Synthetic Bilayer Membranes: Molecular Design, Self‐Organization, and Application

Abstract

Lipid bilayers are a most central building block of the biological molecular organization. Their two-dimensional self-assembly is essential to the generation of biological shapes and sizes on the molecular level. The observation that a totally synthetic amphiphile in water is spontaneously assembled to a bilayer structure suggested that bilayer formation is a general physicochemical phenomenon that is not restricted to particular structures of biolipid molecules. Bilayer formation is now observed for a large variety of synthetic amphiphiles which contain one, two, three, or four alkyl tails. The flexible alkyl tail may be replaced by perfluoroalkyl chains. The supramolecular structures obtained therefrom can be related to the component's molecular structure in many cases. The structural variety and the ease of molecular design make the synthetic bilayer an attractive vehicle for organizing covalently bound functional units and guest molecules. In addition, stable monolayers on water, planar lipid membranes (BLM), and free-standing cast films are obtainable because of the self-assembling property of bilayer-forming compounds. These molecular organizations display common supramolecular features. The use of the cast film as a molecular template provides exciting potential for the production of novel two-dimensional materials.

Controlled self-assembly of amphiphiles in ionic liquids and the formation of ionogels by molecular tuning of cohesive energies

“…16,38,39 Table 1 summarizes their morphology and gel-to-liquid-crystalline phase transition behaviors in aqueous bilayers. Amphiphile 1 formed vesicles in water, with a gelto-liquid-crystalline phase transition temperature T c of 33 1C.…”

“…On the other hand, amphiphiles 2 and 3 showed higher T c (69 1C for 2, 87 1C for 3), indicating that the introduction of amide linkages and longer alkyl chains strengthens intermolecular interactions and consequently enhances the thermal stability of the gel phase. 16,38 Dispersion behavior of amphiphiles 1-4 in ILs Amphiphiles 1-4 were dispersed in ILs (C 1 OC 1 mimTFSA and C 4 mimTFSA, Figure 1) by ultrasonication for a few minutes at room temperature. Table 2 summarizes the appearance of 1-4 (10 mM) in ILs and reports the dissolution temperatures of the ionogels T GS .…”

“…Water molecules compete for hydrogen bonds among the solutes, and this formation of hydrogen bonds in aqueous media requires hydrophobic components to be kept away from the bulk water. 16,22 In organic solvents, the cohesive energy density of the media is generally small and the self-assembly of ordered molecular assemblies requires both amphiphilic (solvophilic/solvophobic) molecular design and increased cohesive energies between the solute molecules. 16,20,21 These points are essentially the same for selfassembly in ILs.…”

“…Traditionally, the structures and properties of amphiphilic molecular self-assembling systems have been tuned by designing the constituent molecules. 16,17 Yet, cohesive interactions between the constituent amphiphilic molecules, their dispersibility (stabilization of the interface between amphiphilic self-assemblies and solvents) and the interactions among solvent molecules all contribute to self-assembly. For example, bilayer membranes are formed not only in water but also in organic solvents including protic and aprotic organic solvents.…”

“…For example, bilayer membranes are formed not only in water but also in organic solvents including protic and aprotic organic solvents. 16,18,19 The doublechained fluorocarbon amphiphiles with solvophilic hydrocarbon chains form bilayer membranes in aprotic organic solvents. 20 The simultaneous pursuit of 'amphiphilicity' and 'intermolecular interactions' has been further manifested by the complementary hydrogen bond networks in organic 21 and aqueous media.…”