Self-assembled biomembranes

Due to the surface sensitivity surface enhanced fluorescence has become particularly popular in the characterisation of thin molecular films, such as Langmuir-Blodgett films and self-assembled biomembranes. Two surface enhanced spectroscopic techniques (surface enhanced IR absorption, SEIRA, and surface enhanced fluorescence, SEF) were recently applied to the study of biomembrane systems by the group of Reiner Salzer [323]. With SEIRA, specific fingerprints of biomolecules could be obtained with a tenfold IR intensity enhancement With SEF signal enhancement factors greater than 100 were obtained. The enhancement factor was very dependent on the properties and structure of the metal clusters used. With the two techniques biomembranes formed from vesicles with embedded nicotinic acetylchoHne receptors were spectroscopically characterized. 

Maeda Y., Yamamoto H., Kitano H., Self-assembled monolayers as novel biomembrane mimetics. 1. Characterization of cytochrome-c bound to self-assembled monolayers on... 

Ottova A, Tvarozek V, Racek J, Sabo J, Ziegler W, Hianik T, Tien HT (1997) Self-assembled BLMs biomembrane models and biosensor applications. Supramol Sci 4 101-112... 

Aqueous molecular assemblies such as micelles and bilayer membranes are formed by the self-assembly of amphiphihc compounds (Figure 11.la, b) [10]. Aqueous micelles have been utihzed for a variety of apphcations in surfactant industry, including emulsification, washing, and extraction processes [11]. BUayer membranes are basic structural components of biomembranes, and their structures are maintained even in dilute aqueous media. This is in contrast to micelles that show dynamic equihbrium between aggregates and monomeric species. Thus bilayers are more stable and sophisticated self-assemblies, and they require suitable molecular design of the constituent amphiphiles. BUayer membranes and vesicles have wide-ranging applications, as exemphfied by drug dehvery [12], sensors [13], and bilayer-templated material synthesis [14]. 

Keywords Aggregation, Biohybrid, Biomembrane, Block copolymer, Colloid, Glycopolymer, Polypeptide, Secondary structure, Self-assembly, Vesicle... 

For decades, colloid and surface scientists have known that amphiphilic molecules such as phospholipids can self-assemble or self-organize themselves into supramolecular structures of bilayer lipid membranes (planar BLMs and spherical liposomes), emulsions, and micelles [2-4]. As a matter of fact, our current understanding of the structure and function of biomembranes can be traced to the studies of these experimental systems such as soap films and Langmuir monolayers, which have evolved as a direct consequence of applications of classical principles of colloid and interfacial chemistry. As already mentioned in Section I, the seminal work on the self-assembly of planar lipid bilayers and bilayer or black lipid membranes was carried out in 1959-1963. The idea started while one of the authors was reading a paperback edition of Soap Bubbles by C. 

In the recent past, there have been a number of reports on self-assemblies of molecules as advanced materials or smart materials . Without question, the inspiration for this exciting work comes from the biological world, where, e.g., the lipid bilayer of cell membranes plays a pivotal role. In this cormection it should be stated that many other researchers have also described self-assembling systems such as the liposome. Liposomes are modeled after biomembranes, which have been extensively investigated since the late 1960s (see Table 1 for references). 

New RRC, editor. Liposomes a practical approach. Oxford IRL Press 1990. Israelachvili JN, Mitchell DJ, Ninham BW. Theory and self-assembly of lipid bilayers and vesicles. Biochim Biophys Acta—Biomembranes 1977 470 185-201. 

Biological membranes, called biomembranes for short, are nature s most abundant interfaces. Or, more precisely, as their matrix is made of a self-assembled bilayer of phospholipids (see Section 11.6), biomanbranes rather form interphases with interfaces at both sides of the bilayer. This is clearly pictured in the classical, generalized presentation of the membrane structure, proposed by Singer and Nicolson in the 1970s and shown in Fignre 19.1. 

The spontaneous self-assembly of surfactants is an active area of research in part because weak interactions in solutions of ionic surfactants depend on both ion type and charge and these ion specific effects alter, sometimes dramatically, the chemical and physical properties of surfactant solutions. However, consensus is absent on how to model these effects. In modem science terms this is an ancient problem because specific ion effects of surfactants solutions, proteins and biomembranes have been known for... 

The central role of biomembranes in cellular function underlines the importance of membrane research, an area that is by its very nature highly interdisciplinary and ranges from molecular biology to physical chemistry. At its core, however, is an essentially supramolecular interaction, the hydrophobic effect, which causes phospholipid amphiphiles to self-assemble into bilayers and then into complex closed compartments. The elegant self-assembly process that forms these remarkably large structures is an area of keen interest in its own right, but much recent study into self-assembled membranes aims to replicate the functions of biomembranes. Indeed, for cells, phospholipid bilayers are more than just delimiting boundaries they are... 

The stractural and functional complexity of biomembranes has ehal-lenged researehers to develop simpler artificial models to mimie their properties. Amphiphilic block copolymers are of particular interest, beeause of the dual environmental affinity that is associated with covalently bound hydrophobie and hydrophilic blocks. These strive to minimize their eontaet, and therefore drive self-assembly into assemblies with different arehi-teetures. Based on their chemical specificity, as for example the hydrophilie-to hydrophobie ratio, amphiphilic block copolymers can self-assemble in dilute aqueous solutions into micelles, vesicles, tubes, wire-like structures, nanopartieles, or planar membranes at water-air interfaces. Synthetic membranes have greater mechanical stability than phospholipids because of the higher moleeular weight (Mw) of amphiphilic block copolymers, and thus are thicker and stiffer than lipid bilayers. 

Apel CL, Deamer DW, Mautner MN (2002) Self-assembled vesicles of monocarboxylic acids and alcohols conditions for stability and for the encapsulation of biopolymers. Biochim Biophys Acta - Biomembranes 1559 1-9. doi 10.1016/S0005-2736(01)00400-X... 

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