in the monolayered membrane composed of 16 and the proposed blocking mode by 17." ...

A new family of crown-ether-based bolaamphiphiles, 21, that aggregate into a previously unknown type of bolaamphisome was prepared by Gokel and coworkers [50]. Evidence was presented on vesicle formation from the aqueous suspension of such bolaform amphiphiles. Several reports describing the synthesis of various macrocyclic models related to archael compounds have also appeared in the literature [51]. Fyles et al. prepared a novel series of asymmetric bis-macrocyclic bolaphiles, 22, and evaluated their transport activities in vesicles and planar bilayer membranes [52]. 

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. 

Fig. 23 Formation of fibers from bolaamphiphiles bearing thymine- or adenine end-gronps. TEM micrographs of the fibers. Reprinted with permission from [109]...

Ether linkages in open-chain bolaamphiphiles were obtained in a 20% isolated yield from a,o)-dibromoeicosane with an alcohol in THF containing sodium hydride (Scheme 2.8). The synthesis of macrocyclic tetraethers was unsuccessful. Attempts to reduce macrocyclic lactones with four ester groups via a variety of methods failed. The production of macrocyclic thioacetals from benzaldehyde derivatives and a,to-dithiols was unproblematic and produced quantitative yields (Scheme 2.8). The cyclization of 2,2-thiodiethanol with a,(o-diols in the melt and in the presence of /7-toluenesulfonic acid is an intermediate case. Apolar macrocycles were obtained in 50% yield. 5-(2-hydroxyethyl)thiiranium ions are presumably formed as reactive intermediates during the ether formation steps. The sulphur atom was oxidized to the... 

Recent reports on monomeric and polymerized bolaamphiphiles1 provide evidence for their potential application in the broader field of molecular organizates (1,2). Thus monomeric bolaamphiphiles have been employed in the formation of monolayer lipid membranes or vesicles (1-3). formation of micelles (4-5) and also for spanning bilayer membranes (1-6) The latter process has resulted in the stabilization of membranes. 

The potential applications of bolaamphiphiles include the formation of monolayer vesicles for drug/gene delivery, ultra thin monolayer membranes, inclusion of functionalities into membranes, and disruption of biological membranes [59a]. 

Fig. 11 Illustration of the proposed mechanism of formation of the oligoadenylic acid template self-assembly of the thymidine bolaamphiphile 17g. Reprinted with permission from Angew Chem Int Ed 2003, 42, 1009...

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.

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