Model Lipid Bilayers at Electrode Surfaces

Biological membranes are by far the most important electrified interfaces in living systems. They consist of a bimolecular layer of lipids (the lipid bilayer) incorporating proteins. Lipid molecules are amphiphilic, that is, they consist of a hydro-phobic section (the hydrocarbon tail) and a hydrophilic section (the polar head). In biological membranes the two lipid monolayers are oriented with the hydrocarbon tails directed toward each other and the polar heads turned toward the aqueous solutions that are in contact with the two sides of the membrane. The resulting lipid bilayer is a matrix that incorporates different proteins performing a variety of functions. 

In view of the complexity and diversity of the functions performed by the various proteins embedded in a biomembrane (the integral proteins), it has been found convenient to incorporate single integral proteins or smaller lipophihc biomolecules into experimental models of biological membranes, so as to isolate and investigate their functions. This serves to reduce complex membrane processes to well-defined interactions between selected proteins, lipids, and hgands. There is 

Advances in Electrochemical Science and Engineering. Edited by Richard C. Alkire. Dieter M. Kolb, and Jacek Lipkowski 

With only a few exceptions, metal-supported biomimetic membranes consist of a more or less complex architecture that includes a lipid bilayer. In order of increasing complexity, they can be classified into solid-supported bilayer lipid membranes (sBLMs), tethered bilayer lipid membranes (tBLMs), polymer-cushioned bilayer lipid membranes (pBLMs), S-layer stabilized bilayer lipid membranes (ssBLMs), and protein-tethered bilayer hpid membranes (ptBLMs). 

Apart from hpid molecules, the molecules that are most commonly employed for the fabrication of biomimetic membranes are hydrophilic spacers and thi-olipids. Hydrophihc spacers consist of a hydrophihc chain (e.g., a polyethyleneoxy or oligopeptide chain) terminated at one end with an anchor group for tethering to a support and, at the other end, with a hydrophihc functional group (e.g., a 

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An equivalent circuit can be derived for the surface-bound membrane formed in this work similar in a manner to the approach taken for porous anodic films and porous electrodes (41-46). An equivalent circuit network, proposed in Figure 8a, corresponds to the model in Figure 7. This network has three RC subnetworks that represent the oxide layer, the surface-bound membrane layer, and the double layer. Cox and Rox are the capacitance and resistance of oxide. and Rdl are the double-layer capacitance and the polarization resistance, known as the charge transfer resistance at the membrane-water interface. For the subnetwork of the surface-bound membrane layer, one branch represents a tightly packed alkylsilane and lipid bilayer in series, and the other branch represents the pores and defects through the bilayer. Calk, Clip and Ralk, Rhp are the capacitances and resistances of... 

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